# 67 GTO 400 Heads ?



## 93610 (May 10, 2021)

Does anyone know of Anything to help air flow /cfm on 670's - 72cc Heads. mil 0.040 each, If correct put's them at 64cc, 2cc pr 0.010 With flat top 4 valve relief 30 over pistons, not sure where the compression went ?


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## BearGFR (Aug 25, 2008)

Are those 670's? If so, compression went "through the roof" and now it's going to be unlikely you will be able to run it safely on anything except 100+ octane race gas.

Bear


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## Sick467 (Oct 29, 2019)

Besides the compression "going through the roof"...I'd would definitely look into how much you can deck the heads without effecting the fit to the intake. Disclaimer: I don't know how much you can deck heads before the intake has to be modified to fit properly. If my geometry visualization is up to snuff this morning...as the heads move down and inward, the intake surfaces get closer together and the mating intake surfaces might need to be machined to accommodate. 0.040" sounds like a lot.


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## Sick467 (Oct 29, 2019)

As far as increasing airflow through the heads...you can port match the intake itself, along with the intake ports of the heads, and likewise for the exhaust ports. I assume you would be using headers with this type of high-compression build, but if not, you would want to port match the exhaust manifolds too.

I'm not whiz-bang with cams and rockers, but I do know the proper combination makes what flow is available to happen in a quicker fashion.


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## 93610 (May 10, 2021)

BearGFR said:


> Are those 670's? If so, compression went "through the roof" and now it's going to be unlikely you will be able to run it safely on anything except 100+ octane race gas.
> 
> Bear





BearGFR said:


> Are those 670's? If so, compression went "through the roof" and now it's going to be unlikely you will be able to run it safely on anything except 100+ octane race gas.
> 
> Bear


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## 93610 (May 10, 2021)

Sick467 said:


> Besides the compression "going through the roof"...I'd would definitely look into how much you can deck the heads without effecting the fit to the intake. Disclaimer: I don't know how much you can deck heads before the intake has to be modified to fit properly. If my geometry visualization is up to snuff this morning...as the heads move down and inward, the intake surfaces get closer together and the mating intake surfaces might need to be machined to accommodate. 0.040" sounds like a lot.


You are Right, The Intake was mil to match.


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## 93610 (May 10, 2021)

Sick467 said:


> As far as increasing airflow through the heads...you can port match the intake itself, along with the intake ports of the heads, and likewise for the exhaust ports. I assume you would be using headers with this type of high-compression build, but if not, you would want to port match the exhaust manifolds too.
> 
> I'm not whiz-bang with cams and rockers, but I do know the proper combination makes what flow is available to happen in a quicker fashion.


I did port the Heads & Intake but I m Hoping I didn't port the Ex. now because I heard the over hang on Ex port helped eliminate some back draft from headers back in the motor, Like to Find Truth On This ? I wish to Polish the Inner air flow ports of Heads Before sending em to machine shop.


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## Sick467 (Oct 29, 2019)

Finding the truth on some of this can be frustrating. For example, I have heard that a non polished ported surface can flow better than a finely polished one. I don't know really, I have never tried to get the last ounce of power out of port matching. Improvements have always been good enough for me. And, sometimes the illusion of improvement works fine if it means less money and/or work...lol.


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## 93610 (May 10, 2021)

Sick467 said:


> Finding the truth on some of this can be frustrating. For example, I have heard that a non polished ported surface can flow better than a finely polished one. I don't know really, I have never tried to get the last ounce of power out of port matching. Improvements have always been good enough for me. And, sometimes the illusion of improvement works fine if it means less money and/or work...lol.


I Hear Ya, I never really checked for roughness of the inner pour it could block a lot of air flow, Just give it a good clean up.


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## lust4speed (Jul 5, 2019)

While the 670 heads were advertised at 72cc's, all of them started life right at 76cc's so that helps a little, but while you took off .040" this time that doesn't mean that this was the first cut on them in 54 years. You should really measure out the chambers and find out what size they actually are. I read that you had the intake cut, but the best way to maintain head/intake fit is to have the intake surface on the head milled the same as what you take off the head surface. This way the manifold doesn't end up married to those heads and probably not usable for the next build when heads are changed. Don't forget decking the block also drops the heads down. The good news is the math for milling is ridiculously simple on our Pontiacs and it is a 1:1 ratio on the block-head-intake surface. So remove .040" from head/block surface then remove .040" from head/intake surface.

I've done quite a few 670 heads with good results. 670 Heads for the street can go between 230 to 260 CFM flow with a good safety margin of not getting too thin. Changing the closed chamber design to a semi-open chamber helps out also. Anytime you take a grinder to the heads you are taking a risk because you really don't know how much pitting and erosion has happened during the head's life. First was a pick-a-part head that didn't pass mag'ing so we cut it up to see where the thin spots were, and the second is a stock 670 chamber, while the third is one of the chambers on the 670 heads currently on my '67 GTO. The semi-open chamber modification took the twice milled heads from about 71cc to 83cc. This chamber along with a custom dished piston from Ross put the current compression ratio right at 9.3:1 which works perfect for what passes as 91 octane here in California.

If you are worried about reversion, port the top of the exhaust and leave the bottom of the exhaust port as cast so you end up with a slight wall on the port at the bottom. I haven't seen any signs of reversion with a good set of headers without the wall, but the bottom section doesn't do much for exhaust flow anyway so wouldn't hurt to leave it. 

Remember that just hogging out a port will do irreparable damage and can totally kill flow so either get a book that has a step by step guide or really visualize what the gas/air mixture needs to do to get through the port without pulling away from the wall. Most critical is the short turn and much better to leave it as a large gentle curve than attempt to enlarge the area and have the mixture pull away as it goes through the turn and go into turbulence.

Photo of a bone stock 670 intake port. Notice some areas are really thin. 




















The chamber wall has been laid back considerably, and the crossover ports have also been filled (but you want to live in a location with really mild winters or
you will be hating it).


