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I don't know whether you saw my post on the Performance board, after my recent dyno run. Now, my Aero is quite heavily modified, running with 1.6 bar of boost.
If you remember, I said I had had subjective results that a 1.1mm plug gap gave my Aero better low-down pull than a 0.9mm gap (tested by taking the plugs out, regapping them and refitting the same plugs with the new gap). This was before I fitted the Maptun ECU.
Well, yesterday I decided to experiment again. I bought two new sets of plugs, gapped one set to 0.9mm and the other set to 1.1mm. Then I fitted the 1.1mm gapped ones (the ones I expected to perform better in case they wouldn't let me change the plugs for another dyno run without charging extra) and drove the 20 miles or so to the dyno.
Well, on the first couple of runs, the car achieved an impressive 280bhp and 314lbft - a bit more power and a bit less torque than Maptun claimed, but every car is different. Anyway, I asked if I could change the plugs and try again and it was no problem. The operator expected, as I did, that fitting the smaller-gapped plugs would perhaps hurt torque in the lower RPM range, if it had any effect at all.
Well, we let the engine run for a bit to get the plugs up to temperature and avoid thermal shock. Then the operator got in and did a run. His face was a picture as he got out of the car and shouted (he was still wearing ear protection), "that's given you another 15 brake at the *wheels*!" We checked the figures, which came out at a calculated 305bhp and 330lbft. He did another run and got the same figures.
We overlaid the "1.1mm" figure and the "0.9mm" figure. It showed a torque increase of roughly 10-15lbft across practically the whole RPM range, except right at the bottom of the curve, where there was very little torque and practically no difference between the two torque curves.
My only theory at the moment is that at high boost, the DI is sensing detonation (or perhaps slightly misfiring, although I could hear no evidence of it) with the bigger plug gaps and isn't with the smaller gaps, so allowing more boost with the smaller gaps. This would explain the torque increase over the whole range (my torque, and hence boost, is practically flat from 2500-5000RPM).
So, in addition to what I said the other day (rather than "contrary to", as I think this is a different situation), I am now running 0.9mm plug gaps in my Aero as that seems to be best for its performance in its present state of tune. I think this is due to a limitation of the DI (or at least, my particular DI). On my previous experience, I would still gap the plugs on a standard Aero to 1.1mm. I'll be doing it on my 2.0LPT too, and in fact already have a set of almost new plugs gapped to 1.1mm :)
I just thought this experience might be of interest and add to the the discussion.
posted by 62.253....
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