# 1966 upgrade



## Tom Tom (11 mo ago)

Looking for upgrade advice. Pretty stoke 1966 gto with st300 trans with tri-power. Wanting to upgrade cam, heads and torque converter. Want to get the thump when driving into the car shows. I drive the car a bunch and want it streetable with the awe factor


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## kgantzer (Jun 14, 2020)

389?


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## Jared (Apr 19, 2013)

A little more information about what you're starting with would be helpful


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## Sick467 (Oct 29, 2019)

If you're looking for "lope" when pulling into the shows...that can be done with a cam, exhaust, and the proper slightly off tune. You don't need to touch the torque converter unless your goals are MORE POWER. 

Give us what you currently have in the car and a bit more on your goals.


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## Tom Tom (11 mo ago)

Sick467 said:


> If you're looking for "lope" when pulling into the shows...that can be done with a cam, exhaust, and the proper slightly off tune. You don't need to touch the torque converter unless your goals are MORE POWER.
> 
> Give us what you currently have in the car and a bit more on your goals.


389 and it was built as close to stock as possible. It has the 093 heads and I put the tri-power on it. Y’all know the thump when a car pulls in at a show and people turn their head and wanders what is pulling in. My car runs great but want a little more sound ever if I need to change a few things over the winter


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## ponchonlefty (8 mo ago)

the problem with choppy cams is you will sacrifice power down low where you drive. you may not enjoy the car as much. you may get the chop but have a slower car.


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## Jared (Apr 19, 2013)

I'd consider starting on the exhaust end of the equation if sound is the goal. Louder mufflers, larger diameter pipes (don't go 3" on a stock build), cutouts to run off open headers will all change the attitude of your car. If you're still running the "log" style manifolds, swapping in a pair of RA manifolds or shorty headers should change the note as well.

A top end refresh could send you down the rabbit hole. If your heads are stock, you will nee to replace the valve studs before you go too crazy with the cam. As said, if you get too aggressive with the cam, you could kill drivability. Rear gear ratio and torque converter choice could come into play. If you have an idea what cam shaft is in your engine now, one or two grind profiles up may not hurt too bad and will give you some lope.


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## GTOJUNIOR (Aug 7, 2011)

As mentioned an exhaust upgrade/change can give you some of what you're after in as far as sound.
IMHO shelving the ST300 and upgrading the trans would be another vast improvement to achieve more go.


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## Sick467 (Oct 29, 2019)

My old 67 400 had the small chamber heads (670), a street/strip cam grind, and headers along with 2-1/4 pipes with plain old turbo style mufflers. It had a very nice lope to it. It was not loud by any means, but would make the antenna twitch and shake back and forth. The headers gave it a combination of low, upfront, rumble with a tinny sound while the tail pipes put out a low syncopated whopp-whopp. It would take larger pipes and louder mufflers to make more heads turn than it did already. Jared is spot on with starting with the exhaust. You'd be amazed at the difference new exhaust can make. I won't go with headers again, but will use the HO exhaust manifolds instead. I will lose that added upfront sound, but plan to make up for that with cut-outs...eventually, my drive train build is a few years out currently. My lasts 400 build was a mild build for 87 octane with 6X heads and a RV cam, nothing fancy...maybe 350 hp. For several years while completing the project, I just had some short pipe stubs coming of some old log manifolds (no mufflers) and I really miss the noise it could make. Just goes to show that a mild build can turn heads with the right exhaust. This mild build of mine still has a good shimmy and shake to the antenna. I have found that if you drop the idle down a bit lower than ideal...it adds a bit of lope to the engine.


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> I drive the car a bunch and want it streetable with the awe factor


That's my philosophy!


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> 389 and it was built as close to stock as possible. It has the 093 heads and I put the tri-power on it. Y’all know the thump when a car pulls in at a show and people turn their head and wanders what is pulling in. My car runs great but want a little more sound ever if I need to change a few things over the winter


Like you, I had a fairly formidable parts combination, but just no pizzazz. In fact, pulling into car shows was downright embarrassing! I threw money at the car left and right and I spent 2 years trying to correct it.

At the end of the day, exhaust cutouts did it for me. They gave it the big rumble at idle.


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> 389 and it was built as close to stock as possible. It has the 093 heads and I put the tri-power on it. Y’all know the thump when a car pulls in at a show and people turn their head and wanders what is pulling in. My car runs great but want a little more sound ever if I need to change a few things over the winter


I did swap my cam last winter... was quick and painless and I got to correct some other stuff... but it was the exhaust that did it.


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## michaelfind (Dec 14, 2018)

You could knock a few holes into your muffler, but the cutouts are a better option. If you start changing more than that, you will never stop spending time or money, one thing leads to another...


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## Tom Tom (11 mo ago)

armyadarkness said:


> Like you, I had a fairly formidable parts combination, but just no pizzazz. In fact, pulling into car shows was downright embarrassing! I threw money at the car left and right and I spent 2 years trying to correct it.
> 
> At the end of the day, exhaust cutouts did it for me. They gave it the big rumble at idle.


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## geeteeohguy (Feb 2, 2008)

The cheapest, easiest performance upgrade to your car would be to swap out the ST 300 trans with a TH 350 trans. It's a direct bolt-in swap. The ST 300 has a 1.76 low gear vs the 2.75 low gear of the TH350. Highway performance will be the same, but around town and during most driving, the much steeper first gear with the added second gear will make your car feel like it picked up 100 horsepower. The ST300 is a rugged and dependable transmission, but is a real performance killer in one of these cars.


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## Tom Tom (11 mo ago)

Tom Tom said:


> [/iQUOTE]
> I would like a good recommendation on some cut out, headers and cam. I will pull the heads and install screw in studs and valve springs to match the cam. I have the stainless 3” pypes exhaust system


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## PontiacJim (Dec 29, 2012)

Rebuild the 093 heads. Screw-in studs. You may have to elongate the pushrod holes for a big cam so the pushrods dont hit the head (earlier heads as I recall, do not have the pushrod guide plates), new length pushrods if using 1967 and up rocker arms, iron valve guides, cut down the valve guides for Viton seals and more clearance between the valve retainer and guide for bigger cam lift, new valve springs to match cam selection, Install new stainless steel valves. Do a 3-angle valve job. Gasket match the intake ports and smooth the intake runners which can be done with a sanding roll to remove any burrs or rough areas - keep the walls a little on the rough side, not polished.

To get the "sound," you need a cam with a lot of overlap as that is where the "sound" is found. Keep lift around .425" there abouts so the valves don't hit the piston tops. However, as has been pointed out, a cam with a ton of overlap, like the RA IV with 87 degrees of overlap, will need to be in the 3,000-3,500 RPM range to begin to work. Anything lower and the car will be near impossible to drive, and with an ST300, you won't. You also want 3.90 - 4.33 gears in the rear end so you can drive it at lower speeds.

