I am looking for help in understanding whether torque or horsepower is more important for accelerating me the fastest from zero to sixty. I understand "well a little" that torque is immediate twisting power whereas horspower is something like torque measured over time.

Would a C-6 with 450 lbs of torque and 400 horsepower accelerate faster from zero to sixty than a C-6 with 450 of horsepower and 400 lbs of torque? andy

 

http://www.google.com/search?q=%22To...+Horsepower%22

 

Torque is a force, twisting force.

Work is applying a force over a distance.

Power is doing work through time.

When people ask what's more important torque or power...the answer is yes!

Assuming all esle equal.

In reality the best question is what "torque curve" is best. We concentrate too much on peak numbers, which is what the OE lists.

The most important questions are the shape of the torque curve and the overall area under that curve.

The "curve" is amount of torque produced through the engines RPM band graphed.

The "fatter" the curve the better for the real world. But sometime you can't have it all and you make compromises.

So, you have to decide what you want. A fatter curve in the low RPM range for easy street driving? A high reeving engine that has a small area under the curve in the low RPM and then rise in the higher RPM, good for the track?

Or something in between?

Depends on what the curves look like on these 2 engines. It's possible there's no difference in the 1/4 mile time at all.


A Honda 2.2 liter can make 240bhp, but the area under the curve is actually pretty small because the curve is shallow in the lower RPM's and then rise dramatically (giving that impressive peak number).

Personally I prefer a very even, flat curve for the street. But on the track I find a mid and top RPM heavy curve is best.

Everyone has different opinions on what's best.

 

What you want is 'a', the straight line acceleration of the car. Now F = ma, or rearranged, a = F/m. That tells us that acceleration is proportional to force, and inversely proportional to vehicle weight. So for quick times, we want lots of force and little weight.

Ok, now the straight line force is a result of the turning torque of the rear wheels reacting with the road surface. That torque will be increased by using a smaller diameter wheel, a higher numerical rear diff ratio, or a lower transmission gear, all of which *multiply* torque. Or it can be gotten directly via an engine with more torque. So within the limits of traction, the more torque, the more acceleration you get.

It doesn't much matter how you get the torque. A small high winding engine's torque can be multiplied by gears, or a large low speed engine can deliver torque directly. 6 of 1, half a dozen of the other. Ultimately, the maximum available torque per unit time is proportional to horsepower, so the ultimate limit on how quickly you can accelerate is a function of available horsepower (and gearing, and traction).

In practice, for street driving, a small high winding engine with a peaky torque curve is a pain in the *** to drive quickly. A larger slower turning engine with a broad torque curve is better. The shape of this curve is more important than its peak. We can always manipulate the peak to be whatever we want, within the limits of available horsepower, via gears.

 

The graphs of the torque and the horsepower are really what count from the posts of what I am getting back. The highest torque and the highest horsepower are not all that important if they only come at small times while the engine is accelerating.

The longer that the torque and the horsepower is at highest levels the more power we have to play with during regular street driving. Now i understand why the Corvette pushes you back in the seat at low speeds. It has lots of torque at low rpms. And lots of horsepower at high rpms before we have to shift. To GM.. Keep sending us gobs of torque and horsepower at all the rpms ! That little light weight Honda that makes a fair amount of horsepower needs a lot of rpm before it does.... No wonder all they do is make a lot of noise with those buzz bomb exhausts.... Andy

 

Absolutely the most important thing which determines
a car's acceleration potential is horsepower.

If you know a car's hp and weight, you can make a
pretty accurate guess about it's acceleration. If you
only know the car's torque and the car's weight, you
cannot say anything about how hard it will accelerate.

The key is that hp is basically torque * rpm.

It's true that when you floor the gas pedal, that push
in the back you feel is the engine's torque.

But since torque tends to be a function of engine
displacement, without turbo or supercharging, it is
very hard to get huge amounts of torque. So what
car designers do is to design the engine so that the
torque is generated at as high an rpm as they can and
then to use GEARING to provide additional torque
multiplication at the rear wheels.

So the answer to your question is that assuming the
car was appropriately geared, the higher horsepower
engine will almost always win.

If you doubt this, just compare cars like the Carrera
GT and the F430. Neither makes a ton of torque but
both cars make tons of horsepower 'cause they make
the torque at a high rpm. Result? Face flattening
acceleration.

Pat

 

The Carrera GT has 435ft. lbs, the F430 343ft lbs. Hardly small peak torque numbers for ~3,000 pound cars. They are no doubt super fast but they have the gearing, ample peak torque and of course massive hp to accomplish this.

