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Old 07-13-2016   #1
talonsway
 

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Compression Ratio Question

Hey guys, Im rebuilding my 1g 7-bolt motor that i spun a rod bearing in. My question is about a set of pistons i found. If i remember right a 1g 7bolt piston has a compression ratio of 7.8:1. I found a set of SRP forged pistons with a compression ratio of 9.0:1. This is my first time ever rebuilding a motor. And im more curious about the compression ratio and what it does. Right now im on a 20g going to be on e85 soon. So im wondering what compression ratio would fit me best. My goal is to eventually be around 400-500awhp and switch up turbos eventually. thanks for any input
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Old 07-13-2016   #2
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Re: Compression Ratio Question

Edit: I misread. If you are asking about the benefits of compression, more compression will net more power, but will be more prone to detonation. If you are running E85 or high octane fuel, there is pretty much no worry. See below

The turbo has nothing to do with static compression, only dynamic compression under boost which is difficult to measure. It's a math function of how much base compression you have plus the boost pressure you're running. So going from 7.8 to 9.0 will give you more compression all around, and you'll see more power too. So you would normally have to compensate in the tune, with maybe less timing and less boost. BUT since you are going E85 the 9:1 compression is pretty safe, and you can likely do more timing and boost.

In any case, going from a 7.8:1 piston to a 9:1 piston should give you better all-around driveability, but definitely get a dyno tune for whatever boost level you plan to run. Fortunately E85 should be pretty safe.

Last edited by asshanson; 07-13-2016 at 05:07 AM..
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Old 07-13-2016   #3
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Re: Compression Ratio Question

I run 9:1 in my stroker with 93 octane and occasionally E85, I wouldn't ever go less than 9:1 with today's advanced fuel and timing control options. I ran 10.5:1 in my Evo with no problems, but I ran just E85 in that.
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Old 07-13-2016   #4
talonsway
 

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thank you guys that answered my question !
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