lwdwn1

I have an 04 CTS-V I recently scored a LS3 short block. I want to put my 243's from my LS6 on the LS3. My heads have been decked 20 thousandths, stock head gaskets. I have a TSP 228R cam does anyone have an idea where my compression ratio would be?

jrane

iTrader: (10)

About 11.6:1

lwdwn1

Is that to high for pump gas? I plan on having it tuned after it's all back together..

blk/slvr02ss

iTrader: (21)

Should be no problem to run pump gas but your tuner will let you know better.

jrane

iTrader: (10)

If you run 93 octane you should be fine.

82cetuner

iTrader: (9)

im about to put 12.0 compression on 93 im at 11.5 right now its all in the tune really

batboy

iTrader: (6)

I calculate closer to 11.3 static CR. The cam overlap is a big factor in calculating dynamic CR. If this is with a stock cam, you might be on the edge with pump gas unless you use 93 octane.

FFFASTGTO

I have a LS3 bottom end and 243 heads with a slightly larger cam. my heads were decked .025 and to get compression around 11.6 I had to get a custom cometic gasket at .070. I think you will be fine with what you have.

badazz81z28

iTrader: (6)

I think cathedral port heads would be a shame to use on the LS3! Sell them and get retangular port heads

KCS

iTrader: (20)

Actually, overlap is how long the exhaust and intake are open and has nothing to do with dynamic compression ratios. When the intake valve closes is what is important.

What's wrong with cathedral port heads?

Mr. Sir

Nothing, though the ls3's would do better.

TonyGXP

found this thread doing a compression ratio search. having an engine built right now for my project car and i was discussinf CR tonight with my guy. says my setup is 11.5:1 instead of the 12.5:1 i initially though it was going to be. I was told that the 11.5 is better given i will be using this car primarily for the street and if the wife god forbid doesn't catch the idiot attendants (yes, in NJ you cannot pump your own gas....very lame) i would be in a better position if i didn't realize and started beating on it. I was also told it would be max 20hp difference in the higher CR (from 11.5-12.5) given the variables . when it is tuned i will be tuning it on WaWa 92 octane as another failsafe just in case. So i will be able to tell you how running on less than 93oct ends up. I will also be tuning for 100 octane just to compare differences for future reference/builds. it really pays to have a good friend with a mustang dyno lol.

if this were a pure hobby/show/track car i would've gone ridiculous cam (if i kept it NA like i did now).

In other words, you're more than fine with the 11.5-6:1 lol

nothing, unless you're going over 400cu. that's where the L92's really pick up steam (from what i've heard, wtf do i know? lol)
im sure there's threads on this forum but here's a quick interesting read
http://www.yellowbullet.com/forum/sh...=473542&page=2

lilaaron233333

iTrader: (10)

LS3/L92 heads will flow way more then the 243's i hav a set of L92 heads for sale. the only difference between the LS3 an L92 is the intake valve is hollow stem in the LS3 heads and solid in the L92's

redgto4u

iTrader: (8)

I'll be doing the same thing on my 418 ls3 motor. AI 243 heads and Fast92/92 combo with a texas giant cam. Not optimal heads but since its the setup I have its what I'm going with. Once I get it broken in and tuned well I'll post up some dyno numbers. I wont have any track numbers since there isnt one here....If it makes 500/500 through my 4k stall I'd be extremely impressed!