l know the definition of Torque. Force that causes rotation. Measured in FT-Lbs.

l know the definition of HP. Power over time.

However, lm not really sure about how they interact. Which is better to have, high HP or hight Torque. (Both, l know, but if you had to choose.) We are talking street application.

I know they both have benefits, so please, explain them to me.

Clayton

 

EG,

That's a questions that just about answers itself. It would be best to have high torque ove a very broad RPM range. That would net a high HP output as well. Unfortunately, unless you can infinitely vary stroke on the fly, it's tough to have the best of both. All engines are a bit of a compromise, and street engines tend to lean toward the torque output and sacrifice high end power. Since very few of us often run their engines past 5,000 RPM in daily driving, torque is what gets it done on the street.

If you don't want to lose sleep over low gas mileage, and can install 4.11, 4.56, or 4.88 gearing, a high HP engine in a light car can be a real blast to drive. You'll get a lot more revs on the engine, so it probably won't have the life expectancy of a high torque - low RPM engine, and you'll use a lot more fuel in daily driving.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

this has came up and resulted in flame wars over time. it's unreal how loyal some people get to one school of thought. vader said all and more than i can about the subject. do a search and see if you can find any of the old post about this.

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ICON Motorsports
1st & 3rd

 

Yup, vader pretty much covered it. The most important thing you can do, when attempting to increase a certain powerband, whether in broadness, or in peak, is to have all of the parts working in similar efficiencies at similar engine speeds. In other words, don't put the edelbrock performer RPM cam in a 406 motor, with stock TPI intake parts. The next most important thing is to match up the rest of your drivetrain. I personally love HP. Most street cars are more into torque - this is why the first MPFI cars from Ford and Chevy were designed to produce gobs of power below 5k. However, a stroker motor, or one of larger displacement (383-434) will be able to provide enough torque at lower RPM ranges to be tolerable on the street, while also being able to sport intakes, a cam, and heads able to flow well enough to make peak torque at 4200-4600 RPM and peak HP at 5900-6300 RPM. I do NOT advise drag racing on the street what so ever, but it does happen to even the best of us. When is does happen, maybe only 1 out of 4 times will it happen from a spotlight, everything else is from like 20-40MPH, then it starts. With higher (numerically lower) gears, the torque motor will get the jump when the tranny downshifts, but that's if the downshift in the high HP car doesn't leave it around it's torque peak. In that case (which would be had to be able to do), I would give the race to the high HP car. In summary, most street cars are torque based creatures (as Vader said), but you can have acceptable torque and decent HP levels with larger displacement motors.

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86 IROC-Z, Retired for winter, weird oil leak (drains out in about 3 minutes), new 355 other than that, TPI, 700R4, edelbrock headers, removed AC/Air pump, heater plate conversion - no heater (loL). 14.8@90MPH

 

Its better to make your peak torque at a higher RPM because you can take advantage of gearing

 

Both, you can't choose! If you want higher HPs, you need higher TQ. Likewise with low rpm TQ, you'll have low rpm HP. HP is a direct result of TQ (somebody post the formula, it escapes me right now), without TQ you are not going to have HP. But with TQ you will have HP (very low depending on setup). I would have to disgree with "On the street you want TQ", maybe if you live in a city where there is a buttload of traffic lights every 60', then yes. But the engine and rpm capability depends on what you plan to use the vehicle for and around what conditions. "One size fits all" doesn't apply here. For example where I live, the closest two traffic lights are is 1/2 a mile (if any at times). In my area if you have higher HP, you can experience that with a . Low rpm TQ gets good gas mileage on lower rpms (where it was designed to work, depends on setup), but when you wind it out, it's mileage goes downhill because you are operating of of it's realm. Sure you always want TQ, it gets you moving, but you really only need a certain amount to "push" the car. When you have 500-600 lbs-ft of TQ it becomes difficult to drive (especially on wet/icy roads). Any excessive amount of acceleration could be dangerous. Consider everything when selecting/building an engine not just one factor.

And yes there are faults to the "higher HP" arguement as well.

What I like in a setup (keyword here: setup) is an extremely flat, broad TQ curve that doesn't really peak (that way you have a wider power band, unlike a very selected band around where peak occurs) and a high rpm HP peak that tappers off slowly. This way, basically any gear will work with any trans combo. The TQ doesn't even have to be 1000, but could be 300 and still be potent. There is more than peak numbers than meets the eye.

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George P. Lara
Z28s Owned:
1984 "L69" A4
1994 LT1 M6
Member: SCCA, SCFB, SC3GFB
Camaro Info: MadMike's

[This message has been edited by MRZ28HO (edited January 01, 2001).]

