Horsepower versus torque

[KimB]

Well, I know that there are some gasoline engine cars that run at very low RPM's at highway speeds, but most of those that I've driven have had rather large engines, in addition to being rather heavy, and as such have gotten really poor mileage in town.

The economy cars that I've driven, such as my current 1.6L 4 valves/cyl Chevy Aveo have run at rather high RPM's on the highway, in the highest gear. Unfortunately, I haven't driven many mid-range cars in the 2-2.5L range.

 

[_xxx_]

It's not about the driver in this instance. It's about how the car is geared coming out of the factory. Cars with smaller engines are typically geared to run at rather high RPM's in the highest gear at freeway speeds. This is, of course, done to make the car feel responsive. You'd get the same feeling with a higher gearing in a diesel.

You wouldn't, since the torque falls dramatically with increasing rpm. Diesels are best at 2000-3000 rpm.

 

[KimB]

You wouldn't, since the torque falls dramatically with increasing rpm. Diesels are best at 2000-3000 rpm.

Which is why you'd gear it higher.

 

[chavvdarrr]

Which Lada would that be exactly, you do realise that we are talking about mph and not kmh?

ok, 0.00417 hours , who will discuss in MpH ?! Ever heard of SI ?
[off] gets popcorn and starts reading new posts in the topic [/off]

 

[_xxx_]

Which is why you'd gear it higher.

Oh, I got you wrong there.

 

[_xxx_]

ok, 0.00417 hours , who will discuss in MpH ?! Ever heard of SI ?
[off] gets popcorn and starts reading new posts in the topic [/off]

But then it should be m/s, heh?

km/h is just as wrong as mph... and what's hp again? How about kW?

 

[scooby_dooby]

Sure, if you floor it and drop the clutch at 7500rpm's.

Well, doing a normal launch at 2000rpm's might add a whole 0.5 off your 60ft times, still doesn't support this myth that torque is necessary for acceleration off the line. Gearing can make all the difference.

 

[Moloch]

Which is why you'd gear it higher.

...Which in effect makes diesels lose a bit of their torque advantage.

 

[KimB]

...Which in effect makes diesels lose a bit of their torque advantage.

But gives them better fuel economy.

 

[Moloch]

But gives them better fuel economy.

Indeed, as far as hybrids vs TDI (screw non FI diesels) I'm all for TDI since you get way more power and still get comparable or better gas milage.

 

[dizietsma]

There's more to driving than power and torque. I drive a V8 and that has power and troque but also has a lovely sound when you are pootling along which turns to a snarl as you rev it out.

You will not get that in a diesel.

 

[KimB]

There are people that remove their mufflers for the same basic effect. I never understood it myself.

 

[_xxx_]

There's more to driving than power and torque. I drive a V8 and that has power and troque but also has a lovely sound when you are pootling along which turns to a snarl as you rev it out.

You will not get that in a diesel.

In a V8 diesel from Mercedes or Audi (both 4.2l displacement), you will.

 

[ShootMyMonkey]

There are people that remove their mufflers for the same basic effect. I never understood it myself.

It's fairly well known that American manufacturers (in their big V8-carrying cars) make an effort to design mufflers and resonators around a goal of producing "appealing exhaust notes." In general, getting a throaty bellowing sound has the psychological effect of making the engine feel stronger and more powerful.

AFAIK, removing cats and mufflers is done by many but more than a little bit illegal in most states as it will often push you above the noise limits, and you'll probably also fail emissions tests (particularly if the cat is removed).

 

[Dooby]

I prefer the rumble of a diesel engine to the high pitched chatter of a petrol engine any day. Diesel engines are leaps and bounds beyond what they used to be.

A 2.2lt diesel (138bhp 0-62mpg ~8sec) is compareable to a 2lt petrol (195bhp ~ 7sec) in terms of acceleration now, but can also do 70mpg compared to 30mpg. I'd even put forward that diesels are cleaner than petrols too. Particulates are next to gone, and they give out much less CO2. And they can carry MUCH more weight (ie, peoples) before the performance takes a hit. Id like to see a petrol car with four people in still be as nippy as a similar spec'd diesel.

AND diesel can be made from renewable sources (although not as potent), so if we run out of oil tomorrow, theres still a chance that diesel cars will keep going. Diesel engines also last longer, inpart due to the lower RPM, its why they are used as farm/hard labour vehicles - they just dont quit.

 

[KimB]

A 2.2lt diesel (138bhp 0-62mpg ~8sec) is compareable to a 2lt petrol (195bhp ~ 7sec) in terms of acceleration now, but can also do 70mpg compared to 30mpg.

I don't buy that at all. I've never seen any data that suggested anywhere close to a doubling of mileage in going diesel. The difference is closer to 20%.

I'd even put forward that diesels are cleaner than petrols too. Particulates are next to gone, and they give out much less CO2.

They may be cleaner today (though I'm not convinced of this). But they only give out less CO2 because of the lowered mileage. They give out more CO2 per gallon of fuel used.

And they can carry MUCH more weight (ie, peoples) before the performance takes a hit. Id like to see a petrol car with four people in still be as nippy as a similar spec'd diesel.

I doubt it. Carry weight is a function of power, and if you want the fuel economy improvement, you're going to want a diesel of about the same amount of power. Sure, the low-end torque may make the diesel feel a little bit more snappy off the line when loaded, but won't provide any driveability benefit once you get past first gear.

AND diesel can be made from renewable sources (although not as potent), so if we run out of oil tomorrow, theres still a chance that diesel cars will keep going. Diesel engines also last longer, inpart due to the lower RPM, its why they are used as farm/hard labour vehicles - they just dont quit.

I don't buy that diesel engines last longer. Gasoline engines basically never go out unless the owner doesn't perform basic maintenance (like changing the oil).

 

[mkillio]

Without reading the entire thread. I just want to see torque hp curves in car magazines. It's great to have a lot of hp at a high rpm but if it's really low at lower rpm's then it doesn't mean much to me.

 

[Moloch]

Without reading the entire thread. I just want to see torque hp curves in car magazines. It's great to have a lot of hp at a high rpm but if it's really low at lower rpm's then it doesn't mean much to me.

Just stick to turbocharged 4 bangers or 6 bangers and above

 

[DuckThor Evil]

A 2.2lt diesel (138bhp 0-62mpg ~8sec)

Umm which car is that?

 

[Frank]

Ok. So, do we all agree, that:

- Total hp is the best checkmark figure for overall power.
- The torque curve determines the handling of the car.
- The gearbox ratio and weight of the car are very important in determining acceleration.
- High torque at low rpm makes a car feel much more responsive.
- Turbocharged engines have better performance than naturally aspirated ones.
- A comparable diesel engine saves you up to 50% in fuel costs.
- For all-out performance, you want a turbocharged gasoline engine that revs to 10,000+ rpm.
- For responsive driving you want a V8 gasoline or turbo-diesel engine.
- For cheap and responsive driving you want a turbo-diesel engine.

And:

- Great engineering and handling (suspension, steering, gearbox, brakes, tyres and all) make a car perform much better than one that has a better engine but lacks in those.