CoopDog

iTrader: (17)

I have a motor with Ross dished blower pistons and 241 heads that come out to about 9:1 CR.

I am switching heads, going to Patriot LQ9s, that will drop the CR more, I am trying to figure out what CR I will end up with after the head swap. Pistons only or LQ9 heads only each do 9:1, logic would say that the CR should be 8:1.

My guess is that it would be somewhere between 8.5:1 and 9:1. I'm sure this has been done many times, can anyone tell me where the actual CR will be?

3.905 bores, 3.7 in. stroke, fed by a Vortech YSi.

maxgee

iTrader: (5)

I don't have the answer to your question, why do you want such low CR?
How much boost are you planning to run?

DeltaT

iTrader: (5)

What chamber size do your current heads have, and what chamber size do the new heads have? What compressed thickness is your head gasket? How many cc's are the dishes in your pistons? If you know, do your pistons, at TDC, a) stick out of the bore in the block, b) sit flush with the block or c) sit down in the bore a bit? Those are the 4 main things you need to supply, then I can roughly tell you current CR and future.

Jim

CoopDog

iTrader: (17)

I did forget a few things. The current chamber size is 65cc, the LQ9s have the standard 72cc size.

I'll have to see if I can find out how many cc's are in the pistons though. as far as how far the piston travels, whether it protrudes above the deck line, I'll have to find that out as well. I didn't check that out the last time the heads were off.

as for how much boost? I don't really know to start, I won't know until it fires up. very scientific for sure. It is an RMCR YSi conversion kit with a cog belt drive.

CoopDog

iTrader: (17)

Forgot the gaskets, they are just standard GM MLS, I can't remember what they compress to, .41 or .51.

Pro Stock John

iTrader: (34)

Might end up around 8.5:1, that's okay. What pulley combo are you running? Did Chris build you brackets that has the blower up top or down low like mine used to be?

CoopDog

iTrader: (17)

The brackets are from RMCR. Even with the cog belt setup, there is an inch and a half between the blower and the hood. I was afraid it would not fit. That is the only part that still resembles the original Vortech kit, I have an air to water IC under the dash inside the passenger side of the car.

I was fairly happy with the original 9:1, I bought the new heads to solve a valvetrain issue, lower compression is a bonus.

Interestingly enough, out of the 3 blowers I have had, the original little G-trim unit sat the highest. The T-trim and the YSi sit a touch lower.

I have been meaning to ask, what are the specs of the cam you ran with your YSi? I've been meaning to ask.

Pro Stock John

iTrader: (34)

John, it was a 236/246 and the LSA was hmmm 114?

NAVY

i think 236/240 .605 .609 112 lsa

CoopDog

iTrader: (17)

Yikes, I am way off with a 224/230 .581/.588 on a 114. recomendation to do something clidose to what you guys did? Did a 112 hurt the performance at all, worse than a 114 or higher? I know the general rule for the spread on FI motors, you never know with these cars though.