Torque and power quiz 4

[yoshimitsuspeed]

I spend a lot of time in the automotive community and a lot of time on car forums and groups.
Ever since I started to learn the actual relationship of torque and power it drove me crazy how few others in the automotive world actually understood this basic formula. People capable of building motors that make 500 hp per liter and who still think that torque is low end power.
I have gotten into enough arguments with people to learn that most would rather argue relentlessly cause that's what theys daddy taught them than sit down and think about the simplicity of the formula long enough to understand the relationship of the two.
I have decided to try a different tact and make a little quiz that gets people thinking about this from a different angle and maybe hoping they will get the point that torque and power can't be compared, and that torque does not mean low end power.
I just started on this tonight and it's 3AM. I want to do more to improve it but I also would love some input from others on ways I could improve it.
I would like it to be as detailed and informative as possible while still being interesting and keeping the person engaged and interested.

Tell me what you think of what I have so far.
What could I do better?
What are other questions I could ask or ways I could put things to get people thinking about the relationship without getting too bogged down in the math to loose too many people?
On that note should I focus more on the math or stay more with the basic relationship and principles?

http://matrixgarage.com/content/think-you-understand-torque-and-power

 

[Tmoose]

Hi 140Air.....POWER,

The Joules are wimpy, not the metric system.

1 Joule < 3 quarter pounders raised 1 foot in the air, or a 2700 lb corvair about 0.003 inches off the ground, .
Then again, Me getting up off the couch prior to heading to the fridge is about 350 Joules.

 

[140Airpower]

Tmoose, you are right that joules are wimpy. No good for raising Corvairs. Quarter pounders are another matter. With those, I only have to add a jack to do it.

Gruntguru, Roger about the chassis dyno. I never thought of it.

Yoshimitsu, I guess enough questioning will eventually bring out the misconceptions.

 

[dgallup]

Pascal is the really wimpy metric unit.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[SomptingGuy]

There's nothing wimpy about 1Pa RMS (94dB). Difficult to get youself heard over that.

- Steve

 

[Tmoose]

Only if the Pascals are not DC.

Standard atmospheric pressure is about 100 kPa.

 

[GregLocock]

You won't get much heard in 1Pa DC either, in space no-one can hear you scream.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[NormPeterson]

8/8 earlier today, but the wording is still a bit confusing to this retired structural guy. I'd go back into the quiz, except that it would skew your results regardless of how I might choose to answer the questions on a second run through it.

I'm a little confused about this ↓↓↓ statement.

They cannot be compared and they are definitely not two sides of the same coin. That insinuates the general misconception of what torque and power are.

To me, any misconception is that they're unrelated; that an engine could have one torque curve and an unrelated power curve. Is that what you're trying to clear up? Or just that peak torque and peak HP are somewhat more loosely related?

FWIW, I prefer to work with the torque curve for mathematically estimating vehicle acceleration and ignore the power curve beyond any use it may have in defining the torque curve. If nothing else, it's easier to deal with rotational inertias and their rotational accelerations (which must necessarily be consistent with the straight line vehicle acceleration, absent wheelspin) that way.


Norm

 

[yoshimitsuspeed]

That is what I was trying to get at norm. I think there are many people who don't realize that a 10% increase of torque at a given RPM means there will also be a 10% increase in power at that RPM.
What I mean by they can't be compared ties directly into that. People will say for their build torque is more important than power or use torque to mean low end power.
The hope is to get people to understand how they are connected and the relationship between them.

Torque curve definitely has it's advantages in some situations as long as you know what the torque represents.

 

[Tmoose]

Using the power curve to determine a best guess best shift point is pretty easy. If mechanically safe and possible Rev beyond the power peak to the point the HP in the lower gear will be higher than the HP at the shift point. HP cuts out a bunch of "red tape" calkulating the effect of gear ratio torque multiplication.

Ed Iskenderian described there is frequently an advantage of revving 10-20% beyond the power peak in "Valve-Timing-for-Max-Output"

 

[NormPeterson]

Tmoose - agreed. Aside from matters involving ultimate top speed there's nothing inherently special about the rpm at which peak power is developed.

