[C2] Compression ratio

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Mar 2, 2023 | 12:53 AM

JIMNAN

Thread Starter

Racer

Joined: Sep 2022

Posts: 251

Likes: 50

From: CALIFORNIA

St. Jude Donor '25

Compression ratio

I am going to use Kieth Black KB 156 or KB 157 pistons in a 327 rebuild. The KB specifications indicate that with 62 cc heads it should be 9.8 and with KB 156 pistons and 10.7 with 157 pistons.
When I input the info into one of the compression calculators I do not get those results. It is off a significant amount. Have i made an input error?
KB 156 calculation

KB 157 calculation

Mar 2, 2023 | 01:40 AM

silver837

Le Mans Master

Joined: Mar 2017

Posts: 5,113

Likes: 1,605

From: Nor- Cal

The engine volume of 333,3 is indicative of a .030 over bore.

Last edited by silver837; Mar 2, 2023 at 10:27 AM.

Mar 2, 2023 | 06:06 AM

Charles55

Racer

Joined: Nov 2020

Posts: 320

Likes: 110

Check your deck clearance again. Typical without decking block is about .020.

Mar 2, 2023 | 10:14 AM

Scott Marzahl

Le Mans Master

Joined: Apr 2005

Posts: 6,349

Likes: 419

From: Seattle Area WA

Deck of .025" in the hole typical and tough finding a gasket at .20" Mahle 5746 run .027", Felpro 1019 run .015". Typical rebuild head gaskets .039"

Why not use the speedpro L2166f pistons like OEM L79 instead of KB hypers?
Also Autotec makes a very nice set of pistons for 327.

https://cnc-motorsports.com/auto-tec-pistons-1000761-forged-283-302-327-dome-4-030-bore-sb-chevy-331.html

Last edited by Scott Marzahl; Mar 2, 2023 at 12:20 PM.

Mar 2, 2023 | 01:33 PM

domenic tallarita

Burning Brakes

Joined: Aug 2013

Posts: 1,071

Likes: 322

From: palm springs ca

I would keep the same compression ratio that the engine came with or you have a morphidite that you cannot say it is a 300 340 350 HP and so on.
The engine is the vette also, and modifying the engine to me is like changing the color of the car. Just my opinion. If gas is the problem then get the right gas for the compression.

Dom

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