i was curious..

is horsepower and torque completely unrelated to acceleration? what is a good indicator for how fast a car accelerates?

what does it mean when you get __ torque at __ rpm? is it "better" when the peak torque is at a lower rpm than higher rpm's?

and what exactly is horsepower? i don't understand why a car with 200hp like tsx and a car with 200hp like rsx-s could have the same horsepower, yet one accelerates much faster than the other. i assume this has something to do with torque also, but i don't really know.

please let me know!! i keep wondering why my tsx isn't as quick as other lower-hp, lower torque cars.

 

Acceleration has a number of factors.

HP and torque determine the ability of the car to get off the line, gain speed, and maintain that speed. However, you must also look at transmission ratios and spacing. Weight is another big factor. Rotational mass at the wheels and on other drivetrain components. Final drive ratio is yet another factor. Then of course, there is grip.

For the TSX, it boils down to weighing too much. Less weight, both unsprung and rotational, would go a long way towards improving the TSXs acceleration.

 

Also wanted to add that HP is a function of torque and rpm.
HP = torque x rpm / 5252

The more torque you have, the more HP you have at the same RPM.

What would you rather have 1000 ft lb of torque at 1 rpm or 1 ft lb of torque at 1000 rpm?
In terms of horespower, they're both the same (about 0.2 HP).

 

I remember reading somewhere that bhp is the mathematical product of torque, rpm and some numerical constant, which translates the rotational aspect of power into one that is linear.

So in terms of 0-60 times, torque is rather irrelevant since such trials are launched at high rpms. However, as mentioned by CGTSX2004, the most important aspects are weight-to-hp ratio and grip.

if you want a faster TSX, lose weight, get stickier tires and disable the rev limiter.

 

Here we go again


You might want to try a search.


Torque is the actual "force" that moves you, however its not a good indicater of overall acceleration. Horsepower is the best indicator of accelration, as it takes into account many variables (hp = torque x rpm / 5252 ). More specifically HP to weight ratio will tell you fairly accuratly how fast a car will be. For example the main reason teh RSX with 200 hp is faster than the TSX with 200 hp is because the RSX is lighter (has a higher hp to weight ratio).

Engine torque really tells you nothing at all about how fast a car will be. its simply one factor that can increase HP. However if we look at the forumula we can also increase rpms to gain horsepower, and this will pretty much have the same effect on the over all accelration performance of a car. Just look at an F1 car, which has relatively low torque but can rev really high and thus take advantage of better gearing to go really really fast

My explanation is a bit simplified but the point is HP is king.

EDIT: 3 replies ... I think I took too long writing this post

 

Think of it kind like this: torque is how much "push" you're getting out of the engine at any moment, while horsepower is a measure of how much work the engine can do over a fixed period of time. (Think of trying to tighten a bolt with a wrench. The torque you are applying is how hard you are pushing on the wrench times the length of the wrench. You can apply more torque with a longer wrench, which is why you need a bigger wrench to loosen a really tight bolt). Whatever the torque on the bolt is, if you keep applying it over a period of time, you are doing work.

Accelerating the mass of a car is doing work, as is keeping the car at a constant speed while overcoming opposing forces such as friction and gravity (if going uphill). 1 HP is 550 foot pounds/second (i.e. the ability to lift 1 pound 550 feet in 1 second, or 550 pounds 1 foot in 1 second). Torque is measured in foot pounds.

In effect, if you multiply torque at any given RPM by the RPM, you have an indication of the horsepower. (Technically, Foot-pounds x rpm)/5252 = Horsepower). Looking at the engine in isolation, (ignoring mass and gearing for a moment), to know how "powerful" it is, what you really need to know is the torque curve. That is, if you know how much torque the engine puts out at each RPM, you pretty much know everything you need to know about the engine, because the horsepower curve can be derived from that. However, it is the horsepower curve that will really tell you how much work you can get out of the engine. When you are told the horsepower of an engine, you are really being told the "peak" horsepower (ditto for torque). This is why knowing only the torque and horsepower of the engine doesn't tell you everything you need to know. You can guess some of it: if the torque is high and the horsepower is low (relatively speaking--diesel engine or electric motor, e.g.) you know that the torque peak occurs at low RPM (or the engine has a low redline). If the torque is low and the horsepower is high, then you know that the torque peak is at high RPM, or at least that the engine maintains torque near its peak to a high RPM. (RSX/TSX, e.g.)

So, to answer your question about whether it is better to have torque at low or high RPM, the answer is, "it depends." Ideally, you would have maximum torque all the way from idle to redline. That would give you the most horsepower. Then, the higher the redline, the more horsepower the engine would have. The reality is, internal combustion engines have "torque curves"; the torque reaches a peak at some RPM range or point, and then descends at higher RPm's. Therefore, the horsepower peak will generally be at the torque peak, or at some higher RPM point, depending on how fast the torque falls off as the engine speeds up.

