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I heard it can be bored out to 83.5mm is this true???

I am rebuilding my RS4 2.7T block and have been offered by my parts source the following pistons:
a) JE Forged 81.5mm with 8.5:1 compression
b) JE Forged 82.5mm with 9.0:1 compression

Which PISTONs should I choose???

FYI, I have no imediate plan of replacing my K04-25/26 turbos.

I really would appreciate your comments guys!!! Thanks again guys!

Manny
'01 RS4
Philippines

wossner do a set of pistons for £750 with a 8.0.1 compresssion they are good to

whats the advantage of bringing down my compression if will NOT be replacing my K04-25/26??

you would drop cr if you are packing more air in than standard, i doubt you are with the k04's

The only reason for dropping the compression ratio would be to increase boost pressure, which you will not get from KO4's so seems little point. If you were going for RS6/hybrid turbos then a drop in compression would be an advantage. Bearing in mind that I dont build engines for a living, I could very well be corrected here....

I thought you could run more aggressive timing if you had a lower CR???

Blue_Thunder wrote:I thought you could run more aggressive timing if you had a lower CR???

and more boost.

surfpilot wrote:whats the advantage of bringing down my compression if will NOT be replacing my K04-25/26??

if you dont want to drop your compression why buy je pistons standard rs4 pistons are good enough I was just giving you another option.

also if your rebuilding the block why not do CR drop so if later your turbos fail you can buy rs4/rs6 hybrids or use rs6 turbos with no problems

standard RS4 pistons are more expensive than JE's from my supplier.

try o34 motorsport they do both

If standard bore is a requisite (i.e. no rebore needed) I wouldn't go for anything other than OEM pistons, no matter how much cheaper anything else is!!!!

i would also!...but my bore #6 has some scratches after one of my exhaust valves broke. would a 82.5mm piston with a 9.0:1 compression ratio be advisabble in my situation?? thanks!

standard CR is 9.3:1 iirc , if thats the case yes

Standard CR on an RS4 is 9.0:1.

What is that anyway. 9 degrees, 0 minutes, 1 second.........

The relation of total cylinder volume divided by clearance volume, just a ratio