question about max torque versus flooring the gas pedal

[lostatlantis]

This might be a dumb question, but curious minds want to know [img]smile.gif[/img]

I was wondering, since our 3.8L v6 makes 200hp @ 5200rpm and 225 ft lb @ 4000rpm, when one tries to accelerate as fast as possible, shouldn't he(or she) try to keep the tach at a specific RPM?
If so, I have two questions:

1) our max horsepower and torque occur at different RPMs. Granted, we do have a pretty flat torque curve, but which rpm, 4000 or 5200, should we try to keep the tach when doing max acceleration?

2) I have an automatic, so do i simply floor the gas pedal when I want to do maximum acceleration? Should I keep an eye on the tach and keep it at a specific rpm? if so, 4000 or 5200 (going back to question 1)?

[AMinor65]

Even though we know about the max. numbers, most of us just floor it anyway. Pretty sure that the manual guys do too.

[Dominic]

Well, you need to learn about torque and how it relates to horsepower...


http://www.howstuffworks.com/horsepower.htm

also, to answer your question - floor it in an automatic.

[V6Bob]

The short answer is that, for maximum acceleration, you want maximum torque _at the rear wheels_, after it has been multiplied by the transmisssion.

It would be ideal to have the engine at one rpm, but, with almost all transmissions, that's not possible.

As a practical matter, with the wide ratio transmissions we have, for maximum acceleration it is best to take the engine to maximum revs in each gear before shifting to the next. The torque curve is pretty flat, so keeping the maximum torque multiplication available by using a lower gear as long as possible is most important.

[Jason S]

i got a manual, i dont just floor it if i really wanna get on it [img]smile.gif[/img]

Usually when i step on it im on a 45, so lets say im doing 45-50 in 4th, a mustang pulls up, go into 3rd for about a second to let engine get up in rpms a little, then put in 2nd and take about 2 seconds to let clutch out so i dont lock up front tires, and im now at 4,000 rpms [img]smile.gif[/img] Max torque [img]smile.gif[/img] hammer it, and throw it in 3rd, easy kill. [img]smile.gif[/img] Works for me everytime. Ive killed some things i simply shouldnt have, beacause i start at such a high RPM, and they will be in 3rd (using same car/speed for comparison) at 3000 slowly creeping up to max rpms.

[mickeys]

when i'm between 3 and 4k RPMS I accelerate fastest, I shift at 5,000

but when I'm just driving normally on the street i shift at 4k

[bu-bye]

<blockquote>quote:</font><hr>Originally posted by Jason S:
i got a manual, i dont just floor it if i really wanna get on it [img]smile.gif[/img]

Usually when i step on it im on a 45, so lets say im doing 45-50 in 4th, a mustang pulls up, go into 3rd for about a second to let engine get up in rpms a little, then put in 2nd and take about 2 seconds to let clutch out so i dont lock up front tires, and im now at 4,000 rpms [img]smile.gif[/img] Max torque [img]smile.gif[/img] hammer it, and throw it in 3rd, easy kill. [img]smile.gif[/img] Works for me everytime. Ive killed some things i simply shouldnt have, beacause i start at such a high RPM, and they will be in 3rd (using same car/speed for comparison) at 3000 slowly creeping up to max rpms.<hr></blockquote>

Your shifting sounds good. When you downshift you want to be right around 4000 for the best take off and the longest run in that gear. This is why you want to know your car very well and it sounds like you do. There is also something you need to take into account, upshifting. If you only take your RPM to 4000 in say 3rd then upshift you will be entering 4th gear at a lower RPM which is far worse then passing your max TQ and HP. You want to enter the next gear in as high of an RPM as you can get which is redline in the gear before.

Edit: Jason, this was not to correct anything you are doing. You shifting skills sound right on. I just quoted you to reinforce what you said. Re-reading my post I thought I should say that.

[ July 08, 2002: Message edited by: bu-bye ]</p>