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Old 08-05-2015, 12:00 PM   #1
Scooby Specialist
Member#: 210371
Join Date: May 2009
Chapter/Region: MAIC
Location: York, pa
2002 wrx wrb
'03 Lifted TS

Default stroker compression ratio question

I've been doing research on pistons for my 2.1 stroker build. Most piston manufactures use the 8.5:1 ratio. However, looking at JE pistons, one can choose between the 8.5:1 and 9.5:1. I know that a higher compression ratio means less max PSI (which I don't care about), but helps with off boost response. As this is the first time I am doing a motor build, I'm unfamiliar with just how much of a difference this is. The build is not a "big" one compared to most of the builds I've been reading about. Plans for the car is a weekend/nice weather driver, with the occasional weekend warrior status. I would like to see a few autocross events per year if possible. Any suggestions/guidance on which ratio to go with?
Other engine mods to consider:
Blouch 16gxt
850cc injectors with 255 pump
upgraded intercooler
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Old 08-09-2015, 03:50 PM   #2
Scooby Specialist
Member#: 29292
Join Date: Nov 2002
Chapter/Region: SCIC
Location: Orange County CA
2004 WRX wagon


i think a good question to ask yourself is what type of fuel you wanna use. The 9.5 compression is pretty high for pump fuel. you might only be able to run somewhere around 10 psi on pump, but on e85 you can go up to 24ish. but you will need bigger injectors at least 1000cc. so if you going to only run pump, then i would stick with the 8.5
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Old 08-10-2015, 06:18 AM   #3
Scooby Specialist
Member#: 149674
Join Date: May 2007
Chapter/Region: SCIC
Location: at your moms
2006 LimitLess STI


For the past 3 motors I've used they were all Hi-Comp motors ((10 to 1) no joke). I ran no higher than 32psi. All of these motors ran only E-85 or E-98, however if you have a standalone engine management then you can also do multiple map switching with a trim pot switch. Also put a flex fuel sensor in there for alcohol content.

You can run crappy gas on Hi-Comp motors however you can't run any boost (like no more than 5psi, but to be safe I would say 3)
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