Best pistons to use and Comp ratio?

[Fabron757]

Whats the best pistons to use and the highest comp ratio to go with on a built motor? I'm not a fan of the 9: comp ratio..... Power goal is 600+rwhp

[D K]

9: ???

What has 9: ?

[FreshFRS]

Originally Posted by Fabron757

Whats the best pistons to use and the highest comp ratio to go with on a built motor? I'm not a fan of the 9: comp ratio..... Power goal is 600+rwhp

you probably don't have to drop it that much, pump gas or E85?

Pump gas i'd say 11:1 would probably be okay up to 20psi? E85 you shouldn't need to drop it even that far considering FBM made 600+ on factory Internals. built internals at 12.5:1 would probably be fine with E85 maybe bring it down to 11:1 to be on the safe side and be able to run decent boost with Pumpgas too.

High compression Turbos are the way to make power with less boost, just need a really good tuner to minimize the risks with smaller tuning window.

[FreshFRS]

Originally Posted by D K

9: ???

What has 9: ?

FBM is 9.5:1 IIRC

[FullBlown]

It will all depend on the quality of the gas. We did a 9:1 and 10:1 build within the same week and the 10:1 was a little finicky on pump gas.

[FullBlown]

Originally Posted by FreshFRS

FBM is 9.5:1 IIRC

Those were our custom sets that we made a batch of. We have since made just 9:1 or 10:1.

[cdrazic93]

All hp goals are relative to engine interals. 9:1 comp is fine for a high hp application engine. 10:1 is alright, although 9:1 is safer with the amount of boost running. 20psi is safer on 9:1 pistons vs 10:1 or 10.5:1 pistons. The STI and WRX have 8.5:1 ratios. the risk of changing the comp ratio of the engine means you will burn through piston rings, faster among other things. Remember a built engine must be rebuilt every 60,000 miles. Even if it's built perfectly.

[King Tut]

I would probably go 9:1 on 93 octane and 10:1 to 11:1 on E85.

[Jesse@JDLAutodesign]

I went 9:1 with my setup.

I'd like to be able to run 91 octane at times and the heat out here can be extreme.

I see a lot of people on here saying the compression helps spool...I'd like to see proof of this. I've had similar motors at different compression ratio's before. The higher comp motors can be slightly more responsive out of boost but that is different than spool. They still would hit XX psi at the same XXXX rpm.

[FreshFRS]

Originally Posted by cdrazic93

All hp goals are relative to engine interals. 9:1 comp is fine for a high hp application engine. 10:1 is alright, although 9:1 is safer with the amount of boost running. 20psi is safer on 9:1 pistons vs 10:1 or 10.5:1 pistons. The STI and WRX have 8.5:1 ratios. the risk of changing the comp ratio of the engine means you will burn through piston rings, faster among other things. Remember a built engine must be rebuilt every 60,000 miles. Even if it's built perfectly.

@FullBlown Curious to know how much boost you were running at 10:1 on pump gas to make it finicky? What turbo? and i agree gas quality is one of the bigger factors.

Lower compression is always safer but at the cost of responsiveness and needing more boost to make the same power. the EJ is a totally different animal and isn't quite apples to apples for comparison. the turbo FA's are 10.5:1 IIRC so that would be a much better guideline though its not apples to apples either.
@Jesse@JDLAutodesign: Spool is one thing that will be debated till the end of time, however off boost response with be greater with higher compression. needing more boost to make the same power could be the "difference in spool" say needing 20psi to make 500whp at 12:1 vs 27psi to make to the same 500whp at 9:1. (just a scenario) full boost will be different on the cars. but you'll be able to run 30+psi and generate more power without knock on the lower compression engine.

[cdrazic93]

Originally Posted by FreshFRS

@FullBlown Curious to know how much boost you were running at 10:1 on pump gas to make it finicky? What turbo?

Lower compression is always safer but at the cost of responsiveness and needing more boost to make the same power. the EJ is a totally different animal and isn't quite apples to apples for comparison. the turbo FA's are 10.5:1 IIRC so that would be a much better guideline though its not apples to apples either.

While this is true, I would assume it's general for most engines. Regardless, in a high hp (600+whp) application the FBM short block is probably the best way to go. Even at that I would still sleeve the block, and sprinkle some forged valves n springs with that mani they are making. We still don't have cams yet for this engine

Another issue to address is, 600hp from a 2L = monsterous lag.

[FreshFRS]

Originally Posted by cdrazic93

While this is true, I would assume it's general for most engines. Regardless, in a high hp (600+whp) application the FBM short block is probably the best way to go. Even at that I would still sleeve the block, and sprinkle some forged valves n springs with that mani they are making. We still don't have cams yet for this engine

Another issue to address is, 600hp from a 2L = monster pus lag.

Twin-Scroll for the win. @FullBlown what rpm are you reaching full boost at with your 6466? i'm assuming single scroll?

i would think the at high compression a 4000rpm boost threshold ( i.e. max boost achieved at 4000rpm would be fairly decent on the street)

[FullBlown]

I'd have to look at the logs. If i remember correctly it was somewhere around 5600

[Ironsquid]

IMO, 9:1 would change the "86 feel". 10:1 should be completely fine to get 600hp. Stock compression on better internals might even get you there.