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## 93610 (May 10, 2021)

lust4speed said:


> While the 670 heads were advertised at 72cc's, all of them started life right at 76cc's so that helps a little, but while you took off .040" this time that doesn't mean that this was the first cut on them in 54 years. You should really measure out the chambers and find out what size they actually are. I read that you had the intake cut, but the best way to maintain head/intake fit is to have the intake surface on the head milled the same as what you take off the head surface. This way the manifold doesn't end up married to those heads and probably not usable for the next build when heads are changed. Don't forget decking the block also drops the heads down. The good news is the math for milling is ridiculously simple on our Pontiacs and it is a 1:1 ratio on the block-head-intake surface. So remove .040" from head/block surface then remove .040" from head/intake surface.
> 
> I've done quite a few 670 heads with good results. 670 Heads for the street can go between 230 to 260 CFM flow with a good safety margin of not getting too thin. Changing the closed chamber design to a semi-open chamber helps out also. Anytime you take a grinder to the heads you are taking a risk because you really don't know how much pitting and erosion has happened during the head's life. First was a pick-a-part head that didn't pass mag'ing so we cut it up to see where the thin spots were, and the second is a stock 670 chamber, while the third is one of the chambers on the 670 heads currently on my '67 GTO. The semi-open chamber modification took the twice milled heads from about 71cc to 83cc. This chamber along with a custom dished piston from Ross put the current compression ratio right at 9.3:1 which works perfect for what passes as 91 octane here in California.
> 
> ...





lust4speed said:


> While the 670 heads were advertised at 72cc's, all of them started life right at 76cc's so that helps a little, but while you took off .040" this time that doesn't mean that this was the first cut on them in 54 years. You should really measure out the chambers and find out what size they actually are. I read that you had the intake cut, but the best way to maintain head/intake fit is to have the intake surface on the head milled the same as what you take off the head surface. This way the manifold doesn't end up married to those heads and probably not usable for the next build when heads are changed. Don't forget decking the block also drops the heads down. The good news is the math for milling is ridiculously simple on our Pontiacs and it is a 1:1 ratio on the block-head-intake surface. So remove .040" from head/block surface then remove .040" from head/intake surface.
> 
> I've done quite a few 670 heads with good results. 670 Heads for the street can go between 230 to 260 CFM flow with a good safety margin of not getting too thin. Changing the closed chamber design to a semi-open chamber helps out also. Anytime you take a grinder to the heads you are taking a risk because you really don't know how much pitting and erosion has happened during the head's life. First was a pick-a-part head that didn't pass mag'ing so we cut it up to see where the thin spots were, and the second is a stock 670 chamber, while the third is one of the chambers on the 670 heads currently on my '67 GTO. The semi-open chamber modification took the twice milled heads from about 71cc to 83cc. This chamber along with a custom dished piston from Ross put the current compression ratio right at 9.3:1 which works perfect for what passes as 91 octane here in California.
> 
> ...


Milled heads & manifold up comp for cam 12/87 still not sure if it's yet right. 180 / 190 was all I'v heard about 670's 72cc's cfm, I hope it's better. Like that sludge in the intake port 's what I 'll look for, Ive heard bad pours leaving ledges instead of smooth curves that are here shone. Why plug crossover ports ?


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## PontiacJim (Dec 29, 2012)

Sick467 said:


> Finding the truth on some of this can be frustrating. For example, I have heard that a non polished ported surface can flow better than a finely polished one. I don't know really, I have never tried to get the last ounce of power out of port matching. Improvements have always been good enough for me. And, sometimes the illusion of improvement works fine if it means less money and/or work...lol.


The "old school" thinking was to mirror polish the runners. Then it was changed to leaving a rougher finish, like finishing up with something like an 80 grit sanding roll. The rougher finish is said to keep the gas molecules from dropping out of suspension . Guess all those head porters of the 1950's - 1970's didn't know this and neither did their engines as they continued to set new records back then. I think some of these things are just overthinking it and you may not see any difference on a street engine if the intake runners are left, stock, mirror polished, or slightly rough - its just one of those "feel good" things just because you did it and can tell your buddies about it. Oh, it also adds 100 HP according to Hot Rod magazine. Add headers - 75HP, 780 Holley carb and aluminum intake - 30 HP, Accel dual point and coil - 22HP, K&N air filter - 8 HP, hood scoop/ram air - 15HP. It doesn't take much to get that factory 360HP from Pontiac right on up to a blistering 610HP with just a little work and some add-on parts.


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Milled heads & manifold up comp for cam 12/87 still not sure if it's yet right. 180 / 190 was all I'v heard about 670's 72cc's cfm, I hope it's better. Like that sludge in the intake port 's what I 'll look for, Ive heard bad pours leaving ledges instead of smooth curves that are here shone. Why plug crossover ports ?


Good info and pics from *lust4speed*.

On average the Pontiac heads flow around 205 @ 28" Hg, so the "Hg" is very important because many will list head flow at 25"Hg, or even 20"Hg, and flow numbers will be lower.

Important area is the pushrod bulge - this is the "pinch point" that can impede flow. I used an inside snap gauge and widened all the pushrod bulges to match the widest I found when checking each runner. Then I equalized all my runners to that size. You can grind more, but if yo break through the wall, you have to sleeve it with a tube - which is often done when doing an all-out port job.

You want to smooth out any casting lines/bumps. You may not get them perfectly smooth if they are a bit deep, so just clean up what you can and smooth things out. The biggest improvement is to open up the valve throats, but this is not really for home doing and better left to someone who knows what to do.

Port match the heads/intakes, You can use a stock sized intake gasket or go RAIV which is slightly larger. When opening the ports to RA IV size, blend the port opening in about 1" into the runner, ie taper it back to blend the larger opening into the smaller stock runner wall.

3- angle valve job is another big improvement with flow numbers.

You don't have to go crazy on the exhaust port, just clean them up. Headers are going to help flow as well as a well chosen cam that has a little more lift/duration to get the exhaust gases out.

Filling the exhaust crossover smooths out the air flow and any turbulence created by the openings. Not sure how much it improves CFM or flow. Have not seen a comparison between filled or non-filled exhaust crossover. It may actually be more of a means to keep heat off the bottom of the carb and out of the intake where heat can affect engine power.

With the 670 heads and milling them, you will need racing gas if you do not get dished pistons to lower the compression.