So to get the "sound", big valve overlap on the cam spec, idle speed around 1,000 - 1,200 RPM, high stall converter around 4,000 RPM's, and 3.90-4.33 gears, and a good 3" Dia exhaust system and mufflers.


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## Baaad65 (Aug 29, 2019)

Tom Tom said:


> 389 and it was built as close to stock as possible. It has the 093 heads and I put the tri-power on it. Y’all know the thump when a car pulls in at a show and people turn their head and wanders what is pulling in. My car runs great but want a little more sound ever if I need to change a few things over the winter


Exhaust cutouts would be cheaper 😉


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## Tom Tom (11 mo ago)

Baaad65 said:


> Exhaust cutouts would be cheaper 😉
> View attachment 157709


What cutouts do you recommend? I would want electric and I could put the button in the console storage box


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## Baaad65 (Aug 29, 2019)

I did Doug's because the gate goes up and around so there is no leaking and no restrictions, I hid the button under the steering column but within reach. It's fun rolling into a show with them open 👍


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## Tom Tom (11 mo ago)

Baaad65 said:


> I did Doug's because the gate goes up and around so there is no leaking and no restrictions, I hid the button under the steering column but within reach. It's fun rolling into a show with them open 👍
> View attachment 157710
> View attachment 157712
> View attachment 157713


Those are nice! What header does everyone recommend for a 66?


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## armyadarkness (Dec 7, 2020)

I installed a Pypes exhaust with built in cutouts... so, if you want a "show pleazer" I would go that route and get some beefy mufflers! The whole kit is the pricier way to go, but it's stainless so it'll last forever, it's easier to install, and you'll be done with it all.

Individual cutouts are a little cheaper, but potentially harder to install.

It's really preference. What do _you_ want?


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> What cutouts do you recommend?


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> Those are nice! What header does everyone recommend for a 66?


Dougs... However, IME, you can get just as loud with mannys, and save a lot of time, money, and aggravation! Especially if squeezing horses isnt your thing.


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## Tom Tom (11 mo ago)

armyadarkness said:


> Dougs... However, IME, you can get just as loud with mannys, and save a lot of time, money, and aggravation! Especially if squeezing horses isnt your thing.


Any issues I need to look for when installing headers?


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## Sick467 (Oct 29, 2019)

Headers on a Pontiac can be more fun that some are prepared for. It's been too long since I installed a set to offer the steps, but the headers typically have to be placed in close position as the engine is going in. Meaning, they are laying down on the frame, maybe wired up to stay in place...and there are bolts that have to be put in first otherwise they will not go in. You may have to get the engine mostly in place and then bring the headers up to the engine and then go the rest of the way with the engine. The header flanges will have keyholes in a place or two...those bolts have to started in the manifold before the headers are mated up and then the header flange slipped over the bolt head and slid over so the bolt head catches the skinny part of the keyhole. You also have to have the right bolts. Typical bolts will have a larger head...Pontiac header bolts will have a smaller hex head. This is so you can get a smaller wrench on the hex head...otherwise you will not be able to tighten the bolt all the way down...a larger wrench will hit the header and you will not be able to get the last turns in.

Some have experienced problems with the oil filter too. Not enough room for a larger more desirable filter. And, oil typically runs all over the header pipes since the filter has to be turned sideways to get it out. It is a tight fit to get the filter in and back out.

I'm not a headers nay-sayer, but I'll never put another set in. Manifolds are just less resistant to leaks, fit better, and sound better IMO...quieter up front so the sound is produced by the exhaust out back. My 67 build will get the HO manifolds and cutouts given the budget when it comes time to spend on the exhaust. The 2.5" manifolds are on the shelf, port matched, and painted...ready to go.


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> Any issues I need to look for when installing headers?


Yes!! So many!! Have a box of Kleenex. You'll be crying a lot.

Aside from actually fitting them on, you'll then have the joy of blowing header gaskets and losing bolts, for decades to come... but there are better gaskets and bolts to help with those issues.


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## armyadarkness (Dec 7, 2020)

The performance gains between headers and manifolds is small. Even smaller with Ram Air manifolds. I would _not_ do headers again, if I had the opportunity.


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## Baaad65 (Aug 29, 2019)

Sick467 said:


> Headers on a Pontiac can be more fun that some are prepared for. It's been too long since I installed a set to offer the steps, but the headers typically have to be placed in close position as the engine is going in. Meaning, they are laying down on the frame, maybe wired up to stay in place...and there are bolts that have to be put in first otherwise they will not go in. You may have to get the engine mostly in place and then bring the headers up to the engine and then go the rest of the way with the engine. The header flanges will have keyholes in a place or two...those bolts have to started in the manifold before the headers are mated up and then the header flange slipped over the bolt head and slid over so the bolt head catches the skinny part of the keyhole. You also have to have the right bolts. Typical bolts will have a larger head...Pontiac header bolts will have a smaller hex head. This is so you can get a smaller wrench on the hex head...otherwise you will not be able to tighten the bolt all the way down...a larger wrench will hit the header and you will not be able to get the last turns in.
> 
> Some have experienced problems with the oil filter too. Not enough room for a larger more desirable filter. And, oil typically runs all over the header pipes since the filter has to be turned sideways to get it out. It is a tight fit to get the filter in and back out.
> 
> I'm not a headers nay-sayer, but I'll never put another set in. Manifolds are just less resistant to leaks, fit better, and sound better IMO...quieter up front so the sound is produced by the exhaust out back. My 67 build will get the HO manifolds and cutouts given the budget when it comes time to spend on the exhaust. The 2.5" manifolds are on the shelf, port matched, and painted...ready to go.


Sounds less fun than a root canal and a colonoscopy in the same day.


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## Baaad65 (Aug 29, 2019)

If you buy the kit with the cutout Y's they are going to come out in the middle of your door so you won't be able hear anything in the cabin plus you'll have to extend them out so gasses don't accumulate under you. Mine are right before the mufflers and I added a tip to get the gasses out from underneath. Also the electric motors get more heat being closer to the engine which effects longevity.


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## Tom Tom (11 mo ago)

armyadarkness said:


> I installed a Pypes exhaust with built in cutouts... so, if you want a "show pleazer" I would go that route and get some beefy mufflers! The whole kit is the pricier way to go, but it's stainless so it'll last forever, it's easier to install, and you'll be done with it all.
> 
> Individual cutouts are a little cheaper, but potentially harder to install.
> 
> It's really preference. What do _you_ want?


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## Tom Tom (11 mo ago)

Tom Tom said:


> I see the x pipe with the tees and a blind from pypes but I didn’t see where they offered the gate and actuator. What gates did you use


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## Baaad65 (Aug 29, 2019)

For 2.5" the Doug's kit is part # DEC250AK available at all the usual places, like was suggested maybe you need a trans swap to wake the car up or a different rear cog then some 2.5" ram air manifolds and a new exhaust system w/ cutouts and leave the motor alone. You could also swap in a better intake and carb but if the heads don't flow idk how many horses you would get and you can't change to 1.65 rockers if the heads aren't prepped for them.


