# Effect of using closed chamber heads on low rpm 455 build



## 1965 TC4d (9 mo ago)

Hello,

finishing reviving a '65 Tempest 4dr left in a back yard for 15-20 years. Came with a 326 but was disassembled. Using the original ST300 for now to get it up and running.

Found a '66 rebuilt 'stock' 326 that will be also be used to get the car up and running.

As the '65 Tempest is close to being back on the road I am planning a 455/200r combo for the long term. The intent/goal would be to build the 455 to have very low rpm torque, smoothness/quiet and optimized MPG.

Will use a used SP2P intake with q-jet and either headers or the cast HA style exhaust headers. Would also use a Voodoo 700 250 cam. Also considering using 1.65 rockers.

May I ask about thoughts about relative benefits of quench using closed chamber heads for a low rpm engine.

Considering using closed chamber heads with dished pistons that have a crown with a close to mirror image shape to the head combustion chamber. As this will be a daily the static CR would been to be something less than about 9:1. Probably closer to 8.7 or so to use 87 octane fuel.

Utilizing closed chamber heads with an appropriately shaped crown, located correctly in the bore, would maximize the quench effect.

Used in this manner would the closed chamber heads have a significant advantage over later Pontiac open chamber heads in very low rpm torque and optimizing MPG? Or would the advantage, if any, not be worth any other issues that may come from using the closed chamber heads?

Would need to purchase the closed chamber heads so there is that additional expense. Rebuilding and mild porting would be needed for any head used with this build.

The dished pistons needed to obtain the maximum quench and to lower static CR for a daily driver would be about $300 more than stock replacement flat top pistons.

It appears the dished pistons can be ordered in various dish volumes so the static CR can be set as needed. As this will be a daily driver what CR should be used to maximize the quench benefit of the closed chamber heads and still utilize 87 octane fuel?

The closed chamber heads also have smaller valves than the later 2.11 intakes of the open chamber heads. Would these smaller valves increase the charge velocity and therefore power at very low rpm? And if at all would the increase be significant over the larger valves of an open chamber head.

If the closed chamber heads would be a significant benefit in producing very low rpm torque for this build, based on the increase in the quench effect, the fact they come with smaller valves would simply be a given. If the smaller valves significantly benefitted low rpm power production that would just be an additional positive.

A modern heart shaped combustion chamber head would be preferable but the cost is prohibitive for this build. However, haven't seen any aftermarket heads that have ports that are as small or smaller than the OEM Pontiac head port. A larger port may not be as useful with this build.

Have seen positive comments on the 670 head. Would that be the preferred head for this build? Assuming it is recommended to use a closed chamber at all for this build. Also would any other Pontiac heads be useful for this build. Would the 670 be pricier than another closed chamber head that might work as well for this build?

With a tall rear gear and the 200r OD trans it is unlikely that this 455 would see ever see much more than 3500 rpm. The 250 cam and SP2P intake would appear to match this rpm range well.

PS have seen some posts indicating 2.41 gears with a carb engine may be too low to be used with a 200r OD trans. Have also seen posts indicating a 2.73 and or 2.93 gear may work OK. With this low rpm 455 build would a 2.56 rear gear would function well as a daily with a 2.56 gear? The last thing I'd want is finicky or troublesome engine and or trans drivability because of a too tall rear gear with the 200r.


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## Jared (Apr 19, 2013)

If you're going after fuel mileage, why don't you consider building one of the 326 engines instead. Sounds like you're going to add a ton of cost to your project for little gain.


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## 1965 TC4d (9 mo ago)

Jared said:


> If you're going after fuel mileage, why don't you consider building one of the 326 engines instead. Sounds like you're going to add a ton of cost to your project for little gain.


MPG would be a secondary goal/objective. Would be more about optimizing efficiency for this particular build.

The main objective, by far, is to maximize low rpm torque. Starting with a 455 helps with that a lot. A stroker would be even better but that is out the price range of this build.

I suspect using a closed chamber head which can be set up to maximize quench will be a key part of low rpm power and also efficiency. But not sure if there is a significant gain to be made with those heads or if there is other issues that would come up with the closed chambers.


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## Jared (Apr 19, 2013)

Got it. One thing you could consider is going with a smog era head (6X or 4X) which will allow you to run flat top pistons on a 455 and still maintain a pump gas friendly compression ratio. The 6X are decent heads and with some port work, flow like crazy. Added bonus is they were manufactured in two CC sizes and there are a ton of them out there so prices are cheep. Pick the right cam, and you'll have a torque monster even if you use the heads box stock. 1.65 rockers will add cost at the machine shop since the push rod holes will need to be elongated. I'm not a transmission expert, but you may want to reach out to a shop that specializes to figure out what torque converter you'll need to make this all work.

Just curious, what kind of mileage are you hoping for? My car has a 461 pushing somewhere around 500hp built for mid range rpms, a Muncie trans, and 3.23 rear gears and I'm getting ~8 mpg or so back road type driving.


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## 1965 TC4d (9 mo ago)

Jared said:


> Got it. One thing you could consider is going with a smog era head (6X or 4X) which will allow you to run flat top pistons on a 455 and still maintain a pump gas friendly compression ratio. The 6X are decent heads and with some port work, flow like crazy. Added bonus is they were manufactured in two CC sizes and there are a ton of them out there so prices are cheep. Pick the right cam, and you'll have a torque monster even if you use the heads box stock. 1.65 rockers will add cost at the machine shop since the push rod holes will need to be elongated. I'm not a transmission expert, but you may want to reach out to a shop that specializes to figure out what torque converter you'll need to make this all work.
> 
> Just curious, what kind of mileage are you hoping for? My car has a 461 pushing somewhere around 500hp built for mid range rpms, a Muncie trans, and 3.23 rear gears and I'm getting ~8 mpg or so back road type driving.


No specific MPG #. Whatever it comes out to be while focusing the build on producing good low rpm torque.

That goes to my question about the effects of using closed chamber heads. I suspect the increased quench over the open chamber heads will boost both low rpm torque and efficiency/MPG. May allow me to run more CR for a given octane fuel. But I don't know so I thought I'd ask if anyone had any experience with closed chamber heads and low rpm torque.

If the closed chamber heads would not produce the expected benefit and or cause other problems or be too expensive then your thought about the 4/6X heads is right on.

Thanks for the info on the 1.65 rockers requiring the push rod holes to be elongated.

