Compression ratio
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,936
Likes: 9
From: Menifee California
Compression ratio
have a few questions.
1.What would compression ratio be on stock LS1 10:1?
2.What would that ratio go to with addition of LS6 style heads 59cc chamber.
3.What would my new compression ratio be with new motor? Its a APE 347. With flat top pistons and -2cc valve reliefs and 59cc chamber. I think i remember them telling me in the 12.4:1 region but i was on my cell phone so could be didn't hear them.
4.I am thinking I need around 11.5:1 to be able to run pump gas and still not have to pull a lot of timing Is this a good assumption?
5.Why would ratio be 12.4:1 or is it going to be lower what should i shoot for as far as compression and being able to run on 91 crap gas in Ca.
Thanks
1.What would compression ratio be on stock LS1 10:1?
2.What would that ratio go to with addition of LS6 style heads 59cc chamber.
3.What would my new compression ratio be with new motor? Its a APE 347. With flat top pistons and -2cc valve reliefs and 59cc chamber. I think i remember them telling me in the 12.4:1 region but i was on my cell phone so could be didn't hear them.
4.I am thinking I need around 11.5:1 to be able to run pump gas and still not have to pull a lot of timing Is this a good assumption?
5.Why would ratio be 12.4:1 or is it going to be lower what should i shoot for as far as compression and being able to run on 91 crap gas in Ca.
Thanks
Burning Brakes
Joined: Jun 2002
Posts: 996
Likes: 0
From: Frisco Texas
Re: Compression ratio (blackbelt)
I am running 55cc combustion chamber heads. I am right at 12 to 1 compression. You really dont want more than that. My car detonates when under heavy load at part throttle. Getting closer to having it tuned out but it is still there 2 to 7 degress. Was over 14 degrees at part throttle. If we can tune it out I will be getting bigger head gaskets to lower the compression.
The Red coupe bandit has the exact heads you are getting and is 11.5 to 1 compression at most.
The Red coupe bandit has the exact heads you are getting and is 11.5 to 1 compression at most.
Former Vendor
Joined: Aug 2001
Posts: 5,798
Likes: 50
From: Dallas & Chicago TX & IL
Re: Compression ratio (blackbelt)
Blackbelt, I've seen people run up to 12.25 compression with pump gas and no detonation...my brother being one of them. It also depends on your cam selection. To achieve high compression with LS1 or LS6 heads, you need to angle mill them. Many of us here at RPM in Lewisville TX have done it. We run anywhere from high 10's to high 11's on motor. Timing are set between 22 to 30 degrees... taking in cosideration cam size, head ports, car usage and type of power adder usage in conjuction with every day driving. So there, go for it. Good question though, just remember my rule of thumb...if they're not running at least 11.50's in the 1/4, don't listen to them. Scott runs 11.50 to 70's all day long on motor with an A4...very impressive!!! :crazy:
Melting Slicks
Joined: Jan 2001
Posts: 2,635
Likes: 2
From: Aloha, Oregon
Re: Compression ratio (blackbelt)
So i should probably shoot for around 11.5:1 How do I get there?
For example- stock bore 3.898 and stock stroke 3.622 with 60cc heads + Cometic custom gasket thickness .040", 0 deck (stock) and 0 valve reliefs (stock) will get you 11.44:1 static cr. you can play around with the numbers to try different gasket thicknesses, combustion chamber sizes, etc. Keep in mind that you will likely need to cut valve reliefs in your pistons if you cut a head to 60cc's and use a cam cut on 112lsa. I cut 2cc's into my cars when I am trying to get 11.5 or more static with big cams. Some pointers: do not use any thinner gasket than .040" on a stock bore. you must accomodate piston rock as the piston rolls over TDC. If you do not want to have to cut piston reliefs but want to achieve high compression, have a set of heads built with material added to the combustion chambers. This will keep from having to mill the crap out of a head to get a small chamber. This will preserve as much pv distance as posssible. Always check pv clearance, period.
Robert
http://www.gen3motorsports.com
[Modified by rwj383, 11:11 AM 3/26/2004]
