I've I had my car at the track finally, with good results, but I'm a liitle confused. Motor is 388 CNCed LT4 heads/intake w/ GM847. With me in the car it weights 3450. All suspension upgrades and other engine related bolt-ons.

The first time out I had the old 10 bolt with my 4:10's in there, the computer is programmed for 3:73's and the torque converetr was designed for the 3:73's as well. My shift points were a little low-6200.

1st run
1.67 60ft. 2200 stall w/ 4:10 rear gear
12.32 @110mph
2nd run
1.69 60ft. 2400 stall w/ 4:10 rear gear
12.35 @111mph

Replaced rear with the 12 bolt and 3:73's and now...

1.65 60ft. 2200 stall flashed to 3800
12.35 @106 mph

My shift points were much better at 6700.

I thought my MPH and 60ft. would increase with the gear change. I didn't expect to run the same E/T.

I could not stall it any highier on the foot brake than 2400, but it flashed to 3800 under full throttle.

Why did the 60ft. stay the same with a highier gear?

Why did the MPH drop so badly?

This is in Denver; Allltitude sucks!!

Thanks for any help/explainations

 

mph dropped either due to high shift points over powerband or , most likely, because the 3.73 gears took you out of your powerband. You wer able to put more usable torque down to the ground with the 4.11's vs the 3.73's. I had 4.11's in my car at first and ran 11.4's@119. I then switch to the 3.70's for the bottle and ran a 11.6@117mph with 26" tires. Now when I run the 3.73's and my 28" tall tire I usually run 11.9's@114.9 (best of 11.8@115.9 in good weather). All this is due to the gearing putting my engine out of the powerband but it works perfect for me on the bottle.

 

I changed mine for the bottle too, I expect some real quick times then.