Comments on: Second Shift

By: Damon Ethakada

Damon Ethakada — Tue, 23 Feb 2010 13:24:24 +0000

The “point” of engine power output is to be a rating of engine performance that considers the effects of both torque and gearing. Were gearshifts instantaneous, you would want to be in the gear that resulted in greater engine power at all times, because this results in the greatest engine torque multiplied by gearing – that is, the highest rear-wheel torque. The only reason that you might want to shift at an engine speed other than the intersection in the power curves is to attain a higher speed before you lose acceleration for a gearshift – something that is more likely to work in a low gear where the rate of acceleration is high.

By: Ken M

Ken M — Tue, 02 Feb 2010 15:16:04 +0000

Yeah, some one once told me that power gives top speed and torque gives how quickly you reach top speed.

Since you have the torque curves and drag/friction losses, shouldn’t it be possible to determine speed and distance over time (acceleration = applied torque-drag)? If you can do that then studying the effect of shift points, wing settings and gear ratios becomes possible without getting into the car. Though that wouldn’t be as much fun.

By: Ray Bryden

Ray Bryden — Fri, 29 Jan 2010 18:47:51 +0000

Yes, I have that data as well, Ken – as a matter of fact I was plotting some curves of torque v speed last night. And I think when it comes down to it the torque curves are critical for the performance at lower speeds, and the power curves dictate the pace at higher speeds, so really it is important to consider both.
The procedure above was a nice way to evaluate the optimum shift recipe from a more pragmatic approach.

By: Ken M

Ken M — Thu, 28 Jan 2010 16:07:41 +0000

Another great article Ray. Have you tried plotting the applied torque in each gear vs speed? Depending on the gear ratios and the shape of the engine torque curve it may be better to stay in a lower gear past the intersection of the power curves (as given in the previous article). Unless the torque curve falls off dramatically and/or the gear ratios are quite close, the lower gear can give more applied torque near the rev limit because of the shorter ratio even though the engine power and torque have have dropped somewhat. It’d be interesting to see what shift points the torque curves would suggest.

By: CJ Modiano

CJ Modiano — Sun, 17 Jan 2010 06:48:06 +0000

wow.. wish I read this before my skip barber race today! Nice to finally know the shifting recipe for this car though. Cool article.

By: Christiaan LeGrand

Christiaan LeGrand — Sun, 17 Jan 2010 01:59:32 +0000

I was thinking exactly the same thing as Jose … iSpeed and an iPod help the situation.

By: Jose Afonso

Jose Afonso — Sun, 17 Jan 2010 00:01:05 +0000

i wish i could see my rev meter when i use realistic FOV on my triple monitor setup