With an auto trans and a tallish rear gear this build would not be focused on HP. Trying to focus the power to be in the most common/typical rpm range of a daily driver. This would provide the most 'felt' acceleration in the most useable rpm range.


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## Sick467 (Oct 29, 2019)

My mostly stock 67 had the 400/400TH with the 2.56 rear end. It did not need overdrive due to the highway gears of the rear end. I remember getting 20+ mpg on 93 octane so long as I kept it around 55 mph on the highway. I am sure my old set-up with an overdrive gear added would perform poorly in overdrive. It would bog down the engine horribly once OD was engaged with around-town-cruising speeds. 

I would calculate the RPM's of the engine with the 3rd gear ratio of the 400TH at 70 mph (along with the tire diameter you will be using) and then back into the rear gear ratio with the overdrive gear ratio replacing the 400TH 3rd gear ratio (for that same RPM and tire size of the non-OD calculation). That should give you an idea of what rear gear ratio would work well with an OD transmission.

A high torque Pontiac build will deal with a lower rear ratio better then the Chevys and Fords, but my gut tells me you will want to be above a 3.0 rear ratio. With my tastes, I'd be looking at the 3.23 or 3.36 with an OD transmission.


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## 1965 TC4d (9 mo ago)

Sick467 said:


> My mostly stock 67 had the 400/400TH with the 2.56 rear end. It did not need overdrive due to the highway gears of the rear end. I remember getting 20+ mpg on 93 octane so long as I kept it around 55 mph on the highway. I am sure my old set-up with an overdrive gear added would perform poorly in overdrive. It would bog down the engine horribly once OD was engaged with around-town-cruising speeds.
> 
> I would calculate the RPM's of the engine with the 3rd gear ratio of the 400TH at 70 mph (along with the tire diameter you will be using) and then back into the rear gear ratio with the overdrive gear ratio replacing the 400TH 3rd gear ratio (for that same RPM and tire size of the non-OD calculation). That should give you an idea of what rear gear ratio would work well with an OD transmission.
> 
> A high torque Pontiac build will deal with a lower rear ratio better then the Chevys and Fords, but my gut tells me you will want to be above a 3.0 rear ratio. With my tastes, I'd be looking at the 3.23 or 3.36 with an OD transmission.


Sounds right.

The g-bodies appear to have used the 200r with very low rear gears, 2.41 and even lower, but I think they used computer controlled carbs and knock sensors to adjust the mixture and the timing.

I agree that there is a lower limit of the gear that can be used with a 200r on a carb engine. I just don't know what that lower limit is. With a large displacement engine with a very mild cam the signal to the carb may be good enough to run a 2.73 rear gear. I don't know about a 2.56.

Would like to obtain the tallest gear set possible so the car has long legs and makes mid to upper 80s mph effortless. But this is a daily driver and the last thing I want/need is for the engine and or trans to have finicky drivability issues like bucking or bogging. The goal for the engine is to maximize very low rpm torque/power but the goal for the car is to have it run as well or better overall than a well sorted stock vehicle.

The idea is to emphasize the stock car's positive characteristics, like good low end torque, smooth idle, easy starting, quiet high speed driving and reasonable MPG. And to mitigate some of the car's inherent design limitations like bump steer and rear suspension bind. And of course not spend the national debt doing so.


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## 1965 TC4d (9 mo ago)

Sick467 said:


> My mostly stock 67 had the 400/400TH with the 2.56 rear end. It did not need overdrive due to the highway gears of the rear end. I remember getting 20+ mpg on 93 octane so long as I kept it around 55 mph on the highway. I am sure my old set-up with an overdrive gear added would perform poorly in overdrive. It would bog down the engine horribly once OD was engaged with around-town-cruising speeds.
> 
> I would calculate the RPM's of the engine with the 3rd gear ratio of the 400TH at 70 mph (along with the tire diameter you will be using) and then back into the rear gear ratio with the overdrive gear ratio replacing the 400TH 3rd gear ratio (for that same RPM and tire size of the non-OD calculation). That should give you an idea of what rear gear ratio would work well with an OD transmission.
> 
> A high torque Pontiac build will deal with a lower rear ratio better then the Chevys and Fords, but my gut tells me you will want to be above a 3.0 rear ratio. With my tastes, I'd be looking at the 3.23 or 3.36 with an OD transmission.


Forgot to ask. '67 appears to be a tradition year for heads. Seems Pontiac was moving away from closed chamber heads for emissions reasons.

Do you remember if your 400 was a closed chamber head or open?


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## 1965 TC4d (9 mo ago)

1965 TC4d said:


> Forgot to ask. '67 appears to be a tradition year for heads. Seems Pontiac was moving away from closed chamber heads for emissions reasons.
> 
> Do you remember if your 400 was a closed chamber head or open?


Transition, not tradition.


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## Sick467 (Oct 29, 2019)

My heads are the original closed chambered 670 heads.


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## AZTempest (Jun 11, 2019)

I'm not sure I can be much help but I think you're on the right track for mpg. My 67 Tempest convertible that I am going though now has a 326, 2 Jet carb, 140 heads, 2 speed ST300. Back in the 80s it was my daily driver. Everything was stock except I put dual exhaust with blackjack headers and a open element air cleaner. On the interstate I would get 24 mpg if I didn't vary the accelerator. I'm not sure what I can do with todays fuels, but I'd like to go back with this setup with gasket matching and over drive. I would be curious if the Qjet could push this mpg but I'd have a hard time keeping my foot out of it.


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## PontiacJim (Dec 29, 2012)

AZTempest said:


> I'm not sure I can be much help but I think you're on the right track for mpg. My 67 Tempest convertible that I am going though now has a 326, 2 Jet carb, 140 heads, 2 speed ST300. Back in the 80s it was my daily driver. Everything was stock except I put dual exhaust with blackjack headers and a open element air cleaner. On the interstate I would get 24 mpg if I didn't vary the accelerator. I'm not sure what I can do with todays fuels, but I'd like to go back with this setup with gasket matching and over drive. I would be curious if the Qjet could push this mpg but I'd have a hard time keeping my foot out of it.


He is wanting to put a 455 in place of the 326. 455 and fuel mileage just doesn't go hand-in-hand. Head choice probably won't make much difference. Fuel Injection, timing, cam selection, exhaust, and final gear ratio/RPM's will provide the improved fuel mileage. Build for max Torque at low RPM's - like for pulling a motorhome or boat.


