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Coast Down losses calculation  

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(@admin)
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@dev, you are not correct on the calculation. 

The dyno measures the retardation loss much like an inertia dyno in reverse. YourDyno knows the MOI and measures the deceleration and from there calculates the torque required to slow the rollers down like that retardation curve. This negative torque curve is added across to the positive torque curve (i.e. the torque loss at each RPM is added to the torque at each corresponding RPM at ramp up), and the result is the engine torque curve. Same for HP. It does not use speed or anything like that, it just measures the torque at every RPM.

The losses that are not accounted for are: 

  • Additional drive train losses due to the extra load under power. This is typically larger for higher hp cars. Loss at coasting, which is what we measure, is not the same as the loss at full power. High performance cars have gear box and diff cooling for a good reason...
  • Tire to roller loss. This can be significant (the tires get hot...) and again is typically higher for higher hp cars. Loss is higher at smaller diameter rollers.

Complicated field. If anyone has algorithms to use to account for these losses, let me know!

 

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Posted : 08/08/2019 8:47 pm
 Dev
(@dev)
Member

Hi Jostein.

The calculation you describe is what I would expect.  When i talk about speed, I am saying that the losses are related to the roller speed.  Greater speed = greater power loss.  

The tire loss and loaded losses are exactly the algorithms I'm asking about.  Tire losses are probably related to tr active effort, weight of the vehicle and "flex" of the tire.

Dev

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Posted : 08/08/2019 9:04 pm
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(@walter)
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id say, if too much power affect to drivetrain loosses, it Would be measured on dyno, It's like when i dynoed 2 cars that had some problems with brakes, i tuned many of these cars (Civic EGs) and i know already drivetrain loosses when any car has a specified engine/gearbox, anyway there is minimal difference between engines/gearbox, 2 of these cars had brake problems then i noticed was Reading too high drivetrain losses, after we get rotors spin freely, got the right losses. im pretty sure, if a gearbox get more losses by load, heat, it would be measured perfectly.

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Posted : 08/08/2019 10:21 pm
(@mach_1)
Member
Posted by: Walter

id say, if too much power affect to drivetrain loosses, it Would be measured on dyno, It's like when i dynoed 2 cars that had some problems with brakes, i tuned many of these cars (Civic EGs) and i know already drivetrain loosses when any car has a specified engine/gearbox, anyway there is minimal difference between engines/gearbox, 2 of these cars had brake problems then i noticed was Reading too high drivetrain losses, after we get rotors spin freely, got the right losses. im pretty sure, if a gearbox get more losses by load, heat, it would be measured perfectly.

So what are the RIGHT engine power loses percentage % engine to front/rear wheel vehicles (and 4WD vehicles) drivetrain losses for chassis_dynamometer and hub_dynamometer ?

 

 

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Posted : 11/08/2019 4:54 am
(@mach_1)
Member

Give us some power losses numerical figures for these Honda Civic EG you have been tuning and testeing?

Q1 -Year of the Honda Civic EG ?

Q2 -Engine BHp of the Honda Civic EG ?

Q3 - FWDH_Hp of the Honda Civic EG measured on your hub_dynamometer?

Q4 -What gearbox/differential is used on this Honda Civic EG ?

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Posted : 11/08/2019 5:07 am
(@walter)
Member
(@mach_1)
Member

I'm very familar with that thread.

Your hubdyno results are only good for your own dyno comparison! As you stated " it's  only a tool " comparing with other dyno's seems very mmm........ ??????

Who's dyno reading is right or wrong ?

Quote from that thread link you posted " one in particular example sticks out like a sore thumb " Rover 2.0 turbo 242Fwhp /252hp - 3.97% " there is no way in hell it only loses 3.97% powertrain losses from the flywheel back to the driveshafts coupled up to a hub_dyno.  You seriously have to question this. Drivetrain losses are greater than some people think. I haven't yet proven it but in due course. I need more input from these quoted figures." 

PLEASE EXPLAIN THE LOSSES HERE ?

To answer this unexplained phenomena that occurred on you hub_dyno with i can't explian why your findings was a 3.97% powertrain losses ???? I'm  still at a loss ?

Anyway keep dyno'ing 

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Posted : 11/08/2019 5:46 am
(@walter)
Member

mmmm i didnt say my dyno is the best, no way, im still say it doesnt just i see many dynos readings wrong or having problems with readings as Reading wrong losses by tire deformation,etc.

Ok, you choiced a car i cant remember somethings exactly but i Will tell you experience with this car..


That car , customer fitted a old 820ti rover T-series, with 220 engine head, he rebuilt it. we just wiring the whole car because he tried to run with oem ecu and didnt work properly, many cutted wires in the chassis,etc, we wired everything and after to see didnt work properly with 3 ecus he has, 220 turbo, 820 one, other i dont know which one was , made downpipe, fabricate rear motor mount, ic pping ,etc.


Finally after to do many research found Emerald was the best option for this car. after many emails, finally we ordered a P&P ecu, including he have a map tuned already, so everything was really easy, that map has comments , i can't remember exactly but was about 250hp. yes, they use dyno chassis. coincidance? well, we upload the map, put on dyno, always start tuning in steady mode, after first pulls, got only 199hp, was stock boost, this car has oem boost controller so was very easy to do, started to raise up the boost, was 3-4 psi more, i can't remmeber exactly really, so we got about 224hp, (im checking all dyno pulls right now ), that was first day, then for second day we go for more boost, then got 250hp, 251hp, 252hp, after more pulls , go slow to 248 and 246hp, just by IAT was too highs, checking external temperatures was 38-39ºC.


