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Discussion and questions related to the course Launch Control
I am currently working on an ongoing project. It is a AE86 4-Cylinder drag/street car running a Turbo 400 Transmission and custom converter. I would like to improve the launch consistency and would like to decrease the spool time. This last season we were running a 64mm turbo and are moving upwards to a 76mm turbo. It is running a Vi-Pec ECU with a switched "two-step" launch strategy tied to the trans brake input. Currently it is just spooling off the trans-brake and throttle controlled. The car does not have a speed input to the ecu from trans or any wheel speed sensors. Torque convertor stall is technically 5000rpm but does transition into the stall gently starting around 3000rpm.
I have heard many automatic and turbocharged cars launch while engaging a limiter or "launch control" of some sort...
What methods do you use to spool the turbo more effectively than just engine load against the convertor without adding nitrous?
What have you found aids launch consistency and traction without speed inputs? e.g. Time based boost trims, using MAP as an axis on the ignition cut table,...
As far as spooling the turbo with a convertor, retarding the ignition timing doesn't work. The convertor requires engine torque to work and when you retard the timing the engine makes less torque. The best option is to tune the engine for MBT timing in the spool area while you've got the trans brake active. A slightly leaner mixture than you'd normally run can show a small improvement by building more heat in the turbo but this is going to be a minor help. If you still can't get the thing to come up in a reasonable time frame you're limited to either changing to a smaller turbo, a looser convertor or a shot of gas.
As for options for controlling the rpm after launch, there are two ways I'd consider trying. The easiest and potentially best option would be to use a timer function to control the rev limit after the trans brake is released. This will need some testing but can be very effective. Alternatively you could use a ground speed based method off a front wheel speed sensor. With an auto and a convertor the relationship of engine rpm to ground speed in 1st gear is a little less defined than it is with a manual transmission so you'd need to log what's happening during a good launch and try applying that.