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## 93610 (May 10, 2021)

lust4speed said:


> While the 670 heads were advertised at 72cc's, all of them started life right at 76cc's so that helps a little, but while you took off .040" this time that doesn't mean that this was the first cut on them in 54 years. You should really measure out the chambers and find out what size they actually are. I read that you had the intake cut, but the best way to maintain head/intake fit is to have the intake surface on the head milled the same as what you take off the head surface. This way the manifold doesn't end up married to those heads and probably not usable for the next build when heads are changed. Don't forget decking the block also drops the heads down. The good news is the math for milling is ridiculously simple on our Pontiacs and it is a 1:1 ratio on the block-head-intake surface. So remove .040" from head/block surface then remove .040" from head/intake surface.
> 
> I've done quite a few 670 heads with good results. 670 Heads for the street can go between 230 to 260 CFM flow with a good safety margin of not getting too thin. Changing the closed chamber design to a semi-open chamber helps out also. Anytime you take a grinder to the heads you are taking a risk because you really don't know how much pitting and erosion has happened during the head's life. First was a pick-a-part head that didn't pass mag'ing so we cut it up to see where the thin spots were, and the second is a stock 670 chamber, while the third is one of the chambers on the 670 heads currently on my '67 GTO. The semi-open chamber modification took the twice milled heads from about 71cc to 83cc. This chamber along with a custom dished piston from Ross put the current compression ratio right at 9.3:1 which works perfect for what passes as 91 octane here in California.
> 
> ...





PontiacJim said:


> Good info and pics from *lust4speed*.
> 
> On average the Pontiac heads flow around 205 @ 28" Hg, so the "Hg" is very important because many will list head flow at 25"Hg, or even 20"Hg, and flow numbers will be lower.
> 
> ...


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## 93610 (May 10, 2021)

Lonewolf said:


> Milled heads & manifold up comp for cam 12/87 still not sure if it's yet right. 180 / 190 was all I'v heard about 670's 72cc's cfm, I hope it's better. Like that sludge in the intake port 's what I 'll look for, Ive heard bad pours leaving ledges instead of smooth curves that are here shone. Why plug crossover ports ?


Thank's for the Pic's . ?


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Can one find a Cam Compression Range by the Cam Specs, Race range, how does one estimate before the build ? Thank's for the Pic's . ?


Use the Wallace Dynamic Compression Calculator. It may not be the best way to go, but it can give you a little edge in knowing.



Wallace Racing: Dynamic Compression Ratio Calculator



Your actual compression is called Static Compression and it is simply adding up all the "CC's" of the head, piston height, head gasket thickness, valve reliefs, etc..



Compression Ratio Calculator - Wallace Racing


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## 93610 (May 10, 2021)

PontiacJim said:


> Use the Wallace Dynamic Compression Calculator. It may not be the best way to go, but it can give you a little edge in knowing.
> 
> 
> 
> ...


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## PontiacJim (Dec 29, 2012)

Yes, the grind will include the cam's profile, duration/lift/lobe separation angle/lobe center. This can then be used to match up a similar cam or find the actual cam and check the cam manufacturer's website/email and they may have an online cam card or tell you the power band.


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## 93610 (May 10, 2021)

PontiacJim said:


> Yes, the grind will include the cam's profile, duration/lift/lobe separation angle/lobe center. This can then be used to match up a similar cam or find the actual cam and check the cam manufacturer's website/email and they may have an online cam card or tell you the power band.


I find no one who speaks of a Compression formula to find the Best Compression needed for a Cam to run it's best peak by it's grind, other than, They say, IT will run at, 9.5:1- 10.5:1- 11:1. That will not be any where of it's best ? These racing for business know & present what's needed for the parts before the build ? The cam card has no RPM range / band or Compression needed for best out come for the Cam. How one get's it is up to them. But ea. grind has that Compression number for the run ? I'd like to find the formula, Ha Ha to where one doesn't need an engineer.


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> I find no one who speaks of a Compression formula to find the Best Compression needed for a Cam to run it's best peak by it's grind, other than, They say, IT will run at, 9.5:1- 10.5:1- 11:1. That will not be any where of it's best ? These racing for business know & present what's needed for the parts before the build ? The cam card has no RPM range / band or Compression needed for best out come for the Cam. How one get's it is up to them. But ea. grind has that Compression number for the run ? I'd like to find the formula, Ha Ha to where one doesn't need an engineer.


You are looking for the "Holy Grail" and never going to find it. Ask 100 people what the best cam grind is for your build and you will get 100 different answers and then when you install the cam - it may be a failure.

It really isn't too hard to figure out if you do a lot of reading and pick up several books that explain the cam basics and theory.

More duration and more overlap is what requires more compression. Big duration numbers and a lot of overlap blows cylinder pressure out the exhaust - lowering compression at lower RPM's and you lose a lot of power. So compression must be increased to compensate and even then, you may still have a lowered compression at lower RPM's which is picked back up at the higher RPM's - it is a trade off. If you did not have a higher compression to match the larger duration and/or valve overlap, the engine will have no power and all you have is a big cam that does nothing.

Most cams WILL give you an RPM range that they work best - but the key word is BEST. Outside of the best range and your car my be a dog. No good having a big cam if the heads/intake/carb are too small and don't flow enough CFM's. On the other hand, you don't want to small a cam with a big flowing top end as this will choke HP.

Note that the cam companies will suggest the compression ratio, stall converter needed if automatic, and rear end gears to go with the cam choice - there is a reason for this. You also have to match your engine parts to work with the cam choice or you may have a poorly performing car. So a lot to consider and just looking for the "right" cam with just an idea of what you want won't cut it. Have a cam in mind, then build the engine for the cam.

Plenty of info on the internet worth reading as well, just have to do a lot of reading. Build a Pontiac for torque, not horsepower, as that is their design. Determine your intended use of the car. There is no single cam that will give you everything. Decide what RPM range you want your power/torque to be the best. But, if you pick a cam that has upper RPM power, it'll be a dog in the lower RPM's. Fine for racing, but you will be unhappy if you do a lot of cruising around town.

Buy and read the book by David Vizard, 
HOW TO BUILD HORSEPOWER*, *as he explains much of this and it should answer many of your questions. Here is a YouTube video you may be interested in:








Here are some basics to consider. Cam duration and power band, Factory AND aftermarket cam choices. The last pic goes with this explanation:

*Overlap Estimator Section* - One Is For Street Towing, Two Is For Regular Street, Three Is Street Performance, Four Is For Street/strip, Five Is For Race, And Six Is Pro Race.


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## 93610 (May 10, 2021)

PontiacJim said:


> You are looking for the "Holy Grail" and never going to find it. Ask 100 people what the best cam grind is for your build and you will get 100 different answers and then when you install the cam - it may be a failure.
> 
> It really isn't too hard to figure out if you do a lot of reading and pick up several books that explain the cam basics and theory.
> 
> ...


BINGO, You Said IT. Build The Engine For The CAM. I have said this to all, I don't think they allow them or, don't know how. They only say size the Cam to the Engine. I have not seen this lower Cam chart, The last one 51-330-4 is mine. They say my RPM is 3000 / 6500. In 87 when bought I was told 7000. This is the project I'm seeking Compression & CFM for & Build the Engine To. I think these shops are afraid of Truth, or just don't know it . Insurance ?