You say, it's not posible only gearbox has that 3% , yes sound really crazy, i can't remember what gearbox he used, i know he told us that gearbox is still weak, but the best he can install it, very small gearbox, what i 'd say im pretty sure in a dyno chassis,including tires there Will be more drivetrain looses. maybe whp was hight? i really dont think so, even i'd noticed in high drivetrain looses.


the first year after rebuilt my dyno, using yourdyno, every car i tested, always compared with other dynos, i was very paranoic with these because i wanted the best dyno (who doesnt wanna it?) then made a lot comparing, affortunatelly you can see tons of dyno pulls for many cars on YouTube and was comparing, and really the results was very close, after 3 years, i know everything is good, you can see in some dynos only read whp making 150-155whp b16s with bolt ons.. and other dynos only read hp, you can see yourself in YouTube readings 170-175hp, that's what the numbers i get normally with these EGs/Eks, B16s with bolt ons… same for other cars...


that's just my experiance, this tool years for design, for learn more about dynos, indeed, i had before a roller dynos (i Will rebuild it and sell), learned a lot, still learing, i dont have any dynosheets for comparing with the other dyno, complete industrial state got burnt, many shops including my old shop, roller dyno was ok, just wires and pneumatic system was damaged, (plastics,etc).. what a  tragedy.. im up after many years. for example.
Thats was my experiance with this car, so you can make your own conclutions. i'd like to go with 4WD i'd like to see what drivetrain looses i can see for 4WD cars..


Im pretty sure if i test in other gear, i'd get different drivetrain looses..the best one for to get "close Reading" to hp in a dyno chassis is to test using the gear closest 1:1.... still repeat, im not saying i have the best dyno, no way! but my goal as always in my life, try to learn, and to make things good. that's just my 2 cent. (as US ppl would say, does it? :D), pretty sure running with tires, you Would get more drivetrain looses, i'd say +4-5% depend of tire size/Wheel weight/total weight of tire-Wheel.

PS: sorry for edite it, just Reading and found some wrong words, i means, my english isnt my first language and i dont write correctly in many times. sorry!

This post was modified 7 months ago 4 times by Walter
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Posted : 11/08/2019 12:40 pm
(@mach_1)
Member

Do me a favour next run of the mill standard unmolested vehicle you test  ( manual gearbox)  do  power graph pulls in all the individual gears and scale and overlay the graphs and post the picture of the graph  please.


 

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Posted : 11/08/2019 1:25 pm
(@walter)
Member

one time i tested in differfent gears, just for to see how does Will affect to whp (or hub BHP or whatever you want) , almost the same whp, different hps..

was Civic MB3 fullstock.

what i can't remember the gear , i means which gear i used and power i get but i have here the differences..

GearX?? : 121hp/102whp

GearY?? : 112whp/ 103whp.

What i remember too was adjusting noise filter, was ago long time, anyway i can do some test for the next cars. 

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Posted : 11/08/2019 1:34 pm
(@walter)
Member

if Jostein is Reading, should be good to make different line style for HP and whp  

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Posted : 11/08/2019 1:35 pm
(@admin)
Member Admin

Hi Walter, all,

Walter's hub dyno will have less loss than a roller based dyno obviously since there are no tire to roller losses, but 3% is indeed too little.

To be really accurate you need to set the MOI for each car you test. MOI of the drive train is also slightly different in different gears. Note that for a hub dyno with little inertia a slightly wrong setting in the MOI can make quite large effects. You should get the same results (close) in either gear, if the whp is the same. 

The whp and HP graphs are actually visually different, dashed vs non-dashed lines, but it is hard to see unless you zoom in because of the high number of samples. I will see if I can modify that so it is more clear.

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Posted : 11/08/2019 3:23 pm
(@walter)
Member

sure, mine has 9.8kg*m2. my old roller dyno was around 13.5 or so. i think it's not really bad for a hub dyno with that MOI.

Yes, definitely think every dyno even for the best calculation would be needed to set MOI for each car. About same whp than hp, i always thought whp is the most important than hp, i means, on dyno hp would be affected by a wrong gear, instead whp is the power you have on the hub/tires always, not matter which gear..

lines should be amazing something like this:

I not means for shadows, i means for different type of lines. i noticed it's a bit different but using normal resolution, it always look the same , if you zoom it a lot yes, you noticed the difference.

 

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Posted : 11/08/2019 6:40 pm
(@admin)
Member Admin

Oh really, 9.8 that's higher than I thought! So then you are not more sensitive to MOI accuracy than typical roller dynos in this respect.

Indeed, whp is what we measure, and as such will be the most accurate. 

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Posted : 11/08/2019 7:04 pm
(@walter)
Member

yes, the first versión i had set it up 9.8.. until the newest versión needed to put for dynos with 2 hub/brakes, then we talked i have to divide it and it's done. have 4.9 for each hub.

I was really impressive too when i got this MOI, main reason was for using very big brakes..:-D

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Posted : 11/08/2019 7:40 pm
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