Thread: How much KR does it take to chip a piston?

pulley up or pay up.

the more boost you're running, the more heat you're creating, the more likely that minimal detonation will do damage.

There is no set number as you are gathering from the posts above this one.. Sometimes it happens..sometimes it doesn't. Reality is.. if you constantly see knock you'll end up on the low octane table and all you are doing is robbing power.

Yeah, think of the heat and pressure you are making with that 2.6. I'm sure you are either maxing or nearly maxing the stock map sensors at 14.7 psi. You are riding a fine line for sure. I'd go back to a 2.8 pulley.

Is that extra boost worth the timing penalty AND potential piston damage?

Biggest reason pistons break from kr is because lower timing puts more heat into the piston and weakens it, and sticks it in the bore to the point of breaking off the ring land.

from what i can figure, its not how much, its total cycles, with cycle count inverse to kr amplitude

the aluminum pistons are fine, but focused high pressure waves from preignition/too much timing stresses the pistons typically near the 12-2 o'clock position. and aluminum does not take to repeated stresses without work hardening and crack propagation.

while i feel that chamber design does seem to focus the pressures to (at the least) the inboard side of the piston, the adding factor is that area being right next to the intake valve where it also contributes to thermal cycling of that area as its washed with liquid/vaporized fuel at each intake event.

the thing is that aside from metallurgy/tooling of the pistons, and the usual results of unicorns and knock lobsters due to parts bin lottery of assembly line production. you looking at it being just as bad to have low levels of knock over a long time as it is to have high levels for a short time.

with the sc setups having such short fuel vaporization time (injector quite close to valve) id hazard a guess that even a partially streaming injector would screw with fueling. ive found just the fuel rail positioning can change fueling. i now try to lay my injectors over farther/higher angle, to shoot towards the inside wall.

while it took the riv's non bbv'd whipple and 150lbhr's to find this damned issue at lower rpm's it'd hold true for a smaller injector/air volume even if its to a lesser degree....(along with finding out the fuel rail pressure fluctuations are a real thing, and do affect adjacent cylinder fueling)

test ****. make one change and test. hell just rotating the maf on most air intakes will change the fueling and sensitivity.

not all improvements are wholly electronic table modifications, some can be quite simple as making sure you assemble parts consistently....

then again if i had been consistent, we probably wouldnt have found the riv's odd changes in idle quality/tune with just small changes in assembly

craploads of things are interrelated but keeping detonation counts at zero should be everyones goal since you can mostly look at chipping a piston being accumulative knock.

build it for efficient flow and you likely wont get knock, even when lean

ah who am i kiddin, i just shake up my magic 8 ball and make my life's choices