Think I made a big block boo boo?

[Sparky dave]

Hi I'm going through a 1985 454 chevy engine clearances etc. I decided is bump up compression as it was a dish piston penut port truck motor. I ordered the -22cc speedpro hyper from summit thinking I had 119-122 cc chambers anyhow I cc'd then yesterday and they have come out at 114. That puts my compression at 9.7-1 with .039 head gasket. From what I understand I'm in detonation danger zone! Iv thought about cleaning up the chamber's a bit. Has anyone got any advice on where to go from here? The intention is to build a nice running street truck with the penut ports for my 69 c10 700r4 3.73 gears. 29 inch wheel diameter.

Known engine measurements
Std bore/ stroke
Std deck clearance
-22cc h ypers
114cc 045 penut port iron heads
This is not a race truck only ever used on the street so a balance of power/fun/economy is the target.
I'm getting hung up on this compression thing can i just use a cam that will bleed off compression? Kind regards dave

[cadillac_al]

I want to build a higher compression peanut port truck engine for a fairground cruiser. I was planning to use a Muther Thumper cam. I don't have much big block experience but I would think yours could run on 9.7:1 compression with a normal rv cam. If not, then it should on premium fuel. Good luck and keep us posted.

[Tom]

Yes, a bigger cam with overlap to bleed pressure would help. But that will defeat the point of peanut port heads and be a bad combo. Either change the pistons, or change the heads. Or just try running premium and see what happens who knows. You might even be able to open the dish in the pistons more, I'd consult the manufacturer first though.

[Sparky dave]

Originally Posted by cadillac_al

I want to build a higher compression peanut port truck engine for a fairground cruiser. I was planning to use a Muther Thumper cam. I don't have much big block experience but I would think yours could run on 9.7:1 compression with a normal rv cam. If not, then it should on premium fuel. Good luck and keep us posted.

Thanks I checked into the mother thumped cam and plugged the numbers into a dynamic compression calculator and came out just over the 8-1 target on iron heads but closest yet by far!! So I tried the summit 1302 with similar duration numbers but on a 114 lsa and hey presto 8-1 good idle and vacuum and should be a good to drive! Thanks a lot for the inspiration!!!

[b454rat]

I ran 10:1 on a 454 with 781 heads and Extreme 268 cam. I ran 93 in it, and once I got the timing right it never made a noise. Pulled like a freight train too.

[HAULIN' IT]

I would not intentionally pick a cam to "bleed off" an engine with what you believe to be 9.7 compression. Have you measured how far down in the hole the pistons are? I didnt do the math on what you posted but .020-.025 down (if not included in your figuring already) will be about a 1/2 point less on a bore that big. Most engines built by an average diy guy in a garage has LESS compression than they think. If you havent factored in the deck clearance, piston top to top ring cc's ect. you are 9.7, six, five...9.0 in a hurry & now pick a "too big" cam to help "bleed-off" compression & you end up with a inefficient turd.
Likewise, Ive driven my true 9.7 motor thousands of miles on 92-93 octane without trouble. My Two Cents, Lorne

[AussieinNC]

If you are not intending on spinning the BBC over 4800 rpm, peanut port heads will be fine...

If you want a better breathing head set, consider Vortec heads...although these Vortecs do need some port work to blend casting flash and smooth the humps in the exhaust ports....

and check the "pointy vane" in the chamber clearance on the domed pistons...

[burnin oil]

Not a big block but I run 11.5:1 on 93 octane with a pretty aggressive cam and alum heads. Cranking pressure is the key to look at really. I have 195 psi. Keep it cool and play with the timing and I bet you are fine. Most people pick a cam that's to large to start with so you will probably be fine.