just for the record:
my stock 1127 bores are +3mm enlarged
piston to wall clearence is is about 0.500" up measured from the bottom of skirt.
the spec sheet says "Min. Gap Per Inch of Bore" for
"High-Perf. Street-Strip" use. sheet also says "Clearances listed below are minimum. Some applications such as supercharged, turbo, nitrous and endurance applications may require additional clearance (.001-. 003")"
so 81mm piston = 3.188"
spec sheet says for bore range from 2.500" to 3.625" min piston to wall clearance required
is between 0.0030 to 0.0036.
these pistons are forged with lower silicon content, so they are less brittle, but they expand more.
it says "Your pistons are manufactured from 2618 non-silicon aluminum alloy".
the piston to wall gap is looking kinda big now tho! imo they're gonna rattle like a diesel lol!
even the sheet says "Some applications such as supercharged, turbo, nitrous and endurance applications may require
additional clearance (.001-. 003")."
how about that!
some pointers for end gap:
End gap is the clearance between the two ends of a piston ring as it is installed in a cylinder (fig. 7). Most high performance and racing engine builders purchase piston rings slightly oversized in order to file fit them to very precise end gaps. Testing has shown measurable increases in horsepower and decreases in blow-by as a result of properly fitting the ring end gap to the operating conditions. Factors such as supercharging, turbocharging, nitrous oxide, endurance racing and different fuels determine proper ring end gap. Proper ring end gap can be more than double from one engine to the next depending upon the above factors.
At operating temperature, the top ring end gap should be as small as possible. Precise machining of the cylinder bores is critical, and is the reason why rings should be fitted to the cylinder in which they are to be installed. A diameter variance from one cylinder to the next changes the end gap of the rings in that cylinder by a factor of pi (3.1416).
For example, a cylinder .001” larger in diameter will increase the ring end gap by .001 x 3.1416 = .003”, rounding off, which could increase cylinder leakage in that cylinder and decrease performance"
since i'm building it for street use,
bore X 0.0045" for 1st ring
bore X 0.0050" for 2nd ring
0.0015 oil ring
3.188" X 0.0045" = min of 0.014346" gap 1st ring
3.188" X 0.0050" = min 0.01594" gap 2nd ring
min gap of 0.0015 for the oil ring
someone verify my calculations there fer me? it's muh 1st build! i'm scairt, paww!
and haven't tried the test start without plugs removed yet (if it doesn't turn so my starter is gone yes?)
either way will know soon enuff.