longrange4u

iTrader: (2)

Ok guys.. trying to figure out what heads I want... So post up your CR's if your below 8.9

I am debating between a 9.06 CR and a 8.49 CR

Thoughts... and DONT FORGET to list your CR. (What is driveability with a 8.5 CR?)

ABeasst

iTrader: (5)

I'm running 8.5.

MECHAM

iTrader: (4)

8:8

your cubes are into effect on this too..

408 8.5CR > 370 8.5CR


if u got the cubes..u can go lower compression..spool time wont be greatly affected.

67Firebird455

iTrader: (27)

Wish I could help you with driveability, I'm running #317's with a 75cc chamber (deshrouded and polished, dropped the spark plug boss quite a bit) and -8.7cc pistons, should be around 8.5:1. Wanted to make DAMN sure I could run a decent timing curve and a ton of boost if I wanted to.

Turbo LS1 SS

iTrader: (7)

8.2 CR on a 366. spooling a 76gts. no lag issues whatsoever. car was even quite peppy NA for what it was.

i say this all the time.... IF YOUR FI....DONT WORRY ABOUT HAVING THE HIGHEST POSSIBLE CR. A COUPLE TENTHS WONT MAKE A DAMN DIFFERENCE IN RESPONSE. GO WITH THE LOWER CR SO YOU CAN RUN MORE BOOST ON PUMP AND NOT WORRY SO MUCH ABOUT DET.

that is my opinion of course. i just see too many people sweatin over the CR deal when it really doesnt much change the feel of the car on FI. especially if ur going for 900hp.....go with the lower CR

low CR, low timing, pump gas, ~11.4 afr, lota boost. that makes power. NOT
high(er) CR, high(er) timing, pump gas, and less boost to avoid the DET

Zombie

iTrader: (2)

My motor is 8.7:1, wish it was 7.8:1 though. I can only run 12psi without meth on 91 octane with 11 degrees peak timing ramping up to 15 by 6k. Well, thats my summer tune where intake air temps can be 125+ degrees.... PRE TURBO

If I would have had a choice in comp ratio it would have been as low as I could have gotten it so I could run more boost on pump. Got my pistons for $200 though so I can't complain that much Hoping to run 15psi in the cooler months.

Turbo LS1 SS

iTrader: (7)

THANK YOU FOR PROVING MY POINT EXACTLY

mdhmi

iTrader: (1)

Mine is 8:8 if I recall correctly. Partial throttle / streetability is outstanding..

longrange4u

iTrader: (2)

Great feedback fellas... I think based on this I am not so hesitant to go with 72cc chambers leaving me with 8.49:1 CR

longrange4u

iTrader: (2)

Hah hah ha brother... you are truly the king of budget turbo.

fastlt1

iTrader: (4)

I wish I could find fordged pistons with 7.8:1 compression with stock heads.

bboyferal

iTrader: (9)

I decided on an 8.5 CR based on much of this information a while back... I figure whatever low-midrange feeling is lost is made up by the power adder... High CR max-effort NA is peaky as hell anyway... 8.5 with a decent-spooling turbo will still have a curve to beat over 600 rwhp compared to much of everything else...

chuntington101

i say anywhere 8-1+ should be fine! i mean imports these days are running 9.0-1.

i would not recomend going as low as 7-1 though! lol back in the 90's thats what some ford cosworth guys over here had to do to run good boost! turned an already lagy turbo motor into an on off switch, activated at about 5krpm! lol but that was on a 2.0ltr motor but the principle still aplies!

Chris.

MIGHTYMOUSE

iTrader: (59)

mine is something like 8:1.. last time it was calculated was 8.3:1 or something and then i went with a larger cc head

ty_ty13

iTrader: (42)

mine will be around 7.5-1 CR with a procharger on a 408...

wiseco -32cc dish with bigger fly cuts and home ported 241's

youd be suprised how much fly cutting and a valve job drops your compression ratio.

longrange4u

iTrader: (2)

Wow no ****? Ok thanks guys.... That makes it solid for me.

Tiago

iTrader: (27)

8.6 here.

Zombie

iTrader: (2)

Nope, far from, my friend Jon who did most of my work is the king, he has a 1998 Z28 (SS Clone too), into the whole car for about $7k including the car. He doesn't have a built motor or rear, just some sweet stock 2.73's with a th400 and a T72 Turbo. Car runs mid 11's. My other friend Joe is into his entire setup (basically a clone of mine (rossler th400, moser 9", still stock motor though) for about 14k including the car and has gone 11.1's @ 124

Now to make this post on topic, both are running 6.0 heads and z06 cams, just like me. There compression should be 9.3 ish.

Zombie

iTrader: (2)

Imports have a smaller bore size. Smaller bore = less prone to detonation.

2000 Tran Zam

iTrader: (2)

8.5 on a 408 here for me.