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## armyadarkness (Dec 7, 2020)

I didnt use gates. They will run at least $500, plus install... and I foresee no situation where I'd ever close them, so...

They come with block off plates, so if you want them closed, two minutes with some wing nuts and you're done. I welded up some extensions with resonators on them and it did exactly what I wanted it to. Now when I pull into a car show, it sounds like a GTO.

Believe it or not, it's not loud at all inside, and when cruising..






That being said, here are their electric units









Pypes Exhaust HVE10 - Pypes Electric Exhaust Cutout Kit (pair) V8 3 inch


Buy our Pypes electric exhaust cutout kit, a popular choice for muscle car owners. Our electric exhaust cutouts are designed for maximum power.



www.lmperformance.com


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## armyadarkness (Dec 7, 2020)

Pypes Exhaust SGA11R30 - Pypes 2.5 w / Xchange RacePro


Pypes Exhaust Pypes 2.5 w / Xchange RacePro - SGA11R30



www.lmperformance.com


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## Tom Tom (11 mo ago)

Baaad65 said:


> For 2.5" the Doug's kit is part # DEC250AK available at all the usual places, like was suggested maybe you need a trans swap to wake the car up or a different rear cog then some 2.5" ram air manifolds and a new exhaust system w/ cutouts and leave the motor alone. You could also swap in a better intake and carb but if the heads don't flow idk how many horses you would get and you can't change to 1.65 rockers if the heads aren't prepped for them.


I have 3.23 rear gear and with the 2 speed and tri-power it is faster than this old man needs to go on the road and still want it street able. I try to put a couple of hundred miles on it a week and do the cruise-ins with the occasional show. I think for now I will install the cut outs first and see where I am at. This car was a trailer queen when I purchased it. The information you guys have given me is great and very helpful!!!!


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## Tom Tom (11 mo ago)

armyadarkness said:


> I didnt use gates. They will run at least $500, plus install... and I foresee no situation where I'd ever close them, so...
> 
> They come with block off plates, so if you want them closed, two minutes with some wing nuts and you're done. I welded up some extensions with resonators on them and it did exactly what I wanted it to. Now when I pull into a car show, it sounds like a GTO.
> 
> ...


Thanks Army!!! Sorry for any slow reply as I am in Louisiana fishing


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## Baaad65 (Aug 29, 2019)

Sounds good, do you have 2.5" exhaust because I believe the Doug's only come in 2.5 and 3". Also be careful because some cheaper ones have plastic gears, Bear has a post about his experience, all the more reason I put them farther back. I don't know your neighborhood or how the cops are there but you might want the electric ones for convenience (if you know what I mean) so you're not under the car every time you want to open or close them like Army, although he has no neighbors and the cops don't want to deal with him


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## Tom Tom (11 mo ago)

Baaad65 said:


> Sounds good, do you have 2.5" exhaust because I believe the Doug's only come in 2.5 and 3". Also be careful because some cheaper ones have plastic gears, Bear has a post about his experience, all the more reason I put them farther back. I don't know your neighborhood or how the cops are there but you might want the electric ones for convenience (if you know what I mean) so you're not under the car every time you want to open or close them like Army, although he has no neighbors and the cops don't want to deal with him


Pretty sure they are 3’s but I will get under there again befor I order. I’m out of town but we go to the city quite a bit and will definitely need a button. Army sent me a thing and Pypes does offer them. I will be more reading about them before I order but it looks like everything will be bolt on and a little wiring. From what I seen around a grand and not tearing into anything.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> Sounds less fun than a root canal and a colonoscopy in the same day.


Not if you have your head up your butt - they can do both procedures at the same time, might be able to get your eyes and hearing checked as well if it's a good hospital.


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## Tom Tom (11 mo ago)

Tom Tom said:


> Thanks Army!!! Sorry for any slow reply as I am in Louisiana fishing


Has anyone heard of Granatelli cutouts? They have a better review the Doug’s and Pypes at Jegs.


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## PontiacJim (Dec 29, 2012)

Tom Tom said:


> Has anyone heard of Granatelli cutouts? They have a better review the Doug’s and Pypes at Jegs.


The issue with that style of cut-out is that it is a "butterfly valve." Any dirt, carbon build up, or corrosion and the valve may not close or seal well.

I purchased the Doug's for my build, but not in use at this time. The Doug's are not a butterfly valve. They roll open/closed. The early units had a plastic gear that would not hold up and then you had to replace it. There was a You Tube video posted on how to purchase a couple electric motors for cheap and rob the steel gear and replace the Doug's plastic gear with it. I purchased 2 of the motors just in case I needed them in the future, but mine are later models and believe the steel gears. However, from what I have read, that problem was taken care of some time ago and steel gears are now used - no plastic gears. So *always look at the date of any review *as an older version of a product may have been upgraded because negative feedback reached the product manufacturer and they revised it - they want to make money, not make a bad reputation.

I also like the idea that the exhaust pressure has to push on the Doug's valve and it isn't going to flex or possibly open partially like a butterfly valve.


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## Rockinindian (Aug 5, 2021)

Tom Tom said:


> Looking for upgrade advice. Pretty stoke 1966 gto with st300 trans with tri-power. Wanting to upgrade cam, heads and torque converter. Want to get the thump when driving into the car shows. I drive the car a bunch and want it streetable with the awe factor





Tom Tom said:


> Looking for upgrade advice. Pretty stoke 1966 gto with st300 trans with tri-power. Wanting to upgrade cam, heads and torque converter. Want to get the thump when driving into the car shows. I drive the car a bunch and want it streetable with the awe factor


you’ll get a good thump over 280-310 duration min 550-600 lift providing you have the big valve HO heads, I use old school 30” glass packs zero restriction and awesome sound not to loud unless you get in to it,


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## lust4speed (Jul 5, 2019)

It's worth watching the Engine Masters episode on exhaust cutouts and their placement. Lots of information about where to locate them so they actually work and don't loose power over no cutouts in the system. I've had the Quicktime remote wireless cutouts and they continue to work good on my '67 red street GTO that has since moved on to a new owner. I haven't bothered to put cutouts on my blue GTO or wagon and just rely on the 3" exhaust with three chamber mufflers. I've got a friend that went with Flowmaster original 40 Series two chamber mufflers and another that installed Spintech mufflers and both definitely have the sound. Either one can drive down the street and set off car alarms on both sides. They would be way too much for driving a long distance but for around town they really add to the fun.


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## Jared (Apr 19, 2013)

Funny thing is Engine Masters also did a muffler comparison. The worst flowing performance mufflers were the Flowmasters. It was the only chambered muffler they tested. If I remember correctly, there wasn't a huge difference between the straight through style mufflers. I'm running the Pypes Racepro long body mufflers on mine. They were very quiet on the 400 that came out of it. Not so much behind the high strung 461


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## TK69tempest (Feb 28, 2011)

geeteeohguy said:


> The cheapest, easiest performance upgrade to your car would be to swap out the ST 300 trans with a TH 350 trans. It's a direct bolt-in swap. The ST 300 has a 1.76 low gear vs the 2.75 low gear of the TH350. Highway performance will be the same, but around town and during most driving, the much steeper first gear with the added second gear will make your car feel like it picked up 100 horsepower. The ST300 is a rugged and dependable transmission, but is a real performance killer in one of these cars.


