# Cam timing on new engine...



## wooftfd (Apr 6, 2021)

Ok guys, having a engine built for my 64 GTO... Its a 64 421, I'm going for a "Bobcat" build.. Bored out .40, dished pistons to lower compression to 9.75, stock crank, forged pistons and rods, 068 profile cam, in roller configuration, screw in studs, roller rockers, mild porting, center head exhaust passages filled, tripower with larger jetting by Dick, petronix ignition, Ram Air exhaust. Car has a TKX 5 speed, 3.23 rear gearing...
Figure I'll be running premium at 91-92 octane, live in the NW, seldom gets above 90...
Now, I'm not a Pontiac expert, but understand they love advance, I know about distributor and vacuum advance timing, but what about cam timing? Should we set it at zero, or add a degree or two? Car WILL NOT be raced, HARD LAUNCHED, or see much time above 5000 RPM...


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## wooftfd (Apr 6, 2021)

Forgot to add, double roller gear and chain, shouldn't be much stretch..


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## lust4speed (Jul 5, 2019)

My first suggestion would be to keep static compression with the 068 cam between 9.1 and 9.3 with the lower number being safer. Dropping a full point of compression only drops the power output by 4%, and reducing the ratio from 9.75 to 9.25 is a half point or 2% max. With the safer compression ratio you can run full distributor advance and make the most of your timing curve. If you go for the 9.75:1 and have a marginal tank of gas on a hot day during the summer and have to set timing lower because of detonation, you will be loosing 10% or more horsepower. We have the original 421 block in the 2+2 and it has rip-your-head-off power and is a blast to drive. We first put a Summit 2802 cam in and compression was 8.8:1 at the time we were in the High Performance Pontiac shootout article. That was quite a few years ago and the car was still managing about flat 13's on a day where the ambient temperature was 105° and track surface temp was 149°. Things happen and since then we had to replace the cam. We went back into the engine a few years ago and the new cam is a RAIV and we had the heads milled a little to raise compression up to 9.1. ET dropped to 12.80's with the RAIV so the engine liked the cam change. Only side effect with the RAIV was gas mileage took a sizable hit with the bigger cam. Anyway, pushing the compression ratio just isn't worth it and you might end up with less horsepower if timing has to be retarded. The HPP article can be found here: Shootout Article

Getting to your actual question, cam manufacturers go through a tremendous amount of research getting the cam specs dialed in and it's foolish to think we can improve on their specs. You can pretty much bet that if Comp (or Crower or others) says to set the intake centerline at a specific point that anyone is going to improve on their research. Every time I've spent money on dyno time and moved the cam around it has always run the best numbers where the cam company said to put it. Now that doesn't mean dropping the cam in dot-to-dot because things probably won't be where they should be. Manufacturing tolerances can add or subtract from the true number. Here's a list of problems: Crank keyway cut incorrectly; Crank gear slot cut incorrectly; Cam gear slot cut incorrectly; Cam keyway cut incorrectly, and finally chain stretch either initially or after normal wear. So you have to degree in each cam to your engine because nothing is precise. If you are really lucky half the list will offset the other half and you end up fairly close to where you want to be.

Now the next fun part is related to the above tolerances, and after carefully aligning and measuring everything you find that it is almost impossible to score a 50 point bullseye and compromises will have to be made. You will almost always have the choice of picking a cam position either slightly advanced or slightly retarded. Chains stretch and gear teeth slightly wear in and that retards the cam timing -- so the basic rule is to go slightly advanced on the compromise and let things wear in towards a true straight up position. Everyone finds out that reality sucks and when you end up at 2 degrees advance on the first try you think you can just choose the 2° retard slot in the crank gear. Then you find out that the slots are rather random in outcome and you end up quite a ways on the other side of ICL. Add cam timing to horseshoes and hand grenades and you will find that getting close is good enough. If you can get between a 1/2 degree retarded to 1-1/2 degrees advanced I would call it good. Anything on either side of those numbers you need to keep playing with it.


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## geeteeohguy (Feb 2, 2008)

Lust's post= Pure Gold. He has BTDT and I have to a lesser extent and agree 100%.
The 421 is all about stump pulling power from the jump, so a cam advanced 2 degrees is a good thing. I will add, I have run Cloyes double roller chains since the '70's, and ALL of them have stretched quite a bit initially, and then stop stretching and seem to last a long time. The one in my '67 is closing in on 90,000 miles of service. It will be replaced by a less stretch prone, but possibly weaker, link type. Good enough for Cliff Ruggles= good enough for me. 

