Actual HP at the wheels not crankshaft
04-06-2005, 07:07 AM
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Originally Posted by wolverine' date='Apr 5 2005, 04:04 PM
[quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Back in the late eighties manufacturers went from gross to net HP ratings. Look up a 1986 Lamborghini Countach, 0-60 times in Road & Track was 5.2 sec, quarter mile was 13.7 sec and Horsepower was a gross 425. Look at the 2004 545i, in Road & Track 0-60 was 5.3 sec, quater was 13.8 sec and Horsepower is a net 325. I would think the Lambo weighs less and with a hundred more HP it only goes .01 sec faster to both 0-60 and quarter mile. So the Lambo is actually making less net horsepower than its stated gross numbers.
04-06-2005, 08:25 AM
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Originally Posted by pennetta' date='Apr 6 2005, 10:07 AM
[quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Back in the late eighties manufacturers went from gross to net HP ratings. Look up a 1986 Lamborghini Countach, 0-60 times in Road & Track was 5.2 sec, quarter mile was 13.7 sec and Horsepower was a gross 425. Look at the 2004 545i, in Road & Track 0-60 was 5.3 sec, quater was 13.8 sec and Horsepower is a net 325. I would think the Lambo weighs less and with a hundred more HP it only goes .01 sec faster to both 0-60 and quarter mile. So the Lambo is actually making less net horsepower than its stated gross numbers.
[snapback]111944[/snapback]
[/quote]Gross, Net and RWHP are all different.
Gross = engine without anything (alternator/exhaust/cat converters etc)
Net = Engine with the above but measured before tranny/driveshaft loses
RWHP = dyno tested
Obviously Gross>Net>RWHP. I agree that in the late 80s they went from Gross to Net ratings.
Someone correct me if I am wrong. The gross definition could change - ie alternator connected but not water pump but the idea is the same.
04-06-2005, 10:10 AM
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My Ride: 2008 535i: June 6th start build, complete June 17th, at NY Port July 5th, at dealer July 10th, took delivery Friday July 13- Plantimum Bronze/Natural Brown Leather/Light Poplar, Sport Package, Sport Auto, Active Steering, Premium Package, CWP & PDC. Dinan Performance Software 384hp & 421 ft/lbs.
Originally Posted by Guest_300TTto545_*' date='Apr 6 2005, 11:25 AM
[quote name='pennetta' date='Apr 6 2005, 10:07 AM'][quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Back in the late eighties manufacturers went from gross to net HP ratings. Look up a 1986 Lamborghini Countach, 0-60 times in Road & Track was 5.2 sec, quarter mile was 13.7 sec and Horsepower was a gross 425. Look at the 2004 545i, in Road & Track 0-60 was 5.3 sec, quater was 13.8 sec and Horsepower is a net 325. I would think the Lambo weighs less and with a hundred more HP it only goes .01 sec faster to both 0-60 and quarter mile. So the Lambo is actually making less net horsepower than its stated gross numbers.
[snapback]111944[/snapback]
[/quote]Gross, Net and RWHP are all different.
Gross = engine without anything (alternator/exhaust/cat converters etc)
Net = Engine with the above but measured before tranny/driveshaft loses
RWHP = dyno tested
Obviously Gross>Net>RWHP. I agree that in the late 80s they went from Gross to Net ratings.
Someone correct me if I am wrong. The gross definition could change - ie alternator connected but not water pump but the idea is the same.
[snapback]111967[/snapback]
[/quote]Yes you are correct, they now use net hp ratings at the flywheel but with all drive belts and accessories attached. This is in contrast to the older gross HP which excluded water pump and all accessories.
Nice fact about the Lambo though. My friend has an 1986 Countach, I'll go race him.
04-06-2005, 02:27 PM
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Originally Posted by wolverine' date='Apr 6 2005, 05:15 AM
[quote name='Guest' date='Apr 5 2005, 08:19 PM'][quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
[snapback]111690[/snapback]
[/quote]Absolutely - minimizing the rotational inertia of the wheels and tires is one of the most important things in 'tuning' a car for maximum performance. If you have heavy wheels and tires, you will show lower outputs on a rwhp dyno test, and on top of that you have a heavier car! Going to lightweight wheels and tires is probably the best single thing you can do to improve acelleration and overall performance.
