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Coast Down losses calculation

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 Dev
(@dev)
Posts: 61
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Topic starter
 

Does anyone have any data as to how power output effects losses?  Currently the losses are related to roller speed only.  While it's impossible to do a true calculation, it would be good to have some kind of power based factor to improve the accuracy.

 

Thanks.

 
Posted : 07/08/2019 10:52 pm
(@walter)
Posts: 244
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you have to calculate MOI of your dyno, once you do, you can read correctly coasting losses then you get WHP and HP.

 
Posted : 08/08/2019 11:30 am
 Dev
(@dev)
Posts: 61
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Topic starter
 

You misunderstand me,

Currently the calculation is ONLY related to roller speed and not the power output.  As power output increases, so does the loss.

 
Posted : 08/08/2019 11:35 am
(@walter)
Posts: 244
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still no get it , sorry! if you know drivetrain losses calculated of your dyno, once you read drivetrain looses with the car, you can know percentage of drivetain losses have the car, then make the calculation, does it?

 
Posted : 08/08/2019 11:44 am
 Dev
(@dev)
Posts: 61
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Topic starter
 

No 🙂

Try it yourself - run a car standard, then run a car once it is tuned with more power.

You will see the drive train loss is identical - the percentage drive train loss actually drops.

 

 

 
Posted : 08/08/2019 11:55 am
(@walter)
Posts: 244
Member
 

why should it increase? have similar conversation some days ago.. i means, theorically, more power, more friction, heat,etc, but how does really affect more power in the real life? i means, you have same gearbox, same shafts, clutch, these parts have X inertial/drivetrain losses, no matter how much power you Will have these parts Will have the same interial. if you increase rpm, then you are getting more drivetrain looses, but in the same rpm? i'd say not, i get always same drivetrain looses. ive seen a lot of ppl haveing problems with tires, slippage, these factors Will give you different drivetrain looses, maybe i have a bit advantage by using hub dyno and all runs are controlled, same time for ramps,etc, for rollers if you have a bit slippage you are getting wrong drivetrain loses, or a deformed tire.. ive seen some tuners increase power just by drivetrain looses..i think thats a hacked real readings , using different gear Will modify too drivetrain losses. attached some examples of cars i tested. i'd say maybe if power increase affect , in my dyno it's less tan 0.1%..

"lanzada 1" : NA car, many pulls.

"lanzada 2": another car, many pulls, you can see an increase of drivetrain looses by increase rpm, that would make sense to me.

"lanzada 3" : a turbo RWD car..nothing special, just i think it's very important to get always same drivetrain looses readings.

"Lanzada 4" : Testing a turbo car with different maps, so different boost pressure. 

while im writing this, i noticed i only can upload only one image lool. i Will upload other images later.

 
Posted : 08/08/2019 12:09 pm
(@walter)
Posts: 244
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"lanzada 2": another car, many pulls, you can see an increase of drivetrain looses by increase rpm, that would make sense to me.

 
Posted : 08/08/2019 12:10 pm
(@walter)
Posts: 244
Member
 

"lanzada 3" : a turbo RWD car..nothing special, just i think it's very important to get always same drivetrain looses readings.

 
Posted : 08/08/2019 12:10 pm
(@walter)
Posts: 244
Member
 

"Lanzada 4" : Testing a turbo car with different maps, so different boost pressure.

 
Posted : 08/08/2019 12:11 pm
 Dev
(@dev)
Posts: 61
Member
Topic starter
 

It does increase with power, more thrust loading on helical gears etc.

 

But, the biggest increase in loss is through tire flex.  Especially when you are running 500bhp through a narrow 225 tire on twin rollers - the heat generated is immense.  

 
Posted : 08/08/2019 12:20 pm
(@walter)
Posts: 244
Member
 

i'd say in acceleration yes, not in desaceleration , but talking in numbers, how many hp? or percentage Will be noticed on dyno? i already said what i see in my dyno above.

yes, that's why i said maybe i have a bit advantage by using hub dyno, ive seen some ppl having a lot of drivetrain looses by using drag slicks! 

 
Posted : 08/08/2019 12:26 pm
 Dev
(@dev)
Posts: 61
Member
Topic starter
 

Yes with Hub dyno you will not see that much difference.  On car that starts off at 230bhp and then goes to 450 bhp - it's quite a lot of difference.

 
Posted : 08/08/2019 12:28 pm
(@walter)
Posts: 244
Member
 

i guess so just doesnt have nothing to do with power increase as i said, there are other factors or i'd say even important problems on roller dynos by tires 

 
Posted : 08/08/2019 12:30 pm
 Dev
(@dev)
Posts: 61
Member
Topic starter
 

Have a look at some Maha dyno graphs, they are have a nice model.  

 
Posted : 08/08/2019 1:15 pm
(@walter)
Posts: 244
Member
 

it's used a lot in SPain maha, a lot of slippage problems.. in Germany , some of shops strap it down the car using engine support modified!

 
Posted : 08/08/2019 1:22 pm
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