I swapped out my ST300 with a TH400. I thought the case dimensions were closer to each other and they both use the kick-down switch mounted on the throttle pedal.


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## geeteeohguy (Feb 2, 2008)

TK69tempest said:


> I swapped out my ST300 with a TH400. I thought the case dimensions were closer to each other and they both use the kick-down switch mounted on the throttle pedal.


Thank you for bringing this back on the topic of performance gains rather than going slow and making noise. 

Appreciated. Maybe the OP will get the message?


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## lust4speed (Jul 5, 2019)

There is always someone faster, and it's cheaper to sound powerful than toss a lot of money and still have people blow your doors off because there is always someone that has deeper pockets. If you spend enough money you can move up on both lists, then the cops bust you and you loose your license and you get to sit around and tell people how fast you were.

Sometimes the best sounding muffler (read noise and bad attitude) isn't the one producing the most horsepower. The OP asked for something that will turn all the heads when he pulls into a show. There is a rather legendary test done by Jim Hand on a bunch of mufflers back in the day. Very comprehensive test and it's referenced quite often. The one thing I took away from the test that many missed is the complete spread of the worse to the best muffler was under 7 horsepower. That difference at the horsepower his engine was making on the dyno could have simply been different atmospheric conditions throughout the day. You adjust the results based on rough formulas but that little difference over the couple of days the testing was conducted leaves a question in my mind if there really was even 7 horsepower difference.

Now sometimes a muffler will just suck. I have Cherry Bombs that I use on my run stand that are two-chamber turbo mufflers. 2-1/2" in and out but when I look inside, the tubes reduce down to 1-3/4" at the muffler case. Now that's got to destroy performance and sound. Some of their other mufflers are probably great, but these are not. Same with the Engine Masters tests, the guys can only test so many models and the next model of the company's line might be better or worse but we will never know. I have a tendency to yell at the TV screen when the guys start off with a great premise and then blow it by choices made further into the video. Okay, I'm also not happy that I sometimes have to wait months to run a new engine on the Westech engine dyno because they lock up a full month or more when they are filming their episodes, and the waiting line is sometimes three months because of the backlog. Westech does have two complete engine dyno cells, but the second can't be used because the noise on the other cell would screw up their filming.


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## geeteeohguy (Feb 2, 2008)

Hmmmm.....1:76 first gear vs 2.75 first gear
Or 2" vs 2 1/4'' vs 2 1/2" vs 3"
I wonder which 'upgrade' would actually make the car perform better?
I guess the loud exhaust beats the superior gearing by about 45 to 3.


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## DustyOldGTO (Jun 26, 2019)

Okay, 3.23 with ST300 gives a "launch number" of 5.6848.
swapping in a TH350 with 2.52 first gear makes that 8.1396.
To get the same launch with the ST300 would require 4.62 gears.
Exhaust will get you some attention, TH350 will give you a noticeable performance boost.
YMMV, etc. etc.


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## geeteeohguy (Feb 2, 2008)

DustyOldGTO said:


> Okay, 3.23 with ST300 gives a "launch number" of 5.6848.
> swapping in a TH350 with 2.52 first gear makes that 8.1396.
> To get the same launch with the ST300 would require 4.62 gears.
> Exhaust will get you some attention, TH350 will give you a noticeable performance boost.
> YMMV, etc. etc.


TH350 has a 2.75 first gear. The Muncie M-20 4 speed manual '66-'74 has a 2.52 first gear.
So an 8.8825 number. So it would require about a 5.00 rear gear with the ST300 for the same launch. And that's not even taking into account the benefit of a second gear. 
Again, the best, easiest performance mod to be made to a first-gen GTO with the 2 speed, which is a performance killer.


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## PontiacJim (Dec 29, 2012)

We aren't talking small block Chevies. Pontiac engine have torque. A road test comparison was done between a GTO with 4-speed and GTO with ST300 - both having same engine/rear gears. The ST300 and 4-speed were equal UNTIL the 4-speed went into 4th gear.

Motor's Road Test. 1966 GTO: 335 HP, ST300, 3.23 gears - 0-60 6.6 seconds, 15.6 seconds 1/4 mile
Car Life Road Test. 1967 GTO Ram Air: 360 HP, TH400, 4.33 gears - 0-60 6.1 seconds, 14.5 seconds 1/4 mile
Car Life Road Test. 1968 GTO Ram Air: 360HP, 4-speed, 3.90 gears - 0-60 6.6 seconds, 14.5 seconds 1/4 mile
Car & Driver Road Test. 1970 GTO: 455/360 HP, 4-speed, 3.31 gears - 0-60 6.6 seconds, 15.0 seconds 1/4 mile

In these examples, just like the ST300 versus 4-speed comparison, the ST300 holds its own in the 0-60 MPH times with a lesser HP engine and stiffer rear gear ratio, and no surprise that the RA and 455 GTO's out run it in the 1/4 mile.

So in making the statements about tran gear ratio's, which one multiplies more torque, which one will accelerate faster - has really no merit in the 0-60 MPH run where most street racing/stoplight-to stop light would fall into. Many a winning drag cars used the powerglide and there must be a reason for this. Torque is king and with enough torque, you can move a car quite well and don't need to worry about the gearing so much.

The OP wanted that muscle car "sound" which comes with matched engine parts. Then it seems he switched gears when he realized where the muscle car sound came from and what it would take. Now he has dropped back and punted with a loud exhaust system - which will always be a loud exhaust system. I can put a straight pipe on a Ford Pinto, but the loud exhaust isn't going to give it a muscle car sound.


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## DustyOldGTO (Jun 26, 2019)

geeteeohguy said:


> TH350 has a 2.75 first gear. The Muncie M-20 4 speed manual '66-'74 has a 2.52 first gear.
> So an 8.8825 number. So it would require about a 5.00 rear gear with the ST300 for the same launch. And that's not even taking into account the benefit of a second gear.
> Again, the best, easiest performance mod to be made to a first-gen GTO with the 2 speed, which is a performance killer.


google shows 2.52 as 1st gear for the TH350 and 2.74 as first for a 200R4.









TH350 Vs TH400 Vs 4L60E Vs 700R4: Which Is The Best?


How are these four transmissions - the TH350, TH400, 4L60E, and 700R4 - different from each other? Find out in this article with our comparison chart.




angf35eis.com




many other sites show the same numbers


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## geeteeohguy (Feb 2, 2008)

PontiacJim said:


> We aren't talking small block Chevies. Pontiac engine have torque. A road test comparison was done between a GTO with 4-speed and GTO with ST300 - both having same engine/rear gears. The ST300 and 4-speed were equal UNTIL the 4-speed went into 4th gear.
> 
> Motor's Road Test. 1966 GTO: 335 HP, ST300, 3.23 gears - 0-60 6.6 seconds, 15.6 seconds 1/4 mile
> Car Life Road Test. 1967 GTO Ram Air: 360 HP, TH400, 4.33 gears - 0-60 6.1 seconds, 14.5 seconds 1/4 mile
> ...


