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Discussion Starter #1
i'm trying to get feed back on what compression ratio to go with for my current rebuild. i'm looking for opinions & reasons why. here is some info, if you need more, just ask.
6 bolt 4g63
ross pistons bore .020" over
93 octane
aem ems
evo 3 turbo
560cc evo 8 injectors
mitsu mls headgasket
i would like to run 20+ lbs of boost or whatever the evo 3 can handle ?
i was thinking 9.0 : 1 ? or should i be 10.0 : 1 ?
 

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10 to 1 is too high for pump gas. Running pump gas you don't wanna get past 11 to 1. The turbo boosts compression too so it probably would be over that 11 to 1 ratio. You need to caclulate your compression of the turbo and the pistons together.
 

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Discussion Starter #3
So should i stay with the stock cr ?
or go with 9.0 : 1 ?
yes the car will be tuned to 93 pump gas.
 

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I ran 9.0 compression for a while, then tried 8.5. I like the lower compression better. It's easier to run high boost. You're going to be pushing your turbo a little past it's efficiency peak, so the lower compression should let you run a little more boost or timing on pumpgas. I definately would not recomend 10:1 compression unless it's a high rpm race motor.
 

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If you're running pump, you will definitely want to go with lower compression pistons.
I'm doing a build on mine right now and will personally be going w/ Wiseco 8.3:1's on Eagle rods...
I'll be running a good amount of boost on pump w/ the 60-1.
 

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about 8.5:1 to 8.8:1

im gonna be running 8.8:1 wisecos on my stroker on 91 octane fuel.
 

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I would get the CR to be something close to 8:5:1...The 2g compression ratio in a 6-bolt block

Also, if I was planning on building a big boost built motor, I probably would not stick on a 16g variant...I would look more into the full garrett size turbo's...possibly a 60-1 or GT30R setup...At least a 50trim would make more sense than an evoIII b/c 50trims start making the most power in the 22+psi range, where as 16g's are better for 15-20psi range power

Just a thought....
 
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