Compression ratio with 9-12psi blower? - Third Generation F-Body Message Boards

Brett · 09-13-2000, 01:45 PM

I'm rebuilding the LT1 I swapped as a 355 that's set up for a strong blower. Right now I have TRW forged 21cc dished pistons that should yield 9.5:1 down from stock ratio of about 10.2:1

Is 9.5 low enough to work effectively with a 12psi D1sc? Or should I order the 24cc dished pistons and drop the compression closer to 9:1?

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1991 RS LT1
every imaginable bolt-on, and an all-forged 355 on the way with an ATI following in '01

2000 C5 Coupe
black/black 6-spd, optional polished rims, 'mostly' stock....

"So what DOES the back of a Mustang look like?"

89ProchargedROC · 09-13-2000, 02:31 PM

with 9.5 you are at the ragged edge of stock timing with 12psi. 9psi would be okay. But i would still bring it down to 9.0 or even 8.5 because maybe later you might want to up the boost. I think with 8.5 and an intercooler you can almost run 20psi and stock timing.
go with 8.5 or 9.0.

bhoward · 09-17-2000, 03:30 PM

I THINK YOU WILL BE JUST FINE WITH THE 9.5 COMPRESSION RATIO.I'M CURRENTLY RUNNING 9.1 RATIO BUT WISH I WOULD HAVE STEPPED IT UP A LITTLE MORE.

FastBroker · 09-18-2000, 01:08 PM

I'd go 9.0 or less, too... As eluded to, bumping up blower pressure later is a disease and too little CR is better than too much with a blower. Too much CR will beat the sheet out of any motor, never mind a blower motor. Call theblower mfr and get their recommendation. I bet 8.5:1...

Guido · 09-18-2000, 05:13 PM

Im running 9.3:1 and Ill be running around 13psi if its close to what it was on my 355. Just make DOUBLY sure, that you get yours rings gapped for a blower. Its different than with a normally aspirated motor.

I think thats what killed me before.

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-86 IROC
Vortech stuffed EFI 406 in progress
-=ICON Motorsports=-