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## AZTempest (Jun 11, 2019)

Yes, I was thinking of the mpg portion. If I was understanding his posts it’s about torque first mpg second. Even if we don't think of a 455 as a good mpg engine, I tend to think along the lines of what kind of mpg is good for a certain engine. If an engine gets 15 what can be done, if anything, to get to 17. Of course under the parameters of the original goal. We all tend to think along the lines of more power to enjoy the hotrods we’ve all admired. With that efficiency (mpg) tends to take a back seat. It kind of fun to try to look at the other side of the equation at times.


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## 1965 TC4d (9 mo ago)

PontiacJim said:


> He is wanting to put a 455 in place of the 326. 455 and fuel mileage just doesn't go hand-in-hand. Head choice probably won't make much difference. Fuel Injection, timing, cam selection, exhaust, and final gear ratio/RPM's will provide the improved fuel mileage. Build for max Torque at low RPM's - like for pulling a motorhome or boat.


The main focus of the build is optimizing very low rpm torque. Any impact on MPG would just be a consequence of the parts used to build an engine with that characteristic. Not trying to build a 455 for MPG. (the opening post lays out the build and the question/s with some detail)

You mention that head choice would not make much difference. For MPG? probably. But what about low rpm torque production? Wouldn't a closed chamber head with a matching dished piston optimize quench and allow for a greater CR for any given octane and produce more low end torque? Wouldn't the increased quench by itself improve low rpm efficiency and therefore more low end torque?

Would a closed chamber head improve low rpm power and if so would it be significant enough to justify the added expense. (cost of the closed chamber heads and $300 additional for the dished pistons)

Or is a 4/6x just a better head and would produce more very low rpm torque than any closed chamber head even with a dedicated matching crown piston?

Also the closed chamber heads have smaller valves than many of the open chamber heads. Would the smaller valve have any impact of very low rpm torque. Is it possible the smaller valve would produce a higher intake charge velocity and benefit low rpm power? And again, if so would the effect be significant? Or at all?

Thanks


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## 1965 TC4d (9 mo ago)

AZTempest said:


> Yes, I was thinking of the mpg portion. If I was understanding his posts it’s about torque first mpg second. Even if we don't think of a 455 as a good mpg engine, I tend to think along the lines of what kind of mpg is good for a certain engine. If an engine gets 15 what can be done, if anything, to get to 17. Of course under the parameters of the original goal. We all tend to think along the lines of more power to enjoy the hotrods we’ve all admired. With that efficiency (mpg) tends to take a back seat. It kind of fun to try to look at the other side of the equation at times.


Very well said.

Trucks, busses, RVs and other heavy vehicles are continually modified to produce more low rpm power and efficiency.

Already have a q-jet and SP2P intake and will use a Voodoo 250 cam. The benefit, if at all, of using closed chamber heads aside, it is conceivable this 455 with the 200r trans with the listed components will get better fuel economy than the 326 2bbl with ST300 that is in the Tempest now.

Even with very tall overall gearing the Tempest with this 455/200r combo will accelerate immensely hard and be able to maintain 85 effortlessly and still get better MPG than the current 326.

Moving the peak torque up the rpm band can result in higher peak torque. Having to rev the engine to get to that rpm is not the goal here. Producing maximum torque from idle is the goal. It is my speculation that maximizing low rpm torque will also maximize MPG; whatever that happens to be for a 455.


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## 1965 TC4d (9 mo ago)

AZTempest said:


> I'm not sure I can be much help but I think you're on the right track for mpg. My 67 Tempest convertible that I am going though now has a 326, 2 Jet carb, 140 heads, 2 speed ST300. Back in the 80s it was my daily driver. Everything was stock except I put dual exhaust with blackjack headers and a open element air cleaner. On the interstate I would get 24 mpg if I didn't vary the accelerator. I'm not sure what I can do with todays fuels, but I'd like to go back with this setup with gasket matching and over drive. I would be curious if the Qjet could push this mpg but I'd have a hard time keeping my foot out of it.


The '65 Tempest four door is almost identical to your '67. Even down to the duals. After I pulled the '65 from the back yard I noticed it had virtually no exhaust at all. Bought a complete dual kit with H pipe and those box type mufflers. Probably gong to be way too loud but looking now to just get it on the road again.

As the trans is out had thought about swapping in a 200r now. But the '65 probably has a 2.56 rear gear and even if the 455 build could pull that combo, and I don't know that it could, the 326 certainly would have problems with the 200r and such a tall rear gear.

The 80s g-bodies ran even taller rear gears with the 200r with no problems but they used computer controlled carbs and detonation sensors.

My 2 cents is that the q-jet has smaller primaries than the Rochester 2bbl. They do seem to deliver even better MPG than the 2bbl.

While I assemble the 455 parts and have the engine built installing the SP2P intake with the q-jet on the 326 might be an interesting experiment. Could compare the two intake and carb set ups.


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## PontiacJim (Dec 29, 2012)

1965 TC4d said:


> The main focus of the build is optimizing very low rpm torque. Any impact on MPG would just be a consequence of the parts used to build an engine with that characteristic. Not trying to build a 455 for MPG. (the opening post lays out the build and the question/s with some detail)
> 
> You mention that head choice would not make much difference. For MPG? probably. But what about low rpm torque production? Wouldn't a closed chamber head with a matching dished piston optimize quench and allow for a greater CR for any given octane and produce more low end torque? Wouldn't the increased quench by itself improve low rpm efficiency and therefore more low end torque?
> 
> ...


Closed chamber vs open chamber may not show any advantage one over the other in a low RPM, low compression engine.

I get the larger quench aspect and the D-dished pistons, but this may be offset by the efficiency of the open chamber.

Let's loosely compare the open chamber head of the 1971 455 HO, 8.5 compression, which produced a gross HP rating of 335HP @ 4,800 RPM's and 480 TQ @ 3,200 RPM's to the closed chamber head of the 1967 428 with 10.5 compression, rated at 360 HP @ 4,600 RPM's and 472 TQ @ 3,200 RPM's.

This is an apples to oranges comparison in my book, but still illustrates that the low compression, open chamber head, can still produce similar torque numbers at the same low RPM's.

Here is another snippet I ran across in comparing a Chevy closed chamber vs open chamber head:

"I built 2 454's at the same time. Both engines had similar camshafts (SFT) and same compression (10.5). One 454 had the closed chamber heads and the other had open chamber heads.
The closed chamber head 454 made 560 hp 540 tq and was VERY sensitive to timing changes and coolant temp. It would drop serious HP/TQ above 160F water and it was very prone to detonation. The open chamber '781 headed 454 made 540HP 560TQ and didn't care if the timing was 34, or 40 or 160F or 200F it always made the same power. It also had a much smoother power curve."

