Dyno question
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Originally Posted by Incubus,May 6 2005, 12:36 PM
You'd have to look at how Honda originally arrived at their figure. Then, think about 17%...it sounds like a big percentage for drivetrain loss (but I could be wrong).
Barrett.
Barrett.
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The original question was xx% loss from CRANK to wheels.
If you had an engine on a stand and measured HP at the crankshaft, then modified it and rerun that test you would get an increase in horsepower which would include only internal friction losses in both cases. What the increase in internal engine friction caused by the mods is a good question. Another question is did the mods change the RPM at which the max HP was obtained.
Now supposing you dyno the same engine at the rear wheels before and after mods. I think the drive train losses(tranny, diff, shafts, rear wheel bearings, rear tires) would be roughly the same for both of these tests and would not be directly proportional to the HP difference. I am assuming that the drive train components are designed so that the increased HP is not deforming them out of spec and the drive train is turning the same RPM in both tests.
I suspect the real world situation is that only engine builders know what the internal friction effects of engine mods are. To most people it's not important because there isn't much you can do about it.
So install your mod, dyno it before and after and assume that your drive train is eating about the same power and that the increase in power is the net of some unknown change in internal friction.
If you had an engine on a stand and measured HP at the crankshaft, then modified it and rerun that test you would get an increase in horsepower which would include only internal friction losses in both cases. What the increase in internal engine friction caused by the mods is a good question. Another question is did the mods change the RPM at which the max HP was obtained.
Now supposing you dyno the same engine at the rear wheels before and after mods. I think the drive train losses(tranny, diff, shafts, rear wheel bearings, rear tires) would be roughly the same for both of these tests and would not be directly proportional to the HP difference. I am assuming that the drive train components are designed so that the increased HP is not deforming them out of spec and the drive train is turning the same RPM in both tests.
I suspect the real world situation is that only engine builders know what the internal friction effects of engine mods are. To most people it's not important because there isn't much you can do about it.
So install your mod, dyno it before and after and assume that your drive train is eating about the same power and that the increase in power is the net of some unknown change in internal friction.
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Originally Posted by i_heart_my_DB8,May 6 2005, 01:19 PM
That's what I said! I think the HP would be lost in generating the same amount of friction, but only faster.
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From: Bellingham, WA
Originally Posted by mr.B,May 6 2005, 09:40 AM
The faster you rub your hands togather the more friction that motion creates. I am just trying to come up with a good analogy
You run the drivetrain through the same speed range unmodified and modified, but the load on the gears, bearings, etc is increased in proportion to the horsepower increase. The friction and the power loss will also increase in the same proportion. Roughly speaking.
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