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## 93610 (May 10, 2021)

Lonewolf said:


> BINGO, You Said IT. Build The Engine For The CAM. I have said this to all, I don't think they allow them or, don't know how. They only say, size the Cam to the Engine. I have not seen this lower Cam chart It's Correct, The last one 51-330-4 is mine. They say my RPM is 3500 / 6500. In 87 when bought I was told 7000. This is the project I'm seeking Compression for & Build the Engine To. HaHa 1.65 Rockers would be Interesting. I think these shops are afraid of Truth, or just don't know it . Insurance ? Hears a Cam card they E-mailed me a yr ago. Must be new cut ?



View attachment 145059


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> BINGO, You Said IT. Build The Engine For The CAM. I have said this to all, I don't think they allow them or, don't know how. They only say size the Cam to the Engine. I have not seen this lower Cam chart, The last one 51-330-4 is mine. They say my RPM is 3500 / 6500. In 87 when bought I was told 7000. This is the project I'm seeking Compression for & Build the Engine To. I think these shops are afraid of Truth, or just don't know it . Insurance ?


OK, you have a race cam - Comp Cam 305-AH-8 cam 108* LSA 253/260 @.050 duration, .524/.540 lift w/1.5 rockers and .577/.594 lift w/1.65.

I then took these numbers and plugged them into one of the on-line calculators trying to get some idea of what the cam's opening/closing specs are. This is what I came up with* IF* I am correct.

Results at .050 duration -

Intake Open: 22.5BTDC
Intake Close: 50.5ABDC
Exhaust Open: 62BBDC
Exhaust Close: 18ATDC

Intake Centerline: 104ATDC
Exhaust Centerline: 112BTDC

Played with my Dyno 2000 engine program and plugged in the cam numbers @ .050". Used 400CI, 11:1 compression, big valve heads, dual plane intake, 750 CFM, open headers.

The cam has a 3,500-7,500 power band. Under 3,500 RPM's it is dead, very little power.

HP @ 3,500 RPM - 241, HP @ 7,000-7,500 RPM was max power - 468HP. Best Torque number was 442 @ 5,000 RPM's.

So this is for a high winding engine, ie race engine. This would not be too good on the street. You would need 110 race gas, high stall converter if automatic, and probably 4.56 rear gears.

So that should give you some more info to think about.


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## lust4speed (Jul 5, 2019)

I'll word it a little stronger - the combination will suck on the street. Big cams and street use simply don't go together because to make them work you need higher compression, very low gears, and a really high stall converter. A good example is some of the dyno testing we did back in the mid-1980's when we took a couple weeks swapping cams, intakes, and carburetors on the engine dyno. One of the larger solid roller cams in our testing back then was comparable in duration to your HFT cam and produced an additional 30 horsepower at 6,300 RPM* over a more moderate cam -- but was down 90 horsepower at 3,500 RPM and was even more of a disaster below that. At the dragstrip with proper gearing and a 5,000+ RPM stall converter and race gas it would out perform a more reasonable cam. On the street it would not only be miserable, but would be extremely weak pulling up through the gears - and a more reasonable stall converter and a moderate build engine will run away from it.

You can sound mean and run like crap or have a properly engineered engine and be quick. If you pick out the wrong cam that looks good on paper and build the engine around it as stated above then you will end up with the wrong engine assembly. Back in the day I tooled around town with all the race items paying for race gas, and it's a bunch more fun and easier on the budget to start with a pump gas diet and proper engine parts and then pick out the cam to complement the running gear. You might also ask yourself whether you want to pay for pump 91/93 octane or spend $16.00 a gallon for race gas so you don't hammer the bearings out.

* We were initially running the engine up to 7,200 RPM on the dyno but quickly found out that the 260 CFM 670 heads were done at 6,300. If you have a more moderate port job, lesser intake, and run through mufflers that will lower peak power down to 5,800 RPM pretty quickly.


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## 93610 (May 10, 2021)

PontiacJim said:


> OK, you have a race cam - Comp Cam 305-AH-8 cam 108* LSA 253/260 @.050 duration, .524/.540 lift w/1.5 rockers and .577/.594 lift w/1.65.
> 
> I then took these numbers and plugged them into one of the on-line calculators trying to get some idea of what the cam's opening/closing specs are. This is what I came up with* IF* I am correct.
> 
> ...


Found my file / Original Cam Warranty Card.


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## Machinest-guy (Jul 19, 2019)

Good morning, I appreciate the accurate information found here. Especially those head cut away photos. My GTO engine is similar to the one first discussed. '65 389 block @+.030 with 4 valve relief pistons. O67 heads and HO manifold / Holley carb. Isky cam .440 lift/ 280 duration and valve train running however it was installed on Cloyes sprockets. Ineffective port work at the manifold junction typical of 1970's kids working on cars was done. It ran great back then. Took 7th in county SCCA auto crossing it in mid '70's. But a bunch of other life events like marriage, kids, work, came up so I parked it for 40 or so years thinking I'd do the engine over dropping compression to eliminate need for 100+ octane fuel. After getting the car out last year and running again, it really doesn't like modern pump gas, so I'm even less able to have fun with the car despite adult kids, semi retirement, and my wife being far more welcoming to motor sports. 

So my input is; don't get too crazy over maximizing compression ratio. 

I've been a professional mechanic for over 50 years and own an engine machine shop (now dedicated to just fooling around). I've built several hundred hot rod street engines over the years. IF divided into two categories - Fun vs Painful - the dividing line is about 10 to one static compression ratio when you get the heads breathing well and 9.5 is even easier to tune.

When you look at the head deck surface in the cut away photo it's not that thick compared to modern race heads where minimum thickness is greater than .500 inch. In my opinion don't mill the OEM heads at all unless absolutely necessary - the thicker deck will bring more joy because it won't leak and fail gaskets. Maybe, maybe, mill the block a bit instead. Or get some longer rods made up to set your deck height as proud as the gasket / block can stand. OEM Pontiac rods scare me for over 5500 RPM full power road racing. In my opinion money is well spent upgrading that part of your build and having them made just right for a particular engine. Or offset grind the crank and pick up a bit of stroke while setting the deck clearance at proper quench and so on. Thick castings are safer on vintage engines. Don't take chances on creating / finding a hole or cracking them.