To maximize area under the power curve you'd ideally want to have half of that area coming from the high side. That power curves aren't likely to be symmetrical about the peak power point would also be behind the "10% - 20% beyond" shift point suggestion, since gear spacings are typically wider than double that. (Side note, or maybe it's your main point - this very matter of setting shift points at rpms above the peak power rpm vs at it occasionally comes up on "enthusiast forums", where a couple of people will "get it" and the rest won't.)

This is a slightly different and I think more specific question than yoshi's, where vastly different powertrains are being compared against each other.

Geared appropriately, running at max HP will provide maximum acceleration at any given speed (traction permitting and ignoring rotational inertias and other secondary effects). But the maximum acceleration with that same gearing will still occur at max torque.


Norm

 

[Tmoose]

Isky "Valve Timing for Max Output" page 28

 

[yoshimitsuspeed]

Another one from this morning.

Here we go with the science lessons. So when we put a V8 in a pick up we're wasting time, so put in a proper transmission instead? Torque and HP are related, give me something with torque then and forget the HP. Our 9 second Evo had 600 HP and 500 ft/lb, bu the 8 second dragster V8 had 600 HP and 900 ft/lb. Need we say more? Our Type R Honda had 650 HP and 450 ft/lb, it was not as fast as the Evo.

I'm not a scientist or math wiz, but I understand what I read. I have also tuned enough cars to know that torque is more important than HP. I've tuned all kinds of car producing the same HP, but the car with the higher torque is faster in every case even with similar gear ratios. Can you explain to me in physics why that is? Maybe it will help me to produce more 9 second Evos or even lower my times.

These are the communities I spend way too much time in.
People who can get 200 hp per liter out of a motor but could believe it's due to fairy dust and unicorn sparkles and it wouldn't matter.

I actually came up with an analogy the other day.
A great chef doesn't need to know biology or chemistry to make a world class meal. They don't need to know exactly how yeast and sugar interact or how two different components combine to create a new flavor. In fact most will really know very little about that. They may think that bread rises because of little fairy farts making air bubbles in the dough. It wouldn't make their meal any less good or their cooking any less effective.

 

[BrianPetersen]

Sometimes it's best to just smile and nod.

Your facebook group member is unknowingly commenting about the shape of the torque curve.

Let me add something that I saw with my own eyes at a local drag strip on test-and-tune night.

A very stock-looking and stock-sounding Mazda 3 lined up beside an older VW that was quite obviously hot-rodded and turbocharged. The VW made all sorts of chirpy and whiny noises in the process of staging. The Mazda made none.

When the light turned green, the Mazda took off in a very unremarkable, nondescript, completely-bone-stock manner. The VW, which had been making all sorts of noise from the engine being held just short of the rev limiter during staging, bogged and fell on its face. The revs dropped below the power band, the engine fell off the cam, the oversized turbo went off boost, and it slowly crept away from the line. Then, after a good couple of seconds, the engine woke up, the turbo spooled, the engine instantly revved to the limiter, and the front tires briefly lit up until the car caught up. Then the driver had to change gear.

And the engine bogged, and the car went nowhere fast, for another couple of seconds, until again it managed to creep into the RPM range where the turbo and the cam actually worked. Same thing. Lit up the tires, bounced off the rev limiter, time for a gear change.

Meanwhile, the Mazda with its driver-friendly bone-stock wide torque curve, was gone.

Obviously the VW had a too-big turbo and a too-big camshaft in the interest of making who knows how many hundred horsepower at 50 rpm short of rev limiter ... but anything below that, the engine was off the cam and the turbo wasn't spooled, and a lawn tractor would outrun it.

Your Facebook member would make a whole lot more sense if he simply plugged in the word "mid-range" prior to every incidence of the word "torque".

