Finally got out last Friday with my pal to test with his Competition Eliminator Cobalt. It's been a big program change for this car to take maximum advantage of the class rules. The engine is now 24 cubic inches bigger, the Liberty 5 speed has been replaced with a Pro Trans automatic with a Coan aluminum convertor and the car can be 80 pounds lighter than with the Liberty 5 speed. Dyno numbers show a bunch more torque and flatter torque curve with the new cubes and updated heads/intake.
Initial results were pretty promising. The shift points need to be picked up as they are too close to the torque converter 'flash' rpm. That confused the automatic shift sequences that are triggered by the MSD ignition....the car wants to shift into second gear when the trans brake released on the starting line.
Basically, as soon as the trans brake is released at 6,500 rpm the convertor flashes to 9,100 rpm. Ideally, the 1-2 shift should be about 8,800 rpm...which happens aotumatically. So...as the convertor is coming up, the ignition system is telling the trans to shift. Effectively, it leaves in second gear. The easy fix would be to pick up the 1-2 shift rpm to about 9,500 rpm. The problem with that approach is that the Pro Trans transmission is a TH350 case with Chrysler 904 internals...and they have a 400 rpm 'over run' before they shift..even after the shift lever is moved. It's a quirk of that system that you live with to get the lower drag of the light weight 904 internals. Taking the shift point to 9,900-10,000 isn't what you want on the 1-2 as the engine is well out of it's torque range.
Might have to abandon the ignition-based shift rpm approach and go to a timer that shifts the car at a preset time rather than an rpm-based shift point.
Some pics, for those interested:
Out with the Liberty clutchless 5 speed:
In with the Pro Trans automatic:
Fresh bullet:
A bath for 'baby' before loading up:
On the road:
At the track. It's an 1/8th track 2 hours South of us. The starting line is always killer good..the #1 prerequisite for testing!
Initial results were pretty promising. The shift points need to be picked up as they are too close to the torque converter 'flash' rpm. That confused the automatic shift sequences that are triggered by the MSD ignition....the car wants to shift into second gear when the trans brake released on the starting line.
Basically, as soon as the trans brake is released at 6,500 rpm the convertor flashes to 9,100 rpm. Ideally, the 1-2 shift should be about 8,800 rpm...which happens aotumatically. So...as the convertor is coming up, the ignition system is telling the trans to shift. Effectively, it leaves in second gear. The easy fix would be to pick up the 1-2 shift rpm to about 9,500 rpm. The problem with that approach is that the Pro Trans transmission is a TH350 case with Chrysler 904 internals...and they have a 400 rpm 'over run' before they shift..even after the shift lever is moved. It's a quirk of that system that you live with to get the lower drag of the light weight 904 internals. Taking the shift point to 9,900-10,000 isn't what you want on the 1-2 as the engine is well out of it's torque range.
Might have to abandon the ignition-based shift rpm approach and go to a timer that shifts the car at a preset time rather than an rpm-based shift point.
Some pics, for those interested:
Out with the Liberty clutchless 5 speed:
In with the Pro Trans automatic:
Fresh bullet:
A bath for 'baby' before loading up:
On the road:
At the track. It's an 1/8th track 2 hours South of us. The starting line is always killer good..the #1 prerequisite for testing!