Throw in gearing: lower gearing means higher acceleration because the engine can turn faster for any given speed of the car, meaning more horsepower available at that speed (because HP is torque times RPM). (That is, the engine is capable of doing more work at that speed.)

Then, throw in factors such as the mass of the car, rotational mass, tire, drivetrain and air friction, transmission energy losses, traction, and you complicate things more.

I hope this helps, because the thing about torque and HP always used to confuse me.

David

 

Best answer ever!

 

to answer the question of acceleration. Lets say, we have a model car with same horsepower and torque and we can change the way the power goes to the ground. ( ie. FWD vs RWD vs AWD ). AWD will accelerate faster than RWD and RWD will accelrate faster than FWD. But AWD cars usually weight more than RWD cars. So its hard to say! Ah gravity, can't live with it. Can't live without it.

 

so i take it that if the tsx was brought to a weight that was similar to the rsx-s, then their acceleration would be relatively the same? i didn't know the tsx weighed that much more.

 

There are other factors, but hp and weight are the big ones so yes they would be relatively the same.


RSX type-s curb weight - 2767
TSX 6MT curb weight - 3246

 

I don't think so.. You still have one power source, the engine, generating the same amount of hp. So that power gets distributed to all 4 wheels, not duplicated to 4 wheels on AWD vehicles.. So, it'll still be the same acceleration if everything was equal and there is no wheel spin.

If you're strictly talking about the layout of the drivetrain, maybe RWD has an advantage over FWD because the wheels are pushing, not pulling, but I don't think that's what's being discussed here..

 

actually RWD is inherintly better for straight line acceleration because it will have more traction. When accelating, all the weight of the car shifts to the back, which will be good for traction in RWD and bad in FWD.

 

PREACH!!! FDL PREACH!!!

Best answers about this topic, fdl... nice.

Junkster, who thought this might turn into a trollfest

 

Quiet...TROLL!!

 

Hopefully not all.

I know this topic has been discussed here ad nauseam, but why Acura insists on FWD is beyond me. Especially given the "performance" association with VTEC/i-VTEC.

 

FWD is just safer for the general driving public. Oversteer is a lot more difficult to control if the car loses control, but understeer can be corrected by lifting the throttle, which is the first instinct of any inexperienced driver.

Honda is big on safety and the general market that they target with cars like the TSX and TL are usually more family and safety oriented people. For their truly high-performance cars, like the S2000 and NSX, Honda/Acura does go to RWD.

 

FWD is much safer in general conditions for the general public... and that happens to be the larger portion of the market. That's why most companies that sell to the masses all have FWD models as their main sedan.

Junkster, who doesn't mind FWD

 

Holy shit...

I guess great minds do think alike...

 

dang, beat me to it...

Junkster, who's losing a step at his old age

 

I think people give Honda more credit than they deserve. The majority of their cars are fwd so they are "concerned with safety". They have no v8 so they are "a green company". I don't buy it. I think its more of an economical decision than anything. The TSX and TL are both built on the accord platform and that is why they are fwd.

 

Sounds like you guys spend waaaay too much time together.

Unfortunately, I have to disagree with both of you guys. I don't belive the general driving population push their car to its limits ... um ... generally. The only time the drivetrain configuration is thought to make a difference is in bad weather. Well, I've seen plenty of AWD SUVs and WRXs facing the wrong direction in highway medians during snow storms. And I am sure there are a significant number of FWD drivers who have done 180s, if not 360s, in wet/snowy conditions.

Most times, it's the tires but it is always the driver. Perhaps this is why [at least for me] it is more expensive to insure my TSX than a 325i.

Not that BMW drivers are better ... they're just older. :killer:

 

Yeah, I agree with both of you that FWD are safer than RWD in wet/snowy conditions, but FWD being much cheaper to build than RWD probably has more to do with the manufacturers' decision than just the safety issues.

 

well, of course, that has to be factored in as well. Especially in CO, there is a certain advantage to having most of the public drive FWD rather then most driving RWD, especially when there's so many Cali peeps moving here.

Junkster, who also don't like East Coast peeps moving to CO and tryin to take over

 

You nailed right on. A BMW 325 is just as safe and economical as the TSX and even if everything else was equal it would still be more to make simply becasue of the RWD layout.
All of this paper debate on HP, TQ, weight, drivetrain layout will only give a rough idea of actual performance. There's nothing like a "butt dyno" and/or actual street/track numbers to really tell about performance.