 

[yoshimitsuspeed]

Yes exactly. I told him that what he was really talking about was power curve. You could use torque curve as well but until you add RPM the torque curve doesn't mean anything and once you add RPM you are essentially talking about power anyway.
But yes that is exactly the point and I think a lot of the problem is that people get so sucked into the 2 datapoint frame of mind that they actually think that torque number means something it doesn't.
Where it gets really bad is

give me something with torque then and forget the HP

and

I have also tuned enough cars to know that torque is more important than HP

it really shows that this view of getting too invested in staring at peak tq numbers and thinking that is what means something it doesn't.

Your example above is a good one and shows the importance of tq/power curve. On it's own knowing peak power isn't a whole lot more useful than knowing peak torque but at least it gives you some idea of how much work the motor is capable of doing. If the VW had a CVT transmission he probably would have smoked the Mazda. Or maybe if the driver just knew how to drive the car.
I have had the same thing happen. My friend and I were just messing around, he was in his V6 or V8 Toyota pickup. I was in my MR2 with my 1.6 liter 11:1 compression, 256 cams turbo 4A. With a perfect launch I can have full boost by the time the clutch is all the way out. With that perfect launch I would have smoked him but I don't drag race, I don't practice my launches and I'm not terribly comfortable or smooth in a situation like that so I stuff it, drop the clutch too quick and might be lucky to be at 3k RPM by the time the clutch is all the way out. By that point he was already 4 car lengths ahead of me. Had we raced to 120 mph or so I probably could have reeled him in.
My car could easily take his truck with the perfect launch but because of his power curve just about any driver could get in it and take off at a similar rate because you let out the clutch, stomp on the gas and it will go.

 

[140Airpower]

I keep coming back to the fact that IC engines are tuned systems. All complaints about not having enough low-end torque (or power) are really about operating the engines off tune. This is especially the case with turbocharged systems where having the turbo operating in its proper range is so vital.
Most of these problems just need the proper gear ratio. The maximum torque that counts is the torque at the rear wheels which is always best at the max POWER rpm AND the proper gear.

 

[yoshimitsuspeed]

I always laugh about this 140
The 4AGE came in the 16 valve NA 4AGE, supercharged 4AGZE and the later 4AGE 20 valves.
People are always praising the 4AGZE because of it's amazing low end and how superior it is to the high strung 20 valve or a turbo setup because the supercharged motor accelerates 40% harder than either 20 valve or turbo at 2500 RPM. I am constantly trying to point out that even the lowest horsepower NA 4AGE makes twice the power at 6000 RPM as the supercharged motor does at 2500 so who cares on a motor that spins to 7500 RPM stock how hard it accelerates at 2500 RPM?
There are still those who insist that makes it a superior motor.

 

[BrianPetersen]

An engine that has a narrow powerband up high in the revs will need the driver to row the gears all the time.

A torque curve similar to a typical diesel, will be less fussy about what gear it's in.

It makes a difference.

Sure, a turbo Suzuki Hayabusa engine makes about the same power as the engine in a tractor-trailer rig. Sure, you could tow 80,000 lbs with it if you had enough gears in the transmission. That doesn't make it a good idea.

 

[140Airpower]

Brian, what you say is true for transmissions that require rowing, a dying breed these days.

Paddle shifting is a lot simpler than working gearshift knobs. With more speeds you can keep the revs closer to the power peak. Even with a torquer engine, you would want to run as close to the power peak as possible. If you had a CVT, you'd run at the power peak all the time, never at the torque peak. Then again, with a CVT you can design the engine to have the torque peak as high as possible. Forget the low end.

 

[BrianPetersen]

Okay ... An engine with a narrow power-band up high will demand constant and repeated downshifts from the 9-speed automatic transmission on every grade or will demand its CVT to send the revs way up on every uphill, thus leading to driver complaints. A diesel-like torque curve will usually get into whatever gear ratio it wants at cruise, and pretty much stay put.

In a normal road car with a petrol engine, in this day and age, normal revs on flat-ground highway cruise are well below both the power peak and the torque peak, in the interest of economy.

 

[140Airpower]

Brian, what you say is true, but the discussion of misconceptions about torque and power only becomes interesting when talking about the response of an engine to demand. As you say a CVT will respond to maximum demand by allowing the engine to rev up, I say to max power, not max torque.