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Rob 930 Rob 930 is offline
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Join Date: Dec 2002
Location: Seattle
Posts: 514
Miles, I don't think I can answer your questions, but...

I'm interested in the concept of limiting boost at part throttle. For a road racing application, it's not advantageous to have full boost at part throttle, though that's exactly what happens. It can be disconcerting and dangerous to have too much power too soon. That nonlinear "rubber band" feel is what makes turbocharged cars so spooky to drive, especially when exiting a corner. The last thing you want as you round the apex and slowly advance the throttle is a disproportionate change of torque to the rear wheels. I think it would be ideal to have (say) half the torque available at half throttle and full torque at full throttle (but not before).

We tried doing this during the tuning of my EFI engine. Considerable time was spent mapping the boost controller versus TPS. The boost control solenoid is a VW turbo part and it's controlled by my DTA ECU. What we found was that we were able to limit boost a bit (about 10% less torque at part throttle) from our efforts, but nowhere near enough to give the car a truly linear feel. There just wasn't enough range of controllability with that system (for that particular solenoid, Garrett turbo, and Tial wastegate) to get it where I wanted it.

For one of my 0.9 bar maps, with a TPS-based boost reduction scheme, at 5250 RPM we saw 496 ft-lb at 100% throttle, 478@85%, 464@76% and 448@66%, 451@57%, and 437@47%. So, that's about 10% less torque at 50% throttle. Not much, but it's something. To really interpret how much of this was due to TPS-based reduction, and how much was just because the throttle wasn't open all the way, would require more data, but I'm sure we made a difference with this tuning technique.
Old 12-06-2006, 04:49 PM
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