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Old 07-21-2003, 09:49 PM   #39
Scooby Guru
Member#: 19502
Join Date: Jun 2002
Chapter/Region: South East
Location: Charlotte, NC
2010 Impreza with no
scoop. =(


I'm not going to try and start a flame war here.. But with the way NASIOC has been lately I'm sure someone will come down on me hard for simply stating some common sense of tuning.

Guys.. The easiest way to fix knock is to take some timing out... Hopefully 1-2 degrees will get it done. Or... you can try adding fuel.. but I doubt they'd go that route. To compensate for any loss of power you could try adding some boost, but I don't see that happening. Either way.. it's not going to be a HUGE difference and I doubt you'd notice it without having dyno'd before and after. The last thing Subaru wants to do is hurt the performance in a big way... but it will have to take a minor hit. (By minor.. I'm guessing 3-7 whp based on dyno runs with the car knocking and not knocking)

I know it's been posted 1,000 times by Nathan and some other tuners... but I'll say it again.... The STi ECU is VERY agressive in advancing the timing on it's own. You'll generally find that the first 2-3 runs on a dyno will be knock free.. then the 4-5th will knock audibly.. but the 6th will be knock free again. Between the 1st and 2nd run with an STi I observed on a dyno in GA there was a 20 WHP difference.. That's a huge amount of correction on the ECU's part. Unfortunately the logging utilities we had at the time wouldn't log the ignition timing for some reason so I don't have exact details.

Afraid you might lose a little bit of horsepower? Don't reflash your ECU if you don't HAVE to. The difference is not in the ECU's on the car... EVERY car is different. With the standard WRX's dyno's have shown around 10whp difference in cars from the same year. That's just how it goes. If you only get slight knocking while romping on the car, consider using a higher octane fuel. A mix of 90% 93 octane and 10% toluene (sherwin williams or any other paint store has it) will give you a nice 95ish octane that is safe to run on a daily basis. That should actually help you power wise in theory since the ECU is so agressive in bringing that timing up... Will it know where to stop with the higher octane fuel? I haven't a clue, but I'd love to test it out.

I think it's great that SOA is taking the time to address the issue. As I said in the previous paragraph... If you're afraid of losing horsepower... Do what you should have been doing from the start... compensate for the aggressive timing with a higher octane. That's what those of us with tunable computers do when we want to start cranking up the timing and horsepower.
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