nmstec wrote: ↑Mon Jan 24, 2022 11:42 pm
mk e. you keep saying im off, dyno says i'm not. You said curve would be flat up top, as you saw, its not.
I would have to dig up the original words, but I recall it looked exactly as expected, all lopsided due to leakage. The pressure curve would never be flat, it will start to drop as soon as leakage rate exceeds pressure gain rate. So a pressure rise and peak is expected ...2-5 degrees or so before true top, depending on how well sealed the rings are. I think what I probably tried to explain is that there is virtually no piston movement in the center 5 degrees and almost none in the center 10 so even a dial indicator is a very inaccurate way to find TDC in that area and standard practice is to stop .100" or so down in one direction and reverse to .100 the other direction and set center in the middle.
I have no idea how the dyno is telling you its correct? You could tell the ECU TDC is almost anywhere and still tune it just fine on the dyno so I'm not sure how that tells you anything? But this also means it doesn't really matter unless you're trying to share tuning tables with somebody who set TDC differently, but it you use you're setup and you tables you have no problem at all.