455 cam theory

[G-Body_Vet]

As far as the stock 455 low compression heads, I like burning cheap gas and never pinging

That's part of the reason I want to know what's the best set-up for a decent street car. What would be the best cam to run with low CR to make it worth the trouble?

By the way I lived in Rogers Park as a kid and when I used to go back and visit I marveled at the lack of traffic and the general cleanliness of Chicago. NYC is a bumper to bumper toilet in comparison.

I don't know what it was like back then, but that area has really gone downhill in the past few years. The worst of the traffic is rush hour in the loop and the expressways. Driving in the city isn't terribly bad though.

 

[Bonnewagon]

Shotgun! It's been a while, how's by you? G-body_Vet, meet Shotgun, he is pretty much the Pontiac Guru. Wouldn't the 068 be too much duration for a stocker 455? I know it is sweet in a 400 but the 400 can rev higher. But I'm sure you've tried it, so how was the idle and how far did the 455 rev? Am I off base thinking a 455 needs less duration? G-gody_vet last time I was in Chicago about 15 years ago I stayed in Hyde Park, right on Lake Shore Drive (?) across from that cool museum with the WWII sub, and the cabbie said why are you staying in a slum? You coulda fooled me, the streets were spotless.

 

[shotgun]

Been a little "under the weather" as of late but on an up swing.

Anyway, the 068 would match up great for the goals stated with mild enough idle and power everywhere. Melling makes the most accurate copy spc-7.

If you want more lift add 1.6 sbf rockers , they "should" be ok for push rod clearance. 1.65 will require grinding.

Another option is Nunzis "high lift" version of the 068 , part # 2041.

You can usaully go .470 with stock type springs. I remove the stock oil deflectors on the springs just to add a margin of error.

 

[deanlemans81]

Hey guys,Let me hop in here and throw a few things around, On a street pontiac you don't really want more that about 9.5:1 compression because it will ping when you get junk gas. Most d-port pontiac heads from 67 to 79 flow pretty much the same but the combustion chamber sizes are what affect compression ratio. Your 75-76 455's with a 7.6:1comp have heads with a casting number 6X cast into the center exhaust port and a combustion chamber size of +- 114 ccs.

Just switching to a set of heads from a 75 up 400 with 98-99cc chambers will bump compression pretty close to 9:1
The same goes with using 350 heads with a +- 89-90cc chamber on top of a 400 block from 75 up.
The 5c and 6X heads are all prety much the same except forthe combustion chamber size, Have screw in rocker studs and flow ok. Using any of the pre 70 heads will have about thesame flow but bump compression too high for todays gas.
This of course is for standard d-port heads and not round port ones, whole different ball game here.

The 068 cam should give you a good power curve. I have an old summit cam with 224/234 degree @ .050 lift that is going into my 400 because I want a little more rumble at idle. Bigger cubes will generally smooth out a longer duration cam allowing you to go with a little bigger number but your valvesprings will be more of a limiting factor.

 

[Bonnewagon]

OK but what about the fact that the 455 peaks at a low rpm vs. the long duration cams? That's what I was really getting at. It would seem to me that a cam that peaked at 5 or 6000 rpm would be wasted on a stock 455. Something that ran out of breath at 4 or 5000 would seem on paper to be more appropriate. I'm trying to get this squared away before I swap cams and regret it.

 

[shotgun]

Not a flame, but I use actual results vs theory.

I am sure you now a bigger engine can absorb a larger cam (not that the 068 is big).

The cams will have strong mid rpm and pull to 4500/5000 depending on exhaust ( needs to breath read min RA manifolds 2 1/2 exhaust).

 

[tdvick]

A 455 will not act anything like a 400 with the same cam. As Shotgun said, the larger motor will eat up a cam that sounds lopey in a 400.

Years ago I ran a 744 (H) or original R/A 3 cam in my old '70 GTO. That car had a 4 speed and a 3.31 rear. It ran and drove great, no vacuum problems at all. The motor was a +.030 '73 455 block, stock rods, TRW pistons with a set of 6x-8 heads on it. Just a simple valve job on the heads and the stock '73 cast iron intake with a quadrajet. The car ran 13.40s. I can't remember the exact MPH, but it was ~105. Personally I think the 068 is a little too small. I just sold one that I had setting on a shelf for about 15 years. I bought it years ago and could never bring myself to use it. I actually went with that 744 cam in it's place and never regretted it. After that I knew that I would never use it.

 

[Bonnewagon]

Ok so what you are saying is a 455 can and will use that longer duration and continue to make power right up to redline with those cams. I guess I've been reading too much from various sources. I used that Crane 262 in a 350 and it was almost too much, so yeah, I understand a larger motor will absorb more. It just struck me that since the 3" main motors all used a 3.75" stroke, a 3.25" main 4.21" stroke motor would have different needs with the long stroke. Yes, it will have a set of the long branch HO/RA manifolds (I hate headers) and a manual transmission. The motor right now is a stock 76' 455 automatic so that is why I was curious about what kind of cam would work best without going crazy with modifications. Thank's to all for your input and I'm glad Shotgun is here because I normally would have asked this at Classical Pontiac but that site is in a coma lately.

 

[tdvick]

I forgot to mention, I had R/A manifolds on my GTO too.

 

[Bonnewagon]

Tdvick, how high could you safely rev that motor?