Torque vs. HP Revisted

[AL427SBF]

This topic has been debated extensively on CC. I've read many posts on the subject, still looking for the "golden rule" on how one would try to tune/build their powerplant for best performance regarding torque and HP. We know both are tied at the hip: HP = TORQUE X RPM / 5252 and their respective curves will ALWAYS intersect at 5252 RPM. If we agree that torque is what moves you (acceleration), and HP is what keeps you there (speed) then it seems to me Torque is king and all efforts go to giving you the most torque relatively early in the RPM range (say @ 3K) and holding strong (flat or better) for as long as possible past the RPM range of 5252 where HP passes torque in terms of raw numbers. I figure, if you have maximized your torque curve in that way, who cares about peak HP in a practical sense. Not withstanding bragging rights, I see no reason to give a damn about HP if you have nailed the torque curve. If this hypothesis is wrong, please share why. Otherwise, I would be curious on what the tuning or engine building tricks are to get that strong torque curve from say 3-6.5K?

[patrickt]

I have two other cars that have CVT (continuously variable transmissions). You accelerate best by holding the engine speed at the highest torque RPM, say 4000, and the car speeds up without ever changing engine RPM. The point being, torque is king, but torque at a higher RPM is a better king, because you can take advantage of gearing. If you have a CVT, then you don't need much of a torque curve at all.

[Jerry Clayton]

well--with my race car in my 44 ft triple axle trailer--2200 rpm at 73 mph 19gpm makes me happy-----------


so torque is for tralers--whether hauling a RACE car, SHOW car or just a trailer queen------Horse Power is for pulling FARM impliments------

In high performance or racing---its going to settle out on checker flags or finish positions(if you finish)

[bobcowan]

Originally Posted by AL427SBF

Not withstanding bragging rights, I see no reason to give a damn about HP if you have nailed the torque curve.

I think you're exactly right. The HP figured was originally developed in the late 1700's to sell steam engines to people who were still using horses for work.

Torque is measured, HP is calculated. The Dyno measures the torque of the engine, and then calculates the HP curve at each points.

When you're coming out of turn 3 and heading for the back stretch, do you want torque or HP? A broad flat torque curve will give you excellent power and performance everywhere.

[AL427SBF]

This is the vid that got me thinking about it again -

Factory Five Kit Cars vs a Lamborghini Gallardo! - HOT ROD Unlimited Episode 27 - YouTube

No CVT, more like the aluminum blocks here with TKO600 and 8.8" 3.27 rearend

[AL427SBF]

Originally Posted by bobcowan

I think you're exactly right. The HP figured was originally developed in the late 1700's to sell steam engines to people who were still using horses for work.

Torque is measured, HP is calculated. The Dyno measures the torque of the engine, and then calculates the HP curve at each points.

When you're coming out of turn 3 and heading for the back stretch, do you want torque or HP? A broad flat torque curve will give you excellent power and performance everywhere.

Bob, exactly my thinking.

[ERA Chas]

You can forget all the classroom academics-when the platform is a Cobra.
Cobras don't tolerate maximum torque unless you have a live axle and slicks.

[Jerry Clayton]

Turn 3 isn't headed for the backstrech------turn 4!!!!!!!!!!!!!

[Rich A]

Originally Posted by bobcowan

...Torque is measured, HP is calculated.
The Dyno measures the torque of the engine, and then calculates the HP curve at each points.

...A broad flat torque curve will give you excellent power and performance everywhere.

x2...

[AL427SBF]

Originally Posted by ERA Chas

You can forget all the classroom academics-when the platform is a Cobra.
Cobras don't tolerate maximum torque unless you have a live axle and slicks.

My spin on that would be Cobras tolerate maximum torque better if you have a live axle and slicks - and that's for strip performance only. I don't think I would want a live axle on a road course

[ERA Chas]

Originally Posted by AL427SBF

My spin on that would be Cobras tolerate maximum torque better if you have a live axle and slicks - and that's for strip performance only. I don't think I would want a live axle on a road course

Yes, you've figured that out.
Since you now define road course use, build for HP. You only leave from rest once there. If you build 600+HP, you'll have more than abundant torque to get off corners provided you can put that power down.
Cobras= 90" WB, IRS and poor aerodynamics; not good for high torque applications.

[AL427SBF]

Originally Posted by ERA Chas

Yes, you've figured that out.
Since you now define road course use, build for HP. You only leave from rest once there. If you build 600+HP, you'll have more than abundant torque to get off corners provided you can put that power down.
Cobras= 90" WB, IRS and poor aerodynamics; not good for high torque applications.

Sort of gets back to the original proposition, maybe were talking past each other. Don't need to build for 600+ HP, need to build for the broadest torque curve the motor will support, HP will fall in-place as a derived result.

Since you now define road course use, build for HP. You only leave from rest once there.

Actually, anytime I want to accelerate I will be calling on torque, all gears over a broad RPM range. Ohm's law analogy ...

V=RI
Torque = Current (I)
HP = Volts (V)
Motor Efficiency = Resistance (R)

High Voltage without Current, will power nothing
High Resistance without Current, will power nothing
High Current, regardless of Voltage or Resistance, will kill your ass

[ERA Chas]

Dude-drop the formulas; you're overthinking this.
Close-ratio gearbox, 3:50 or taller dif, 27" tires and 450HP (even) will provide a higher rate of acceleration through the gears.
The torque will take care of itself as long as you don't overwhelm grip.