So, in my opinion, whatever you go with will be a personal choice. More importantly is "port velocity." Higher port velocity is what I would shoot for in producing a responsive and torque making engine. 

The small runners of the SP2P intake will keep port velocity up since it was rated as having an RPM range from 1,000 - 4000 RPM's and probably less with the 455.

Match the cam to the engine specs you go with.

Then gear the trans/rear end to the cruising speed/RPM you feel you will be mostly running at. I might also get a tighter RV torque converter that has less slip and a lower stall which can add up to better mileage.


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## 1965 TC4d (9 mo ago)

Jim,

thanks for such a relevant and useful response.

This kind of analysis and comparative examples are exactly what I had hoped for.

Based on your comments and past experience I do not see any real advantage to using closed chamber heads for this build. And certainly not any advantage that would be worth the added expense of the heads and pistons.

The q-jet, SP2P intake and 250 Voodoo cam are pretty much set for this 455 build. Operating range should be about 600-3800 or so.

The 4/6X heads have been recommended a number of times. For this build would they be the choice or are there other heads that would work as well, perhaps for less $, with this low rpm build?

Have seen your posts regarding various Pontiac engine topics in the past and had hoped that you would weigh in on this thread.

Thanks again.

ps understood about picking a cruising rpm and working backward to identify the rear gear. However, do you have any thoughts about the lowest useable rear gear with a 200r OD trans and an analog carb engine? 

80s GM g-body, and many b-body, used the 200r with very low rear gears. 2.41 and even lower. However, I believe most of those cars used a computer controlled carb and knock sensors.

Would like to gear the 455/200r Tempest as tall/long as possible but as a daily driver would need to avoid, and by a significant margin, any trans and or engine drivability issues. I'm sure there is a gear that is too low to be used with the 200r. Some experienced based evidence would indicate that 2.41 causes problems. Also some experienced based evidence that 2.73 would work. What about 2.56?

Also, yes, will be using the tightest 200r factory torque converter GM made.


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## geeteeohguy (Feb 2, 2008)

I think you are on the PY forums with this same thread. Maybe it's another guy fixated on running early closed heads on a 455? 2.56 gears came in 215 CID 6 cylinder cars 55 years ago. They came in 326 cars. I put them in my '67 GTO convertible (TH400, 406, stock q-jet and points distributor) about 15 years ago and personally get 21 MPG at 75-80 highway and have gotten 23 mpg at a steady 65. RPM's are 2450 at 80 and 3,000 at 91 mph. And this is with E-10 fuel. I take the '67 all over the place as it gets better fuel mileage than my '05 Tundra and can haul more people and almost as much stuff. Had a friend with a '74 Firebird with a 455, dual Q-jets, and 2.41 gears, and we went 145 mph easily and were still pulling but ran out of road. Also, if you want, you can get a higher first and second gear for the TH400 to snap up lower end response. My 9.3:1 less-power-than-stock 400 burns posi rubber with zero issues. These cars with 2 series gears don't need overdrive transmissions and are simple and user-friendly.


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## geeteeohguy (Feb 2, 2008)

I'll add, all my GTO buddies who run 3.55 gears think I'm lying to them when they ride with me and I say I'm going 80 mph....until they get out their phones and verify. The difference in fuel economy, low engine temps, low noise, etc. is very deceptive. Reconsider re-inventing the wheel and consider a mild 455 with a 2 series gear and a stock TH 400 trans. I've been driving first-gen GTO's non stop since the '70's.


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## PontiacJim (Dec 29, 2012)

1965 TC4d said:


> Jim,
> 
> thanks for such a relevant and useful response.
> 
> ...


OK, as always, my opinions/suggestions and not gospel. LOL


With the 455, to make it easy, use a flat top piston and then match the combustion chamber CC's to the bore/stroke to get you in the realm of 9.0 or under. I would go with a big valve 2.11" intake head that has screw-in studs. Even though you won't be aiming for high RPM's, you still do not want to choke out the engine. I would want big valves that will in turn aide in the use of the smaller runners of your intake to develop some really good air velocity - the valves won't be a restriction, but the intake will, so I would want the heads at the valve to not be your bottleneck. I would go with a performance 3-angle valve job, gasket match the intake entry of the heads/ports, using an inside "snap gauge" (which can be bought inexpensively in a kit) I would equalize all the intake ports at the pushrod bulge using a high speed die grinder and carbide cutter, and then use the dir grinder to smooth, not polish, the intake runners to remove any rough castings. Nothing fancy, but easy enough to do. If you want to go a step further, get some sanding rolls and using a rough grit, smooth out the ports a little more and you are done.

Clean up any casting flash on the inside of the heads where the pushrod holes/oil drain back holes are found. You may see jagged edges and even rough return holes. Cleaning this up aides i oil return and you don't have to worry about any casting flash breaking off and going into your engine. Do all this after the heads have been disassembled and magnafluxed and before you have new valves/valve job done.

You could also build the 455 as it would have been in stock form with the 8.2 compression. Why? Then you can take advantage of one of the 110 LSA type cams which will build more cylinder pressures at lower RPM's and this may be what you want with your low RPM build. I used the Comp Cams XE274 with its 110 LSA on a 1972 8.0-ish compression 7K3 heads I port matched and cleaned up the rough ports, and it was a real torque/pulling engine that I was happy with, and I like HP. It pulled hard at the lower-to-mid range and was all done by 5,400-5,500 RPM's. RPM range would be lower using the bigger cubes of the 455.

The Lunati cam seems to offer the torque at the lower-mid range you are after and it has more lift than factory. It has the 112 LSA vs the 110 LSA, but should still work well. A short-duration camshaft makes more low-rpm power than a long-duration cam because the intake valve closes sooner, allowing the cylinder to squeeze more air and fuel - so the short duration numbers of the Lunati cam matched with the slightly wider 112 LSA may have been a somewhat equivalent to the Comp Cams longer 274 duration and 110 LSA that I used. Get matching springs for the cam/head you select. At .455" lift, you are right on the edge where you could use press-in studs, but screw-in would be the safer bet.

