Shane@DBPerformance
01-23-2004, 02:53 PM
It just doesn't make sense. I don't know why the compression is so high, we tried 2 testers and both were higher than factory spec. I am sure his rings have some wear and the aftermarket cams should lower the compression a tad also. His ARPs aren't cranked down crazy high either. When we do a boost leak test there is a fair amount of air coming out his breather hole like boost is getting past the rings. We also had a lot of oil blowby in his catch can after dynoing. So I am not sure how with those signs pointing to wore rings we also have 185+ compression.
We pulled the valve cover off to make sure the rockers, cams and lifters looked ok, we didn't see anything out of the ordinary. A lifter could still be failing us at higher rpms though.
We tried every combination of stock timing, more timing, less timing, very rich, somewhat rich, and normal A/Fs. We could only keep the knock down by either running a somewhat rich A/F of around 11.0:1 and pulling a lot of timing out of the stock maps or by running stockish timing but with an extremely rich A/F on the edge of misfiring. It's not like we are trying to run some crazy amount of boost with a poor setup. He has a decent sized turbo, with a good FMIC, big i/c piping, sheetmetal intake, big injectors, etc and we are only try to run 17psi creeping to almost 19psi. I don't think we can blame the knock sensor, unless its just way too tight or something. We can make it knock less by tuning, so it isn't just picking up random noise, but the A/Fs and timing we need to run to make it not knock are nowhere near normal. There were some old logs from around October that John Lacroix had done and he was able to get away with adding a fair amount of timing and running higher boost with very little knock. If we tried to run those setting now, the motor would probably blow up. Maybe it's just bad gas or the gas tank is full of crap.
We pulled the valve cover off to make sure the rockers, cams and lifters looked ok, we didn't see anything out of the ordinary. A lifter could still be failing us at higher rpms though.
We tried every combination of stock timing, more timing, less timing, very rich, somewhat rich, and normal A/Fs. We could only keep the knock down by either running a somewhat rich A/F of around 11.0:1 and pulling a lot of timing out of the stock maps or by running stockish timing but with an extremely rich A/F on the edge of misfiring. It's not like we are trying to run some crazy amount of boost with a poor setup. He has a decent sized turbo, with a good FMIC, big i/c piping, sheetmetal intake, big injectors, etc and we are only try to run 17psi creeping to almost 19psi. I don't think we can blame the knock sensor, unless its just way too tight or something. We can make it knock less by tuning, so it isn't just picking up random noise, but the A/Fs and timing we need to run to make it not knock are nowhere near normal. There were some old logs from around October that John Lacroix had done and he was able to get away with adding a fair amount of timing and running higher boost with very little knock. If we tried to run those setting now, the motor would probably blow up. Maybe it's just bad gas or the gas tank is full of crap.