Torque and Horsepower Peak Speeds

I would agree to construct an SBC to preform in such a manner would be ludicrous, but I think I could be done, if only to prove a point.

codrus wrote:

edizzle89 wrote: is there a need to be at peak HP frequently in an off highway application? i assume they spend most there time closer to peak torque rather then peak HP? just curious as to why you would need both HP and torque to peak in the same place

Because if you gear it properly, you make more torque at the wheels at peak power than you do at peak torque. That's what the power number means.

You always make more torque at the wheels at peak power.

However, there are benefits to cruising at above the torque peak. When you start to go uphill and the truck slows, you slow down into a region of greater torque.

It's a lot like how you tune an engine to idle at a modest amount of timing instead of at highest vacuum, so when the engine sags under load it gains torque instead of stalling.

alfadriver wrote:

Fueled by Caffeine wrote: If it made it all at 5250. Sure

That only works if we are talking lb-ft for torque, horsepower for power, and revolutions per min for engine speed. For watts, newton-meters, and rad/sec or deg/sec- that does not apply.

I think you nailed it, and the answer is that ALL engines can make peak power and peak torque at the same speed, because the only difference between power and torque is rotation speed.

So if an engine doesn't make peak power and torque at the same engine speed in the units you use, change your units until it does.

codrus wrote: you won't see it in a real-world gasoline engine because it's a stupid way to design an engine. :)

You haven't driven a 22re.... mine falls on its face at 4500 rpm. No more torque beyond that. Engine won't rev to 6k at all. (It will, it just takes forever)

As far as I can tell, there are only two ways to technically accomplish this...And, in my opinion, only one of them would be realistic to do so.

First requires the torque curve to begin falling off too sharply and instantaneously upon hitting the torque peak to actually accomplish outside of a laboratory. You might be able to get close-ish, but I'm skeptical that even electronic wizzardry can make the inertia of an engine performing a continuous sweep to react suddenly enough in the real world.

The second is to have the maximum torque value occur at redline. I would think this to be most easily accomplished via neutering the engine with an artificially low rev limiter just before torque peak, or with centrifugal supercharging.

Regardless of how it's accomplished, it would be an engine that suddenly quits (and hard) right when you get to the best part, leaving you wanting for more.

Trackmouse wrote:

codrus wrote: you won't see it in a real-world gasoline engine because it's a stupid way to design an engine. :)

You haven't driven a 22re.... mine falls on its face at 4500 rpm. No more torque beyond that. Engine won't rev to 6k at all. (It will, it just takes forever)

It may fall on its face at 4500, but it also probably has greater torque before it gets there and/or still doesn't drop off sharply enough for peak power to arrive there as well.

Huh, got a lot more interesting responses than I was expecting, but then this is GRM. I should have expected as much, haha.

Fueled by Caffeine - I'm not saying that torque and horsepower peak values would be the same, just that the speed they occurred at is the same. For example, let's say 332 ft lbs at 1600 rpm, and 101 horsepower at 1600 rpm. But yes, it all relates back to the horsepower/torque conversion factors regardless of what units you use.

Alfadriver - Again, not necessarily limited by the mechanical performance of an engine. For example, an engine that is capable of making 170 hp and 370 ft lbs, but is sold with the aforementioned rating of 101 hp and 332 ft lbs and an essentially flat power curve.

Knurled - interesting; I'll have to look into that Ford. I'm not surprised it was also a diesel application.

Codrus - I know you can alter the performance of the engine mechanically, however most diesel engines are not sold with ratings that are at (or even near) their mechanical limits. They are indeed typically deliberately restricted. I'll have to look into the two strokes; I've not spent much time around their dyno curves. Here's a KTM 200 (my woods bike) fwiw.

Edizzle - yeah, I would say we do work at the same place, haha. No, off highway doesn't necessarily care about peak HP speed. The only reason for revving the engine out in most applications is to either achieve higher roading speed, to achieve higher hydraulic function speed, to provide more of an engine speed buffer for lugging back to prevent falling down past peak torque (engine will typically stall if this happens), or to achieve a specific operating condition like generator power frequency. I don't need the numbers to be at the same place, but in lower ratings we are often in the position where we could run at rated power from something like 1100 rpm all the way to 2500 rpm, which would be rated (max) speed. We just don't tune them that way, but no one really had a reason why. Based on your plots, the ISF and QSF are tuned very differently.

Robbie wrote:

alfadriver wrote:

Fueled by Caffeine wrote: If it made it all at 5250. Sure

That only works if we are talking lb-ft for torque, horsepower for power, and revolutions per min for engine speed. For watts, newton-meters, and rad/sec or deg/sec- that does not apply.

I think you nailed it, and the answer is that ALL engines can make peak power and peak torque at the same speed, because the only difference between power and torque is rotation speed. So if an engine doesn't make peak power and torque at the same engine speed in the units you use, change your units until it does.

Uh, that's not what I'm saying.

The fact that in hp and lb-ft- the numerical value of power and torque are the same at 5250 is a function of the math, and not some kind of definition. And really isn't what is being asked.

What is being asked is if you can have peak power and peak torque at the same speed- 2000rpm, 4000rpm, 5250, 6000- where the max value is at the same location, not the same value.

For that to happen, it would be really hard, as torque would have to drop at a rate of 1/engine speed just to keep the power constant as engine speed went up. At some point, that happens, but near the peak torque engine speed- it's very hard to set an engine up to do that.