 

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1984 Camaro Z28 Astral Silver w/ 2 1/2" cowl induction hood
Engine: Decked 383 cid 4 bolt w/ oil cooler, 9.6:1 compression, ARP fasteners, 600 cfm Performer carburetor, Torker II intake, Performer RPM Heads, XE268H cam, Magnum roller tip rockers, MSD6AL ignition, Blaster2 coil, recurved HEI distributor
Exhaust: Terminator headers, Custom 3" TIG welded stainless exhaust, Twister muffler
Transmission: 4L60 w/ Corvette servo, .500 boost valve, TransGo 7-CS clutch springs, 700 PKH pump rings, 700-2 reprogramming kit, Borg-Warner High-Energy frictions & bands, 2400 RPM lockup torque converter
Drivetrain: 2.73:1 limited-slip Dana 44 w/ disc brakes
Tires: Front P225/50VR15 Rear P265/50VR15 Eagles

 

Go to corvetteforum.com and click on the 1968-1982/C3 Corvette section. Go to page #3 and read about 50 posts on this very topic. It gets technical at times, but very informative.

 

Torque is the work done and HP is how fast it can be done. Lets say you have 2 engines both putting out 300 pounds feet of torque over the same power band. One engine only has 250 HP and the other has 300. The 300 HP engine will make the torque work quicker. If there wasn't any gearing involved, the 300 HP engine would go from idle to redline quicker but wouldn't move any more weight than the 250 HP engine.

The best example I can give is this web page. It's on a few other sites as well.
http://www.calgarydragracing.ab.ca/hpandtorque.html


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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

It's better to make hp high in the powerband than low for pure acceleration since as has been said this takes advantage of gearing. I prefer low rpm hp/tq for the street b/c I don't want to rev the hell out of the engine all the time to feel the power. The reason 5 ltr. mustangs beat 305s is that they make more hp up high (and in fact can rev higher to begin with) and they compensate for lower rpm torque with bigger gearing. That's a strategy used a lot: make the hp/tq up high, then use gearing to make up the difference down low. But as for me, I prefer the tq down low for the street but of course you want it everywhere! The LS1 comes to mind...nice high flat power curve - those must be a blast to drive. That's why I prefer a thirdgen to a stang - besides looks and interior and just about everything else of course! Man Mustangs suck! lol

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89 Iroc-Z LB9 305 TPI auto 2.73 posi:
3" Dynomax "cat" back,K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, 180' thermo, mild ignition mods, synthetic oil, kicker sound system, soon to attempt engine swap...

 

Does this work: Horsepower is how fast you can go, your top speed, while torque is how fast you get to that top speed. Am I on the right track?

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Horsepower is a function of torque.

Horsepower = (Torque * rpm) / 5252

One horsepower is the work done at the rate of 550 foot-pounds per second and it is equivalent to 745.7 watts.

I found this example doing a search on HP vs torque and thought it made sense:

OK. If torque is so all-fired important, why do we care about horsepower?

Because (to quote a friend), "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.

For an extreme example of this, I'll leave carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice :-).

On the other hand, twelve rpm of the drive wheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 HP.

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power* (ability to do work over time) is severely limited. http://www.datsuns.com/torquehp.htm


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

I got a book for Christmas that covers this and does not present it as an argument, but rather a decision to make based on what you want the car to do.

The book is a guide to performance upgrades on Chevy V8's. This book was written by Lingenfelter (the aftermarket guru) - forget the name of the book and don't have it handy.

In an early chapter, he graphs the RPMs of a car running through the gears in the 1/4 mile. The y (vertical) axis is RPM and the x (horizontal) axis is time. He then does an analysis of the percentage of time the engine spends in each RPM range to determine which mods to make. So, if you are looking at a street application. As said in one of the above posts, unless you plan on spending alot of time in the high RPM ranges, peak horsepower isn't necessarily the most important item.

Of course, the book then goes into the different mods in some detail describing what you are buying.

It's a pretty good book from a pretty reliable source...

 

And to throw a real curve into the formula.

Gearing is a big part of HP and torque. When you look at your 300 HP car doing lets say low 13's in the 1/4. Now take a stock eliminator car with a factored 250 hp running unported cast iron heads, cast iron intake manifold and a q-jet and runs low 12's. They also must weigh what the shipping weight is so they can't strip it down to nothing. What are we doing wrong?

When you look at the stock eliminator car it's not just engine. Even though they have a factored HP and cam specs are limited to .430 or OEM whichever is higher, duration, LSA and overlap are wide open. Increasing that duration builds torque. Then they play with tranny and rear end gearing to best use that torque. Suspension is tuned to use all that power and the cars get unreal et's with low HP.

Go to the race track when they have stock/superstock cars there and ask the drivers how they go so fast.

 

Chrissakes I feel smarter now..... that waterwheel thing makes me want to go to Denmark on my next Med Cruise.... really, and I'm not being sarcastic... you guys amaze me....

Kevin

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/