Dyno numbers
11-30-2001, 02:34 PM
#1
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Join Date: Jul 2001
Posts: 45
Dyno numbers
Hey guys,
In reference to Soundmike's dyno post, is the loss from published hp to wheel hp just parasitic (accessories and drivetrain?)
I can understand why you'd want to run a 1:1 ratio, but don't understand why there's roughly a 55hp loss from crank to wheel.
In reference to Soundmike's dyno post, is the loss from published hp to wheel hp just parasitic (accessories and drivetrain?)
I can understand why you'd want to run a 1:1 ratio, but don't understand why there's roughly a 55hp loss from crank to wheel.
11-30-2001, 02:48 PM
#2
Dyno plot says I have the most area under the Administrator curve
Join Date: Jul 2001
Posts: 7,060
yep, parasitic losses.
The transmission itself, the axles, shafts, wheels, tires, engine accessories (alternator, water pump, etc..) all require energy to spin, and no transmission of power is 100% efficient so there are always going to be losses from the engine's crank power output to what finally gets to the wheels.
Figure about 22.5% average loss for automatic transmissions.
Figure about 15.0% average loss for manual transmissions.
The only way to get 100% of the engine's crank power to the wheels would be to hook up the wheel right to the crank, but you'd have a helluva time mounting the engine like that, and you'd have no transmission
I think manufacturers rate the engine's crank horsepower and torque output with engine accessories running though, because you sorta don't have an engine w/o an alternator or water pump, etc...LOL
The transmission itself, the axles, shafts, wheels, tires, engine accessories (alternator, water pump, etc..) all require energy to spin, and no transmission of power is 100% efficient so there are always going to be losses from the engine's crank power output to what finally gets to the wheels.
Figure about 22.5% average loss for automatic transmissions.
Figure about 15.0% average loss for manual transmissions.
The only way to get 100% of the engine's crank power to the wheels would be to hook up the wheel right to the crank, but you'd have a helluva time mounting the engine like that, and you'd have no transmission
I think manufacturers rate the engine's crank horsepower and torque output with engine accessories running though, because you sorta don't have an engine w/o an alternator or water pump, etc...LOL
11-30-2001, 04:39 PM
#4
I think back in the old days engines were rated at the crank without any accessories... but I guess back then you really didn't have too many accessories to begin with... Now engines are rated at the crank with the accessories hooked up since they are an integral part of the engine.
Now engines are rated at the crank with the accessories hooked up since they are an integral part of the engine.
11-30-2001, 09:02 PM
#5
If i'm not mistaken, i think the current generation sports cars (Lamborghini's and the like) are advertised with the HP to the wheels and not the crank.
Originally posted by sllloyd
Wouldn't it be nice if the manufacturers would publish figures for wheel hp for autos and manuals (Given a full accessory load out?)
Wouldn't it be nice if the manufacturers would publish figures for wheel hp for autos and manuals (Given a full accessory load out?)
12-01-2001, 07:28 PM
#6
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Join Date: Oct 2000
Posts: 244
Originally posted by soundmike
If i'm not mistaken, i think the current generation sports cars (Lamborghini's and the like) are advertised with the HP to the wheels and not the crank.
If i'm not mistaken, i think the current generation sports cars (Lamborghini's and the like) are advertised with the HP to the wheels and not the crank.
On any car made before 1974, the HP was rated with no accessories. Just like an engine dyno would. After 74, HP was rated with all accessories included. All cars sold in the US are rated like this. However, It should be noted that some companies purposely underrate the HP figures on their vehicles, for example all Japanese cars are limited to 276 HP in japan, even though the Skyline has 300+.
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