PDA

View Full Version : Compression Question



DanielIser
08-03-2005, 05:46 PM
I searched and couldnt find what i was looking for.. Ok i am embarking on the great adventure of a full build up on my SR. I know a good bit about motors and all but the bottom end, other than actually putting it together, is new to me.. I just need to know how different things affect other things. Like compression, stroke etc. What I am really looking to get out of this other than a basic understanding is what different compression ratios mean. like is 9:1 better for what application compared to 10.5:1 etc.. Thanks alot. BTW will be posting all the pics from the build up.

BlazedGlory
08-04-2005, 03:12 PM
I don't really know enough to answer your question thoroughly, but I do know that forced induction engines usually have a lower compression, and n/a engines have higher (12.0:1, etc) compression...

That's all I got for ya =P

cardriver
08-04-2005, 03:31 PM
http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio.htm

this is kool too

http://www.csgnetwork.com/compcalc.html

TS4l
08-04-2005, 03:59 PM
Lower comression is easier to tune safely as its easier to hear knocking on a lower compression engine. However higher compression will help with low end and off boost driving. I like 9:1 on a boosted motor, unless your goal is to run really high boost, then maybe consider 8.5:1. You probably already knew this but just my 2 cents.

DanielIser
08-04-2005, 05:02 PM
Thanks for the replies all.. Those links are what i needed to get the understanding of it. And TS4l gave me the second answer as for what would be good for me. Just so you know i am currently working on the build up and am gonna be using a GT25R and am looking for a max boost of prolly around 18 maybe 20 if i can do it safely but that would be track only just for the numbers and only on a race gas setup.. So from what i have read so far and what im getting from this. I would definately rule out 10.5:1 and consider 9:1 or 8.5:1 for extreme safety. Is that correct? THanks

TS4l
08-05-2005, 10:14 AM
I'd go 9:1 and get an Entalpy tune. You could then safely run 18 daily. I run 18 daily on my 3076 and have had no problems, other than you can't really hit full boost daily too much as you'll be speeding on any street. Plus 9:1 will help with off-boost power.