Horsepower versus torque

[Mize]

Diesels produce more low end torque, period. That's why all heavy hauling and moving is done with diesels. Until turbo and TDI they've tended to have crappy torque at higher rpms though so they really didn't accelerate all that well unless you have a six speed manual and quick reflexes and, even then, most gasoline cars could trounce them by winding out each gear (as gas engines tend to have upward torque curves).

They're aren't too many diesels of any variety that can hang with the likes of a normally aspirated V8/V10 cranking out 450 bhp and 600 ft lbs and winding the revs over 5k.

 

[WhiningKhan]

Turbocharged gasoline engines typically do not compare to turbocharged diesels, not even close in fact. Particulary not at low RPMs, as many gas engines hit max torque above 4000RPM. Most people rarely revv their engines that high, ever.

You are getting confused about gasoline turbos and normally aspirated gasoline engines here. The max torque of typical gas turbo comes at around or under 2000 RPMs nowadays.

Right?

Unfortunately, diesel fumes are full of that microscopic particle crap that clogs up our lungs, so they're not ideal from every aspect either...

That's last century, nowadays it can be handled with particle traps.

 

[KimB]

In response to the original post:
Yes, it is somewhat of a travesty that torque isn't advertised instead of horsepower. After all, with a well-designed gearing system you can operate at high speeds with a high low-end torque just fine. You just have to have the gearing set so that your engine runs at lower RPM's even at higher speeds.

Advertising the horsepower unfairly gives an advantage to engines that have just a little bit more torque at higher RPM's. Of course, this sort of engine does have the advantage that to give the same sort of feel of power to the driver, you don't need as many gears for it to provide a smooth ride.

 

[Mize]

In response to the original post:
Yes, it is somewhat of a travesty that torque isn't advertised instead of horsepower. After all, with a well-designed gearing system you can operate at high speeds with a high low-end torque just fine. You just have to have the gearing set so that your engine runs at lower RPM's even at higher speeds.

Advertising the horsepower unfairly gives an advantage to engines that have just a little bit more torque at higher RPM's. Of course, this sort of engine does have the advantage that to give the same sort of feel of power to the driver, you don't need as many gears for it to provide a smooth ride.

Hmmm...low rev diesel speedster using a CVT? Good idea!

 

[Neeyik]

Pah, you car drivers. We bikers get HP and torque figures all the time...

 

[Mize]

Pah, you car drivers. We bikers get HP and torque figures all the time...

Ah yes, but you tend to leave entrails on the road making it more slippery...hence AWD on my car

 

[nelg]

Diesels produce more low end torque, period. That's why all heavy hauling and moving is done with diesels.

That and the ability to work off of engine knock.

 

[Frank]

And, when the gasoline distribution fails, you can still power your electric car from a wall socket, or your diesel one from whatever oil or liquid fat you can find lying around.

 

[KimB]

Gasoline distribution won't fail, not for a long time yet. Sure, it'll become more expensive, but as long as people are still willing to pay, there will be gas stations selling it all over.

 

[Snyder]

From the Tesla car (assuming equal power, which isn't specified, but looks on target):

Well, since Power is rotational speed x torque, AFAICS according to this image there's no way both engines have the same power, at any rot. speed.

 

[KimB]

Well, since Power is rotational speed x torque, AFAICS according to this image there's no way both engines have the same power, at any rot. speed.

Of course. They're probably attempting to give a comparison that relates to the extreme fuel economy of the car. They do mention, after all, that it's just a 4-cylinder high performance engine they're talking about.

 

[Frank]

Yes, I was assuming input power.

 

[Guden Oden]

You are getting confused about gasoline turbos and normally aspirated gasoline engines here. The max torque of typical gas turbo comes at around or under 2000 RPMs nowadays.

Um, that's a Saab you're linking to. Not really a typical example of a turbocharged gas engine I'd say. In fact I'd be amazed if even half of today's turbocharged gas engines have torque peaks at 2000RPMs, and much less below.

Turbos are generally reserved for high-performance (and hence, high-revving) engines with most car makers. Saab works rather different compared to pretty much every other company out there when it comes to engine philosophy.

That's last century, nowadays it can be handled with particle traps.

These filters don't catch the smallest particles, which incidentally are also the most dangerous. Some are so tiny they pass through cell membranes and go out straight into the bloodstream. Sounds quite unappealing to me. I don't see how any filter's going to catch those...

 

[Mize]

I don't see how any filter's going to catch those...

No problem then as the lungs/kidneys are just filters

 

[MPI]

Um, that's a Saab you're linking to. Not really a typical example of a turbocharged gas engine I'd say. In fact I'd be amazed if even half of today's turbocharged gas engines have torque peaks at 2000RPMs, and much less below.

Turbos are generally reserved for high-performance (and hence, high-revving) engines with most car makers. Saab works rather different compared to pretty much every other company out there when it comes to engine philosophy.

Um, no. Firstly, most low-pressure turbo engines(Volvo 2.0T, VW1.8T, et.c.) are tuned to a flat torque curve, with the plateu kicking in about at 2000 rpms or so.

Secondly, with turbocharging you don't necessarily have to have high-revving as a requisite for high performance. For instance, the WRC engines(2.0L) with ~300-320hp have an ENORMOUS amount of low-end torque, in the order of 600Nm@4000rpm, with the top end petering out at 6000 or so.

