Hi !

As you may know, I have head gasket failure
I'm in shock because I've never take part in any track day runs !

I have used search engine but i haven't found any useful (for me) information about forged pistons.

Subject: Stock Subaru Impreza STi MY06 with EJ257

I'm very keen on buying and rebuilding my engine on Cosworth forged rods and pistons, but my goal is to minimize piston slap. Is it possible ?

Cosworth is the only brand i know and wich I trust. i dont like go with Mahle or CP piston or other brands.

I've read that the pistons are gaining volume when there get to right temperature, and the oil consumption will much increase, due to lose piston fitment to cylinder.

I'm using my Car as a daily car but i'd like to have circa 320-340 hp

Please help guys !

 

My 2.5 is using Cosworth pistons and is very quiet and uses very little oil , about 250 ml every 2k miles .

 

CP's in mine, quiet and uses a dribble of oil only when im beating the crap out of it

 

The correct procedure is to re bore to the next oversize and hone to fit the pistons. We use stress plates to ensure accuracy.
Cosworth supply a plus .25 piston which would suit you. I wouldn't recommend just "dropping in" a forged piston in the hope it'll fit.
We can offer you various solutions, some of them with a discount!

 

Wiseco and Manley rods on mine still building it

 

Thanks chaps for quick reply. It wlil be first time that im doing this operation, not by my self but well respected tuner. But im concerned about the piston, it will be smaller about 0.007 than the bore and is it a bit loose ? Could it be more thigher ? Like 0.005 ? Will it be safe for the bore to avoid scraching it ? How much forge pistons expand in optimal working temperature ?

Im a bit frightened this whole operation.

 

7 thou seems a lot, my cp's run at 3 thou clearance.

 

and there's no issue ?

 

0.007 is massive! It'll rattle and I would imagine use a fair bit of oil too.
I've always used 0.003 and has served me well over the years.

 

Any bigger clearence it'll save you buying a ring compressor.

 

LOL !

 

0.003 will be good even for these cosworth pistons ?
Cosworth Impreza EJ25 99.75 mm 8.2:1

without scratching the bore ?

 

0.003~0.004" honed finish would be good for the power you want to run.
Ring Gaps should be set accordingly too.

Mick

 

Well, my tuner done it ! works perfect ! Coswoth pistons are awesome

http://www.youtube.com/watch?v=IdFHroZfMmU this is how it works after 134 km's

Now im after 2600 km and still i dont hear any pistonslap

Im very pleased with the result !

 

give it 20000 miles see if its got any slap then : > but yeah so ok to me

 

you might be right but untill now is perfect ! Cheers lads

 

Sounds good. Supertech pistons are what I have on mine and they are extrememly quiet. You will get some slap as the engine beds in though; should be nothing to write home about and it'll go when the engine warms up.

 

next step will be a TS for EJ257