bhvrdr

Thought this would be helpful for those interested in drag racing or drag testing their cars and figuring optimal shift points.

Here is the power curve that I eventually converted to lb/ft to make it easier for us who are from the US.

<img src="http://img.photobucket.com/albums/v714/bhvrdr/RS4-chp-output-curve-1.jpg">

Here are the transmission ratios.

<img src="http://img.photobucket.com/albums/v714/bhvrdr/RS4-trans-ratios-1.jpg">

Here is the resultant outputs.

<img src="http://img.photobucket.com/albums/v714/bhvrdr/RS4-ShiftingAlgorithm-pic-1.jpg">

In essence you would want to shift at redline in each of the gears in order to maintain best torque output.

Examples...

6500rpm "powerband" shifting (not taking into account power to the wheels)...

<img src="http://img.photobucket.com/albums/v714/bhvrdr/RS4-ShiftingAlgorithm-6500rpm-pic-1.jpg">

8000rpm shifting taking into account gearing (or power to the wheels)...

<img src="http://img.photobucket.com/albums/v714/bhvrdr/RS4-ShiftingAlgorithm-8000rpm-pic-1.jpg">

ToblertheDog

...wouldn't shifting at or just over 5500RPM be ideal to maintain the most torque? I'm not really following why you'd "...want to shift at redline in each of the gears in order to maintain best torque output."

Thoughts?

daves4izzle::ASP 3-

in the powerband of the current gear.

bhvrdr

you see the max torque for the next gear is FAR lower then the torque in the lower gear at redline.

EG...

Max torque in 3rd gear is 482 lb/ft but max torque in 2nd gear at redline is 603 lb/ft due to the transmission ratios.

bhvrdr

and the lower gear is going to have more torque in the v8 S4 and RS4. Your power is being routed through the transmission so going by the power curve of an SAE net dyno would not tell you about what the car is actually making for power at the wheels (which is what is important). In the lower gear at redline you are making MUCH more torque than even at peak torque in the higher gear.

craiglieberman

Factoring in my experience that at each shift, the rpm drops about 1,000 rpm, it would appear that 6,500rpm seems to put you in peak torque longer.

If you run 1st gear out to 6500 rpm, you're making 1141 tq.
2nd gear shift brings a drop to 5500rpm, and 701tq. etc., etc.

Anyway I look at it, 6,500 rpm looks to be the best shift point...on paper.

Since I haven't experimented at the strip often enough, it'd be interesting to hear what the dragstrip kings are doing.

bhvrdr

you see that if you are in 2nd gear and shift at 6500rpm when you are making 688tq then you are now in 3rd gear at say 5000rpm making only 473tq. On the other hand if you rev out 2nd gear to redline you are using WAY more torque up to redline where you are making 603tq and then you shift into third putting you at 6500rpm making 473tq and dropping. The point is that by using all of 2nd you stay in a gear that is making an average of around 200lb more torque which is obviously much better than going to third earlier.

So lets say you shift from 2nd at 6500rpm and are then in third at 5000rpm. In third gear from 5000rpm to 6500rpm you are making only about 60 lbs on average more torque then being in 3rd gear from 6500rpm to redline.

Now on the other hand if you are in 2nd gear to 8000rpm you are making well over 200lb more torque from 6500rpm to redline in 2nd than you would be in third gear from 5500rpm to 6000rpm. Then if you shift at redline in 2nd you are at 6500rpm to 8000rpm in third where again you lose out that 60lbs or so compared to being at peak powerband in third but you already gained 200lbs by staying in 2nd so you are still WAY up and add to that you are now using MUCH more torque then 4th gear would now have to offer.

I ran the 13.20 in the S4 using a raised rev limiter of 7600rpm. Thats with just a chip (for the raised limiter) and exhaust. For reference the only US spec RS4 on the forums that posted a time ran a 13.20 and that was with a decent 1.9x 60ft (launch).<ul><li><a href="http://www.allpar.com/eek/hp-vs-torque.html">http://www.allpar.com/eek/hp-vs-torque.html</a</li></ul>