Now that has much to do with a particularity in the regulations(34mm intake restrictor), but the point is that turbocharging is inherently suited to boosting the low end of the powerband, because there's were the largest gains are to be had. In the top-end the limitations are often thermal in nature -too much energy in too little space- whereas in the low-end the limitations are mainly getting as much fuel-air mixture in as possible. Which, of course, is where a naturally aspirated engine is inherently limited.

 

[scooby_dooby]

To explain a bit better what I mean: here in Europe the horsepower figure has become almost meaningless. Like, if you buy a new BMW or Mercedes, you might see a 3 liter V6 gasoline engine with 250 hp, next to a 2.5 liter turbo-charged diesel engine with only 180 hp. While the gasoline engine only has 230 Nm of torque at 6000 rpm and the diesel engine has 400 Nm at 2300 rpm.

Which one would the consumer buy, looking at the spec sheet? Which might only state the amount of horsepower. Or they might not know the relevance of torque, as most people don't.

The problem is Torque is irrelevent without the proper context, without knowing what RPM it occurs at, you have absolutely no idea how much power it actually produces. It's truly a meaningless number.

While HP can be misleading, it's still much more meaningful than Torque as it provides a good indication of the power of the vehicle. Something a torque number can not do on it's own.

Of course, as a consumer what you really want is 0-60 times, 1/8mile, 1/4mile, those are the true indicators of performance, which is a combination of weight, peak horsepower and torque/powerband. There's N/A Honda's out there with 155ft-lbs of torque that run 9 second 1/4 miles. Of course these are professionals, but it show how important weight and powerband truly are. Try telling those guys that HP does not accelerate cars. They'll show you an 11,000 rpm redline, and a powerband starting at 9000rpms.

No, torque is about accelerating, horsepower is about maximum power.

While this is true, it is not the PEAK torque that determines acceleration, but torque at any given RPM (also known as horsepower).

The true measure of power is the average horsepower under the entire powerband, this takes torque into account as well as RPM's, as well as gearing. By powerband I mean the 2000-2500rpm range where you would be making the most horsepower, of course the powerband for each car is highly dependant on it's transmission.

 

[Moloch]

that old saying- horsepower sells car, torque win's races couldn't be further than the truth.
Torque's good for pulling you off the line, but if say you make 500 foot pounds of torque at 2000 rpm (diesel perhaps) but it goes down to 200 by 4500 rpm you're only making 171 horsepower, that would be good for a big truck that needs the low end torque (and hence low end horsepower) for moving it from a stop but for a sports car it would only be good for breaking drivetrains and doing burnouts
All things equal, a car with 200 foot pounds torque at 8000 rpm will be faster than the above example, but of course would get off the line slower but once it get's goin look out
If you truely believe that torque is all that matters, I challenge you to explain why a honda S2000 with 159 pound feet of torque manages to do a quarter mile in the mid 14s
A perhaps easier comparison is to compare the different models of acura integra's since they all use 1.8 liter engines, just the higher end versions use vtec to make more horsepower... and they are quite a bit faster than the lower end version with similar torque.
That brings me to my next point- gearing.
A honda may make, say 140 foot pounds at the engine, but once it gets though gearing ( and to the wheels), it will make a helluva lot more, prolly in the realm of 1400 pound feet depending on gear.
A bigger engine may make more torque, but a smaller engine can act like a bigger engine by having numerically higher gearing.. mechanical advantage
Just has to shift more than the bigger engine :smile:

In the end, it's all down to what you perfer- a small high reving engine, or a big engine that makes more torque above idle than a small one does period.
Ok that's about all you'll get from me.
Oh and you can't increase torque without increasing horsepower and vice versa

 

[scooby_dooby]

A honda may make, say 140 foot pounds at the engine, but once it gets though gearing ( and to the wheels), it will make a helluva lot more, prolly in the realm of 1400 pound feet depending on gear.

Yup. Gear ratio x Final Drive x TQ, so a 1.8 litre Integra makes 3.16x4.4x120 = 1671ft-lbs in first gear.

People totally underestimate the impact of gearing.

 

[Blitzkrieg]

I dont know squat, just asking. How do rotaries compare to normal v4s, v6s, diesels etc?

 

[WhiningKhan]

Um, that's a Saab you're linking to. Not really a typical example of a turbocharged gas engine I'd say. In fact I'd be amazed if even half of today's turbocharged gas engines have torque peaks at 2000RPMs, and much less below.

Turbos are generally reserved for high-performance (and hence, high-revving) engines with most car makers. Saab works rather different compared to pretty much every other company out there when it comes to engine philosophy.

No no no. MPI already posted what I would have answered, I won't repeat it here.

I picked Saab on purpose since I thought you'd be familiar enough with it... No offense to your national pride - Saab did revolutionize the use of turbochargers in mainstream gasoline engines, but that was 20 years ago. No-one can stay unique in automotive business for long, others have adopted the same ideas long time ago.

These filters don't catch the smallest particles, which incidentally are also the most dangerous. Some are so tiny they pass through cell membranes and go out straight into the bloodstream. Sounds quite unappealing to me. I don't see how any filter's going to catch those...

Why not? The smaller the particle, the faster it evaporates when you burn it.

I'm not too convinced that you could have invented the now-standard catalytic converters, either... Luckily, there are other people thinking about these things.