Optimal shift point for a stock 03 GT???

[WallyKilla]

What do you guys shift at to get your best times with a stock 99-04 GT?

 

[40oz]

Depends. I downshift right before I brake for the corner, so it depends on how long the straight is. Coming out of the corner, I'll usually run it up to 6K, shifting just before the limiter. Peak torque is at 4000 rpms and shifting 2nd to 3rd at 6000 puts me right there.

If you shift 3rd to 4th at 5300 rpms, you hit 4th right at 4000. Conventional wisdom says to shift where you get back to max torque, since max torque gives you max acceleration regardless of rpm. You can run 4th all the way to 6000 rpms and still hit 4000 rpms in 5th if you are going that far.

I'm not sure how important precise shift points are because I seem to make up the most time in the corners by improving my line and throttle application rather than playing with shift points too much.

And all that assumes my gear-speed chart is correct. But it seems to match my car's tach and speedo

 

[WallyKilla]

What about for a 1/4 mile run??? 1-5th gear where should I shift at?

 

[ChillPhatCat]

Realistically, on the quarter mile you'll save time by running up to 6000 in 1st-3rd and hoping you don't hit the limiter. Shifting to 4th at 5300 would be silly IMO unless you hit 6000 in 3rd and still have a short distance to go, then I'd factor in where the 3-4 shift would get you back to the power band and make the 3-4 shift there. You won't have to worry about 5th gear on a quarter mile pass without some serious work under the hood and elsewhere.

 

[WallyKilla]

so shift at 6k? 1-4th?

 

[32ValveRom]

Lol at the newbity

 

[peepeeskillz]

Realistically, on the quarter mile you'll save time by running up to 6000 in 1st-3rd and hoping you don't hit the limiter. Shifting to 4th at 5300 would be silly IMO unless you hit 6000 in 3rd and still have a short distance to go, then I'd factor in where the 3-4 shift would get you back to the power band and make the 3-4 shift there. You won't have to worry about 5th gear on a quarter mile pass without some serious work under the hood and elsewhere.

even if your max power is higher at 4000 rpms, after the gear multiplication im willing to bet that you will still have more power in 3rd gear at 5300 rpm than you do at 4000rpms in 4th, plus it takes some time off shifting to 4th.

if your car is stock you dont even need to shift into 4th in the 1/4.

edit: oops i quoted the wrong person meant to quote 40oz lol

 

[40oz]

Actually, what he said ^

Conventional wisdom is meant to be tempered with practical observation lol.

I ignored the gear multiplication thing. But really you'd have to experiment or compile your own data using the dyno from your own car. Assuming all stock, the crank torque at 4000 rpms is 300. 3rd gear ratio is 1.33, 4th is 1. You'd want to shift at the point where the torque * 4th gear (1.00) is greater than the torque * 3rd gear (1.33). Based on a few stock dyno sheets, it looks like that would be around 5700 rpms in 3rd to ~4300 in 4th. But shifting to 4th actually costs you time if you can stay in 3rd until the end of the acceleration run. And the difference is minimal, ~20 lb-ft. if you shift 3rd to fourth at 6000 vs. 5700.

The harder you accelerate at the start of the run the faster you will be going at the end, and the faster you will get there. Small differences up top are of minimal importance compared to how the start goes.

 

[patman0911]

5300 RPM is where NPI cars should be shifting. NPI motors lose power really fast above 5000 RPM.

edit: What he said

The couple of graphs I found put the shift points above 6K for a PI motor - we may have been looking at different shaped graphs.