Torque versus Horsepower question
?
11-20-2008, 07:45 AM
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Originally Posted by geokr1' post='725736' date='Nov 19 2008, 05:37 PM
Can someone explain (in real simple terms) why horsepower and torque aren't exactly related. For example, I was on the E60 engine info page and see that the 550 has 360 hp and 360 ft-lbs torque. The M5 has 500 hp and 383 ft-lbs torque. It seem odd that with 140 more hp that only 23 more ft-lbs of torque are produced in this huge V10 engine. The specs for other engines are all over the map. You would think torque and hp would vary more or less directly. And Part 2 of the question - isn't torque really the final measure of how much power you get to the wheels anyway? Appreciate any answer or references to other posts. Thanks.
In simple terms, The V10 has a shorter stroke than the V8 which is a key factor. And the V10 has more cylinders but they are smaller. so they design the camshafts to make the power up top instead of low to mid range of the rpms
Smaller the stroke of the piston in the cylinder the higher the rev will be, hence the less torque it will make down low, but the camshafts and gearing play a role also. to have the best of both worlds the V10's cylinders would need to have a bigger bore size, but then you have more rotational mass due to the bigger pistons.
Big bore short stroke lots of low end and slight upper max rpm about 6000rpm
medium bore and a little bit longer stroke makes power mid to high rpm 7500
To answer the second part: Torque is a pushing force, to get you 383ftlb torque 4000lb sedan to move you need gearing in trans and rear to push the car form a stop
horsepower is a pulling force, you see it on you tube the people racing from a dig of 40 mph and one car with more horsepower is pulling away.
11-20-2008, 09:43 AM
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so what would be the winner in a hypothetical race between the same cars/weight/driver/etc
1, with 400 BHP..the other with 400 lb/ft torque??
0-60
quarter mile
top speed
obviously its speculation but im curious?
1, with 400 BHP..the other with 400 lb/ft torque??
0-60
quarter mile
top speed
obviously its speculation but im curious?
11-20-2008, 10:52 AM
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So if I'm understanding this correctly, if Dr Dave's diesel (which has much more torque than an M5) was able to rev to 7,500 rpm, then it would generate more BHP than an M5 and naturally be faster than an M5 ?
After having driven things like a 535d and my 545i and thinking that it's hard to tell the difference between them in performance, it's basically because that push-you-in-your-seat feeling is the same up to about 5,000rpm. The difference is that the 545i can continue on up to 6,500 and continue to increase BHP while doing it, but the diesel is forced to change gear and drop down it's torque curve?
This is something that's troubled my tiny little mind for quite a while. Why that massive torque of diesels doesn't translate into better performance figures than petrol engines with substantially less torque.
After having driven things like a 535d and my 545i and thinking that it's hard to tell the difference between them in performance, it's basically because that push-you-in-your-seat feeling is the same up to about 5,000rpm. The difference is that the 545i can continue on up to 6,500 and continue to increase BHP while doing it, but the diesel is forced to change gear and drop down it's torque curve?
This is something that's troubled my tiny little mind for quite a while. Why that massive torque of diesels doesn't translate into better performance figures than petrol engines with substantially less torque.
11-20-2008, 11:07 AM
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Originally Posted by DD_545i' post='726629' date='Nov 20 2008, 11:52 AM
So if I'm understanding this correctly, if Dr Dave's diesel (which has much more torque than an M5) was able to rev to 7,500 rpm, then it would generate more BHP than an M5 and naturally be faster than an M5 ?
After having driven things like a 535d and my 545i and thinking that it's hard to tell the difference between them in performance, it's basically because that push-you-in-your-seat feeling is the same up to about 5,000rpm. The difference is that the 545i can continue on up to 6,500 and continue to increase BHP while doing it, but the diesel is forced to change gear and drop down it's torque curve?
This is something that's troubled my tiny little mind for quite a while. Why that massive torque of diesels doesn't translate into better performance figures than petrol engines with substantially less torque.
After having driven things like a 535d and my 545i and thinking that it's hard to tell the difference between them in performance, it's basically because that push-you-in-your-seat feeling is the same up to about 5,000rpm. The difference is that the 545i can continue on up to 6,500 and continue to increase BHP while doing it, but the diesel is forced to change gear and drop down it's torque curve?
This is something that's troubled my tiny little mind for quite a while. Why that massive torque of diesels doesn't translate into better performance figures than petrol engines with substantially less torque.
The engines components would have to withstand high revs. The steel crank, steel rods and cast this cast that. Its hard for all that metal to withstand high revs. but slow them down and add a turbo,.
because the diesels make all their power down low like 1500rpm, why do you think big rigs have so many gears.
Look at the diesel hitting the states 425ftlb at 1700 rpm 250 horse..its awesome
The reason the performance numbers aren't there is because they don't gear them for performance
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