Quote:
Originally Posted by ashtray
Re: "hearing" knock. I still think the driver shouldn't hear audible knock - the sensor should detect slight knock and start adjusting timing. There shouldn't be 5 seconds of rattle from under the hood before the engine reacts.
Re: hp. On my WRX, stage 1 tuning, I use the 91 octane map. It's rated at 5hp less than the 93 map. Extrapolating you might say we're losing 3-4hp on the BRZ, but I don't think you can make a direct comparison between the two engines. And 3-4hp is probably the variance from one identical engine to the next anyways, and likely not noticeable.
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Yes, if you are hearing audible knock at high RPM and throttle, at least on my STI, you have probably already done damage to your engine. Today's computers are very sensitive, so much so that road vibration can even cause phantom knock that can pull timing temporarily. Older engines weren't tuned nearly as aggressive, so knock wasnt as big of an issue.
As far as running a 91 stage 1 map, you have less hp because the timing map has been retarded in the tune. You are basically not making as much EXTRA hp in those maps. But on a stock map there are larger tolerances and as long as the computer isnt pulling timing you should make the same amount of power as if you were running 93 (at least Im pretty sure). Running high octane fuel in my old car wouldn't make the car feel fast, it would just feel a bit smoother.