For pistons, unless you have to have forged, I would go with the KB Hypereutectic pistons for your lower RPM build . They are a cost saver and a good piston. Butler has them as do other parts sellers. The show compression ratio's to range from 9.5 with a 96 CC chamber to 8.5 with a 111 CC chamber, so this makes it easy enough to find a head having a chamber size within that range. If you get the larger 111 CC's, which would be many of the 455 heads having 114 CC's and then milling them .030" to reduce the CC's about 5-6 CC's, you would have a good pump gas compression ratio.

Doing a quick compression calculation using the Wallace site, I input, 455 .030" over, 110 CC head, 6 CC valve reliefs, .020" deck clearance (piston down in hole), 4.3" diameter head gasket, BUT . 027" Cometic head gaskets to get a quench (what little there is of it) of .047".

Compression comes up at 8.46. You might have less on the chamber CC's, or you could zero deck the block and use a typical Felpro .041" compressed gasket and get 8.51 compression. With head/deck milling, you will want to make sure your intake side of the heads are milled so intake manifold-to-head will bolt up, and you might have to trim the valley pan edges. I am not a fan of milling the deck if not needed, but others swear by it and zero-deck all blocks.

With regards to rear gears, keep in mind that when looking at gas mileage, the stiff 2.56, 2.73 gears need a lot more gas pedal to get the car rolling from a dead stop like a red light, stop sign, or everyday speed up/slow down traffic. On the open road, steady state, gas mileage will be very good. Have a '76 Lemans with 350/auto Q-jet and 2.56 gears. Around town, 13 MPG's. Out on the highway at 70 MPH I got 18-20 MPG depending on road terrain. I did most of my driving in town, so the 2.56's hurt me.

The OD, depending on how stiff, can also be a problem if you have 2.56 or 2.73 and add the OD to that. The trans may not even shift into OD until you hit some really high speeds, so you would be wasting the OD. The OD trans should have a much better lower 1-3 gear ratio so this makes it far better when taking off from a stop or stop/go traffic than the older TH-400 or TH-350. With that said, I would still gear the rear end ratio to give you an RPM range 1600-1800RPM's at 70 MPH. You don't want a lot less as you don't want the engine to be bogging down or struggling to keep a steady lowered RPM - if you ever tried taking off in 4th gear with a manual trans, you get the idea, the engine struggled even though it was able to do it.

As *geeteeohguy* pointed out, you can get a lower gear set for the TH-400 or TH-350 and with the 2.56 gear, tight RV converter, and 70 MPH cruising your RPM's would be about 2,290 RPM's which is OK, but not really taking advantage of the low RPM torque of the 455. I would go with the TH-350 if I went that route because it uses less HP to turn it, just have it built for HD use.


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## geeteeohguy (Feb 2, 2008)

The TH 350 also has a slightly lower first gear than the TH400 for a bit more grunt out of the hole with a lazy diff gear. 2.52 vs 2.48. Keep in mind, the 2,56 diff was used with the 6 cylinder and the 326 v8's with a superturbine 300 2 speed auto, which had a terrible 1.76 low gear.....yet thousands were sold and driven. Sluggish by today's standards, but driven by somebody graduating from a 216 Chevy or 218 Plymouth of ten years earlier, totally an improvement. It's all relative. Today, we are spoiled by flush glass, high end stereos, great brakes, and deep overdrives. Most of us old timers didn't even think of overdrives 40-50 years ago. We just drove with high winding engines, wind noise, and the AM cranked. There was nothing better to compare to, at that time.


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## AZTempest (Jun 11, 2019)

Your original post had caught my attention as a few month ago I was tunneling into the web about the advantages of close chambered heads vs open. As usual I found lots of opinions but nothing I was really looking for.

It seem to me that many changes made in the designs of the day are leaning into the emissions that were up and coming. Was the open chamber better for emissions, power, etc as compared to the open. I was never able to find an answer that didn’t seem to be someones opinion. Jim brings up some good numbers that seem to show there isn’t much difference, but I do question, why change if something was working.

It’s pretty easy to swap the heads if I need to. I personally just run what I have as it’s just my hobby and they work. It would be nice know the manufactures reasons at the time so we could choose, hopefully getting closer to our goals.....and I'll still install my chrome valve covers cause I know it makes it go faster.


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## 1965 TC4d (9 mo ago)

PontiacJim said:


> OK, as always, my opinions/suggestions and not gospel. LOL
> 
> 
> With the 455, to make it easy, use a flat top piston and then match the combustion chamber CC's to the bore/stroke to get you in the realm of 9.0 or under. I would go with a big valve 2.11" intake head that has screw-in studs. Even though you won't be aiming for high RPM's, you still do not want to choke out the engine. I would want big valves that will in turn aide in the use of the smaller runners of your intake to develop some really good air velocity - the valves won't be a restriction, but the intake will, so I would want the heads at the valve to not be your bottleneck. I would go with a performance 3-angle valve job, gasket match the intake entry of the heads/ports, using an inside "snap gauge" (which can be bought inexpensively in a kit) I would equalize all the intake ports at the pushrod bulge using a high speed die grinder and carbide cutter, and then use the dir grinder to smooth, not polish, the intake runners to remove any rough castings. Nothing fancy, but easy enough to do. If you want to go a step further, get some sanding rolls and using a rough grit, smooth out the ports a little more and you are done.
> ...


Jim,

thanks very much, again.

All very well taken. Especially appreciate the very specific suggestions like the desired rpm at 70. Also the process to arrive at the prospective CR for the 455. That 8.46 might be a bit low, but then again maybe not. A low rpm daily on 87 octane may require a lower CR to avoid detonation. Had hoped to get up to around 8.7(X) or so but that may be too high.

Your posts may not be gospel, (although the book of James in the Pontiac bible might be appropriate), but for me they are very relevant and useful.

ps - would probably just leave the ST300 in place if having a 1:1 top gear was adequate. For this build the 200r provides a bit more flexibility. The downside of course is the cost. Those 200r transmissions are pricey.


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## 1965 TC4d (9 mo ago)

AZTempest said:


> Your original post had caught my attention as a few month ago I was tunneling into the web about the advantages of close chambered heads vs open. As usual I found lots of opinions but nothing I was really looking for.
> 
> It seem to me that many changes made in the designs of the day are leaning into the emissions that were up and coming. Was the open chamber better for emissions, power, etc as compared to the open. I was never able to find an answer that didn’t seem to be someones opinion. Jim brings up some good numbers that seem to show there isn’t much difference, but I do question, why change if something was working.
> 
> It’s pretty easy to swap the heads if I need to. I personally just run what I have as it’s just my hobby and they work. It would be nice know the manufactures reasons at the time so we could choose, hopefully getting closer to our goals.....and I'll still install my chrome valve covers cause I know it makes it go faster.


