[Stan Weiss]

Originally Posted by 455Grandville

Appreciate the responses.I might stick the old one back in as this engine has low miles, but the gaskets my friend and I put in back in high school are getting old and that’s the main reason I’m pulling it.
Looking at possibly a RA3 cam as this is just a mild engine with Air and 3.08 gears.
I went with 6x-4 heads and a Comp cams 255 DEH on my 455 GV and that combo gave me 9.4 : 1. I’m happy with that setup but I have to go out of my way to VP fuels to get 93 octane and I’d rather avoid that.

When talking about CR remember what cam he has and that he likes.

Stan

[66beaumont]

I run 87 with a 467 with 62 heads and stump puller cam. Never heard it ping,never overheats and no heat soak issues. 9.5 comp

[455Grandville]

Originally Posted by Stan Weiss

What psi do you see when you do a cranking compression test on this engine?

Stan

145-150 psi. Engine has maybe 70,000 miles.

[455Grandville]

Originally Posted by 66beaumont

I run 87 with a 467 with 62 heads and stump puller cam. Never heard it ping,never overheats and no heat soak issues. 9.5 comp

I never tried anything less than 91 on my 9.5 : 1 455 just out of fear.

[455Grandville]

Originally Posted by Jay S

Would that 71 455 use an 067 cam?

The 66 heads are pretty the cavernous 114+cc chambers, are those heads going back in the car?. If I was picking factory heads and the cam is the 067 would use a 6x-8, that would be a 87 octane set up. I would make sure the cam is installed similar to the factory (almost straight up).

We have been as high as 10.3 SCR with stock heads in a 455 on 91 octane with a big solid cam. Ported heads with the right cam, single plane intake and headers, I don’t mind going clear up to 11 on 91. Over the years we had 455 combo’s, spc-7 (068) and the Spc-8 (041) at around 9:1 (8.8-9.3 on several engines). We were never impressed with the 041 with the compression that low, it would run on any crappy gas you put in it though. In that 9.0 compression range we have been more impressed with the Spc-7 (068) with 1.65 rockers. With the bigger rockers on the 068 I think it performs as well or better than the 2801 summit, and is has a little lower octane requirement (easier to tune).

A friend runs a 455 with ported 96 heads in a 4x4 pickup with a Crower 60919 (later version 112 LSA). and Rhoad vmaxs set at .009 lash, very ported intakes ports (260 cfm) lightly touched up exhaust (170 cfm). The compression is between 9.3-9.5, I don’t know the exact scr, he had it decked after I helped him with his heads. It tows 18,000 lbs trailers, has a mammoth aluminum radiator, q jet and rpm intake, it will start to ping a little pulling it to its knees on 87.

Octane requirements the timing curve, jetting, spark plug heat range, compression, piston design (quench and piston shape), operating temp, head flow, chamber design, head material, cam events, cam intensity, induction and exhaust all make a difference. Lol, maybe I am forgetting something. A lot of factors, any combination of factors can make a combo act different. I have seen 8:0 engines get messed up from a couple of those being wrong.

I have a stack of heads and blocks. But I’d like to keep the engine original (not original to the car) as it was when my friend and I found it in high school found it in a yard and installed it as cancer took him out about 10 years ago, so it’s sentimental as he sold it to me before he died.

[steve25]

In regards to the 467 motor in post 22, I can’t see how the heck your at only a 9.5 to 1 compression without the help of a dished piston!

[Dragncar]

62 heads are about that on a 400. Not a 4.25 stroke engine.

[geeteeohguy]

Originally Posted by 455Grandville

What’s the Max compression you can have with 87 or 89 octane gas ?
I’m going to freshen up the never rebuilt passenger car 1971 455 in my 79 T/A (# 66 heads) but don’t want too much compression as premium 91 or 93 isn’t at most of the rural stations around here.

Rule of thumb is put a decimal point between the two octane digits and that is your safe CR with iron heads on a Pontiac. So, 87 octane = 8.7 CR, 89 Octane = 8.9, 91 octane= 9.1 CR, and so on. It's held true to me in my experience with stock street Pontiacs for the past 40+ years. You can run higher CR if you are at different elevations or climates (more humid) and with a sharp tune, as some here (Cliff) have. In hot, dry, central CA, 10+ CR with iron heads on pump gas has never worked out for me.....at least in the summer time.

[Formulajones]

I quit playing with 87 or 89.

We run 91 here in Arizona, same stuff California is using, and I get away with 10.13:1 in a Pontiac with iron heads and an 068 cam but careful tuning is needed. I wouldn't dare try lesser octane in it, but I do beat the snot out of it at the track and driven regularly on the street without issues for several years now.

I'm even running 11:1 with iron heads in a Chevrolet on the same 91 octane. That one with a more aggressive camshaft that is much more forgiving. It actually likes a lot of timing. On this one I could probably get away with less octane if I really wanted to try it, but the price difference between 89 and 91 isn't enough to make me want to bother trying it.

Daily driving both cars for years now and it works. In the Arizona heat here and both cars have been in 110+ ambient temps every summer. It's imperative that engine coolant temps are maintained, both cars have functional cold air hoods, and a lot of little things everywhere throughout the engine builds that are critical to make it happen as Jay and others mentioned earlier in this thread.