Please keep us updated on your project.


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## Jim K (Nov 17, 2020)

I agree with Lust4 on the compression ratio. Assuming you are running one of the Iron heads that came on a 421, at 9.75:1 CR you'll need more octane than is readily available today which means you'll need to run expensive racing gas purchased in 55 gallon drums or one of the octane booster brands that actually work or run the risk of punching a hole in something due to detonation.
As for cam timing, I've always read and understood Pontiacs like a little more advance in cam timing. I went back to my cam card (Crower mechanical roller) and it states very plainly that 4 degrees of advance have been ground into my camshaft. When I degree'd it in, that's exactly what it showed. but me being me, I don't take much of anything as stated and have to be sure that's what I am looking at. I would presume you plan on degree-ing what ever camshaft you get..


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## wooftfd (Apr 6, 2021)

lust4speed said:


> My first suggestion would be to keep static compression with the 068 cam between 9.1 and 9.3 with the lower number being safer. Dropping a full point of compression only drops the power output by 4%, and reducing the ratio from 9.75 to 9.25 is a half point or 2% max. With the safer compression ratio you can run full distributor advance and make the most of your timing curve. If you go for the 9.75:1 and have a marginal tank of gas on a hot day during the summer and have to set timing lower because of detonation, you will be loosing 10% or more horsepower. We have the original 421 block in the 2+2 and it has rip-your-head-off power and is a blast to drive. We first put a Summit 2802 cam in and compression was 8.8:1 at the time we were in the High Performance Pontiac shootout article. That was quite a few years ago and the car was still managing about flat 13's on a day where the ambient temperature was 105° and track surface temp was 149°. Things happen and since then we had to replace the cam. We went back into the engine a few years ago and the new cam is a RAIV and we had the heads milled a little to raise compression up to 9.1. ET dropped to 12.80's with the RAIV so the engine liked the cam change. Only side effect with the RAIV was gas mileage took a sizable hit with the bigger cam. Anyway, pushing the compression ratio just isn't worth it and you might end up with less horsepower if timing has to be retarded. The HPP article can be found here: Shootout Article
> 
> Getting to your actual question, cam manufacturers go through a tremendous amount of research getting the cam specs dialed in and it's foolish to think we can improve on their specs. You can pretty much bet that if Comp (or Crower or others) says to set the intake centerline at a specific point that anyone is going to improve on their research. Every time I've spent money on dyno time and moved the cam around it has always run the best numbers where the cam company said to put it. Now that doesn't mean dropping the cam in dot-to-dot because things probably won't be where they should be. Manufacturing tolerances can add or subtract from the true number. Here's a list of problems: Crank keyway cut incorrectly; Crank gear slot cut incorrectly; Cam gear slot cut incorrectly; Cam keyway cut incorrectly, and finally chain stretch either initially or after normal wear. So you have to degree in each cam to your engine because nothing is precise. If you are really lucky half the list will offset the other half and you end up fairly close to where you want to be.
> 
> Now the next fun part is related to the above tolerances, and after carefully aligning and measuring everything you find that it is almost impossible to score a 50 point bullseye and compromises will have to be made. You will almost always have the choice of picking a cam position either slightly advanced or slightly retarded. Chains stretch and gear teeth slightly wear in and that retards the cam timing -- so the basic rule is to go slightly advanced on the compromise and let things wear in towards a true straight up position. Everyone finds out that reality sucks and when you end up at 2 degrees advance on the first try you think you can just choose the 2° retard slot in the crank gear. Then you find out that the slots are rather random in outcome and you end up quite a ways on the other side of ICL. Add cam timing to horseshoes and hand grenades and you will find that getting close is good enough. If you can get between a 1/2 degree retarded to 1-1/2 degrees advanced I would call it good. Anything on either side of those numbers you need to keep playing with it.


 Thank you!!!!!! Great info, I'll look into dropping the compression!!!!