I found very similar info about the advantages and or disadvantages of closed chamber vs open chamber head design. Very little. There was so much in the responses that was attached to memories and emotions and very little about why some perception or experience would be true or not.

I was particularly interested in how, if at all, a closed head might be better at very low rpm torque production vs the later Pontiac open chamber heads. Quite a number of posters took it quite personally that someone would want to discuss optimizing low RPM power and efficiency.

Before internet forums were available I read magazine articles and books about engines, design and performance. Virtually all the 'known' builders stressed building for low end torque and efficiency for street cars. Such a build would accelerate better, get better MPG and last longer. Then of course the entire rest of the magazine would be about how to get higher peak HP value by moving the power up the RPM range. After the over eight decades of this focus on peak HP at high RPM its engrained in the car culture and people are just going to have an emotional reposes to anything else.

Was grateful to get Jim's response. He leaves out the judgement, focuses on the issue/question, explains WHY he thinks X or Y and gives relevant examples from his personal experience.

Found a complete '65 Tempest Custom four door that I'm getting back on the road. Have always wanted to have a lighter/ish, sub 3500 lb., car with an engine that produced a high amount of very low rpm torque, smooth idle, quiet and optimized efficiency. The combined high torque, within the typical street rpm range, and low/er vehicle weight should produce good results without having to resort to trying to utilize high engine rpm or having to compensate for lower quality engine function and/or poor mpg.

Attempting to bring up the topic of, do closed chamber heads benefit low rpm torque was met with quite a high level of emotional response. Until Jim's response there were little to no direct answer to the closed chamber/low rpm power question. Many would simply say use this X head and never explain why.

I guess its just another reflection of how we don't want to have to question or explain what beliefs we hold that give us comfort and stability.

Your post is appreciated.


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## geeteeohguy (Feb 2, 2008)

If you're thinking of leaving the 2 speed trans in place due to cost considerations of an OD unit, consider installing a TH350. They are cheap, durable, and with the 2.52 first gear instead of the 2 speed's 1.76 first gear, your car will feel like it has 100 more HP off the line and will get better fuel economy in town and overall, due to the extra gear. Highway rpms will be the same, but the engine won't have to work as hard to get up to cruise speed with the gearing advantage of the TH350. It's a direct bolt-in, as well.


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## PontiacJim (Dec 29, 2012)

AZTempest said:


> Your original post had caught my attention as a few month ago I was tunneling into the web about the advantages of close chambered heads vs open. As usual I found lots of opinions but nothing I was really looking for.
> 
> It seem to me that many changes made in the designs of the day are leaning into the emissions that were up and coming. Was the open chamber better for emissions, power, etc as compared to the open. I was never able to find an answer that didn’t seem to be someones opinion. Jim brings up some good numbers that seem to show there isn’t much difference, but I do question, why change if something was working.
> 
> It’s pretty easy to swap the heads if I need to. I personally just run what I have as it’s just my hobby and they work. It would be nice know the manufactures reasons at the time so we could choose, hopefully getting closer to our goals.....and I'll still install my chrome valve covers cause I know it makes it go faster.


A BRIEF history - Pollution.

Cars presented a pollution problem is the larger cities where population density was the normal and to that add all the vehicles - cars, trucks, buses, etc.. So bad was the emissions from vehicles that the air on certain days looked like a fog had set over the cities - called smog. 

It all began in 1959 in California. 20 million gallons of gas were being burned daily and 2 million gallons of unburned gas (hydrocarbons) were being sent into the air every day. Hydrocarbons and oxides of nitrogen are the main make-up of smog. In 1961 the Motor Vehicle Pollution Control Board (MVPCB) was created in California (Later, and presently, called the State of California Air Resources Board (ARB) ). The first requirements by the Board was that all new vehicles sold in CA had to be equipped with a crankcase emissions device - or the PCV valve. Prior to this the crankcase emissions (blow-by & other gases) went out a "road tube" vented to the atmosphere. CA ever required used cars for sale to be fitted with a PCV valve. The PCV valve was very effective in lowering crankcase emissions that it was a requirement adopted nationally in 1963.

So California was the state that began emissions requirements that became national requirements and it continued on from there with CA requiring certain controls for new cars sold in their state, while other states did not have the same requirements. The auto industry fought some of these requirements stating costs of the requirements and the addition of increasing the price of new car sales.

But, the ball was in motion both on the state level and Federal level - as well as safety regulations. One of the things looked into was "quench," that small space between the top of the piston and the flat underside of the head found around the combustion chamber of the typical closed chamber head design.

What the scientist found was that exhaust emissions consisted of about 1/10th of 1% of unburned hydrocarbons which were being sent into the atmosphere. A study was made of the quench area of the typical engine and what they found was that during acceleration, (engine vacuum @ 4Hg) the flame front would travel and approach a "cold wall" due to the quench area and snuff out the burn process and leave unburned fuel - but at a small amount, but during deceleration (engine vacuum @ 20 Hg) the quench area became greater and produced a larger amount of unburned fuel and thus even more hydrocarbons.

So 2 thoughts evolved in lowering the unburned fuel and lower hydrocarbons out the exhaust. Combustion shape changes and increasing engine/cylinder temperatures. Chrysler began to experiment with chamber design on the 170 CI 6-cyl and 273 CI V-8. What they found was that the standard closed chamber head produced 245 parts per million (PPM) of hydrocarbons, a modified tapered quench combustion chamber produced 232 PPM of hydrocarbons, and an open chamber head produced 220 PPM of hydrocarbons.

Next was an increase in engine temperatures. Thermostats went from 180 degrees to 200 degrees. It was found that at an engine with closed chamber heads and a temp of 180 showed hydrocarbons at 215 PPM and dropped to 205 PPM with an engine temp of 200 degrees. Open chamber heads showed 175 PPM hydrocarbons at 180 degrees and dropped to 170 PPM at 200 degrees. BUT, the problem was increased underhood temps so larger cooling systems were required. This also required a change in carb venting to prevent gas percolation issues - so carbs were modified as well. And there was more still - ignition. It was found that if you retarded the timing at idle you reduced hydrocarbons, so ignition timing was altered.

