Camshafts - GTO Factory Specs - Pontiac GTO Forum
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post #1 of 19 (permalink) Old 02-14-2016, 03:10 PM Thread Starter
 
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Camshafts - GTO Factory Specs

I put together the specs on the factory installed GTO camshafts for the 389/400/455. They are often referenced by their last part number digits, ie "066," "067," "068," etc.

They go from mild to radical with the "068" often suggested as a good solid performance street cam in a 389/400 that doesn't get into street/strip territory. Cubic inches plays a role in what "mild" or "radical" is. A bigger cam that may be on the radial side for a 400CI will be milder on a 455CI or 461CI stroker build.

I have shown the "041" Ram Air IV cam using the 1.5 ratio rockers instead of the 1.65 ratio which puts the lift at .518". On a stock iron head GTO 400CI, going over .470" lift won't really produce more power. Once you begin to go past .460" lift, you have to make sure your valve springs do not go into coil bind and that spring parts are not hitting each other. The factory 1.5 rockers are said to be closer to 1.48 and the .470" lift is said to be closer to .460" when measured. Going to 1.65 rocker with the "041" cam requires matching valve spring rates, may require longer valves, slotting the push rod hole for clearance, 7/16 BB rocker studs & adjusting nuts with the allen set screws. You may also want to check valve to piston clearance so the valve does not hit the top of the piston. But, having a cam that will spin your 400CI well past 6,000 RPM's is not going to cut it if you don't have the forged pistons & rods to go there. So more things to consider once you add the 1.65 ratio rockers to the "041" cam.

All Pontiac engines benefit from exhaust upgrades such as the RA exhaust manifolds or headers. The "744" and "041" require better flowing exhaust. You may also need a higher stall converter for automatics and better gearing. These 2 cams are more street/strip type cams in a 400CI.

Of course there are many cam types and specs going aftermarket and some may be more fitting for your build. This is just a listing of factory cams if for comparison sake only.
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post #2 of 19 (permalink) Old 02-15-2016, 11:11 AM
 
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Nice job, Jim. Do you think you can find the duration at .050" lift? This would help alot especially in comparing these with the aftermarket cams. I understand some of these OEM grinds are no longer available new, so .050" specs would help in finding an aftermarket cam that resembles a Pontiac OEM. Thanks!!
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post #3 of 19 (permalink) Old 02-15-2016, 01:15 PM
 
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Jim Hand listed those specs in this article.

Jim Hand Article #5


"....050" specs would help in finding an aftermarket cam that resembles a Pontiac OEM..."

As most probably know, Melling has some cams that are close to the specs of some of these cams.

SPC-8 = 041, SPC-7 = 068, SPC-3 = 744, and I think an SPC-5 = 067. Anyhow, the numbers are not exact, but
fairly close.

http://www.melling.com/Portals/0/Siz...on%20Chart.pdf

And, of course, several cam grinders have their version of the 041 grind. Crower's 60919 is a popular cam.

http://www.summitracing.com/parts/CRO-60919/

This is the CC version.

http://www.summitracing.com/parts/cc..._2zBoCrBjw_wcB

Lunati has their version of the 041 & 744.

https://www.lunatipower.com/Product....d=1755&gid=340

http://www.lunatipower.com/CamSpecCa...rtNumber=10704

I like the looks of the Howards 041 version. It has less advertised duration, and should work better in slightly lower compression engines, for those who don't like Rhoads lifters. Haven't read of anybody running one, tho.

http://www.summitracing.com/parts/hr...9pzBoC1bXw_wcB

And to me the Summit 2801 looks to be a higher lift version of the 068, and the 2802 looks to be a higher lift 744.

http://www.summitracing.com/parts/su...RUgxoCEgLw_wcB

http://www.summitracing.com/parts/su...jlHhoCOUzw_wcB

Last edited by oldskool; 02-15-2016 at 01:49 PM.
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post #4 of 19 (permalink) Old 02-15-2016, 07:03 PM Thread Starter
 
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Originally Posted by 1968gto421 View Post
Nice job, Jim. Do you think you can find the duration at .050" lift? This would help alot especially in comparing these with the aftermarket cams. I understand some of these OEM grinds are no longer available new, so .050" specs would help in finding an aftermarket cam that resembles a Pontiac OEM. Thanks!!

This is what I came up with from the internet.

[email protected]"[email protected]"


9779066--------273---------------282---------------200----------------210
9779067--------273---------------289---------------200----------------213
9779068--------288---------------302---------------212----------------225
9785744--------301---------------313---------------224----------------236
9794041--------308---------------320---------------231----------------240
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post #5 of 19 (permalink) Old 02-16-2016, 10:25 AM
 
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Thanks, Jim and oldskool, appreciate the info. Although I have seen articles by Jim Hand before, I have never seen that Jim Hand cam article before. All this is much appreciated. Thanks, you all.
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post #6 of 19 (permalink) Old 02-19-2016, 06:11 PM Thread Starter
 
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This info is found on Bad Ass Cars.com How do cams affect compression?

