# 455 Cam suggestions



## maw2078826 (May 1, 2020)

My 1967 GTO motor is a four bolt main 1972 455 block with #16 Heads...1966 Tri-Power, Nodular Iron Pontiac Crank,1962/3 Super Duty Forged Rods, TRW forged pistons (L2358) approximately 10:1 compression...currently running a H.O. Cam HC-01A...Ram Air Exhaust Manifolds with 2.5" Exhaust....Drive train is M-21 Muncie & 3.55 Posi. I've been considering a different cam...Any suggestions from my Goat Brothers would be appreciated.


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## Old Man Taylor (May 9, 2011)

You need to start by identifying exactly how you expect to use your car, and what your willing to sacrifice.


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## LATECH (Jul 18, 2018)

10 to 1 is too high for pump gas
Those rods are not as good as a inexpensive set of 5140 or alternatives
We do need more info .
What are you doing with the car? Street daily driver or strip killer machine?


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## PontiacJim (Dec 29, 2012)

Yep, you are going to need to help us out a bit more.

Why the change?
How does it run now?
Specs on the HO-01A cam?
What do expect/want out of the cam change?
What power range do you want the most out of the engine - no one cam will do it all.
Flat tappet or roller. Solid or hydraulic.

As noted, 10:1 compression with iron heads is probably not pump gas friendly and we assume you use an additive or race gas mix? A cam can effect Dynamic Compression effectively changing cylinder pressure.

Are you at high altitudes? Higher altitudes can use/need higher compression and will not detonate on pump gas.......until you get into lower altitudes.

#16 heads - factory bottleneck studs or converted over to BB 7/16" rocker arm studs and poly locks?

The SD rods, as noted, can be "soft" even though they are forged. It has been suggested that they get heat treated to get their rockwell hardness increased to prevent failure if you run the engine hard.

Just a few things to consider.


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## maw2078826 (May 1, 2020)

Thanks folks...I guess my post was a bit lacking in detail. sorry about that. My '67 GTO is primarily a show car...rarely driven, and only drag raced many moons ago when I was young and not bald. However, I do on rain free days get out on a back road once and a while and try to tear the wheels off. I've built several engines in my time for it, the 455 being the last. The reason I was curious about running a different cam was that I was experiencing valve float at high rpms..my guess either over revving or lack of cam duration. So I'm curious to simply get suggestions on how to achieve maximum performance considering the restrictions of stock #16 cylinder heads...as I realize too big a cam, in other words more lift than the motor can use, and too high a duration will kill bottom end torque (without 4.33 gears of course)... 10.1 Compression has never been an issue because I only run 100 Octane, (and yes, Pontiac Jim, I live @ three -to- four thousand ft. elevation) the HO-01A cam specs with 1.5 roller rockers & 3/8" studs (RA-IV Pushrods) w/poly locks are- Intake: .465, Exhaust: .492, advertised duration Intake: 276, exhaust: 288...I was surprised to hear the distrust of the 1962/3 Forged Pontiac Rods, as they were used in some of meanest Pontiac Motors to ever leave the assembly line, I guess no comparison to those you can buy today. Thanks for the input folks...remember I'm only an old time backyard motor head.


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## PontiacJim (Dec 29, 2012)

I would not change the cam. Sounds like your combo should work well. Valve float at higher RPM's (?) may more likely be weak valve springs, lifter pump up, valves not correctly adjusted OR your oil is too thick. Possibly ignition problems or fuel delivery issues.

With the listed cam, you need more than a stock spring. If you did install new when you rebuilt the engine, it is possible they have lost some of their spring pressure.

Any spring binding issues? Verify that you have the needed clearances at full lift.

Lifter pump up/valves incorrectly adjusted can be checked/remedies by "zero lashing" the valves/lifters. Easy enough with poly locks and with engine running.

Oil can be too thick. If the oil is too thick, it may not be draining fast enough from the lifter bodies at higher RPM's and this will pump up the lifters and keep valves open. Some manufactures will recommend a specific viscosity just for this reason.

Are you sure that it is not an ignition problem at higher RPM's? Too much initial/total advance, weights sticking or not operating correctly, vacuum advance hooked up?, or weak ignition.


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## maw2078826 (May 1, 2020)

Thanks Jim I will look at the issues you cited.


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## Old Man Taylor (May 9, 2011)

The duration specs you gave are measured at about 0.007" lift. At 0.050" lift the duration is about 222/232. If you don't have taller valves or machined pockets on the heads, then you've got too much lift. Especially on the exhaust. I would make sure your heads are set up right first. Also, with a cam that small in a 455, it will probably want to be shifted at about 4700. Any more RPM would just be wasted. If you wanted more power you should have the heads ported, and then you could take advantage of a cam with more duration.


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## LATECH (Jul 18, 2018)

Valve float? Sounds like weak valve springs to me.
Much of your trouble sounds like cam and distributor curve to me also.