Hell, some old drag cars have an in and out box and no trans at all. Because 1000+ HP. Not relevant for street applications which we are talking about. Apples and Oranges.
I respectfully strongly disagree with what you state about the 2 speed----and I'm pretty surprised, knowing your history and background. , I have owned and driven both, and have driven many, many first-gen GTO's with the ST300 and the 4 speed manual over the years. The two speed cars were MUCH slower off the line and all the way to the top end. Not even close. Not even a little bit. It all changed in '67 with the TH400,_ but we're talking about the ST300 here._ Not the same. The ST300 is a performance killer, period. A friend, at my advice, pulled the ST300 out of his wife's '67 Firebird this year (326 4bbl) and swapped in a TH350. Mileage went up, drivability went up, and she is thrilled with the increased performance. She lives in the mountains, and really appreciates the flexibility 3 speeds give, and the increased performance. Drive two identical cars....one with an ST300 and the other with a TH350 or 4 speed manual and get back to me. There are members here who have made the swap and I am sure they will verify my statements.


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## PontiacJim (Dec 29, 2012)

geeteeohguy said:


> Hell, some old drag cars have an in and out box and no trans at all. Because 1000+ HP. Not relevant for street applications which we are talking about. Apples and Oranges.
> I respectfully strongly disagree with what you state about the 2 speed----and I'm pretty surprised, knowing your history and background. , I have owned and driven both, and have driven many, many first-gen GTO's with the ST300 and the 4 speed manual over the years. The two speed cars were MUCH slower off the line and all the way to the top end. Not even close. Not even a little bit. It all changed in '67 with the TH400,_ but we're talking about the ST300 here._ Not the same. The ST300 is a performance killer, period. A friend, at my advice, pulled the ST300 out of his wife's '67 Firebird this year (326 4bbl) and swapped in a TH350. Mileage went up, drivability went up, and she is thrilled with the increased performance. She lives in the mountains, and really appreciates the flexibility 3 speeds give, and the increased performance. Drive two identical cars....one with an ST300 and the other with a TH350 or 4 speed manual and get back to me. There are members here who have made the swap and I am sure they will verify my statements.


Disagree all you want. A 389 tri-power in my book has a lot more torque/HP than a 326 - talk about apples and oranges. I posted the 0-60 MPH results of the 2-speed ST300 as compared to the manual trans equivalents. Did you even look at those times? Proof right there in my book where a lot of street performance_* is relative*_. I guess you also missed the part that the 4-speed and even the TH-400 pulled away when looking at 1/4 mile times - which is the other side of the coin, so I gave a balanced comparison.

The ST300 has a first gear (Low) ratio of 1.765:1 plus the additional low-speed multiplication of the torque converter. In Drive at full throttle, it would upshift from low gear to high gear at 60–65 mph - with no shifting taking place while the 4-speed would have to go through several gear changes (ie time to shift it) to keep up with the Low gear of the ST300. And, the 389 tri-power used the same standard rear gearing, 3.55's so no slouch off the line with those gears in either car, manual or ST300. You are getting confused with the optional highway gearing like 2.56, 2.78, and 3.08's.

You did know the ST300 in a GTO used a higher stall converter, right? - 12" diameter versus the TH-400 13" diameter. The ST300 used with V-8 engines also had additional clutches in the clutch packs.

I guess you don't recall how popular the Powerglide became with the drag racers who had the HP/Torque to pull them. There were many Chevrolet full sized wagons with built 396CI and Powerglides pulling 10 second 1/4 mile times. Using the "right" torque converter, higher RPM's, and gearing will put a 4-speed on the trailer.

More gearing multiplies the engine torque on small engines - that is a fact. From a standing stop, I could put a 4-speed behind me with the Dearborn 3-speed. Why? Torque and less gears to go through. Catch me out on the road cruising, and the 4-speed, or even a 5-speed, will pull away from me because I can't down shift due to my RPM range without the gear spread of the 4 or 5-speed.

The old Mack trucks of yesteryear had duplex & tri-plex transmissions, ie 2 and 3 transmissions that had to be shifted in series to multiply the torque of those smaller engines pulling heavy loads. Fast forward to today, drive a 425 HP Caterpillar engine and you only need 9 speeds and this is because the diesel engines only turn 2,100 RPM's, so the multiplication allows you do get up to a road speed or better. The larger engines use 15/18 speeds only because they are strong enough to handle the torque of a 500 or 600 HP diesel.

*Would I invest and build up an ST300?* *No,* not anymore than I want a Powerglide. I prefer to shift my cars and if I went for a 3-speed automatic I would opt for a well prepped TH-350 over a TH-400 because it is lighter and requires less HP/TQ to spin it. Next up would be a modified and contemporary OD transmission to take advantage of the OD gear.

And that's the rest of the story - 2-speed transmissions forever.


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## armyadarkness (Dec 7, 2020)

I confess that, like MANY other aspects of the GM cars I spent my life around, I never learned much about transmissions, and so for the last year, Ive been getting a crash course.

I will say that the TKX transformed my TH400 car, but that's like comparing raisins to coconuts... It's interesting to note that most of us who love the manual transmissions (including the songs written about them) love them for the fun, not the performance.

During my research, one thing that I consistently heard was that the TH400 sucked up horsepower, so yesterday I decided to dig deeper. I spent several hours on the Covette, CHevelle, and Camaro forum, and I read at least 30 pages of heated debates, but NOT ONCE did anyone mention gear ratio's.

So how are there 30 pages of people swearing that their car had the same strip times with a th350 as when they had a th400, if the trans's had different ratios?

And how, if the dyno numbers were accurate, could a trans that sucked as much as 100hp off a car, still produce better strip times?

Obviously I still have a lot to learn, but although Im intrigued, Im happy to not be a victim of these transmission performance issues... More so, Im grateful that I have a TKX and TH400, because I suspect one or both are good to have


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## Baaad65 (Aug 29, 2019)

This is my M23Z ratios so is it considered a wide or a close, and is it ideal paired with a 3:42 rear gear? My shift light is set at 5700 rpm but it isn't floating valves or seem like it's running out of pull yet but I don't want to push it any further because of the cast crank and no lifter bore bracing. Rev limiter is set at 6000 rpm.


