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Re: Bob thanks, another question (more) (archive)

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Posted by Bob ///M3 on October 10, 2000 at 21:18:05:

In Reply to: Bob thanks, another question (more) posted by BD on October 10, 2000 at 10:00:33:

Brad, at 6,200 rpms your engine is producing 200 lb/ft of torque. Multiply the 200 lb/ft times the transmission gear ratio of 1st gear which is 4.20 and you get 840 lb/ft of "driveshaft" torque. Now when you engage 2nd gear your rpms will fall to 3,676 rpms and the engine at this speed is now producing 234 lb/ft of torque. Multiply the 234 lb/ft times the transmission gear ratio of 2nd gear which is 2.49 and you get 583 lb/ft of "driveshaft" torque. The difference in "driveshaft" torque between the 1st to 2nd gear shift is 840 lb/ft (1st @ 6,200 rpms) minus 583 lb/ft (2nd @ 3,676 rpms) which equals a loss of 257 lb/ft of "driveshaft" torque.

You want to keep the figure as close to zero as possible with either a slight loss or gain.

If you had performance enhancing software allowing a 7,000 rpm shift from 1st to 2nd gear you would have a loss of only 94 lb/ft of "driveshaft" torque.

This is a pretty good reason alone to have performance enhancing software even though some people doubt its horsepower and "engine" torque increasing ability. Even if the engine's horsepower and torque stayed exactly as stock the ability to shift at a higher rpm would offer tremendous benefits. And I believe the performance software does enhance horsepower and engine torque therefore the overall gains are even more that much more beneficial.

Bob ///M3


Bob,

Is this true, a loss of 257 lb/ft driveshaft torque?

1st to 2nd @ 6,200 rpms producing *200 lb/ft torque and *236 horsepower and engaging 2nd gear @ 3,676 rpms producing 234 lb/ft torque and 164 horsepower at a speed of 34 mph losing 257 lb/ft of driveshaft torque with the shift.

Also, can you explain the loss of driveshaft torque concept. I'm a little slow this morning and need some help to understand what you mean. Also, how did you arrive to that specifc number? From your above numbers it looks like you would gain torque after the shift. Are we mixing numbers, drive shaft vs. rear wheel torque?

Thanks,

Brad





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