You can nearly always pick up some effective compression by re-timing the intake valve closing if post build tuning indicates the engine can stand it. - Build conservatively then tune aggressively -. But setting effective compression ratio by changing intake valve closing is only one third of the camshaft story. It works out real well if you can set max valve lift (which should equal max air flow point in flow test results) to happen when the rod is at a 90 degree angle to the crank throw. That is max piston velocity and max signal to the intake charge to fill the cylinder. That is a mechanical second part of the cam puzzle I see some club members working toward figuring out with the charts and so on posted above. Another third is like shooting ducks. The shot needs to be fired ahead of the bird so they fly into it. The intake charge needs some time to move into the cylinder so you need to open the intake valve a little early to get things started moving. This is where you need a great cam grinder. They will know where to locate the acceleration ramps on the cam flanks to lead a max air flow point properly. Some computer programs allow for moving lobe centers and changing timing points on model cams. It will make quite a difference in power production and in a large way determine the octane requirement of an engine as those values are modified without changing the gross timing or lift. It is absolute cylinder pressure (and temperature) that determines octane requirements - not compression ratio, which is an indicator of expected pressure rise of the inducted mixture charge. Pontiac heads with closed chambers don't need much valve overlap timing (lost fuel charge for "scavenging" a whole different subject). Those big valves are close together and nothing is in the way of cross flow. Keep an overlap period to a minimum. Better fuel economy will be a nice side benefit.

When looking at the top side of the cut away head photo I see it is very thin. That screams out need for a stud girdle to prevent rocker arms from flexing around. Rocker stud movement is amplified by the rocker arm ratio causing avoidable changes to valve timing.

If the heads and block are cut minimum amounts then an OEM intake manifold will likely fit without re-working it. Pontiac manifolds are big and very strong structurally, stronger than the head casting, so when bolts are tightened it is the head that bends, not the manifold, as happens with some other engines. I invented a universal fixture to hold and re-surface intake manifolds used in conjunction with common automotive machine tools to compensate for head / block thickness changes. It is my preference to re-surface a manifold because it is typically the less expensive part to replace when an engine is reconfigured. I/E you can have thousands of dollars in a head set while only having a few hundred in a manifold, so a manifold become the consumable part. I've re-surfaced manifolds for guys all over the country who send them here for correction / salvage. It is also entirely possible to correct the fit by surfacing the manifold side of a head. My fixture will also hold heads that a builder will want modified. It is really up to the engine builder which way they want to go as an engine project comes together.

I hope these suggestions help move us towards having more fun. Best regards, Ladd


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Found my file / Original Cam Warranty Card.
> View attachment 145067


Yep, there are your numbers at .006" versus the .050" I used/had. Valve overlap using the advertised duration/LSA comes up at 92.5 degrees - that's a race cam territory, not street. That's why you will want a stout/high compression ratio or you will have a dog of an engine and my 2015 Hyundai will out run it.


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## 93610 (May 10, 2021)

PontiacJim said:


> Yep, there are your numbers at .006" versus the .050" I used/had. Valve overlap using the advertised duration/LSA comes up at 92.5 degrees - that's a race cam territory, not street. That's why you will want a stout/high compression ratio or you will have a dog of an engine and my 2015 Hyundai will out run it.


 Would you be willing to run this Card's numbers through your Computer Program ? 400CI +.030, 406 CI 11.44:1 with .00 Deck clearance with .041Gasket on a combustion calculator the other day, what ever you feel best. Thank You Sir.


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Would you be willing to run this Card's numbers through your Computer Program ? 400CI +.030, 406 CI 11.44:1 with .00 Deck clearance with .041Gasket on a combustion calculator the other day, what ever you feel best. Thank You Sir.


Still a race cam using seat-to-seat numbers. Again, my program is not high end, just a general program, so these numbers may not be exact, but should give you an idea of what you'll have. Adding better heads, intake, carb, etc. can improve things.

HP
2000 - 117
2.5 - 171
3.0 -208
3.5 - 252 WHICH IS WHERE POWER PICKS UP

Best HP
6,500 - 485
7.0 - 483
7.5 - 483 THEN DROPS OFF FAST

Torque
4,000 - 404
4.5 - 426
5.0 - 434 WHICH IS THE BEST NUMBER
5.5 - 430 Then begins to fall back down into the 300 ft lb range


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## 93610 (May 10, 2021)

PontiacJim said:


> Still a race cam using seat-to-seat numbers. Again, my program is not high end, just a general program, so these numbers may not be exact, but should give you an idea of what you'll have. Adding better heads, intake, carb, etc. can improve things.
> 
> HP
> 2000 - 117
> ...


This engine should handle it ? it's the same block on the 455CI right just keep rpm under control, After now seeing original cam card what rear gear & stall & Ha Ha what for the street, Both of ea.


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> This engine should handle it ? it's the same block on the 455CI right just keep rpm under control, After now seeing original cam card what rear gear & stall & Ha Ha what for the street, Both of ea.


Throw the cam away, period. It is not a street cam and trying to use it on the street does not make sense at all.

Build a 461 stroker from your 400CI block and select a matching street cam to go with your heads/intake/carb.


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## 93610 (May 10, 2021)

PontiacJim said:


> Throw the cam away, period. It is not a street cam and trying to use it on the street does not make sense at all.
> 
> Build a 461 stroker from your 400CI block and select a matching street cam to go with your heads/intake/carb.


I have looked at strokers, I would like to see this run all out for now. You spoke of rear gear 4.56 range , they say 3500 Stall conv. that wont get it will it ?


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## 93610 (May 10, 2021)

m


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## PontiacJim (Dec 29, 2012)

I am not a racer, so can only go by what others say/post. All I can say is that you will need a high stall converter and good gearing to make up for the lack of power from the bottom RPM band.

The Crower 60213 cam is very similar, so did a search using it. You may be able to tame some of the loss of the bottom end RPM with a set of Rhoads Lifters.






Pontiac Hydraulic Flat Tappet Camshaft - Camshafts


Pontiac 287-455 Hi-Draulic Hauler Camshaft (308-Hdp)




www.crower.com





Head CFM flow will also limit the power. Stock heads may quit early. Using a CFM claculator and stock 205 CFM flow, it comes up at near 5,400 RPM's. If that is correct, your power band will be between 3,500 - 5,400 RPM's which is very narrow. If you are just looking for an engine that sounds good, has no vacuum to operate power brakes, is "balky", and has a narrow RPM band, then your cam will work for you. Everyone has an idea of what they are looking for out of their car.

I did find this post that is close. It is a 428 so going to be some differences, but uses the Crower 60213.