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## geeteeohguy (Feb 2, 2008)

PontiacJim said:


> Disagree all you want. A 389 tri-power in my book has a lot more torque/HP than a 326 - talk about apples and oranges. I posted the 0-60 MPH results of the 2-speed ST300 as compared to the manual trans equivalents. Did you even look at those times? Proof right there in my book where a lot of street performance_* is relative*_. I guess you also missed the part that the 4-speed and even the TH-400 pulled away when looking at 1/4 mile times - which is the other side of the coin, so I gave a balanced comparison.
> 
> The ST300 has a first gear (Low) ratio of 1.765:1 plus the additional low-speed multiplication of the torque converter. In Drive at full throttle, it would upshift from low gear to high gear at 60–65 mph - with no shifting taking place while the 4-speed would have to go through several gear changes (ie time to shift it) to keep up with the Low gear of the ST300. And, the 389 tri-power used the same standard rear gearing, 3.55's so no slouch off the line with those gears in either car, manual or ST300. You are getting confused with the optional highway gearing like 2.56, 2.78, and 3.08's.
> 
> ...


Gee, Jim, once again, I guess your book experience trumps my actual real world experience. I guess I imagined, back in 1982 when I owned 4 GTO's , 2 '65's and 2 '66's, that the stick cars were faster. (same gear out back). I guess Pontiacs have so much torque, they just offered rear gears other than 2-series just to make the catalog read better. I wonder why guys who drag race Pontiacs 1/8 mile have 3.90-4.33-4.88 gears out back? And why aren't they running an ST 300? I guess they didn't read your book. 
Your observations on the truck gearing, etc. is of course correct. I have a CDL and used to drive big rigs, etc. 
I wonder if anybody here, on this forum, who has switched from an ST300 to a manual has anything to say?
In my personal, NOT BOOK, experience, the difference in performance is so drastic it's amazing. When was the last time you even _drove_ a Pontiac?? Seriously.


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## geeteeohguy (Feb 2, 2008)

Baaad65 said:


> This is my M23Z ratios so is it considered a wide or a close, and is it ideal paired with a 3:42 rear gear? My shift light is set at 5700 rpm but it isn't floating valves or seem like it's running out of pull yet but I don't want to push it any further because of the cast crank and no lifter bore bracing. Rev limiter is set at 6000 rpm.
> View attachment 157938


With your steep 2.98 first gear on your WR box, you could easily, easily run a 3.08 rear end and still have excellent performance. I have a 3.42 first gear WR box in my '61 Corvette with a 3.36 rear end, and the only thing it's good for is parades, which I don't do. I'm shifting into second gear before I cross the crosswalk. If they made a 2.75 gearset for my old diff, I'd change to that. Your 3.42 rear end with a 2.98 first gear is excellent for off the line grunt.


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## Baaad65 (Aug 29, 2019)

geeteeohguy said:


> With your steep 2.98 first gear on your WR box, you could easily, easily run a 3.08 rear end and still have excellent performance. I have a 3.42 first gear WR box in my '61 Corvette with a 3.36 rear end, and the only thing it's good for is parades, which I don't do. I'm shifting into second gear before I cross the crosswalk. If they made a 2.75 gearset for my old diff, I'd change to that. Your 3.42 rear end with a 2.98 first gear is excellent for off the line grunt.


Oh it is, I did the rear end before I knew I was going to need a motor and trans so then I found this trans with that first gear and I was wishing I had lower, smaller whatever you want to call it rear gear like a 3:23 but it's fun and I don't have to shift too soon with the stroker. How does that ratio spread look with my set up? I wanted a five speed but the TKX wasn't out yet and I didn't want to tear up the interior as it was just completed for a TKO, if I ever do get a TKX I think the close ratio 2:87 first gear would be fine. It's not bad now as I don't go long distances and I have 28" tires so rpms are 2450 @ 60 mph.


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## geeteeohguy (Feb 2, 2008)

Baaad65 said:


> Oh it is, I did the rear end before I knew I was going to need a motor and trans so then I found this trans with that first gear and I was wishing I had lower, smaller whatever you want to call it rear gear like a 3:23 but it's fun and I don't have to shift too soon with the stroker. How does that ratio spread look with my set up? I wanted a five speed but the TKX wasn't out yet and I didn't want to tear up the interior as it was just completed for a TKO, if I ever do get a TKX I think the close ratio 2:87 first gear would be fine. It's not bad now as I don't go long distances and I have 28" tires so rpms are 2450 @ 60 mph.


Seriously? If I had your car I would be hunting for a 3.08 rear. No need for a 5 speed at all. Best of both worlds. Just got done helping a friend swap a 3.08 into his '65 El Camino with a 383 stroker and a plain Muncie with a 2.52 low gear and its a rocketship. Great on the highway, too. He drove the 200 miles to my house with his 3.36, we swapped the rear assembly with the 3.08 posi, and he drove back, getting 3 mpg more and a much nicer 70-75 mph cruise.


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## Baaad65 (Aug 29, 2019)

geeteeohguy said:


> Seriously? If I had your car I would be hunting for a 3.08 rear. No need for a 5 speed at all. Best of both worlds. Just got done helping a friend swap a 3.08 into his '65 El Camino with a 383 stroker and a plain Muncie with a 2.52 low gear and its a rocketship. Great on the highway, too. He drove the 200 miles to my house with his 3.36, we swapped the rear assembly with the 3.08 posi, and he drove back, getting 3 mpg more and a much nicer 70-75 mph cruise.
> View attachment 157951


Nice! Like I said it's a fun car to drive and I don't go long distances, it's also not a dump truck in first like Army calls his. I really didn't want to re do the rear end although that is cheaper and easier than a TKX, I'm not going to do anything until my big winter list is done and the Paypal credit is paid off then fixing the paint is next. And who knows I might get the racing bug in a couple of weeks and make it a race car....or I'll break something and then can make some changes


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## PontiacJim (Dec 29, 2012)

geeteeohguy said:


> Gee, Jim, once again, I guess your book experience trumps my actual real world experience. I guess I imagined, back in 1982 when I owned 4 GTO's , 2 '65's and 2 '66's, that the stick cars were faster. (same gear out back). I guess Pontiacs have so much torque, they just offered rear gears other than 2-series just to make the catalog read better. I wonder why guys who drag race Pontiacs 1/8 mile have 3.90-4.33-4.88 gears out back? And why aren't they running an ST 300? I guess they didn't read your book.
> Your observations on the truck gearing, etc. is of course correct. I have a CDL and used to drive big rigs, etc.
> I wonder if anybody here, on this forum, who has switched from an ST300 to a manual has anything to say?
> In my personal, NOT BOOK, experience, the difference in performance is so drastic it's amazing. When was the last time you even _drove_ a Pontiac?? Seriously.





geeteeohguy said:


> Gee, Jim, once again, I guess your book experience trumps my actual real world experience. I guess I imagined, back in 1982 when I owned 4 GTO's , 2 '65's and 2 '66's, that the stick cars were faster. (same gear out back). I guess Pontiacs have so much torque, they just offered rear gears other than 2-series just to make the catalog read better. I wonder why guys who drag race Pontiacs 1/8 mile have 3.90-4.33-4.88 gears out back? And why aren't they running an ST 300? I guess they didn't read your book.
> Your observations on the truck gearing, etc. is of course correct. I have a CDL and used to drive big rigs, etc.
> I wonder if anybody here, on this forum, who has switched from an ST300 to a manual has anything to say?
> In my personal, NOT BOOK, experience, the difference in performance is so drastic it's amazing. When was the last time you even _drove_ a Pontiac?? Seriously.


