Pontiac Comp ratio for pump gas - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- 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 04-24-2003, 07:39 PM
Registered User
Join Date: Apr 2003
Location: Minnesota
Posts: 3
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post Pontiac Comp ratio for pump gas

I am ready to put my 455 pontiac together, the only problem is I am putting on 400cu 670 heads. The block is bored .030 and have pistons. I was told I needed the pistons milled down in order to drop the compression to 9.5 to1 in order to run pump gas. The engine guy I talked to estimated .075 off the pistons. (I dont want to mess with the heads) I dont want any estimates when it comes to my engine. Is there any techs out there who could tell me how much to mill them down. 670 heads are 72 cc's

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 04-24-2003, 08:01 PM
Join Date: Aug 2002
Location: Las Vegas
Age: 67
Posts: 175
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts

I'll be the first to admit that this may not be the "percise" answer you're looking for but I rebuilt my Olds 455 with 81cc heads and "medium dished" pistons and the compression ratio is 8.9 to one, according to Keith Black. I can run the auto on regular but I have to reduce the timing a bit but it still has good power. I think that you need to get dished pistons to keep the compression reasonable. If you cut the present pistons tops down then sure, it will lower compression but your quench is going to go out the window. I think that if this auto is a daily driver then you have some decisions to make. Do you still have the bigger chamber 455 heads. I had a "special performance" 1972 Pontiac 455 at one time and it had 8.5 compression but had big valves. The engine came out of a "SJ" Grand Prix. That engine flat boogied! I really don't think that you need mega compression in a big block to make them run. A little head porting a medium performance cam and good exhaust is all you really need for "bristling" street performance! Good luck
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 03:09 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 Hotrodders.com 1999 - 2012. All Rights Reserved.