A nice example at the other extreme would be the 2.0 liter S2000. A typical 240hp, 2,900 pound rwd car should be no brainer for a decent driver to get solidly into the 13s in the 1/4. But the whopping 153ft. lbs of torque of the 2.0 liter combined with its compromised flexibility in the rev band make it one of the worse low end/0-60mph/1/4 mile accelerating car for its hp/weight ratio. The specifications look better than almost everything else on paper though.

 

So is this why ppl put 4.10s in their vettes? How are the 3.42s in the vette? Would it be better to put in 3.73s i dont care so much about top speed or gas milage i want acceleration. Sorry didnt feel like searching

 

The lower the gear (higher numerical value) the higher the torque multiplication.

So a lower gear will give you better acceleration. But it will also give you a lower max speed in each gear if the transmission stays original.

Depending on the original gearing and what changes you make. For instance, if you had to up-shift to 3rd at 62 MPH you may now have to up-shift at 58 MPH.

It's not just top speed outright, but max speed in each gear.

BTW- You Air Force guys are so lazy!

 

HP and TORQUE are not different things.

Torque by itself does not do any work.

HP is the definition of work done.

Gearing is important.

Thrust at the rear wheels is all that matters.

Here is a spreadsheet I made a while back showing thrust and g force at the rear wheels at a given RPM.
http://www.vetteguru.com/apps

Some engines are better for stump pulling and trailer pulling, where off idle TQ is great. Long stroke, fast port velocity, big displacement, are all types of things these engines are built around.

Other engines are better for getting from point a to point b in the quickest time possible. These engines are built for HP, and RPM and Geared for it. Bore over stroke, large high flowing ports, etc. The higher in the RPM range the TQ is made the better.

Two identical cars geared optimally with equal HP but different TQ will ET in the 1/4 mile basically the same.

Two identical cars geared optimally with equal TQ but different HP will not ET the same. The Higher HP one will win.

 

Yes. A higher numerical ratio gives you more torque multiplication, and that translates to more force pushing the car forward provided you can maintain traction. That's the rub. It does no good to develop more torque than the tires can translate to the pavement.

The stock 3.42 rear ratio pushes the stock tires to their adhesion limits. So going to an even higher ratio will just result in more tire spin if you retain stock tires. Now if you go to slicks, big wide wrinkle wall slicks, then you can productively use a higher ratio.

A 4.10 ratio is good for the quarter mile, you can go even higher for an eighth mile strip, again provided you can maintain traction. You will start running into the rev limit on the top end with a high numerical ratio. For road racing, a 3.73 ratio would be a better choice on tracks with long straightaways. That's also about as high as you'd want to go on the street to maintain some semblence of fuel economy.

 

kewlbrz, Try putting a 240hp 2.0 S2000 engine in an '87 Grand National with an automatic transmission and see if you can run a 14.0 1/4 with it. That's What the stock 245hp 3.8 liter V6s could manage with just a decent amount of traction on a cool-ish day. In a 3,500 pound car no matter how you gear it, it's not going to happen with the torqueless 2.0 engine.


Or try putting a 296hp 3.4 liter 911 engine in a 60,000 pound semi. Gear any way you can. I got news for you, that porsche engine will fail miserably. But a 300hp diesel engine, say a cummins with about 1,000 or more ft. lbs of torque could do it.

Yes these are extreme examples but despite torque and hp having a direct realtion, it also shows the differences in the way force and power are quantified. And the differences the two can have applied in the real world.

 

The single best explanation I have ever read about HP and
torque and how they relate to each other and to cars is
here:

http://www.vettenet.org/torquehp.html

This should answer all questions.

Pat

 

If I recall, he mentioned that he didn't care about fuel economy so that might not be a big issue. But with my 4.10's I only noticed about a 7% drop in fuel economy, much less than I'd have thought (going from a 3.42 to 4.10 being about a 20% change in gearing). I think that a lot of this has to do with my ability to use 5th...and especially 6th...much more than before.

And the difference in gearing...including the "fun" factor...way outweighs any drop in gas mileage to me.

 

Simply put, torque is the rate at which horsepower is applied.

- Matt

 

It is a delicate balance between the two that makes POWER

 

Simply backwards.

Horsepower is the rate of doing work.

Force (torque) is one of the components of work done (work equals force times distance).

Horsepower is then work per unit time, or torque times RPM.
(units conversion factors: 550 ft-lb/sec or 33,000 ft-lb/min)

 

Since horsepower is only an expression of torque and rpms, torque is obviously the most significant indicator of the ability to accelerate a vehicle. After all, if you develop a lot of torque in the upper rpm range, you'll obviously also have horsepower. Any gearhead knows that seeing the torque curve on a dyno graph is all you need to know all the characteristics a vehicles dynamics regarding acceleration at all rpms.