This all hit about 1968 when open chamber heads were introduced, 195 T-stats were standard, and Pontiac used a vacuum advance can having 2 ports- one to retard timing, the other to advance timing, and thermal sensing switches.

So, *open chamber heads were a design to meet emissions requirements *outlined by California requirements and enacted nationally. The rest is history.


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## 1965 TC4d (9 mo ago)

PontiacJim said:


> A BRIEF history - Pollution.
> 
> Cars presented a pollution problem is the larger cities where population density was the normal and to that add all the vehicles - cars, trucks, buses, etc.. So bad was the emissions from vehicles that the air on certain days looked like a fog had set over the cities - called smog.
> 
> ...


While they addressed excess unburnt hydrocarbons with less quench of the open chamber and higher operating temps, it does not appear they necessarily lost any performance or efficiency. How did the power and fuel combustion compare with a similar engine, one closed and the other open chamber?

Same CR, same CI, same carb, just one engine open and one closed chamber.

Perhaps the open chamber head had some beneficial characteristic that made up for the loss of quench.

BTW, excellent review of the why behind open chamber heads. Thanks.


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## 1965 TC4d (9 mo ago)

geeteeohguy said:


> If you're thinking of leaving the 2 speed trans in place due to cost considerations of an OD unit, consider installing a TH350. They are cheap, durable, and with the 2.52 first gear instead of the 2 speed's 1.76 first gear, your car will feel like it has 100 more HP off the line and will get better fuel economy in town and overall, due to the extra gear. Highway rpms will be the same, but the engine won't have to work as hard to get up to cruise speed with the gearing advantage of the TH350. It's a direct bolt-in, as well.


The 200r gears have similar benefit and also OD. Might leave the ST300 in place with the 455 but only as a way to keep it on the road while I save up for the 200r.

Apparently in many ways the 200r is a TH350 with an OD gear.

Would like to make a single trans change/swap.


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## 1965 TC4d (9 mo ago)

AZTempest said:


> Your original post had caught my attention as a few month ago I was tunneling into the web about the advantages of close chambered heads vs open. As usual I found lots of opinions but nothing I was really looking for.
> 
> It seem to me that many changes made in the designs of the day are leaning into the emissions that were up and coming. Was the open chamber better for emissions, power, etc as compared to the open. I was never able to find an answer that didn’t seem to be someones opinion. Jim brings up some good numbers that seem to show there isn’t much difference, but I do question, why change if something was working.
> 
> It’s pretty easy to swap the heads if I need to. I personally just run what I have as it’s just my hobby and they work. It would be nice know the manufactures reasons at the time so we could choose, hopefully getting closer to our goals.....and I'll still install my chrome valve covers cause I know it makes it go faster.


Would suggest Jim's new post in this thread. Good, yet concise description of emissions impact on engine design.


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## geeteeohguy (Feb 2, 2008)

I ran the closed chamber 670 heads on my '67 GTO when I first got it in the early '80's. The car ran like a scalded cat. By 1985 or so, leaded gas was not available and 94 octane was not available. The car pinged badly no matter what. I changed over to #12 open chamber heads with the same CC as the 670's. Car still pinged. Ran just as hard. I noticed ZERO performance difference between the closed and open chambered heads on my stock GTO 400. Both were about 72cc chambers.


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## PontiacJim (Dec 29, 2012)

1965 TC4d said:


> While they addressed excess unburnt hydrocarbons with less quench of the open chamber and higher operating temps, it does not appear they necessarily lost any performance or efficiency. How did the power and fuel combustion compare with a similar engine, one closed and the other open chamber?
> 
> Same CR, same CI, same carb, just one engine open and one closed chamber.
> 
> ...


"Perhaps the open chamber head had some beneficial characteristic that made up for the loss of quench."

With closed chamber heads, you need more spark advance, thus you will see some timing numbers such as 42 BTDC due to a slower burn of the air/fuel mixture. Do this with a Pontiac open chamber head and you will find the engine pinging to a horrible death. If you read the magazine articles of old where Milt Shornack of Royal Pontiac would wring out the GTO engine/trans/gearing combo's for the magazine article, the open chamber heads had less advance. In one article, he adjusted timing by retarding the advance from 34 to 32 to 30 and each time the car ran a little faster settling on the 30 degrees total timing. This of course was with the 102 octane leaded gas and timing all in by around 2,500 RPM's.

Open chambers unshroud the valves - so a Plus on that one.

With regards to HP, many will tell you that the closed chamber produces more power than an open chamber. Hmmmm. Did the 426 Hemi have closed chambers? No, pretty wide open chambers in fact, but the positioning of the valves with a centered spark plug made the design work well. Open chambers have more CC's, so with engines like the Big Block Chevy, the pistons incorporated domes to reduce this volume. Butler offers a Pontiac piston with a dome ad is probably aimed at those big 124 CC chambers on later Pontiacs.

What you see today, as a progression of chamber design, is the swirl port designs. Aftermarket heads usually have heart-shaped combustion chambers to minimize chamber volume and increase the quench area. The heart shape allows for two squish regions and the spark plug orientation is almost centrally located. So this design seems to work best.......until the next best design. LOL


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## 1965 TC4d (9 mo ago)

geeteeohguy said:


> I ran the closed chamber 670 heads on my '67 GTO when I first got it in the early '80's. The car ran like a scalded cat. By 1985 or so, leaded gas was not available and 94 octane was not available. The car pinged badly no matter what. I changed over to #12 open chamber heads with the same CC as the 670's. Car still pinged. Ran just as hard. I noticed ZERO performance difference between the closed and open chambered heads on my stock GTO 400. Both were about 72cc chambers.


Good real world experience and data comparing the two head designs and their respective characteristics.

Wonder what the result would have been had the CR been lowered with the use of dished and matching crown pistons with the closed chamber heads. This would have dropped the CR and at the same time retained much of the quench.

This configuration with the closed chamber heads appeared to be an interesting possibility.


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## 1965 TC4d (9 mo ago)

PontiacJim said:


> "Perhaps the open chamber head had some beneficial characteristic that made up for the loss of quench."
> 
> With closed chamber heads, you need more spark advance, thus you will see some timing numbers such as 42 BTDC due to a slower burn of the air/fuel mixture. Do this with a Pontiac open chamber head and you will find the engine pinging to a horrible death. If you read the magazine articles of old where Milt Shornack of Royal Pontiac would wring out the GTO engine/trans/gearing combo's for the magazine article, the open chamber heads had less advance. In one article, he adjusted timing by retarding the advance from 34 to 32 to 30 and each time the car ran a little faster settling on the 30 degrees total timing. This of course was with the 102 octane leaded gas and timing all in by around 2,500 RPM's.
> 
> ...


