How do Compression Ratios work? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

Reply
 
 
 
Thread Tools Search this Thread
Old 01-11-2004, 02:33 AM   #1
Senior Member
True Car Nut
Thread Starter
 
Join Date: Feb 2003
Location: Bloomington-Normal, IL 1997 SE
Posts: 3,734
Thanks: 0
Thanked 0 Times in 0 Posts
macho_mike21 is on a distinguished road
Default How do Compression Ratios work?

Ive heard about this here and there, but how do they work and can you change them?
macho_mike21 is offline   Reply With Quote
Old 01-11-2004, 02:36 AM   #2
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

A compression ratio of 8.5:1 means it takes the 8.5 and compresses it to 1 (in layman'* terms). It takes extensive head work, and perhaps new pistons to change this. If you really want to get nasty, change the crank.

Now you see why nobody does it. (at least not here)
willwren is offline   Reply With Quote
Old 01-11-2004, 04:27 AM   #3
Senior Member
Certified Car Nut
 
Join Date: Mar 2003
Posts: 12,432
Thanks: 0
Thanked 0 Times in 0 Posts
J Wikoff is on a distinguished road
Default

It'* the ratio of the volume of air and fuel before and after the compression stroke. Easy exagerated example: a cylinder has a volume of 8.5 liters at BTC (bottom dead center, the very instant before the piston begins to move upwards), when it has reached TDC (top dead center) the mixture has been compressed to 1 liter.

With a forced induction engine, 8.5 is the general compression ratio used. If it is higher, the fuel will ignite on its own due to pressure, much like a diesel engine. NA enginescan use 10, 11, 12, higher numbers to get more power because the pressure is lower than a blown engine.
J Wikoff is offline   Reply With Quote
Old 01-11-2004, 11:22 AM   #4
Senior Member
Posts like a Turbo
 
Join Date: Feb 2003
Location: Riegelwood, NC
Posts: 400
Thanks: 0
Thanked 0 Times in 0 Posts
BadTA00 is on a distinguished road
Default

BadTA00 is offline   Reply With Quote
Old 01-11-2004, 11:28 AM   #5
Sol
Senior Member
True Car Nut
 
Join Date: Sep 2002
Posts: 8,909
Thanks: 0
Thanked 0 Times in 0 Posts
Sol is on a distinguished road
Default

So that explains why you need high octane gas in a blown engine right? So it won't ignite early.
Sol is offline   Reply With Quote
Old 01-11-2004, 04:03 PM   #6
Senior Member
True Car Nut
Thread Starter
 
Join Date: Feb 2003
Location: Bloomington-Normal, IL 1997 SE
Posts: 3,734
Thanks: 0
Thanked 0 Times in 0 Posts
macho_mike21 is on a distinguished road
Default

i read the howstuff works articles on engines and what not last night. I was wondering if there was an easy way to change this, but I guess not. How much hp does increasing the compression ratio, say, .5
macho_mike21 is offline   Reply With Quote
Old 01-11-2004, 05:47 PM   #7
Senior Member
True Car Nut
 
Join Date: Jun 2003
Location: Purgatory
Posts: 6,313
Thanks: 0
Thanked 0 Times in 0 Posts
PontiacDad is on a distinguished road
Default

You could have the head shaved to add a bit of compression....say 5hp? if you do nothing else to the head.
PontiacDad is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Gear Ratios Merlin 91/97 1992-1999 1 06-15-2006 08:32 PM
Can someone give me a lesson on gear ratios? ComfyCar General GM Chat 12 07-20-2005 12:39 AM
Final Drive Ratios karfreek 1992-1999 1 08-06-2004 10:00 AM
gear ratios macho_mike21 General GM Chat 4 08-04-2004 04:23 PM
Gear/axle ratios questions OLBlueEyesBonne General GM Chat 9 09-23-2003 04:32 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not 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 Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 04:47 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.