Guess you will have to read my book to learn when the last time I drove a Pontiac.

But in any case, from the PY forum:

"*PB*: If you want some significant pickup in pickup, get rid of that 2 speed auto and convert it to a 4 speed. You will be amazed at the difference.

*JH*: I'm not so sure I agree totally with this. While its a no-brainer that a 4 spd will put the excitement into your driving experience, I'm not ready to throw the towel in on the Powerglide (ST300) tranny. Today I have a 4 spd 67' that is simply a blast to drive and I wouldn't have it any other way, but back in the day I had a couple of 66's with the powerglide (ST300) and they were no slouches.* The one I had back in 76' would plant you deep in your seat from a dead stop, put on a nice smoke show and won its share of street races.  The 66' I spoke about above from 1976 had 3.55's and was responsive as hell !!

ZB*: I had a 66 el camino with a glide. That 66 el camino had a 6 cyl, glide, and 4:10 rear. *it could eat alot of v-8's up*. and would smoke the tires easly 245/60-15's."


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## geeteeohguy (Feb 2, 2008)

I'm going to go with my 45 years of personal experience owning and driving these first-gen GTO's over what your book says. We'll let the owners of the ST300 equipped cars do what they choose. Have a great day.


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## Tom Tom (11 mo ago)

Okay after reading what y’all have said here and thinking on it a bit, I have decided to replace my ST 300 with a turbo 400. Can anyone tell me what to be aware of other then cross member relocate, shorter drive shaft and different yoke? Shifter change or modification?


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> Okay after reading what y’all have said here and thinking on it a bit, I have decided to replace my ST 300 with a turbo 400. Can anyone tell me what to be aware of other then cross member relocate, shorter drive shaft and different yoke? Shifter change or modification?


Where are you located?


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## geeteeohguy (Feb 2, 2008)

Be sure to get a short tailshaft 400, not a long one used in big cars. You need it for the proper driveshaft angle. If you look at the parts catalogs, 3 speed shift plates are available so you can use your factory floor shifter. The lens reads PRNDSL instead of PRNDL. Smart move, BTW. A TH350 is a bolt in that requires less relocation of the crossmember, and will work just fine as well. Not as strong as a 400, but takes less HP to run.


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## Tom Tom (11 mo ago)

armyadarkness said:


> Where are you located?
> Near Chattanooga TN


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## Tom Tom (11 mo ago)

geeteeohguy said:


> Be sure to get a short tailshaft 400, not a long one used in big cars. You need it for the proper driveshaft angle. If you look at the parts catalogs, 3 speed shift plates are available so you can use your factory floor shifter. The lens reads PRNDSL instead of PRNDL. Smart move, BTW. A TH350 is a bolt in that requires less relocation of the crossmember, and will work just fine as well. Not as strong as a 400, but takes less HP to run.


I have a 350 but needs rebuild and while looking for someone to do a bench build found a 400 at a shop with a guarantee real cheap. Came out of a 67 gto


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## armyadarkness (Dec 7, 2020)

That's a bit too far for me to help!


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## Tom Tom (11 mo ago)

armyadarkness said:


> That's a bit too far for me to help!


Nah good weekend trip


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> Nah good weekend trip


Well, if you have cocaine, cigars, and hookers, I'll load up my tools and hit the road!


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## ponchonlefty (8 mo ago)

armyadarkness said:


> Well, if you have cocaine, cigars, and hookers, I'll load up my tools and hit the road!


he's not joking.


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## 66COUPE (Jul 23, 2021)

armyadarkness said:


> Well, if you have cocaine, cigars, and hookers, I'll load up my tools and hit the road!


I have a dumb question for you gear heads, my 66 has the stock 2 speed trans, 3.08 gears but not a posi, how hard is it to make it a “saf t trac” posi rear ? Thanks


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## ponchonlefty (8 mo ago)

66COUPE said:


> I have a dumb question for you gear heads, my 66 has the stock 2 speed trans, 3.08 gears but not a posi, how hard is it to make it a “saf t trac” posi rear ? Thanks


change the carrier. i put a richmond power trac in my firebird. you dont have to mess with the ring gear. its pretty simple. and you can change it back if needed. but the firebird has a 8.5 rear i think you have a 8.2. if you change the carrier then you have to recheck the shims to get the ring gear set.


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## Tom Tom (11 mo ago)

armyadarkness said:


> Well, if you have cocaine, cigars, and hookers, I'll load up my tools and hit the road!


I got two of the three and beer on tap


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## armyadarkness (Dec 7, 2020)

66COUPE said:


> I have a dumb question for you gear heads, my 66 has the stock 2 speed trans, 3.08 gears but not a posi, how hard is it to make it a “saf t trac” posi rear ? Thanks


Easy! And hard... If you have basic skills, I can walk you through it. I did it on mine and have done many Jeeps, Blazers, and Firebirds. 

Get an Auburn posi... however, you might wish to move up to 3.36's at the same time, because there's a difference in carrier size, below that.


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## armyadarkness (Dec 7, 2020)

Tom Tom said:


> I got two of the three and beer on tap


Ive ran it through my head several times, and no matter which two you have, I'm in.


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## RMTZ67 (Mar 12, 2011)

armyadarkness said:


> The performance gains between headers and manifolds is small. Even smaller with Ram Air manifolds. I would _not_ do headers again, if I had the opportunity.


Plus the fact that you can't even see much of them...unlike a Chevy. If you are also buying for cosmetic reasons.


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## armyadarkness (Dec 7, 2020)

armyadarkness said:


> you might wish to move up to 3.36's at the same time, because there's a difference in carrier size, below that.


To clarify this... If you were to get a new Posi carrier for your 3.08's, and then down the road you decided that you wanted 3.36, 3.55, or 3.73, you'd need another carrier, yet again!

Whereas if you move up to 3.36 now, then you'll be able to use any of the performance ratios in the future.


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## 66COUPE (Jul 23, 2021)

armyadarkness said:


> Ive ran it through my head several times, and no matter which two you have, I'm in.


I can supply the 3rd. in either scenario 😎


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## 66COUPE (Jul 23, 2021)

66COUPE said:


> I can supply the 3rd. in either scenario 😎


I did promise the wife no more hookers, so that on is off the list. 🤣


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## Jared (Apr 19, 2013)

66COUPE said:


> I did promise the wife no more hookers, so that on is off the list. 🤣


After a couple decades of marriage and three kids, I suspect my wife wishes I did find myself a nice hooker.


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## geeteeohguy (Feb 2, 2008)

armyadarkness said:


> To clarify this... If you were to get a new Posi carrier for your 3.08's, and then down the road you decided that you wanted 3.36, 3.55, or 3.73, you'd need another carrier, yet again!
> 
> Whereas if you move up to 3.36 now, then you'll be able to use any of the performance ratios in the future.


