Drivetrain loss... A percent????

[rudypoochris]

I am in the middle of researching drivetrain loss for my website, and thought I knew what was up... guess not. I didn't think it would be a constant percent... After compairing dyno results from a stock LS2 on an engine dyno vs on a chassis dyno it looks compellingly so. Below are the results. The engine dyno is of unknown make, the chassis dyno was of the fixed inertia type, I believe, but am not positive. Can anyone make sense of this one? I thought since drag is usually proportional to velocity squared that so would power loss... This clearly shows a static percent... hmmm...

 

 

If anyone has engine dyno graphs of common engines could you send them this way?

 

Could the reason for this be explained based off of the way a fixed inertia dyno works in comparison to an engine dyno?

[BobbyZ]

It is true that drag from the air is proportionate to the velocity squared. But drivetrain loss has very little to do with air flow. The loss is all due to kinetic friction, which is not proportionate to the speed at all. This means that as you increase the speed of the engine, the power loss due to friction is going to remain constant.

 

Your plots seem to verify what I am saying. That no matter the engine speed, the drivetrain will absorb a roughly constant power.

[rudypoochris]

I did notice that low speed drag seems to follow a more linear function, but I didn't think gears spinning fluid was low speed.

 

I was also perplexed by the fact that the engine dyno seemed to have proportionally lower resistance until about 4500rpm when the values started becoming the same constant (check hp loss). This might indicate that a certain point all the fluids are flying any way so they don't impart more drag if the speed increases. Just food for thought any way....