*1990 After 3 400s ,those just didn't hold up *

*428* .040 over,, dynoed at 418hp 423ftlbs
sealed power pistons ,dished ,.012 in the hole
block was not decked,stock crank 10/10 
oil system mods ,80psi pump 
Warrior Racing oil pan /windagetray/cr scraper 
*Stock rods*,picked the best out of 24 
shot peened/polished beams,arp bolts and sized 
all balanced 
*Top end*
Torker 2 intake 1 in spacer
Holley 850 dp 78/80jets 36/39 shooters
*HEADS* ,stock #48 
HO racing valve angles , 
stock rockers, 1.5 
*Cam *Ho racing ,HC-03 
244/252 .500 lift 
rhoads lifters,com cam springs
1 3/4 3in headers,4 tube,org company before Blackjack, $60 new in the box
*Exhaust* ,3in straight into org 3in flowmasters ,down spouts at rear
HEI dist,ext coil, no module,MSD 6a ,recurved/ locked vac adv,,,32 in by 1800
*TRANS*- 4spd M20 
stock clutch and flywheel 
*stock pont rear 3:90 gears *

Ce rear shocks and air bags,set the right rear at 15
stock rims and tires,MT slicks 15in 29.5/10.5 used 
battery in the trunk 

69 GTO 3960 with driver 

13.10/ 101 to 
best 12.91/102 

*blew the rear,*,, plus 4th gear crunch ,too many miss shifts 

1991 1st update 

lighten car 
Replaced M-20 for a *T*H400 out of a super stock bbc camaro 
Reverse manual shifting and trans brake 
*10 in 3200 stall* Dynamics, loose converter ,,used
*12 bolt 4:56 gears* $400 swap neet special

New cam *- **Crower 60213*
Carb Shop blue pump+ reg #8 line to the front,fram filter 

weight = 3710 with driver 
12.60/105 same used slicks

Blew the front u-joint and damaged the tailshaft after 11 passes,Chevy case with adapter doesn't work, swapped internals to a Pontiac case


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## BearGFR (Aug 25, 2008)

I looked at your cam card and that's a lot of duration and a really tight separation angle. I don't remember if you said this is a roller or not but if that's a flat tappet cam you're going to hate it on the street.
I'm running a moderately aggressive solid roller in my 461, but it's not as rowdy as that one you have, plus mine has a 110 LSA instead of that 108. It took me 12 solid months to get my carburetion dialed in with the cam I have because very small changes in idle RPM causes vacuum to fall off a cliff. Even with a thousand RPM idle it really ran lean, but as soon as the RPM started to climb and that vacuum came in it was going so rich that I was legitimately worried about fuel wash taking out my rings. You can get away with a little more with a roller because those ramps can give you the duration without adding a bunch of overlap. 
I'm running 3.50 rear gears in my car behind a 3200 RPM converter, and with that at 70 miles an hour I'm turning close to 3300 RPM. Go much taller than that and you can forget about ever taking that car out of the city limits or on the freeway. 
That's definitely a race cam, and you're going to need a ton more head flow than what you have to ever have it prayer of making it work, plus you're going to need a bottom end that's bulletproof to turn the kind of RPM is going to take to make that cam run. 

Bear
.


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## 93610 (May 10, 2021)

PontiacJim said:


> I am not a racer, so can only go by what others say/post. All I can say is that you will need a high stall converter and good gearing to make up for the lack of power from the bottom RPM band.
> 
> The Crower 60213 cam is very similar, so did a search using it. You may be able to tame some of the loss of the bottom end RPM with a set of Rhoads Lifters.
> 
> ...


Correct, the Hydraulic Rhoads Lifters do help, that's probably the only way I was able at times to drive this beast on a stock converter Ha Ha.. Sir Jim, You have helped me so much to see more into this engine that has sat alone for so many yr's, Then one's I have spoke to in 2yr's just seeking compression & true rpm band, with your comp. program as well, I Thank You , and Hope I have not put you through much inconvenience. I Very Much Appreciate Your Time. Just had to share that with you Sir. I was going to ask if you had a shop / were a ol' school mechanic, racer ?


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## 93610 (May 10, 2021)

BearGFR said:


> I looked at your cam card and that's a lot of duration and a really tight separation angle. I don't remember if you said this is a roller or not but if that's a flat tappet cam you're going to hate it on the street.
> I'm running a moderately aggressive solid roller in my 461, but it's not as rowdy as that one you have, plus mine has a 110 LSA instead of that 108. It took me 12 solid months to get my carburetion dialed in with the cam I have because very small changes in idle RPM causes vacuum to fall off a cliff. Even with a thousand RPM idle it really ran lean, but as soon as the RPM started to climb and that vacuum came in it was going so rich that I was legitimately worried about fuel wash taking out my rings. You can get away with a little more with a roller because those ramps can give you the duration without adding a bunch of overlap.
> I'm running 3.50 rear gears in my car behind a 3200 RPM converter, and with that at 70 miles an hour I'm turning close to 3300 RPM. Go much taller than that and you can forget about ever taking that car out of the city limits or on the freeway.
> That's definitely a race cam, and you're going to need a ton more head flow than what you have to ever have it prayer of making it work, plus you're going to need a bottom end that's bulletproof to turn the kind of RPM is going to take to make that cam run.
> ...


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## 93610 (May 10, 2021)

[/QUOTE]


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Just need's small adjustments.


 Can 670 72cc heads in any way produce better CFM ? ALL Options Please.
[/QUOTE]

I grew up with these old cars and owned several GTO's/Pontiacs and many other brands. Learned hands on with most of it. Never raced - except street racing as many of us did. I never did much engine work or rebuilding as back in "the day" there was little money, so we made faster what we had by adjusting things. If an engine blew-up, it was off to a junk yard or someone local and you installed another - same with transmissions/rear-ends.

Being a Pontiac enthusiast, hot rod enthusiast, lead sled enthusiast, and the need for speed to see how many police I could piss off and get tickets from, I simply enjoy all types of cars and all years. I am also a magazine/book reader and have a small library to source info and a good memory. So cars have been my interest for over 55 years and still going strong - its in the blood. So I am no expert, just know a lot of things about a lot of stuff and ca offer advice and then the rest is up to you. It is always good to talk with an engine builder/machine shop as they are the experts and I visit my engine builder regularly with my questions as well - more knowledge for me.

How deep is your wallet? Port work and rebuild will most likely put you close to simply buying a new set of D-port aluminum heads.

