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Going down an interesting tweaking trail that started with getting my 1990 turbo convertible working after a head gasket failure. I purchased new plugs for it and installed them, but botched the plug gap, and didn't figure it out until later. I had gapped the plugs to .045 instead of the spec .027 written on the sticker.
After reassembling the car, it ran like a scared cat...very responsive and lots of boost. It had one issue though that usually surfaced as the weather got warmer and the engine was good and hot. It would stumble some at high RPM and high boost conditions naturally with that amount of plug gap. I had another issue too. I could not set the timing at the factory spec of -16 degrees BTDC. I had to run it a little milder, around -12 degrees, or I would hear preignition / detonation
I troubleshot it and found my error and corrected it, closing the gap down to the factor spec, and corrected the misfire / stumbling. However, after I did this, the responsiveness of the car was a little bit meh. I still developed pretty good amounts of boost, but it did not set in quite as quickly as it once did. I then adjusted the timing back to the factory spec as an experiment, and lo and behold, I did not hear the preignition / detonation pinging going on anymore. Some of the responsiveness returned, but I was not getting as much boost as before...only base boost, around halfway up the yellow zone of the boost gauge.
I went ahead and increased the gap on the plugs to .032, which the car seems to be happy with and I'm not getting any misfire, nor am I getting any pinging noises. This has returned some more responsiveness, but still not getting the great boost levels like I was getting before all this started...so, I have a few questions...
- I have read that the more timing is advanced, the less boost, and this correlates with my findings. Is this because the APC is pulling the boost back because it "hears" preignition that I don't? OR is this because more of the burning fuel's energy is directly going to push the piston down, and not going out the exhaust port and spinning the turbo.
- Second question is that why would decreasing the gap affect preigniton and pinging? I realize that a forced-induction vehicle requires a smaller gap so the spark won't get "blown out" by the turbulence in the combustion chamber, but why would I need to retard timing with a large gap?
Last...anyone else done any tweaking like this and found what the optimal settings are beyond the factory spec? I know they usually set gap for emissions and longevity of the plugs...re-tweaking gap is an easy chore though.
posted by 173.53.92...
1
, Fri, 14 Apr 2017 13:55:06
, Fri, 14 Apr 2017 14:42:431
, Fri, 14 Apr 2017 14:00:08
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