cylinder psi vs compression ratio - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 07-06-2003, 10:09 AM
Last photo:
Join Date: Jun 2003
Location: Oklahoma
Posts: 96
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
cylinder psi vs compression ratio

Hi, guys. After searching through this site as best I can, I am coming to the more knowledgeable for help. I am a newbie so please go easy on me.

In searching for a new camshaft for a mild engine build (Chevy 350), I find that most cam manufacturers have a minimum compression ratio for a specific cam.

My 350 is not original to the vehicle and it seems as though it would be easier to measure cylinder pressure than compression ratio.

Is it possible to convert a psi reading to compression ratio?

The engine will be in a Chevy shortbed 2WD with 3.73 limited slip rearend. As with most people, I want all the performance I can get for the buck. My intentions are to change the cam, lifters, springs and timing chain/gears. Also will install headers,exhaust system, intake and carburetor. A new torque converter is OK if I can run a big enough cam with my compression ratio.

I would also appreciate any recommendations from those of you with more knowledge than I, which is almost all of you.

Many thanks in advance.

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 07-06-2003, 11:01 AM's Avatar
Last photo:
Join Date: May 2002
Location: Holly, michigan
Posts: 8,990
Wiki Edits: 0

Thanks: 88
Thanked 541 Times in 470 Posts
There are many things that effect cranking pressure, engine temp, type and condition of ring, valve seal, atmospheric conditions, position of throttle plates,etc. but the cam can cause low or high cranking pressures by the way it is ground and set up, long duration high overlap cams have low cranking pressure and short duration cams give higher cranking cyl pressure. So compression ratio can't reliably be determined by cranking pressure.

The local circle tracks use a P&G cylinder for checking cubic inch and compression ratio, what a joke, not even close, i've seen the same motor blow(CHECK) three different specs on three different nights. NHRA quit using them years ago because they aren't accurate.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-06-2003, 01:45 PM
Honorary Redneck
Last photo:
Join Date: Nov 2002
Location: England
Posts: 194
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
if the engine is still in the state it left the factory (e.g. no other performance work has been done / hasn't been re-built, bored etc.) probably the easiest way will be to find the casting no.s on the block and heads and post them, we should be able to get enough info from various sources (like to give a best guess.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -6. The time now is 06:38 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.