I am pasting it here to ensure it remains should the link or website disappear. This gives a great explanation of the camshaft.

How do cams affect compression?


This is a good one with no single answer. There are several types of compression such as "static" and "effective" (aka "dynamic") compression. It all has to do with cylinder pressure. Static compression is the actual mechanical compression ratio number that you get by combining a given piston size with a given combustion chamber size, with a given amount of stroke and displacement of the engine. So; bore, stroke, compression height, deck height, head gasket thickness and combustion chamber size, (among others), have to do with the "static compression", but they don't dictate the actual working or "effective" aka "dynamic" compression which directly affects "cylinder pressure". The cam dictates this for the engine.

Example: two identical engines both with 9:1 "static compression". The only difference is in the cam profiles. One has no overlap with a given intake valve timing to go along with the rest of the cam's profile, and the other has a lot of overlap with a completely different intake valve timing to go with that cam's overall profile. Overlap is the time in which both valves are open as the piston pushes exhaust out and starts to suck new fuel and air into the cylinder. When the exhaust valve is closing and the intake valve begins to open, there is a time (on high performance and race cams) where both valves are actually open at the same time. As both valves are open, a little "reversion" gets pushed up the intake valve which slows the overall velocity down of the new fuel & air charge coming into the cylinder, and exhaust gas trying to still get out of the cylinder at low RPMs. This overlap period in the valve timing is what causes that "rumpity rump" sound everyone likes so much. Overlap causes a "scavenging effect" as the engine RPM increases. This is why performance cams "come alive" at higher RPMs. It's not "just" the cam making the power, it's the cam's scavenging effect working as the RPM increases which increases cylinder pressure (dynamic or effective compression). Cylinder pressure makes the power. The downside to that rumpidy rump sound in most street engines is that the overlap also causes a decrease in manifold vacuum, making power brakes a nightmare and throttle response a bit sluggish.

When you have too much overlap, you end-up with a dog for an engine at low RPM's and the car will require things to make up for it such as low rear-end gears and high stall converters to help "spool the engine up" quicker to GET IT TO those higher RPMs where it can begin to do its scavenging thing and increase cylinder pressure. When you have too much overlap in an engine without enough static compression to support it, it is what's known as being over-cammed. Lots of sound but not lots of GO, especially at low RPMs. Lots of engines out there are over cammed because guys like that rumpity rump sound, not knowing that although in many cases it may make more power at a higher RPM, it kills low-end power and torque which is what street performance engines should be concentrating on. TORQUE is what moves the vehicle below 4,000 RPM, not horsepower. Unfortunately, most guys only look at HP numbers, which is why there are a lot of turd cars out there.

Now, I get into arguments all of the time with guys who want to get technical with me, and they lose every time. They want to say that math and physics say horsepower and torque cross each other at 5,250 RPM, which is true, but that's where they CROSS, not where they are most effective! In other words, when it comes to torque, the closer your get to 5,250 RPM, the LESS EFFECTIVE torque becomes because horsepower is coming-up fast and takes over at 5,250. So the further you get below 5,250, the MORE you rely on just torque for moving that vehicle. 95% o the time for most street cars, you are driving below 4,000 RPM, and usually under 3,000, so in those RPM ranges, you are almost solely relying on JUST torque to move that vehicle, therefore, in MOST situations, everything below about 4,000 or so you are pretty much relying on torque, NOT horsepower to move that vehicle. In the real world you aren't always relying on nerd math and literal physics. There is also a real world out there that has other variables working in it.

So back to those two identical engines with different cams; if you did a compression test on either of these two 9:1 static compression engines, the engine with no overlap (or even negative overlap) would probably have about 140 -150psi or so in the cylinders. The engine with more overlap may only have 110 - 120 psi or so, depending on how much overlap the cam has, how narrow the lobe separation angle is, and most importantly... what the intake valve timing is.

Some racing engines with 13:1 or so compression only have 125psi - 150 psi or so of cylinder pressure when a compression test is done. That's less than what most bone stock engines have. It just means that the cam has a ton of overlap and has intake valve timing designed to work with the rest of the cam's profile to create that scavenging effect, which in turn actually increases cylinder pressure at higher RPMs. Not to mention, if you do a compression test on a seriously high performance engine when it's cold, all of the components are at their loosest and don't provide much of a seal because they NEED the heat in the cylinders to expand the pistons and rings to make them seal better.

Static compression always stays the same. You can't change that unless you change the pistons or the heads, the head gasket thickness, etc. This is why race engines have "power bands" and come alive at higher RPM's. It's because the cylinder pressure increases as the engine RPM comes-up. It's from the scavenging effect from the valve timing and overlap in the cam, which raises the cylinder pressure and increases horsepower with RPM. This is what you are feeling when the cam comes alive or hits its power band. if it didn't have the scavenging effect, there wouldn't be much of a power band. It would just be smooth power all through the RPM range like any stock engine has.

