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Re: STX looks like a great class for our cars... (archive)

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Posted by Stan on February 19, 2002 at 19:22:33:

In Reply to: Re: STX looks like a great class for our cars... posted by Robert Puertas on February 19, 2002 at 17:26:29:

Well for one thing 17s have a higher MOI so you hurt accel a hair - bigger, heavier "flywheels". And the taller size of a 225/45 17 hurts a bit more cuz of the diameter. Probably heavy too. Offsetting that is potential higher grip so the net fastest autocross result is what matters. If the 15s have comaprable grip they are likely to be faster than the 17s due to MOI and gearing. The 16s might be very comparable to either and allow the use of E28 M5 or E3 wheels which are 16 x 7.5. Width isn't everything in a tire. A 215 may or may not be as fast.

Robert, imagine your car going hard starting nearly 2000 Rpms sooner than stock. At peak torque, the peak is higher and wider. Peak power is up and afterwards the power fades more slowly than stock.

The E30 M3 does NOT come up on the cams at about 4000. They are mild 248 degree cams anyway.. Instead the car is coming off the AFM at about 4000 where the door is fairly wide open and so restriction is cut but still present. Ditching the AFM also allows you to do some secondary intake tuning, another benefit.

Throttle response and downshift blips are much faster and the part throttle behavior belo 4000 is transformed into what it should have been all along.

Stan




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