If you have a die-grinder/carbide cutting bits, you can gasket match the intake runners, equalize the throats at the pushrod bulge (if you feel comfortable enough grinding a little and not too much so as you don't bust through the pushrod bulge - which can be fixed), smoothing out any rough areas but not to the point of polishing.

New taller RA IV Ferrea stainless steel valves to give you some height for the high lift of the cam, new bronze valve guides, cut down the valve guides for positive seals, 3-angle valve job, new springs rated for the cam, new retainers/valve locks, Big Block 7/16" rocker arm studs with poly-locks, new pushrods, new 1.5 stamped steel rocker arms.

This might get you closer to around 215 CFM's, so a lot of work/money for what you will get out of the heads - unless you send the heads out to a professional head porter.

The D-port aluminum heads will flow big right out of the box and have all the good parts needed above. Keep in mind that the aluminum heads are typically designed on the RA IV head and *you will need the correct RAIV head bolts.*

The bigger flow numbers may hurt your bottom end power even more as port velocity will be less and it'll take some RPM's to get port velocity flowing.

You will also want to make sure the intake will flow with the heads. You don't want the intake to only flow 230 CFM's and the head 280CFM - the intake then becomes your "choke" point and so goes with the carburetor.

The bigger the HP/TQ above factory numbers, the more money you will spend on the engine/trans/rear-end as you find all the weak spots in your build. So trying to go "cheap" and expect big HP/TQ returns is a recipe for disaster, disappointment, and wasted dollars.


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## 93610 (May 10, 2021)

I grew up with these old cars and owned several GTO's/Pontiacs and many other brands. Learned hands on with most of it. Never raced - except street racing as many of us did. I never did much engine work or rebuilding as back in "the day" there was little money, so we made faster what we had by adjusting things. If an engine blew-up, it was off to a junk yard or someone local and you installed another - same with transmissions/rear-ends.

Being a Pontiac enthusiast, hot rod enthusiast, lead sled enthusiast, and the need for speed to see how many police I could piss off and get tickets from, I simply enjoy all types of cars and all years. I am also a magazine/book reader and have a small library to source info and a good memory. So cars have been my interest for over 55 years and still going strong - its in the blood. So I am no expert, just know a lot of things about a lot of stuff and ca offer advice and then the rest is up to you. It is always good to talk with an engine builder/machine shop as they are the experts and I visit my engine builder regularly with my questions as well - more knowledge for me.

How deep is your wallet? Port work and rebuild will most likely put you close to simply buying a new set of D-port aluminum heads.

If you have a die-grinder/carbide cutting bits, you can gasket match the intake runners, equalize the throats at the pushrod bulge (if you feel comfortable enough grinding a little and not too much so as you don't bust through the pushrod bulge - which can be fixed), smoothing out any rough areas but not to the point of polishing.

New taller RA IV Ferrea stainless steel valves to give you some height for the high lift of the cam, new bronze valve guides, cut down the valve guides for positive seals, 3-angle valve job, new springs rated for the cam, new retainers/valve locks, Big Block 7/16" rocker arm studs with poly-locks, new pushrods, new 1.5 stamped steel rocker arms.

This might get you closer to around 215 CFM's, so a lot of work/money for what you will get out of the heads - unless you send the heads out to a professional head porter.

The D-port aluminum heads will flow big right out of the box and have all the good parts needed above. Keep in mind that the aluminum heads are typically designed on the RA IV head and *you will need the correct RAIV head bolts.*

The bigger flow numbers may hurt your bottom end power even more as port velocity will be less and it'll take some RPM's to get port velocity flowing.

You will also want to make sure the intake will flow with the heads. You don't want the intake to only flow 230 CFM's and the head 280CFM - the intake then becomes your "choke" point and so goes with the carburetor.

The bigger the HP/TQ above factory numbers, the more money you will spend on the engine/trans/rear-end as you find all the weak spots in your build. So trying to go "cheap" and expect big HP/TQ returns is a recipe for disaster, disappointment, and wasted dollars. 
[/QUOTE]


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## 93610 (May 10, 2021)

Lonewolf said:


> I grew up with these old cars and owned several GTO's/Pontiacs and many other brands. Learned hands on with most of it. Never raced - except street racing as many of us did. I never did much engine work or rebuilding as back in "the day" there was little money, so we made faster what we had by adjusting things. If an engine blew-up, it was off to a junk yard or someone local and you installed another - same with transmissions/rear-ends.
> 
> Being a Pontiac enthusiast, hot rod enthusiast, lead sled enthusiast, and the need for speed to see how many police I could piss off and get tickets from, I simply enjoy all types of cars and all years. I am also a magazine/book reader and have a small library to source info and a good memory. So cars have been my interest for over 55 years and still going strong - its in the blood. So I am no expert, just know a lot of things about a lot of stuff and ca offer advice and then the rest is up to you. It is always good to talk with an engine builder/machine shop as they are the experts and I visit my engine builder regularly with my questions as well - more knowledge for me.
> 
> ...


[/QUOTE]


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> We ported the heads & Intake when built. After tear down I plane to check port over & clean up the inner heads in the rough, not polish , replace springs on cam card to match cam if not done & Was plaining to chance out valves with stainless & stainless steel seats. you gave me some detailed items Appreciate it.


why the studs, rockers if not scrubbed & oiling rods ?
[/QUOTE]

Factory uses the "bottle neck" studs, base is 7/16 screw-in which necks down to 3/8" for the upper threaded top. The shoulder is how the factory rocker arm nut tightens/torques down. That transition is a weak point and can break when using heavy spring rates or bigger rocker arm ratios.

The Big Block 7/16" rocker arm stud from ARP is 7/16" all the way, so not weak point. The problem now is that you cannot torque the rocker arm nuts down like factory as no shoulder to do so. Some will use a crimped or nylock nut, but these generally back off over time - nylocks don't stand up well to heat over time either, so they loosen up. You now need a set of poly locks to secure the rocker arms - which is not a bad thing as you can "zero lash" your lifters. Rhoads lifters have a procedure for this if you go that route.

Measure the factory stud to get the best height for the BB stud. The get matching poly locks as some are short and some tall depending on stud length and if using a stud girdle. Too tall, and you will need aftermarket tall valve covers OR a spacer to use the factor covers.

You don't need roller tip rockers and if you do, thy are rated for only so much spring pressure at full lift. Your cam may bee too much. The aftermarket stamped steel rockers, which I have used, are a good value for the money and will hols up. They are of a better steel than factory, have a generous slot in the ball cup for high lift cams/no binding, typically have grooved balls for better oiling, and the ratio is accurate where factory is typically less than 1.5 and can vary - plus wear.