[snapback]111723[/snapback]
[/quote]Not really. It's obviously correct that any saving in weight improves acceleration, but, as far as concerning power delivery at the rear wheels, what matters is only (almost) the total losses in the power train. You will be surprised to see how much ponies are lost in much power trains and more so if the car is a 4-wheel drive. And it's correct to say that, compared to most other brands, BMW power trains are, usually, more efficient.
Concerning wheel and tyre weight, the key factor there is to improve the performance of the suspensions: for this reason, it's always highly desirable to keep total weight of "un-suspended masses" as low as possible.
04-06-2005, 05:09 PM
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Originally Posted by Lucky' date='Apr 6 2005, 04:27 PM
[quote name='wolverine' date='Apr 6 2005, 05:15 AM'][quote name='Guest' date='Apr 5 2005, 08:19 PM'][quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
[snapback]111690[/snapback]
[/quote]Absolutely - minimizing the rotational inertia of the wheels and tires is one of the most important things in 'tuning' a car for maximum performance. If you have heavy wheels and tires, you will show lower outputs on a rwhp dyno test, and on top of that you have a heavier car! Going to lightweight wheels and tires is probably the best single thing you can do to improve acelleration and overall performance.
[snapback]111723[/snapback]
[/quote]Not really. It's obviously correct that any saving in weight improves acceleration, but, as far as concerning power delivery at the rear wheels, what matters is only (almost) the total losses in the power train. You will be surprised to see how much ponies are lost in much power trains and more so if the car is a 4-wheel drive. And it's correct to say that, compared to most other brands, BMW power trains are, usually, more efficient.
Concerning wheel and tyre weight, the key factor there is to improve the performance of the suspensions: for this reason, it's always highly desirable to keep total weight of "un-suspended masses" as low as possible.
[snapback]112158[/snapback]
[/quote]Certainly suspension response will be improved with a reduction in unsprung weight, but a reduction in wheel and tire weight does quite a bit more.
You are not only reducing unsprung weight, but you are reducing the rotational inertia of the overall drivetrain. Talk to some of your friends who drag race regularly. They will tell you a reduction in wheel or tire weight has a significant effect in acelleration times. The car's response to the throttle improves as well, since the engine does not need to 'turn' as much weight in the drivetrain. Braking performance improves as well, because there is less rotational inertia. finally, dyno rwhp will increase with a decrease in wheel and tire weight.
Wheel and tire weight reduction is one of the first things you should look at in improving performance.
04-06-2005, 05:16 PM
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Originally Posted by Lucky' date='Apr 6 2005, 04:27 PM
[quote name='wolverine' date='Apr 6 2005, 05:15 AM'][quote name='Guest' date='Apr 5 2005, 08:19 PM'][quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
[snapback]111690[/snapback]
[/quote]Absolutely - minimizing the rotational inertia of the wheels and tires is one of the most important things in 'tuning' a car for maximum performance. If you have heavy wheels and tires, you will show lower outputs on a rwhp dyno test, and on top of that you have a heavier car! Going to lightweight wheels and tires is probably the best single thing you can do to improve acelleration and overall performance.
[snapback]111723[/snapback]
[/quote]Not really. It's obviously correct that any saving in weight improves acceleration, but, as far as concerning power delivery at the rear wheels, what matters is only (almost) the total losses in the power train. You will be surprised to see how much ponies are lost in much power trains and more so if the car is a 4-wheel drive. And it's correct to say that, compared to most other brands, BMW power trains are, usually, more efficient.
Concerning wheel and tyre weight, the key factor there is to improve the performance of the suspensions: for this reason, it's always highly desirable to keep total weight of "un-suspended masses" as low as possible.
[snapback]112158[/snapback]
[/quote]Certainly suspension response will be improved with a reduction in unsprung weight, but a reduction in wheel and tire weight does quite a bit more.
You are not only reducing unsprung weight, but you are reducing the rotational inertia of the overall drivetrain. Talk to some of your friends who drag race regularly. They will tell you a reduction in wheel or tire weight has a significant effect in acelleration times. The car's response to the throttle improves as well, since the engine does not need to 'turn' as much weight in the drivetrain. Braking performance improves as well, because there is less rotational inertia. finally, dyno rwhp will increase with a decrease in wheel and tire weight.
Wheel and tire weight reduction is one of the first things you should look at in improving performance.
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