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Originally Posted by Artisan7471,Jun 27 2010, 09:45 PM
If you want to go low compression on the cheap, you can machine your stock pistons. Im running machined ap2 pistons at 9.6:1 compression ratio. Ive been running these since last fall. They have been very reliable so far, im running 15 psi at low boost and 20 at high, on 91 octane. Cost for machining is around $200. However the amount of labor required is much greater than just installing a head gasket. But at least you dont have to worry about your headgasket failing all the time.
and i know there have been h22's built, but for some reason no one has really done it on the f20. well except for "blues2k3" as of now he is the only one i know of with a running motor using stock sleeves with aftermarket pistons.
Noone has done any f20's with these pistons b/c Mahle JUST got them released a few weeks ago.
They wont make anything bigger than 0.25mm oversize, they say the FRM isnt consistent enough past that for it to be reliable in every block.
I should have my motor together shortly with the shorter NA pistons.
Also, looking at the moded pistons, it looks like they milled them down so the piston-deck is 0 (its hard to tell) Doing this effectively removes all the quench from the chamber, the piston needs to be 1mm out of the hole to work the best.
my old block was pretty trashed and it only took about 3 thou to clean it up.
frm sleeves and the coated pistons are very forgiving as far as the cylinder wall surface goes. There can be pretty significant scratches (as long as they are completely vertical and still work good.
how thick did the crown end up being on those moded stock pistons??
Also, i'd use ap2 pistons for that, ap1 pistons arent as thick under the dome
I measured the dome thickness of both f20 and f22 pistons. The f20's are actually thicker. Honda used the same rear forging die when making both pistons, the top die is the only thing they changed in the forging process. They actually have alot more material in the piston than is needed. I beleive the reason for this is that it is difficult to go very thin using a forging process.
ap1 dome thickness = .340 inch
ap2 dome thickness = .265 inch
After machining, the dome thickness was around .170 in.
I only removed .005 off of the quench pads so they should remain very close to stock. The majority of the material was removed from the center of the piston.
Here is a link to a wossmer frm piston thread, good info here