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## wooftfd (Apr 6, 2021)

lust4speed said:


> My first suggestion would be to keep static compression with the 068 cam between 9.1 and 9.3 with the lower number being safer. Dropping a full point of compression only drops the power output by 4%, and reducing the ratio from 9.75 to 9.25 is a half point or 2% max. With the safer compression ratio you can run full distributor advance and make the most of your timing curve. If you go for the 9.75:1 and have a marginal tank of gas on a hot day during the summer and have to set timing lower because of detonation, you will be loosing 10% or more horsepower. We have the original 421 block in the 2+2 and it has rip-your-head-off power and is a blast to drive. We first put a Summit 2802 cam in and compression was 8.8:1 at the time we were in the High Performance Pontiac shootout article. That was quite a few years ago and the car was still managing about flat 13's on a day where the ambient temperature was 105° and track surface temp was 149°. Things happen and since then we had to replace the cam. We went back into the engine a few years ago and the new cam is a RAIV and we had the heads milled a little to raise compression up to 9.1. ET dropped to 12.80's with the RAIV so the engine liked the cam change. Only side effect with the RAIV was gas mileage took a sizable hit with the bigger cam. Anyway, pushing the compression ratio just isn't worth it and you might end up with less horsepower if timing has to be retarded. The HPP article can be found here: Shootout Article
> 
> Getting to your actual question, cam manufacturers go through a tremendous amount of research getting the cam specs dialed in and it's foolish to think we can improve on their specs. You can pretty much bet that if Comp (or Crower or others) says to set the intake centerline at a specific point that anyone is going to improve on their research. Every time I've spent money on dyno time and moved the cam around it has always run the best numbers where the cam company said to put it. Now that doesn't mean dropping the cam in dot-to-dot because things probably won't be where they should be. Manufacturing tolerances can add or subtract from the true number. Here's a list of problems: Crank keyway cut incorrectly; Crank gear slot cut incorrectly; Cam gear slot cut incorrectly; Cam keyway cut incorrectly, and finally chain stretch either initially or after normal wear. So you have to degree in each cam to your engine because nothing is precise. If you are really lucky half the list will offset the other half and you end up fairly close to where you want to be.
> 
> Now the next fun part is related to the above tolerances, and after carefully aligning and measuring everything you find that it is almost impossible to score a 50 point bullseye and compromises will have to be made. You will almost always have the choice of picking a cam position either slightly advanced or slightly retarded. Chains stretch and gear teeth slightly wear in and that retards the cam timing -- so the basic rule is to go slightly advanced on the compromise and let things wear in towards a true straight up position. Everyone finds out that reality sucks and when you end up at 2 degrees advance on the first try you think you can just choose the 2° retard slot in the crank gear. Then you find out that the slots are rather random in outcome and you end up quite a ways on the other side of ICL. Add cam timing to horseshoes and hand grenades and you will find that getting close is good enough. If you can get between a 1/2 degree retarded to 1-1/2 degrees advanced I would call it good. Anything on either side of those numbers you need to keep playing with it.


 And nice car!!!


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## PontiacJim (Dec 29, 2012)

wooftfd said:


> Thank you!!!!!! Great info, I'll look into dropping the compression!!!!


The 421 has the bigger main journals and oiling is one of those things on a Pontiac engine you don't want to skimp on.

I like to recommend the Butler Pro series oil pumps as they are blueprinted Mellings 60 PSI pumps and designed to flow more oil volume without increasing pressure. The Mellings 60 PSI pump in stock 60 PSI form will work, but I think a margin of safety is a little better. And, make sure the oil pump pick up uses a slightly coarse pick-up screen versus the fine mesh that sometimes seems to pop up. I feel the fine mesh screen can be a restriction and not a good choice when the oil is thicker. My Butler pick up had the coarse screen, but it looks like the photo of the Butler supplied pick up is the fine mesh screen. I attached a PHOTO, fine mesh on the left, coarse mesh on the right.

Here is a video that has some good info. It covers the Butler Pro 80 PSI pump which is the same as the 60 PSI pump, oil drive shaft, and checking oil pick-up-to-pan clearance. Disreguard the windage tray info as your engine was not made with one. The oil pump pick up is an aftermarket Moroso piece. 






Get an aftermarket hardened oil pump drive shaft - do not use the factory one as the increase in oil pressure means more strain on the pump shaft and the factory piece can break off a drive ear - they are softer and older.



https://butlerperformance.com/i-31643887-butler-performance-pro-60-70-psi-oil-pump-w-pickup-screen-bpi-m54ds-pro.html





https://butlerperformance.com/i-31643510-butler-hardened-oil-pump-drive-shaft-std-length-bpi-opds-54.html?ref=category:1234738





https://butlerperformance.com/i-24453396-moroso-oil-pump-pickup-mor-24480.html?ref=brand:99928


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## wooftfd (Apr 6, 2021)

great info, I did get a Mellings HP, I'll change out that screen!!!!!


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