12-23-2012, 11:23 AM
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#1 (permalink)
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A True Z Fanatic
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Quote:
Originally Posted by Fishey
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.
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That's a cast internal issue, not a fundamental design issue. Piston slap after switching to forged internals is common across many platforms, and while it might be trivially more prevalent due to the "mini skirts" on the EJ, I've seen zero evidence that the cylinder walls wear any faster than they do on other platforms. Additional wear from start-up slap is 99% academic. I would not fret it at all.
Your discussion of Cosworth vs others clearly demonstrates that it isn't an inherent design flaw, it is just something that needs to be worked with.
For the STIs, I've seen far more evidence that the ringland issues are due to a bad tune, vs a bad design.
We've still got a lot to see on how the FA performs, since it is clearly it's own beast. Trying to make straight up comparisons to the EJ at this point is ridiculous...almost as ridiculous as saying the EJ doesn't hold up to big power over time.
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