And the only way to do that using things other than spark or fuel restrictions is to have the breathing drop off that fast. It's just that air pumps are not that non-linear- to me that would require a point change in the airflow to happen- which in a real, physical world, does not make sense in my mind. Physics are pretty darned smooth- so to get onto a path that decreases faster than 1/N, you'd already have to be decreasing to do that. Which would mean you hit peak torque before that.

(remember, smooth means first and second order derivatives also can't have points- so the second derivative of air flow still has to be reasonable- not steady- but it won't have a point change)

The only real way you can make it happen is if there's an artificial limit- fuel for diesel or fuel and/or spark for gas.

Appleseed wrote: I would agree to construct an SBC to preform in such a manner would be ludicrous, but I think I could be done, if only to prove a point.

Start with a paper version. One that's not limiting spark or fuel- just that the pumping can drop off that fast and be that non-smooth. I just can't see it happening naturally.

gearheadE30 wrote: Based on your plots, the ISF and QSF are tuned very differently.

that was also a random dyno sheet pulled off the interwebs of what seemed like a somewhat modified ISF swapped into a jeep. I dont know if the production ISF dyno sheet would look similar or not.

gearheadE30 wrote: Knurled - interesting; I'll have to look into that Ford. I'm not surprised it was also a diesel application.

I didn't say it was a Diesel, it was either a 370 or a Super Duty family engine, these are gasoline engines. Very horrible fuel economy, designed to basically run at WOT forever, and as such they are somewhat deliberately hamstrung port-wise and intake-wise in order to keep them from making enough power to hurt themselves.

Remembering a bit more, it was probably a 370 or maybe a 429 truck engine. It was in a reference manual at the library and I was searching the medium duty truck books for info about the heavy duty electronic overdrive trans (E4OD?).

This might apply to the conversation a bit- According to my memory of an article I read awhile back therefore apply buckets of salt to the following: At some point in the WRC specification 300 HP was the limit and turbos were in use so the teams engineered the electronics, turbo sizing, compression ratios, yada yada yada in such a manner that a very convoluted power-band was achieved that sounds something like what Alfadriver describes if i'm understanding correctly.

In reply to Shaun:

With an X sized restrictor, you can only move enough air for Y horsepower. At that point you spend more energy getting the air through the hole than you will get in the engine.

The goal, then, is to make that much power over as wide a powerband as possible. Thus you have engines that can build 45-50psi boost at low RPM and taper off to 7psi at high RPM, so you make 300 (more like 340, IIRC) horsepower from say 3000rpm to 5500rpm and then the power starts falling off anyway. (yes, 500+ft-lb from a 2 liter four...) Boost controlled electronically, because you waste power if you try to pull too hard through the soda straw.

This is why the 1.6l spec WRC engines also have a boost limit, the old 2-liter engines had unlimited boost.

Shaun wrote: This might apply to the conversation a bit- According to my memory of an article I read awhile back therefore apply buckets of salt to the following: At some point in the WRC specification 300 HP was the limit and turbos were in use so the teams engineered the electronics, turbo sizing, compression ratios, yada yada yada in such a manner that a very convoluted power-band was achieved that sounds something like what Alfadriver describes if i'm understanding correctly.

AIUI, the cars were tuned to produce an artificially flat power curve. Since hp = torque * rpm * constant, this means that as soon as you can make enough boost, the torque will jump to whatever value is necessary to make 300 hp, and then decline on a curve such that the power stays at 300 hp until redline. While these engines may well make peak torque and peak power at the same time, they do it in the same way as the electric motor, by having peak power be available across a wide variety of RPMs.

At one point, people were tuning cars for power-to-weight NASA classes (PTE, etc) in a similar fashion.

All entirely irrelevant because peak torque is by definition going to happen at a lower RPM than peak power. A flat powerband means torque starts high and tapers down.

Knurled wrote: All entirely irrelevant because peak torque is by definition going to happen at a lower RPM than peak power. A flat powerband means torque starts high and tapers down.

A flat power band means it makes the same hp everywhere, so no matter where peak torque is, that's peak horsepower as well. :)

In reply to codrus:

But a flat power curve is the opposite of a flat torque curve.

Of all the cars I have tuned I have only seen this with two types of examples (both have been stated above):

1) turbo car where the redline is electronically lowered to keep the engine in one piece but still make pretty big power up top via a large turbo (common to do on SR20s and stock block Hondas)

2) Centrifugal charger with pretty low boost pressure

It sounds as if what you are really after is a way to measure the drivability of a particular engine.

This usually has very little to do with the peak HP number (which really only matters in dragstrip type conditions where you try and stay as close to max RPM as possible and are trying to eek out every bit of power you can)

This is why people tend to prefer to drive 'torquey' motors which are tuned to give more torque at the rpms that you actually run the engine at instead of the really high HP motors where the torque follows the HP, both being very low at low RPMs and both peaking at high RPMs.

Several years ago, I was trying to figure this stuff out when considering an engine swap for my old 4x4 (an International Scout). With the stock diesel engine, I was running out of power before running out of rpm if I hit a headwind or a slight hill. The project got away from me a bit and the result is http://lang.hm/scout/nph-performance6.cgi

What I do there is let you pick engine, transmission, gearing, tires, wind resistance, etc for each setup you want to compare, and then I create a bunch of graphs showing how much forward thrust you have 'in reserve' at any given speed