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Old 07-30-2003, 06:34 PM   #20
Patrick Olsen
NASIOC Supporter
Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
1997 Legacy 2.5GT
1996 Impreza coupe


Well, I only have the Street/Stage 1 heads and cams, so I don't know how much there would be to gain by bumping the rev limiter up. I guess I hadn't mentioned my mods earlier - in addition to the Cobb Stage 1 heads and Street cams, I have an Injen CAI, a Fidanza aluminum flywheel, a full MRT exhaust (header, cat, cat-back), and an S-AFC.

As for the S-AFC and ITC combo, I guess that's a possiblity, but I'm not sure it will do what I want it to do. There has been discussion on this board about the ECU "learning around" the S-AFC, and based on my experience I think that is true. After getting all of the above (with the exception of the Injen CAI) installed, I bought the S-AFC and took the car to a dyno to tune it. Even with the Cobb stuff on the car, it was running quite rich, and we were able to pick up horsepower across the RPM band (particularly up high in the band) by leaning it out. In the end the S-AFC was set to gradually pull out more and more fuel from about 3500rpm on up, with the top of the range set to something like -24%, and AFR was right around 13.0:1 across the entire RPM band.

Fast forward a month or two and I got the Injen CAI and installed it. Back to the dyno again to see how that affected things. The first disappointment was that the car wasn't making any more power - as a matter of fact, it was a couple HP down on power. Then we looked at the AFR and saw why - with the same S-AFC settings my AFR was now up around 14.5:1, with it peaking as high as 15:1! Needless to say we added fuel back in, and the end result was a 12hp increase.

In all cases I performed ECU resets pretty much immediately before putting the car on the dyno, so I really can't explain how the AFR was that far off. Maybe I'm wrong, but I find it hard to believe a cold air intake would have that big an effect on AFR.

Anyway, long story short, all that makes me wonder just how the S-AFC and ECU are interacting. I really wish I had more time to play with the dyno just to experiment, but at the time I didn't and now I'm out here in Hawaii with no AWD dyno to play on.

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