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8.0 or 8.5 compression ratio?

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95/99 Brighton STi
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Discussion Starter #1
Planning on building another EJ20 and was curious to what people would rather have. With a fully forged bottom-end, would you rather have 8.0 or 8.5 compression ratio?
 

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2000 2.5RS/C BRP
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With proper tuning, 10:1 with boost is great. OEM turbo cars these days (with DI, admittedly) are running 10.5:1 at 15PSI.
 

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00RS Coupe, 00RSwaggin
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8.5:1 is where I would go. friend of mine just gone done doing a build like this with CP pistons and eagle rods, on a 20g turbo and it's a dirty setup for sure. he's been blowin through 5 speeds like a blender :lol:

Stock STi is 7.8:1 on the ej25,
 

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11 wrx & 15 fozzy 2.5i
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you need to thing on the stuff around the engine to plan this, with such small displacement i will go with high compression and mid size turbo (18-20g), the 2.0 is small and if you drop the CR is gonna be boring to drive around. my friend with his built 207 bottom end and built wrx heads is able to spool and make decent boost on a 35r .63 at around 4.5k on race gas tho. he is over 10:1 CR i believe.
 

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95/99 Brighton STi
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Discussion Starter #5
The benefits of better off-boost driving and better spool sound, and I'm sure, are very nice but how many people that are looking to buy a shortblock are capable of running and can actually tune for the higher CR?

Honestly driving with 8.0:1 ratio with my 207, to me, doesn't seem that bad; I can only imagine what'd it would feel like with a bump in compression.
 

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depends what turbo, how much boost is planned for that turbo, what fuel, and the most important, which engine management

in the grand scheme of things, static compression is among the least important overall factors to a typical build
 

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95/99 Brighton STi
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Discussion Starter #7
Looks like 8 and 8.5 are the only OTS pistons available for an EJ20
 

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1997 Impreza Brighton
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Isn't this dependent on application?
Seems like for something like autocross you'd want higher compression to fight lag, but may be more trouble than it's worth for more open tracks.

*Disclaimer* I have no experience with turbos (yet) but want to learn what I can before building a motor for 2015.
Did not vote, but am leaning towards 8.87:1 on a 2.5L running E85 and a VF52 for my own potential rallycross build.
 
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