Dyno results and DriveLine Mass
03-10-2005, 10:42 AM
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Dyno results and DriveLine Mass If one were to significatly reduce the mass of the drive line ahead of the differencial, would that provide more reported HP on the Dyno?
weight reduction would be from a Carbon Fiber driveshaft and Dia., Al Flywheel, clutch etc.
weight reduction would be from a Carbon Fiber driveshaft and Dia., Al Flywheel, clutch etc.
03-11-2005, 04:03 PM
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Originally Posted by CTSmechanic
10 percent would be pretty drastic ...
Then 20lbs with a 2 inch center of mass radius at 6000rpm is about 10% of the Dynojet momentum, with a 2700LBs roller at 22 inch radius and say 40rpm. Hope I got that right.
The Dynojet measures acceleration to predict power, which is accurate only if the total rotating mass is known.
My point here is that if 10% or more power can be had by changing the rotating mass of the driveline, one could sell a lot of meaningless boltons along with a driveline weight loss program.
At the track there would be less benefit as the real mass is that of the car which is more plus substantial wind resistance (effectively more mass).
I was hoping that someone had looked at this and could add some insight.
03-11-2005, 04:10 PM
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Basically you are saying a 450 rwhp car with a big steel flywheel and driveshaft will need to make more flywheel power than a 450 rwhp all aluminum driveline car.
But in turn, if you try to calculate the fly whp from the rwhp, one of the cars reading will not be as close to accurate.
But in turn, if you try to calculate the fly whp from the rwhp, one of the cars reading will not be as close to accurate.
03-11-2005, 06:57 PM
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Originally Posted by Derek98z
Basically you are saying a 450 rwhp car with a big steel flywheel and driveshaft will need to make more flywheel power than a 450 rwhp all aluminum driveline car.
But in turn, if you try to calculate the fly whp from the rwhp, one of the cars reading will not be as close to accurate.
But in turn, if you try to calculate the fly whp from the rwhp, one of the cars reading will not be as close to accurate.
And
kinda, the power measured by the dynojet is relative and accurate based on its mass. But on the road were the apparant vehicle mass will be something like 50% greater, the significance of the drive line mass is less. Lets call it the DynoQueen Effect. For example a 10% gain on the dyno from driveline weight loss may only be a 2.5% gain on the road (just a guess)
I could prove it by comparing time from 4000 to 6000rpm in third gear on the dyno vs on the road, but Ive never gone that fast (170mph). But the road test should be about 4 times longer.
But again I could be wrong.
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03-11-2005, 07:58 PM
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Originally Posted by billc5
Yes, a heavier drive line needs more power at the wheels. It is a function of acceleration, the less the acceleration the less the effect of the driveline mass.
And
kinda, the power measured by the dynojet is relative and accurate based on its mass. But on the road were the apparant vehicle mass will be something like 50% greater, the significance of the drive line mass is less. Lets call it the DynoQueen Effect. For example a 10% gain on the dyno from driveline weight loss may only be a 2.5% gain on the road (just a guess)
I could prove it by comparing time from 4000 to 6000rpm in third gear on the dyno vs on the road, but Ive never gone that fast (170mph). But the road test should be about 4 times longer.
But again I could be wrong.
And
kinda, the power measured by the dynojet is relative and accurate based on its mass. But on the road were the apparant vehicle mass will be something like 50% greater, the significance of the drive line mass is less. Lets call it the DynoQueen Effect. For example a 10% gain on the dyno from driveline weight loss may only be a 2.5% gain on the road (just a guess)
I could prove it by comparing time from 4000 to 6000rpm in third gear on the dyno vs on the road, but Ive never gone that fast (170mph). But the road test should be about 4 times longer.
But again I could be wrong.
(Doh... well for us M6s anyway)I dunno what yer looking for exactly, but I've got an aluminum flywheel and lightweight pressure plate (~15 lbs total weight savings) and I didn't see a 10% increase on my dyno. 397 before flywheel, 404 after flywheel, PP and taking off cats. Here the power seems to have come all from the cat removal. The car does rev quicker on the street though and I can hang dead even with 420 hp cars (whereas I could not before). I noticed this same result when I did my ASP pulley. 338 without pulley, 341 w/ pulley, LS6 intake and ported TB added (3-4 degrees KR too so let's say 345ish without the timing pull) I think all the power there came from the intake.
I don't know how much hp is netted from reducing rotating mass, but acceleration is certainly improved so it's effectively "like" a horsepower gain
03-15-2005, 10:34 PM
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The only way you would gain 10% from driveline weight reduction is if the reflected inertia of the driveline was at least 10% of the dyno drum, which it's not.
There are three things wrong with your example. The first is that you only took into account the weight change of the drivetrain, and left out the weight of the drivetrain itself. The inertia reduction has to be ten percent of the roller inertia + drivetrain inertia, not just the roller inertia itself. The second thing is i don't think your numbers are realistic. I know you meant 400 rpm, not 40 rpm, but for that to happen you'd either have to have a real big roller or a real high differential ratio (4.10's, 26" tires, and an 8 foot diameter roller for example). If you had an 8 ft diameter roller, I don't think the center of mass as you call it would only be 22 inches. The third thing wrong with your example is it doesn't take driveline friction into account. In reality you'd have to have reduce the reflected inertia of the drivetrain by more than 10% of the roller inertia to see a 10% gain, because friction is a large part of the drivetrain loss.
I hope you don't think i'm trying to slam you, I like the technical approach you're taking. Just needs to be tweaked.
Originally Posted by billc5
If we could lose 20LBs in the drivelive from the flywheel and driveshaft and clutch,
Then 20lbs with a 2 inch center of mass radius at 6000rpm is about 10% of the Dynojet momentum, with a 2700LBs roller at 22 inch radius and say 40rpm. Hope I got that right.
Then 20lbs with a 2 inch center of mass radius at 6000rpm is about 10% of the Dynojet momentum, with a 2700LBs roller at 22 inch radius and say 40rpm. Hope I got that right.
I hope you don't think i'm trying to slam you, I like the technical approach you're taking. Just needs to be tweaked.