Milling head/block and the taller RAIV valves will require you to check the pattern on the top of the valve stem using a pushrod checking tool to get the correct length pushrod. Don't assume your pushrods will work. If you still have the factory oil splash shields, check clearances between rocker arm and shield to make sure the don't make contact at full lift. You do not have to run them, but they can be a plus. Some engines did not use them and instead ran oil drippers spot welded to the top inside of the valve cover which does the same thing.


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## 93610 (May 10, 2021)

PontiacJim said:


> why the studs, rockers if not scrubbed & oiling rods ?


Factory uses the "bottle neck" studs, base is 7/16 screw-in which necks down to 3/8" for the upper threaded top. The shoulder is how the factory rocker arm nut tightens/torques down. That transition is a weak point and can break when using heavy spring rates or bigger rocker arm ratios.

The Big Block 7/16" rocker arm stud from ARP is 7/16" all the way, so not weak point. The problem now is that you cannot torque the rocker arm nuts down like factory as no shoulder to do so. Some will use a crimped or nylock nut, but these generally back off over time - nylocks don't stand up well to heat over time either, so they loosen up. You now need a set of poly locks to secure the rocker arms - which is not a bad thing as you can "zero lash" your lifters. Rhoads lifters have a procedure for this if you go that route.

Measure the factory stud to get the best height for the BB stud. The get matching poly locks as some are short and some tall depending on stud length and if using a stud girdle. Too tall, and you will need aftermarket tall valve covers OR a spacer to use the factor covers.

You don't need roller tip rockers and if you do, thy are rated for only so much spring pressure at full lift. Your cam may bee too much. The aftermarket stamped steel rockers, which I have used, are a good value for the money and will hols up. They are of a better steel than factory, have a generous slot in the ball cup for high lift cams/no binding, typically have grooved balls for better oiling, and the ratio is accurate where factory is typically less than 1.5 and can vary - plus wear.

Milling head/block and the taller RAIV valves will require you to check the pattern on the top of the valve stem using a pushrod checking tool to get the correct length pushrod. Don't assume your pushrods will work. If you still have the factory oil splash shields, check clearances between rocker arm and shield to make sure the don't make contact at full lift. You do not have to run them, but they can be a plus. Some engines did not use them and instead ran oil drippers spot welded to the top inside of the valve cover which does the same thing.
[/QUOT


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## PontiacJim (Dec 29, 2012)

Lonewolf said:


> Factory uses the "bottle neck" studs, base is 7/16 screw-in which necks down to 3/8" for the upper threaded top. The shoulder is how the factory rocker arm nut tightens/torques down. That transition is a weak point and can break when using heavy spring rates or bigger rocker arm ratios.
> 
> The Big Block 7/16" rocker arm stud from ARP is 7/16" all the way, so not weak point. The problem now is that you cannot torque the rocker arm nuts down like factory as no shoulder to do so. Some will use a crimped or nylock nut, but these generally back off over time - nylocks don't stand up well to heat over time either, so they loosen up. You now need a set of poly locks to secure the rocker arms - which is not a bad thing as you can "zero lash" your lifters. Rhoads lifters have a procedure for this if you go that route.
> 
> ...


So how much Air Flow would be enough for this set up (formula?) What will pick up the Low End, leveling the Engine the way it Should Run High/Low ? I guess this is where those programs come handy ?
[/QUOTE]


Here is an entire list you can play with. Just click on the one you want and put in your numbers.





__





Wallace Racing - Automotive Calculators







www.wallaceracing.com


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## 93610 (May 10, 2021)

Lonewolf said:


> Factory uses the "bottle neck" studs, base is 7/16 screw-in which necks down to 3/8" for the upper threaded top. The shoulder is how the factory rocker arm nut tightens/torques down. That transition is a weak point and can break when using heavy spring rates or bigger rocker arm ratios.
> 
> The Big Block 7/16" rocker arm stud from ARP is 7/16" all the way, so not weak point. The problem now is that you cannot torque the rocker arm nuts down like factory as no shoulder to do so. Some will use a crimped or nylock nut, but these generally back off over time - nylocks don't stand up well to heat over time either, so they loosen up. You now need a set of poly locks to secure the rocker arms - which is not a bad thing as you can "zero lash" your lifters. Rhoads lifters have a procedure for this if you go that route.
> 
> ...


So how much Air Flow would be enough for this set up (formula?) What will pick up the Low End, leveling the Engine the way it Should Run High/Low ? I guess this is where those programs come handy ?
[/QUOTE]
The Crower # 60213 still 3500-6500 Peak HP scroll dn. chart, red line at 7000 / Compression 10.25:1 & above required. Still be a HI Stall


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## 93610 (May 10, 2021)

PontiacJim said:


> So how much Air Flow would be enough for this set up (formula?) What will pick up the Low End, leveling the Engine the way it Should Run High/Low ? I guess this is where those programs come handy ?



Here is an entire list you can play with. Just click on the one you want and put in your numbers.





__





Wallace Racing - Automotive Calculators







www.wallaceracing.com




[/QUOTE]
Thank You Sir, Enjoy


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## BearGFR (Aug 25, 2008)

Lonewolf said:


> How can I Hate


Because it's going to have so much overlap that it's not going to want to idle at all, and won't make hardly any manifold vacuum, so forget about power brakes unless you convert to a hydro boost system or add a supplemental pump. The idle rpm will have to be so high that it's probably going to have a strong tendency to "diesel" when you shut it off. 
Trying to get the fuel mixture dialed in is going to be really tough. With so little vacuum it's going to be hard to get it rich enough to idle, but as RPM increases off idle and the vacuum starts coming in, it's going to go super rich on the transition slots - rich enough that taking out the rings due to fuel wash becomes a real concern. 

Bear


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## 93610 (May 10, 2021)

BearGFR said:


> Because it's going to have so much overlap that it's not going to want to idle at all, and won't make hardly any manifold vacuum, so forget about power brakes unless you convert to a hydro boost system or add a supplemental pump. The idle rpm will have to be so high that it's probably going to have a strong tendency to "diesel" when you shut it off.
> Trying to get the fuel mixture dialed in is going to be really tough. With so little vacuum it's going to be hard to get it rich enough to idle, but as RPM increases off idle and the vacuum starts coming in, it's going to go super rich on the transition slots - rich enough that taking out the rings due to fuel wash becomes a real concern.
> 
> Bear


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## 93610 (May 10, 2021)

[/QUOTE]


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