Quote:
Originally Posted by NoDOHC
I made peak power at 38 degrees total advance last time on the dyno. There was about 4% improvement between 30 degrees and 38 degrees. This was with no hint of pre-ignition, 43 degrees lost power but did not cause any pre-ignition. I was running 8.2:1 polished rotors at that time.
I never heard any pre-ignition on the dyno with 9.4:1 non-polished rotors before the seals failed in the front rotor either (although the AFR was so rich that I really shouldn't have worried about it anyway).
I tried running a higher octane fuel (89) and have not experienced any pre-ignition since. It might just have been that batch of fuel.
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i'm not used to low compression NA, we usually try to run the 9.7 rotors. the last one we did, was IT spec, so its stock 6 port engine, with stock S4 intakes, and custom exhaust.
anyways, that one made peak power with like 26BTDC L, and it dropped on either side of that. this is at an AFR of about 13 too. i can see running more timing with lower compression, but 38 just seems like too much?
we've also learned since, that you won't hear preignition. since the rx7, we've been endurance racing a honda, and stock those run like 12.2AFR, and you pick up power leaning it out. so we leaned it out to 13.2ish. then we advanced the timing 5 degrees, and it didn't pick up any power, but warren just left it.
and that motor died from preignition, the head, block and pistons look like someone took a punch to it and just had fun.
when we put the new motor in, we dynoed the stock map vs the +5 ignition map, and the stock map made more power.....
octane; if you're making a lot of power, you might actually need a little more octane. the competition prep book from 79 is the newest ive seen, and its a 12A PP with a carb, and they want you running 90 octane (doesn't say RON or MON or R/M2) and the cold spark plugs @the 260hp level