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Coast Down losses calculation

36 Posts
4 Users
Posts: 244

I still have photos i sent you ago long time when was calculating MOI.

MOI calculation

Thats what i meant before when whp lines was more different than actual ones.

whp vs hp lines


Posted : 11/08/2019 7:47 pm
Posts: 1383
Member Admin

Yeah, I had forgotten. 

I will bring back those whp/wtorque dashed lines.

Posted : 11/08/2019 8:46 pm
Walter reacted
Posts: 350

Walter please don't take this "l Powertrain Losses " forum discussion as a personal attack that is not my intention.

Problem is we have way to many parameter variations to make a unbiased judgement on what engine (BHp) power produced actaully gets back to the axle flanges/wheel&tyres!

But ! 3'to''4% drivetrain losses is definitely not a realistic number.

As stated by Justine the MOI for every engine/chassis/hub_dyamometer tested engine/vehicle combination is significantly different therefore the powertrain losses amongst other factors cause a different % loss.

I don't care if down the road JoeBlow's dyno figures are higher or lower than mine. Im just interested in making the correct adjustments to the engine/vehicle I'm working on.

Amongst us all here in this forum who has a chassis/hub_dyamometer environmentally control test cell that can monitor many other parameters to workout losses. I certainly don't. Heat is a power loss absorber, I'm certian you are aware.

Anyway keep dyno'ing 

Posted : 12/08/2019 2:08 am
Posts: 244

that car particullary was 4%, normally for FWD cars 6-10%. 

Yes, as said, heat could add some extra losses to bearings, etc, but i'd say it's more on acceleration than desacelerating. anyway i think the percentage that add more losses is definitely not too noticable..

Correct, at the end, dyno is a tool for make the best tune for a car.

Posted : 12/08/2019 8:21 am
Posts: 61
Topic starter

Attached is a plot of a fairly low power car.  Inertia was calculated for this car using sweep up and down and comes out at 3.3.


Two runs, one in 4th the other in 5th gear.  As you can see, the wheel results are hugely different.  The flywheels figures are closer but 4th gear is lower than 5th.  My theory is that there is less tractive effort in 5th, indeed the tires run cooler and so the "loaded" loss is less.



Posted : 13/08/2019 3:35 pm
Posts: 61
Topic starter

And here is a 4wd car - over 130bhp of losses.



Posted : 15/08/2019 3:00 pm
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