Narrowing the lobe separation down also affects the power band. A wider lobe separation will smooth-out and "broader" the power band. On that very same cam, if you narrow the lobe separation, the power band will come-on a little higher in the RPM range, but when it comes-on, the power curve is steep and brutal. This is why hard core race cams have explosive power bands. The static compression never changed, but the effective compression surer did.

As a rule of thumb (and this has a LOT of grey area), you can run upwards of 9.0 - 9.5:1 compression on pump gas with cast iron heads, and "about" one full point higher with aluminum heads because of how quick the combustion chambers cool. Can you run 11:1 static on pump gas? Sure. There are still LOTS of older muscle cars running that have compression ratios that high that run on pump gas. You just have to back the timing off a little. Timing is VERY important when dealing with compression ratios, cams and fuel octanes.
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post #7 of 19 (permalink) Old 03-04-2016, 09:57 PM Thread Starter
 
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What is the most important factor in making the proper cam selection?

The most important factor is determine by what you want from you vehicle. Engine size, type of heads/flow, compression ratio, forged or cast, carb & intake type, exhaust manifolds or headers, etc. is obvious. But most people do not consider the importance of other factors in determining proper cam selection such as transmission type, converter stall if using an automatic, axle ratio, tire size & height, and vehicle weight. Most of us want to maximize the performance of our Pontiacs so transmission gearing, converter stalls, axle ratios and the tire size has to match the required engine speed that we plan on spinning the engine - whether it be stock or some 7,500 RPM screamer. This is because MPH is related to peak horsepower, but ET is related to best average torque in the RPM range -and we typically build a Pontiac engines for torque. Heavier vehicles require a cam with more low end torque than lighter vehicles because it is much more difficult to get a heavier car moving. Cars having an automatic transmission want a camshaft that provides a good idle and RPM characteristics that match the torque converter that will be used. Stick shift cars want to pay more attention to the first gear ratio and the average RPM drop between shifts.

The camshaft regulates the air/fuel flow into and out of the cylinders and must be matched to the other engine components so it puts the power in the RPM range that the drivetrain can use. Once the camshaft is selected, modifications or changes to the components on both the intake and exhaust side of things must be matched to complement the engine as a complete system. For example, there is no benefit in having a high flowing intake system like a large carb, high-flow intake manifold, and a pair of big flowing CFM cylinder heads (or even nitrous) if the exhaust components canít get rid of the burned combustion gases. The Pontiac engineers knew the deficiencies of the exhaust port on their iron heads and added more duration to keep the exhaust valve open longer to scavenge the cylinder more effectively. When selecting a Pontiac grind, whether factory or aftermarket, most all (with a few exceptions) are dual pattern with the cam having a longer exhaust duration as compared to a single pattern where both intake & exhaust are the same duration. You can also play around with changing rocker arm ratios such as using the 1.5 ratio on the intake and 1.65 on the exhaust to gain a little extra flow- providing you know that you have the corresponding spring rates, that they won't go into coil bind, that your pushrods won't rub or bind against the heads, and that the valves won't kiss the tops of your pistons. Be careful not to over-scavenge a cylinder as this will hurt power.

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post #8 of 19 (permalink) Old 03-22-2016, 02:10 PM
 
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Great Article and thread Gents. I seem to remember the mentor for our Car Club we had in High School saying these very things. Only two of us had Pontiacs and would usually beat everyone else in Drags. I do have a question though. I have acquired a long block with the purchase of a '63 Catalina Ventura. The original 389 has 95K on it. The Block I got is a 17M (283 hp 418 Torque ) code. Casting F254 ( June 25 '64 ) 10.5/1 Compression. The heads are #15 casting. ( '68 400 cid/Big Car 72cc chamber ). The factory cam for this 389 is a #470 if I am not mistaken. I am guessing that is derived from the intake lift?
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post #9 of 19 (permalink) Old 03-22-2016, 06:26 PM Thread Starter
 
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Originally Posted by Sammuzzu1 View Post
The factory cam for this 389 is a #470 if I am not mistaken. I am guessing that is derived from the intake lift?
The 283 HP cam is listed as part no. 529472 and stamped in front as "D" to identify. It is the same cam as the later "066" cam. Lift is .406
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post #10 of 19 (permalink) Old 03-22-2016, 06:42 PM
 
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Thanks for the clarification Jim. I am not sure what cam is in the block without taking it out. I may anyways since this sat in a hay barn for a year with no oil pan or valley pan installed. Its rust free but the lifters are not new. * Correction. After pulling them, they are new. *

ANSWER to the question. GM PN# 540233
1961-62 389 SD 8 308 112 .405" .447" 83 312 115 .404" .446" #540233

Last edited by Sammuzzu1; 03-28-2016 at 11:36 AM.
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