400m drag v. rpm limiter

[StreetPro]

lets have 2 identical cars racing from stand to 1/4 mile, each one shifts at its rev limiter (asuming that power goes down after 7k, let say -20 PS at 8k rpm)
a) rev limiter at 7k rmp, Max PS at 7k, Max Nm at 5k rpm
b) rev limiter at 8k rpm, Max PS at 7k, Max Nm at 5k rpm
which car wins the race and why?
does anyone know the right answer + explanation? thx :-)

[LAWLence]

Depends on the gearing and torque curve leading up to the max power/torque.

[Mitch]

It depends on the gear ratios and torque curve. If you plot (torque x gear ratio) vs (road speed) for all gears, you can see where the curves overlap. You want to shift at the overlaps.

Here's a plot for an old Viper:
http://i291.photobucket.com/albums/ll304/mitchellcwall/Auto/gears.jpg

The best shift points are at the overlaps.

For my Si, however, you get a curve like this
http://i291.photobucket.com/albums/ll304/mitchellcwall/Auto/sigear.jpg

You can see that running that shifting at the rev-limiter is the best place.

[nderwater]

great graphs - how'd you collect your data?

[Mitch]

great graphs - how'd you collect your data?

I used the torque curves from dyno readouts and for each gear multiplied the net gear ratio (counting final and tire radius). I then used the gear ratios, engine rpm, and tire radius to find the road speed at any given rpm. Plotting torque x gears against road speed at that rpm gives those curves. I learned how to do that in an SAE Automotive Engineering course.

[BugsB]

anybody got a graph of the curve for the E36 M3?

[Mitch]

anybody got a graph of the curve for the E36 M3?

http://i291.photobucket.com/albums/ll304/mitchellcwall/Auto/m3.jpg

[MrBlonde]

The only way to get an answer is to try both at the same drag strip with the same conditions.