Drivetrain Loss Equation

[scooby]

I am doing a math research project and it may be about anything that I want. I decided to do the loss of horsepower throughtout the drivetrain of a rear wheel drive vehicle. Does anyone know like rotating mass to horsepwer loss or any kind of equation for this.

[pgriffith]

I have no idea. I have alwasy thought it was like 20% for auto's and 15% loss for manuals. I have also heard for every pound you take off the crank shaft you get 2.6 horsepower to the wheels. Does that help?

[DominusEtDeusNatus]

Force required to rotate mass. Look for equation for that. I'll move this lounge since this is a science question now.

[DominusEtDeusNatus]

I just noticed this was moved from here. I though it was more of a physics question so I moved it here. This got ping ponged around. Your serve [img]smile.gif[/img]


I forgot all my physics from HS. Someone probably knows.

[Backfire]

If you are looking for quantative data, that will be pretty difficult! You will have frictional losses in the trans, rolling resistance of the tires, rotating masses, etc. And as far as the rotating assembly "consuming" power, that is tough. You have a rotating mass, not just a linear motion. I think you would need some geometry to determine moments of inertia to find the force needed to accelerate the parts. You might be able to do the driveshaft with its simple shape, but you will need to do a lot of estimating to get a actual number for the system.

I did some lab work on an engine dyno last year to figure out maximum vehicle speed. It was based on engine power output vs road load. Road load estimates included all forces acting against the vehicle motion. We were told to slap in a simple percentage to account for drivetrain losses; we were to use 98% :eek: .I would like to see that drivetrain :D . Gotta love cookie cutter labs(even at the college level). I would guess an accurate number would require dyno work rather than hand calculations; both engine and chassis dynos that is.

If you can still change, and would like to do something with cars, I would say look at aerodynamic drag forces rather than drivetrain losses. The measurements you need, such as coefficient of drag and frontal area are available for some cars (like the vette!!). You could find actual numbers for the resistance and figure out an estimate for max speed or something like that. Much easier IMHO :D

[ May 14, 2002: Message edited by: Backfire ]</p>

[scooby]

I was thinking more specifically of rotating mass. I always heard it was like for every 10lbs of rotating mass adds 100 lbs to the car. The actual project name is Horsepower loss throughout the drivetrain. Im not looking for an exact science but simply rotating mass. Any help would be appreciated.

[Mcaanda]

lol...back to drive train....
ping....
pong...lol
[img]graemlins/toto.gif[/img]

[Backfire]

I have seen calculations that disprove that 10lbs =100lbs approach. It isn't just the weight, its where it's located. There isn't an end all XXlbs or rotating weight = XXXlbs of static weight. It's not that simple. If you add lighter wheels, but alot of its weight falls towards the outside of the wheel, they could actually be harder to spin up than the originals. If you want to simplify it and say the parts are geometrically identical, you could probably show how the weight changes things.

Without looking everything up, and doing the project myself, I can't give you any actual equations. But I would guess you need to find the mass and moment of inertia for the parts. From there you could determine the force/torque and power needed to accelarate the parts.

[scooby]

I have been searching ever where since this was originaly posted and I have found a few sites that claim for RWD cars its anywhere from 15-20% loss in the drivetrain. Does this sound correct? My teacher knows nothing about cars and i know he won't check it so as long as im close then it won't matter all that much.

[Night Rider]

If we assume GM is accurate in rating the 3.8L engine w/ 200 hp stock, and from what i've read most stock 3.8's dyno around the 150-160 rwhp range, we can estimate 155 as the average rwhp, which gives us about a 23% drivetrain loss.

I'm not a physics expert by no means, but i've heard 3.8 autos have about a 22% loss while manuals have a 20% loss.

Now i was reading on the corvette forum that most ls1's rated at 350 hp from the factory usually dyno right around 300-305 rwhp. This would give the C5 a mesely 14% drivetrain loss, WTH??? Why so little, but sooo much for us??? :mad: I guess, lighter mass, better gearing, more efficient tranny, etc.

[Patrick Javert]

there's a lot to consider. first, you have all the accessories run off the crank, then the windage from the wet-sump oil system, next the friction from the piston rings, then the weight of the pistons, rods, wrist-pins, and crank, as well as the aerodynamics of the crank inside the oil pan. next, you have the flywheel,torque converter, and transmission losses, next the driveshaft, yolks, rear gears, differential, and axles, and lastly, the wheels and tires. all of this must be taken into consideration when figuring hp transmission to the wheels.