[AL427SBF]

Originally Posted by ERA Chas

Dude-drop the formulas; you're overthinking this.
Close-ratio gearbox, 3:50 or taller dif, 27" tires and 450HP (even) will provide a higher rate of acceleration through the gears.
The torque will take care of itself as long as you don't overwhelm grip.

Actually, seems the area of focus for motors should be maximizing VE for best torque curve, how well she breathes, leave it at that.

[scottj]

The formula is this simple: Build as much torque as possible in the rpm range you intend to run.

But...

400 lb/ft average torque from 2500-4500 rpm will not accelerate as quickly as 400 lb/ft average torque from 5500-7500 rpm.

If rpm range is not a concern, then the higher an rpm you can make a given amount of torque the faster you will accelerate.

The problem is, rpm is always a concern... which takes me back to my opening statement

[RET_COP]

Horsepower is King!
Its what gets you down the track. Cobra's are light and we don't need a ton of Cubes (torque) to get them moving.
Get your Horsepower up and you'll have more than enough torque.
IMO

[bobcowan]

Originally Posted by ERA Chas

Cobras don't tolerate maximum torque unless you have a live axle and slicks.

Depends on what you mean by "maxiumum", and the application. I'm making a lot of torque, across a broad range. As long as the track is dry, I'm always looking for more torque.

There's no such thing as too much power, only not enough control.

Originally Posted by Jerry Clayton

Turn 3 isn't headed for the backstrech------turn 4!!!!!!!!!!!!!

Not at High Plains Raceway! Turn 3 opens out on to a long down hill back stretch.

Originally Posted by AL427SBF

Since you now define road course use, build for HP. You only leave from rest once there.

Not true. Every time you come out of a corner, you need all the torque you can get. You're not starting out from 0, but you're often coming from 60 and heading for 150.

Since I have a lot of torque everywhere, I don't have to shift much. I use 3rd and 4th only. Every time you shift you lose time, and have the potential to upset the car. And it gives you more things to do while you're already pretty busy.

I'v ridden in other cars that don't have as much torque, and have to work harder to keep the engine in it's power band. There's often a lot of shifting going on. That's especially difficult when pulling a steep hill.

[Tommy]

The best short answer above is, IMHO, scottj's. As he has got more race track experience than most here, I value his opinion.

From an engineers perspective, the burning fuel in each cylinder's power stroke serves only to apply a pushing force to the piston. That force is transferred through the connecting rod to the offset arm of the crankshaft creating a brief rotational torque. (Force of piston X Length of crankshaft arm = Torque on crankshaft). That torque is transferred through the rest of the drive train to the wheel(s). When the drive train tries to rotate the wheel, friction between the tire and ground usually makes it easier to move the car forward than to slide the tire on the ground. In this instance, the rotational torque of the wheel is converted to a linear push against the ground. (Torque of wheel / Radius of wheel = Force pushing car forward). ... As Newton taught us, applying force to an object will cause it to accelerate per the formula: Force = Mass X Acceleration. So, the theoretical rate at which a car will accelerate is directly related to the torque created by the engine.

BUT, we don't drive our cars in a vacuum, so as we gain speed the air begins to push back against us. Consequently, a car producing a steady torque will accelerate from 10 to 20 MPH more quickly than from 80 to 90 MPH. And ultimately we will reach a speed where the push back from the air and everything else will equal the push forward from the engine causing the acceleration to slow to zero (i.e., top speed).

Recall that each piston produces a pushing force and subsequent torque only momentarily during its power stroke. If we increase the number of pistons or the RPM we can increase the number of power strokes from the engine per second. This is what horsepower is all about. Horsepower can be expressed as: Torque / Time or Foot-Pounds per Second. It is a calculated number derived from the average amount of torque produced by an engine over time. This relationship makes it obvious why engine horsepower typically increases as the RPM increases, up to a point.

The horsepower number most often quoted for an engine is its peak horsepower at a specific RPM. IMHO, that is useful information only if you plan to spend most of your driving time at that RPM (e.g., NASCAR Daytona). Otherwise, saying your car performs well because it has a 600 HP engine is kind of like saying a person should be able to fix your car because he has an IQ of 150.

For my use, I value my car's ability to accelerate over a variety of speeds more than it's top speed. For that reason, I had my engine built with a big flat torque curve from 3,000 - 6,000 RPM. I want the engine to last, so I limited it to 6,000. If I were a real competitor like scottj, I would have moved the torque curve higher up the RPM range.

[ERA Chas]

Bob-you quote me twice in your post and I essentially agree with everything you write. What you missed was my point to OP that torque overcoming grip in a Cobra is a. not beneficial, and, b. easier to do than say a DP or Rolex Sports Car.

[vector1]

torque is a mechanical measurement, has nothing to do with time.

horsepower is an equation that uses torque and time. fortunately, or unfortunately, we use time in this world--rpm, mph, lap times, 1/8 mile time, etc.

which would you rather have in your wallet?