timcp on Mar/04/07 said:
When I was at Russell Racing School at Infineon Raceway, the instructor said it was because on street cars the stock factory ecu's air/fuel ratio is better tuned at that throttle position.
he was talking about closed/open loop t/p threshold and load..
closed loop is there to help the ecu maintain a 14.7:1 afr , or close as possible to there.
when the ecu switches into open loop, the computer does not look at primary o2 voltages because the sensor is not fast/accurate enough when more exhaust gases pass by at a faster speed..it just simply cant read it on a .1 -1v non-linear , crosscount setup..
this is why we have widebands now adays, and some manufactueres use them stock. audi/vw etc..
im not sure what the threshold is for closed-open loop transition but id imagine it would be over 70% throttle less than 5in vac.
if you use the auto stick method, as in, shifter gears with the selector shifter, you can have the TCC locked in all the time, therefore the power is right there, IE no slip/delay when you hit the gas..
putting the shifter in D4, using overdrive, the ecu has to lockup the clutch whenever you slam the throttle to the floor to achieve direct drive from the engine.
thats why as you are just driving down the road, you hit the gas a little and the revs come up before the car actually takes off..