Hot Rod Forum : Hotrodders Bulletin Board - Reply to Topic
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> Compression Ratio
User Name
Password
lost password?   |   register now

Thread: Compression Ratio Reply to Thread
Title:
  
Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :

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:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

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.



Additional Options
Miscellaneous Options

Topic Review (Newest First)
01-13-2004 06:43 PM
hemiford Idle feed restrictions are somewhat of a compromise on Holleys, as I've found out. Manufacture recommendations of 1/2 - 1 1/2 turns on the idle screws are pretty good to follow. I use both idle sound and vacuum to set mine. Ideally you want to have an air fuel ratio of 15 or 16:1 at idle and low load (cruising). At full throttle, full load, ignition advance all in, you want about 12:1 for max performance without pinging, or surging. That O2 sensor is actually better for finding your WOT jetting than anything else. I have had some luck canibalizing several carbs of different sizes to get a combo that works good throughout the range. I have about 20 parts carbs laying around my shop. This requires a lot of time patience and a good idea of where, in the power curve, your mixture needs improvement. Use your O2 sensor to get the WOT jetting right and adjust bleed screws by vacuum gauge and ear.
Good Luck
Joe
01-13-2004 06:25 PM
camaroman7d Huskinhano, All VERY good points that most people don't understand or consider.
01-13-2004 05:31 PM
Huskinhano Besides what camaroman7d said, you're measuring cranking pressures. They are different then compression ratio and is not a valid way to determine CR. Cranking pressure have an awful lot to do with cam timing. You could have a 7.5 CR motor make higher cranking compression then a 11:1 motor! All cam timing. It's also important to put 2 & 2 together and realize that with a mild cam timing that a 7.5 motor uses to create high cranking pressure would be disasterous in a motor with 11:1. You'd create stratospheric pressures that would diesel the motor. Conversly is true also, meaning a cam intended for a 11:1 motor would cause such low cranking pressures that the car would be even more of a dog on low end. This is why cam manufacturers tell you what kinda mechanical ratios to run on their cams.

Tom
01-13-2004 03:25 PM
camaroman7d If you were to have an actual 9.5:1 engine you could probably run 4psi of boost maybe 6 with forged pistons. Go here and look at the recommendations most companies will tell you that an "effective" ration should not exceed 12.4:1 on pump gas. This is a little conservative and will depend on many other things. If you are seriously thinking about putting a blower on it and you have forged pistons decent rods/bolts and crank. If you have 64cc heads, I would swap them out for a set of 76cc heads and lower the compression to a blower friendly level. A blower is a big investment, you might as well make the most of it if you are going to bolt it on. This means a compression level of 8:1 - 8.5:1 (maybe slightly higher).
01-13-2004 03:02 PM
ron eckman
Compression Ratio

Hello everyone and thanks for making this site so cool. The knowledge you all share is very helpful especially to a backyard mechanic like myself.
I'm dialing in my 355 trying to get the most out of it. My last thread I asked about if I could run a small blower with 10:5 compression thats what I was told I had. I just bought a compression gauge and tested all the cylinders. My results vary from 160 - 170 is this an accurate way of determining my compression ratio? If my compression turns out to be more like 9:5 how much boost my I be able to run?
Also I have another holley question. I just bought a vacuum gauge and a air fuel mixture gauge with an 02 sensor. Should I tune my mixture screws to the highest vacuum or should I tune it with the air fuel mixture gauge. Any advice is appreciated and thanks for your time

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


All times are GMT -6. The time now is 04:09 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.