I'm looking for a little help, as the title says I have some broken pistons to be exact. I have been calibrating GM direct injection from the beginning and have never had any issues with LT1 pistons. I have worked with every supercharger setup, lots of camshaft packages and all the meth in the world. This setup is a 2017 Grandsport with a basic Procharger HO package on 7 psi, the car is well taken care of and has 16K miles. Something that should make 570-600 at the tires and be off the dyno in no time. So first pull with some timing out of the engine it lays down 522 rwhp. Everything looks good and I add two degrees for a total of 11, second pull the car makes 487 rwhp. The log showed a couple degrees of spark knock on the top end, I'm just about to do another pull and when I start the car up it has a little misfire feeling, nothing major, no flashing light just feels a little off. I decide to check the engine over and I find oil leaking from the procharger bypass valve, nothing under the car and exhaust looks good. Pull PCV and I have pressure, with oil being pulled into the procharger intake. After a quick compression test I find cylinder 5 and 8 are at 50 psi. I'm down not one but two cylinders and I have never even seen a broken LT1 piston before. I was just starting to tune this car and don't have a clue what happened, fueling looked good and timing was still low. No major knock and bingo two down. So it comes all part and the lower ring lands are in twenty pieces and those two cylinders the piston tops where a lighter gold color and the other six where more brownish gold. So in goes new pistons and new injectors on those two cylinders. I drive the car around and after 300 miles we are going back on the dyno. This time, I start logging individual cylinder knock retard and a few other things. First pull is 454 rwhp, I have timing low 8 Degrees. I do see during the pull a scattered a degree or two of timing being pulled on random cylinders. I do the next pull with 10 degrees and cylinder 5 pulls 4 degrees at 4k and suddenly at 6200 cylinder 8 pulls 8 degrees makes 492 rwhp, . These are the same two cylinders that broke, now with new injectors and plugs. I go back to 8 degrees and another pull, and another pull and another pull. Randomly it will or will not spark retard in the midrange, if so always worse on cylinder 5. I was able to make some clean pulls without any spark retard in the midrange and up to 13 degrees of timing up top, still low on power at 537 rwhp as my best. On every run cylinder 8 (the other cylinder that broke) will have zero to 1 degree of retard and then suddenly in the 5800-6200 range suddenly pull 8-10 degrees, that exceeds the individual cylinder knock limit and all cylinders then pull that much timing and power takes a dump. The customer swears its on fresh 93 octane and I did top it off with some after driving around with new pistons. So for the fun of it, I do another compression check, half expecting cylinder 8 to have some problem. Nope 7 cylinders have over 200 psi and cylinder 5 (the other broken cylinder) has 50 psi. Pull her all apart and the new piston has half the lower ringlands missing. So at this point a 7psi procharger setup is low on power, fuel pressure and AFR 12.1 are good at wot and it keeps spark knocking those cylinders with new injectors, colder plugs, colder thermostat. Its going back together again and I don't have a clue. Anyone have any ideas, Problem with piston squirters on those two cylinders?
Bad383TA
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Originally Posted by TriPinTaZ