Depends on what he wants to do with the car. IMO, the 3.08 is a great overall rear ratio with a TH400 trans on a street driven car. Decent everywhere, and great on the open road with decent MPG's.


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## armyadarkness (Dec 7, 2020)

geeteeohguy said:


> Depends on what he wants to do with the car. IMO, the 3.08 is a great overall rear ratio with a TH400 trans on a street driven car. Decent everywhere, and great on the open road with decent MPG's.


Yes... just wanted to make sure he knew that there was no "ONE" carrier to serve all needs, and that he was close to the cutoff. Far be it from me to tell a guy what gears to get.


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## geeteeohguy (Feb 2, 2008)

2.93-3.08-3.23 use the same carrier on an 8.2. Some guys shim the ring gear, but I don't recommend it, personally.


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## Tom Tom (11 mo ago)

Jared said:


> After a couple decades of marriage and three kids, I suspect my wife wishes I did find myself a nice hooker.


Sounds like there’s gonna be a party in Tennessee. Wonder if a transmission would also get changed?


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## Baaad65 (Aug 29, 2019)

Tom Tom said:


> Sounds like there’s gonna be a party in Tennessee. Wonder if a transmission would also get changed?


Either way there's going to be a rear end involved 😉


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## lust4speed (Jul 5, 2019)

In 1964 the first GTO I ever test drove at a dealership was a new white '64 with the ST300. Kind of like being propelled out of a sling shot. Somewhat mild out of the hole but the farther down the block the more insane the acceleration. Even today for getting away at an intersection out in the real world that combination would be hard to beat. That '64 would be smoothly pulling away at full throttle while my '67 with the TKO would be making a scene with me trying to not spin the tires out of the hole or going sideways on the 1-2 shift. Sometimes on the street the fastest way between point A and B is through a mushy transmission.


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## 66COUPE (Jul 23, 2021)

lust4speed said:


> In 1964 the first GTO I ever test drove at a dealership was a new white '64 with the ST300. Kind of like being propelled out of a sling shot. Somewhat mild out of the hole but the farther down the block the more insane the acceleration. Even today for getting away at an intersection out in the real world that combination would be hard to beat. That '64 would be smoothly pulling away at full throttle while my '67 with the TKO would be making a scene with me trying to not spin the tires out of the hole or going sideways on the 1-2 shift. Sometimes on the street the fastest way between point A and B is through a mushy transmission.


So in my case sounds like I’d be better served by swapping out the old st300 with a th350 as my engine is basically stock and I’m not planning on really racing, from what I’ve read here the th350 would swap right in without any modifications , correct? plus then I could actually use the dual gate instead of just pretending.


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## 66COUPE (Jul 23, 2021)

Tom Tom said:


> Sounds like there’s gonna be a party in Tennessee. Wonder if a transmission would also get changed?


I feel a tranny joke coming on. Better not !


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## geeteeohguy (Feb 2, 2008)

Yes, a TH350 would serve you well. Easy install and around town performance will be much better. The 1.76 low gear in the ST300 really impedes brisk take-off. But going 70 mph in low gear has its merits.


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## 68GTOJim (Oct 21, 2020)

Got in on this late, but to your original request I found that the stock cam that came in the '66 tri-power "S" engines gives a suttle lope sound that I like. It's also the same cam in the '71 455HO and my current '68 400HO.. Fairly straight forward change except for labor. Just a thought...


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## Tom Tom (11 mo ago)

68GTOJim said:


> Got in on this late, but to your original request I found that the stock cam that came in the '66 tri-power "S" engines gives a suttle lope sound that I like. It's also the same cam in the '71 455HO and my current '68 400HO.. Fairly straight forward change except for labor. Just a thought...


Thanks. I am currently installing cutouts and a turbo 400.
I have the Pypes exhaust with an X pipe and street pro mufflers. From what I have research the X pipe makes my motor sound smoother then it actually is and the cutouts should make a difference. I agree on the stock tri power cam as a buddy of mine has the same but sounds a lot different with no X pipe. Let y’all know how it works out for me soon.


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## Tom Tom (11 mo ago)

Tom Tom said:


> Thanks. I am currently installing cutouts and a turbo 400.
> I have the Pypes exhaust with an X pipe and street pro mufflers. From what I have research the X pipe makes my motor sound smoother then it actually is and the cutouts should make a difference. I agree on the stock tri power cam as a buddy of mine has the same but sounds a lot different with no X pipe. Let y’all know how it works out for me soon
> 
> 
> Pulled the two speed and stuffed the turbo 400 in this morning. Bolted everything back together and then tried to bolt the torque converter up. LOL it is a different bolt pattern. Anyone know if I just need to get a 67 flex plate (with the two different bolt patterns) and put it in? Will the 67 model 400 and the 66 model 389 swap out?


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## geeteeohguy (Feb 2, 2008)

A friend installed that same exhaust on his '65 maybe 15 years ago. The cut-outs are manual, though. It sounds great and zero leaks. He's running HO cast manifolds. No drone on the open road. His whole system was from Pypes.


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## PontiacJim (Dec 29, 2012)

Here is a past post I pulled up:









Torque converter bolt pattern?


Good morning everyone, I have a simple question that I have a hard time finding the answer to. What is the bolt pattern spacing for the torque converter on a pontiac flywheel? I thought it was 10" between the three bolts, but I cannot confirm. I am about to install a 200r4 trans and need to get...




www.gtoforum.com


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## Tom Tom (11 mo ago)

Tom Tom said:


> Thanks. I am currently installing cutouts and a turbo 400.
> I have the Pypes exhaust with an X pipe and street pro mufflers. From what I have research the X pipe makes my motor sound smoother then it actually is and the cutouts should make a difference. I agree on the stock tri power cam as a buddy of mine has the same but sounds a lot different with no X pipe. Let y’all know how it works out for me soon.


Got the tranny changed but my wife wanted to buy something for the car so I had her get the cutouts. My mistake as now she will not let me have them until Christmas.
On a side note, when I put in the turbo 400 and slide the crossmember back 6” now I need to do something with my e-brake cable as the S rod on the passenger side was connected to the member. Any ideas?


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## geeteeohguy (Feb 2, 2008)

You can change the cable, or, what I would likely do, make a bracket to attach to the floor to connect the S rod to in the original location.


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## Tom Tom (11 mo ago)

geeteeohguy said:


> You can change the cable, or, what I would likely do, make a bracket to attach to the floor to connect the S rod to in the original location.


Yeah that is probably the way to go, I will give that a look at.


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## armyadarkness (Dec 7, 2020)

I have to redo my ebrake cable, too. It moved when I put the Tremec in.


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## Tom Tom (11 mo ago)

Transmission is complete other than need to figure out what driven gear to run. Big gain above the two speed from a stop. Installed Pypes cutouts to match my exhaust and I’m at “it’s okay” but not exactly what I think I want, good thing there on a button.


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