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Originally Posted by Red__Zed
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You build alot of subaru motors?
The factory STI's have alot of problems with piston ring lands and the reason has to do with poor bottom end design. So to make power you have to go away from cast pistons even on the WRX like your own that don't have the same amount of ring land problems meaning that your expansion rates are alot higher in the piston and piston skirt length becomes increasingly important. The problem is that there isn't any room to expand the length of the skirt so with forged pistons you get alot of slap on start up until they expand to fit the bore. Ever driven an STI or WRX with forged internals? They all piston slap because of expansion rates until they come up to temp unless you spring for Cosworth pistons due to metal type. You get Weisco/CP your going to have alot of slap on start up. This slap = mechanical cylinder wall wear you will be lucky to see 50,000mi on a Weisco/Cp setup and 100,000 on a Cosworth setup.