torque vs rpm

PittSpeed Automotive
1

when building a drag car what is more important low rpm high torque or a higher rpm lower torque engine? and why is one better than the other?

2

depends on how heavy. heavy vehicles like more torque.

3
4

what kind of car?

5

Yes They Do :cool:

6

more torque is great to have…but the more torque you have at higher rpms, the more hp you make…as hp is a function of torque and rpm. therefore the faster you are…in most cases

low rpm high torque or a higher rpm lower torque engine

in this case, the higher rpm motor could make more hp overall, and thus might run faster even tho its torque is lower. depends on the combination of parts tho. more rpms doesnt necessarily mean more hp. but it does help

but if a motor is making 300hp at 6000rpms and only 300lb feet of torque at like 4500rpms, and another motor is making 300hp at 4500rpms but with 400lb feet at 3000rpms, the lower rpm motor will win since its torque will get it off the line faster.

7

82-92 camaro or anything basically that is close in weight

8

You can’t gear the higher torque motor as low as the lower torque motor, so the higher torque motor has to have a LOT more torque to make up the difference the gearing gets you.

9

why not?

the only thing i can see is that the higher torque motor will generate its peak hp at a lower rpm and thus too much gear will run it out of its powerband. but taht depends onthe motor tho

10

Just to throw out a quick example, let’s assume that both of these motors have a very flat torque curve.

Motor A (bigger, lower redline) tops out at 45mph with a 3.09 final drive. (final drive = rear end)
Motor B (smaller, higher redline) in tops out at 45mph with a 4.10 final drive.
Motor A makes 400 ft/lbs. Motor A has about 1236 ft/lbs (final drive x peak torque) moving it forward.
Motor B only needs to make about 300 ft/lbs (1236 / 4.10) to accelerate just as hard off the line.

There’s other ratios at work here, namely tire size and 1st gear ratio, but i’m assuming they’re the same for this discussion.

11

there is a simple and easy method when building a v8 drag car…

xxx cubic inch motor, u add compression, cam and fuel.

once it maxes the heads, change heads.

once you max the heads, go bigger cubic inch

repeat

the more compression and cam you start using (adding fuel as necessary), the more the power band is going to start moving up the rpm range. when you go to bigger cubes, it will start at a low power band.

so, if you build a high rpm hp/tq motor, just leave at a higher rpm. If you build a big cube, low rpm motor, leave low. how fast you go just depends on how much motor you physically have.

12

Just make that your torque and rpm intersect at 5250 on an engine dyno.

13

it looks like your confusing gear ratio with
stroke and bore

14

Call me old school, stupid, or whatever, but I would think that the RPM motor would win in drag racing. Foe the following reasons:

  1. assuming all is the same, and there is no major modifications to the suspension, the higher torque motor would want to spin more at the get go, before you make the mid to high range of your powerband.

  2. assuming all is the same, said high torque low rpm motor will run out of power before you run out of track.

  3. rpm makes power, torque can, to an extent, be made up with gearing.

  4. I just a dumb redneck, so my thoughts are based on nothing but my thinking.

good day…

15

I am? Gear ratio determines the max RPM for a top speed in a certain gear, and how much torque multiplication you get.

Stroke and bore determine engine displacement.