Troque vs RPM

[wolbrink471]

After looking back over the archives I have seen many quick little references to whether or not you want an engine tuned for torque or rpm when running on the salt?

Can anyone offer more information and/or stories. I am going to be running a m/c so I am especially interested to what someone like Scott Guthrie might have to say!

thanks
Mark

[aswracing]

Torque, by itself, does not describe performance, because it says nothing about the speed something is moving. You can make a million foot-lbs of torque with a hand held drill motor if you gear it deep enough. But you'd have to time it with a calendar.

Torque is only meaningful when you consider the rpm it's made at. And when you do that, it's called "horsepower". Horsepower is literally torque times rpm (divided by 5252, but all that does is scale the number to what Watt's horse could do).

With equal drivetrain losses, the motor that makes the most horsepower will always put more torque to the rear wheel(s) at a given rear wheel speed. It's a mathematical fact.

[tortoise]

With equal drivetrain losses, the motor that makes the most horsepower will always put more torque to the rear wheel(s) at a given rear wheel speed. It's a mathematical fact.

One situation where you might want a less peaky setup is if you have a wide ratio spread between top and the next lower gear. That peak horsepower won't do you any good if you can't get to it. Also, a motor that makes more peak horsepower but blows up may not always be preferable.

[aswracing]

"peaky" is a different subject. I can show you motors that make lots of torque and yet are very peaky.

[tortoise]

"peaky" is a different subject. I can show you motors that make lots of torque and yet are very peaky.

And I can show you motors that make very little torque and aren't peaky. But generally speaking, you put, say, a milder cam in a motor and even if it (perhaps) makes less torque than before, it makes more torque at a lower rpm, and this is what most people mean when they speak of a torquey motor. Not to disagree with your point, which is correct.

[aswracing]

You're absolutely right, to most people a "torquey" engine is one with a lot of bottom end power. Not technically correct, because you can set a motor up to torque peak most anywhere in the rpm range, but yeah, it's the common usage.

And you're right, the width of the powerband and the gear spacing have to be considered together. Mainly on the shift to top gear. You gotta make sure you have enough power after that gearshift to keep accelerating back up to the power peak. If you have your dyno sheet, and know your gear ratios, it can be calculated, and you can predict exactly what's going to happen.

[SPARKY]

I have heard this refered to as Tractive Effort

TQ X FDR X TC = TE


TQ--Torque
FDR --Final Drive Ratio = Trans Ratio x Axel Ratio
TC --tire correction---to compare one set of tires to another
TE--Tractive Effort---what the tire is putting to the surface

This is what you use to figure your Axel ratio --tire combo.

[hitz]

Without torque there is no horsepower!

Without RPM there is no horse power!

With torque and no RPM there is a lot of power trying to do something but not able to do anything.

Without torque there is no RPM.

I think torque is more important.

Torque wins. Torque is boss.

Harv

[Harold Bettes]

Hi Folks,

I might not be able to call on much experience on the salt, but I am somewhat familiar with the old saw about wanting Torque instead of Power.....IF that is the case, then leave the thing in low gear! Simply put is that Power is what shoves the vehicle through the air or drags it or shoves it across the salt or dirt or pavement. You can have Torque without Power - as in torquing the lugs on a wheel. Sustaining that Torque over Time (RPM) is Power.

Hazarding a guess on what engine characteristics are easier to deal with or easier to ride (or drive) is an engine that has a good spread (broad range) between Peak Torque RPM and Peak Power RPM. That makes the package much more forgiving on gear changes and responses to changing loads.

It is the availability of Power (to the ground/salt) in excess of what the rolling and aero requirements are that provides acceleration of the vehicle.

Regards to All,
HB2

[SPARKY]

B'ville is a 4 mile drag race with a 1 mile trap---most will be able to go faster with a lower gear and max sustainable rpm--because you TE is greater with that set up than gearing for the peak HP or TQ---you will go faster if you are maxed out at the 4 ---usless you have unlimited hp and are limited by traction.

[Rex Schimmer]

Toque is a measurment of force times a lever arm, i.e. pounds-foot. Horse power is a measurement of power or better yet work. Horse power is force multiplied by a distance per unit of time, i..e one horse power is equal to the work required to raise 33,000 pounds, one foot in one minute. (It was either Newcomen or Watt that came up with this definition.) You can have a million pound feet of torque but if it does not turn (rpm) it does no work, makes no horse power.

To go fast you need horse power! period.

Rex

[Sumner]

...............................
....................................To go fast you need horse power! period.

Rex

..........and you have to be geared right.

Last year we ran 241 at 7000 rpm.  With our motor max HP is at 7400.  We couldn't get to 7400 as that is about 15 mph faster and it would take about 150 more HP to run 15 mph faster and the difference in HP with our motor between 7000 and 7400 is only 40 or so.

So in our case we needed to be geared a little lower to get past 241 or make a lot more HP (the plan for next year with more boost) and also with new gearing.

The above holds true for gear changes.  If you run out in 3rd, but fall too far out of the power curve going into 4th you won't pull 4th even though at a higher rpm in 4th you could run the speed.  On the salt vs. the drag strip chances are you are going to drop a lot more rpm between shifts and have to have a wider power band, which some call more torque or a torque motor.  Call it what you want, but gearing and your power band is critical to maximize your performance.

c ya,

Sum

[Seldom Seen Slim]

Once upon a time, a couple of tuneups ago, I went about 195 in top gear at Maxton.  The motor was trying -- but I was geared too high to let the engine get to the hp max.  Next run I left it in fifth (one gear below top gear).  I ran 191 with the motor all happy to be spinning right about at hp peak.

If I could've got the motor to that rpm in top gear I'd have been going in the 210-215 range (if I remember the gears right).  More hp would've got me faster in top gear (I was geared for nitrous, running motor only).

Gear (sprocket, in biker-talk) ratios, tire circumference, shift points -- damn, when I started I thought all you had to do was pin it and hold on -- didn't know you had to think abut stuff, too.

[hitz]

Well written, Sum!

Powerband is the magic word.

Harv

[tortoise]

. . . a lower gear and max sustainable rpm--because you TE is greater with that set up than gearing for the peak HP or TQ . . .

Not so. Do the math. TE at any speed is greatest at the HP peak. You are right that some vehicles need to rev over said peak to go fastest, due to gearing issues, or especially if they're still accelerating as they enter the trap.