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## PontiacJim (Dec 29, 2012)

Old Man Taylor said:


> The duration specs you gave are measured at about 0.007" lift. At 0.050" lift the duration is about 222/232. If you don't have taller valves or machined pockets on the heads, then you've got too much lift. Especially on the exhaust. I would make sure your heads are set up right first. Also, with a cam that small in a 455, it will probably want to be shifted at about 4700. Any more RPM would just be wasted. If you wanted more power you should have the heads ported, and then you could take advantage of a cam with more duration.


From what I read, you are OK up to .500" lift. Keep in mind some deflection of parts and hydraulic lifters. I ran the Comp XE274 with .488/.491 lift and matching springs on a set of 7K3 heads with no issues. As an alternative to machining valve spring pockets, you can get retainers that will increase clearance as they are raised up somewhat and allow for a taller spring height. Take a look in the Jim Hand book as I recall he has an example?

With the higher valve lift, and assuming stronger springs, I might be a little nervous with the 3/8" bottle neck studs and would swap out to the ARP Big Block 7/16" rocker arm studs and poly locks.

Agreed that the cam may be a bit small for a 455, and probably shifts at a lower RPM, but I bet it is a torque monster and pulls hard with street gears. The head flow, as you mentioned could be a "choke" point on power with stock flowing heads. But doing head work means $ and removal and that might not be an option.

The lift and duration, looking at it better, seems a little unbalanced. The lower lift/duration on the intake and the higher lift/duration on the exhaust might be over scavenging? I would think either more lift or more duration on the exhaust, but not both. 

The cam lobe lift, according to my math, come out to .310". If a 1.65 rocker were used on the intake, lift would be .511". If a small block Ford is used (as I read some guys will use these?) with a 1.6 ratio , lift would be .496". The Ford rocker arm, if it can be used, and .496" intake lift and the .492" exhaust lift with corresponding durations, might make for a better cam? I like the duration numbers for a street car.

The clearance between the pushrod and head that it passes through would need to be checked when going to a higher rocker arm ratio, but again, from what I read as long as you use the stock diameter pushrods and stay under .500" lift you should be OK. Coil bind and clearance between the retainer and valve guide should be checked. If you go over .500" lift, then the concern may be piston-to-valve clearance and this should be checked.

Just some thoughts.


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## Old Man Taylor (May 9, 2011)

W/R/T lift on stock Pontiac heads - The flow continues to increase up to about 0.450" lift on stock heads. The intake dies after that. That's why Pontiac's cams had a fixed lift profile with a max of about 0.404 lift until the Mac McKellar #10 and/or the RAIV. So to get more duration they just widened the lobe faces. That's why I made the comment about porting. Jim Hand did his own porting on his own flow bench, so the cams he used were not with totally stock heads. I limited the lift on my cams to 0.450" until I got my heads ported. That brings in a new set of guidelines for cam selection.

The "H" (744) was the first cam where Pontiac ran out of room at the peak lift, hence the lobes are flat at max lift. That created another problem. Originally they used the stock GTO heads, valves and springs. They had to recall them because they were breaking valve springs. Imagine the valve having to float at the top of the lift. IIRC the stock valve spring height is 1.56, the upgraded RA is 1.714 and the RAIV is 1.80". I typically run RAIV valves (or the after market equivalent) and I have the valve pockets machined to get a 1.80" installed height with the shims. 

The RAIV was their first cam that had a computer designed profile, so they had a faster ramp on the lift (steeper angle). In late 68 the RAII's used the 041 cam with 1.5 rockers. The RAIV's used the same 041 cam, but with 1.65 rockers. 

The punchline is that with stock heads you get more bang for the buck by increasing duration more than lift. It gets a little more complicated than that, but I believe the generalizations above to be correct.


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## lust4speed (Jul 5, 2019)

On a 108° LSA also.


H-O Ent.HC-01D276​288​220​232​.470​.500​108​​

Don't think anyone has asked how high up in the RPM range do things go south? Milder cams are easier on springs, so going to a larger cam without heavier springs would make things worse.


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## Droach6498 (Nov 1, 2020)

Old Man Taylor said:


> W/R/T lift on stock Pontiac heads - The flow continues to increase up to about 0.450" lift on stock heads. The intake dies after that. That's why Pontiac's cams had a fixed lift profile with a max of about 0.404 lift until the Mac McKellar #10 and/or the RAIV. So to get more duration they just widened the lobe faces. That's why I made the comment about porting. Jim Hand did his own porting on his own flow bench, so the cams he used were not with totally stock heads. I limited the lift on my cams to 0.450" until I got my heads ported. That brings in a new set of guidelines for cam selection.
> 
> The "H" (744) was the first cam where Pontiac ran out of room at the peak lift, hence the lobes are flat at max lift. That created another problem. Originally they used the stock GTO heads, valves and springs. They had to recall them because they were breaking valve springs. Imagine the valve having to float at the top of the lift. IIRC the stock valve spring height is 1.56, the upgraded RA is 1.714 and the RAIV is 1.80". I typically run RAIV valves (or the after market equivalent) and I have the valve pockets machined to get a 1.80" installed height with the shims.
> 
> ...


I have #12 heads on my block, said to be RAIII can you tell me where to find info on it?


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