All well taken.

For the 455 build it does not appear that closed chamber heads, even with dedicated dished pistons, would offer any significant low rpm power advantage. And certainly not when its higher costs are included.

The aftermarket heads would be the way to go but they are some pretty pricey parts.

Would seem stock Pontiac heads probably have smaller ports in any case which would maintain good charge velocity over the aftermarket heads. Would probably pick up a few ft.lbs. and some MPG with the aftermarket heads but I'll live without that.


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## geeteeohguy (Feb 2, 2008)

What Pontiac Jim printed out about advance requirements is dead on. I can verify it personally. Come to think of it, with the #12 heads, my GTO pinged even worse, but it could be because the gas was even worse . I can tell you from personal experience how dished pistons work with stock closed chamber heads: excellent. 15 years ago I helped a friend build a 389 for a '65 GTO with custom Ross dished pistons (13cc dish) using the stock #76 closed chamber heads that measured 68cc. He used a comp cams 268XE cam and a Holley 700 carb. That car runs as hard as my own '65 GTO. And his car is about 8.5 CR and runs on regular gas. My car has a tripower, 11 CR, and needs race gas. But, that said, I built it 41 years ago and it's still in the car running hard and has never had an issue.


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## 1965 TC4d (9 mo ago)

That 389 is very close to the parameters of the 455 build.

Low CR, smallish cam, closed chamber heads with dished pistons.

How this type of engine build would perform at low rpm, compared to a similar open chamber set up, is still an open question. I suspect it would be fine but would it provide a substantial low rpm benefit over an open chamber that would justify the additional cost.

Would the closed chamber boost low rpm torque over the open chamber? Would the enhanced quench allow a boost in CR above the 8.5 of that 389 engine? To justify using a closed chamber head when the open chamber are common and cheap, or free if they come with the donor engine, using closed chamber doesn't make sense.

Thought the use of dished pistons with closed chamber with the optimized quench would provide a boost in low rpm power and be more efficient. Not sure that's the case.


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## AZTempest (Jun 11, 2019)

So much good information being posted here. Has me pondering different understandings I’ve pondered on in the past. 
Jim, I really appreciate the breakdown you present here. Both of my 67 Tempests were original California emission cars. My ragtop I picked up in 84 already had all the emissions removed when I acquired it. When I picked up my hardtop a few years ago, it still had the air pump installed although it was not functioning. I have removed it and have it shelved with the original intake and carb. A few weeks ago I had decided to install an adjustable vacuum advance to play with and realized it also has the vacuum advance can having 2 ports. I bagged and shelved that as well as I don’t even know if they are available any longer.

1965 TC4d, Thanks for starting this thread. Keep us updated on your progress and findings. I may not be able to contribute much but you really have me thinking. I’m the kind of idiot who will swap out a carb or something just to see how it works even though everything is running fine. 
Geeteeohguy and the others bring up some great points about transmissions and gears. Both my cars came with the ST300. I would not hesitate running that trans again but I did install a TH350 in the hard top and would do that again as well. Hopefully there is a OD I can play with in the near future.


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## 1965 TC4d (9 mo ago)

AZTempest said:


> So much good information being posted here. Has me pondering different understandings I’ve pondered on in the past.
> Jim, I really appreciate the breakdown you present here. Both of my 67 Tempests were original California emission cars. My ragtop I picked up in 84 already had all the emissions removed when I acquired it. When I picked up my hardtop a few years ago, it still had the air pump installed although it was not functioning. I have removed it and have it shelved with the original intake and carb. A few weeks ago I had decided to install an adjustable vacuum advance to play with and realized it also has the vacuum advance can having 2 ports. I bagged and shelved that as well as I don’t even know if they are available any longer.
> 
> 1965 TC4d, Thanks for starting this thread. Keep us updated on your progress and findings. I may not be able to contribute much but you really have me thinking. I’m the kind of idiot who will swap out a carb or something just to see how it works even though everything is running fine.
> Geeteeohguy and the others bring up some great points about transmissions and gears. Both my cars came with the ST300. I would not hesitate running that trans again but I did install a TH350 in the hard top and would do that again as well. Hopefully there is a OD I can play with in the near future.


Seems we think along the same lines.

Bought a '65 GTO in 1980, I think it was a post car. My father helped me drag it back from Missouri to Chicago. No engine and or trans but it was an ST300 car. Found a 455 that was in a junk yard in a mid 70s station wagon. Ran it stock with a TH350 and it was a wonderful car. Sold it to pay off my school loan. poo.

Have two girls, 9 and 10, and was looking for the four door version of that '65 GTO. Did not find a Lemans but rather a Tempest Custom. The 'Custom' part appears to be some additional exterior trim pieces.

Even though the engine was disassembled and both it and the trans were out of the car, the car is very complete. Found a '66 326 that was advertised as rebuilt with about 1000 miles. Hoping to have the '65 Tempest back on the road soon.

Once running and sorted out intend to reproduce the general qualities of my '65 GTO. 389 4bbl, auto trans, P/S, P/B. A smooth, quiet fast daily driver car. The addition of the stock 455 wagon engine only enhanced those positive characteristics.

The 455 build for the four door Tempest is intended to further enhance those same characteristics. Focusing the build on enhancing very low RPM torque will also promote good acceleration, even with tall gears, a smooth idle and will even optimize efficiency. (yes, it is understood that a 455 engine will only ever be so efficient)

To this end a 250/256 Voodoo cam and an SP2P intake will be utilized. Also tallish rear gears and a 200r trans will help the car operate within the rpm range that produces the enhanced torque/power.

To increase low rpm efficiency I wanted to explore the possibility of closed camber heads allowing a higher static CR using a given octane fuel. Thanks to Jim and others I have seen no evidence that there would be any significant benefit that would justify any additional expense to use closed chamber heads.

An aluminum aftermarket head may be a possibility but they are a pretty pricey option.

GM/Pontiac had a similar idea with the 1970 big car 455. Big low end torque to maintain the acceleration of ever more heavy big cars. I just intend to put that engine in a smaller/lighter car. Pretty sure this was the idea behind the '64 GTO which for many defined the muscle car genre.

Would describe the intention to address a-body suspension/steering factory engineering limitations, but that would be another thread.


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