Drivetrain Power Loses

[sub205 5]

Hello,

 

i need information about how much power is lost in the drivetrain of the BE-based engines.

 

i've got 155bhp and i'm only getting about 110bhp out to the wheels. seems not enough for me.

 

rr-diagramms would be great also!

Edited November 2, 2009 by sub205

[Galifrey 1]

Hello,

 

i need information about how much power is lost in the drivetrain of the BE-based engines.

 

i've got 155bhp and i'm only getting about 110bhp out to the wheels. seems not enough for me.

 

rr-diagramms would be great also!

 

Depends on the dyno, some show around 30% transmission loss, some show a more accurate 15%. The ones with 30% generally have some drag in the dyno itself that is accounted for. You can usually add 15% to the wheel figure to allow for those dynos.

 

You should not be having more than 15% transmission loss on a FWD car.

[dcc 855]

from what I understand, the power at the flywheel (your 155) is guestimated from the power at the wheels.

[M_R_205 5 1 Cars]

As dcc said the power shown on they dyno is wheel BHP,yhey the "calculate" you engine bhp from there, T

 

he average transmition loss is around 10% for a FWD car and closer to 15-20 for a 4WD car, so if your engine is 155bhp you should see around 140 through the wheels on the dyno, if your wheels are showing 110bho your engine is only giving out 120 ish,

 

Paul.

[sub205 5]

As dcc said the power shown on they dyno is wheel BHP,yhey the "calculate" you engine bhp from there, T

 

he average transmition loss is around 10% for a FWD car and closer to 15-20 for a 4WD car, so if your engine is 155bhp you should see around 140 through the wheels on the dyno, if your wheels are showing 110bho your engine is only giving out 120 ish,

 

Paul.

 

 

nope, the dyno engine power value should be correct, this dyno is used much for rally cars. would there be a difference, the owner had a big problem.

 

rather i think the wheelbhp value is to low. the dynos of that brand are know for counting high drivetrain loses, as i know found out.

despite of that the engine is running way to good for only 120bhp.

maybe i'll change the gearbox, just to be sure and go to another dyno, just for reference

 

edit: maha (the manufacturer of the dyno) tells whats going on:

 

its a big difference whether the run was in gear 3 or 4. in gear 4 the loses are much greater. to get an accurate reading, the 3rd gear should be used. thats because its a steady state dyno and its complicated to "emulate" a inertia dyno. ;-)

 

engine power is correct, the loses are because of the rollers and the breaks of the dyno.

Edited November 2, 2009 by sub205

[Batfink 201]

Surely as it is measuring the losses so it does not matter what gear it is in??

[sub205 5]

Surely as it is measuring the losses so it does not matter what gear it is in??

the dyno measures parts of his own loss, so the higher the power on the rollers, the less the own "loss" of the dyno is counted.

 

in 3rd gear the engine pulls / brakes much harder, the factor of the dyno stays the same, so the result is closer to reality.

 

(btw, i think the line in your footer should be "Der unzerstörbare Panzerwagen" ("der" wagen, germans and the f***ing der/die/das ;-), the rest of the sentence should be just like english grammar. sorry if i didn't get the point, maybe its an english joke about german language i, as a german, dont understand ;-) )

Edited November 2, 2009 by sub205

[Sandy 191]

It does, because no rolling road correction model is perfect, it will be optimised to produce close results on regular cars at a given speed range. Because the losses involved and nowhere near linear or even predictable curves, all corrections are based on compromised estimates. I've done a heap of research on this recently and although all rolling road manufacturers (and hence operators) claim to have accuracy, at best it's a good estimate; the variables involved are not directly measurable. The biggest fallacy being coast down loss.

[Batfink 201]

the dyno measures parts of his own loss, so the higher the power on the rollers, the less the own "loss" of the dyno is counted.

 

in 3rd gear the engine pulls / brakes much harder, the factor of the dyno stays the same, so the result is closer to reality.

 

(btw, i think the line in your footer should be "Der unzerstörbare Panzerwagen" ("der" wagen, germans and the f***ing der/die/das ;-), the rest of the sentence should be just like english grammar. sorry if i didn't get the point, maybe its an english joke about german language i, as a german, dont understand ;-) )

 

the joke would be I cannot speak or write German. If I thought about it a tank would be masculine

[sub205 5]

the joke would be I cannot speak or write German. If I thought about it a tank would be masculine

 

the only real tanks on 4 rubbers are the swedish volvos :-D

[Galifrey 1]

As dcc said the power shown on they dyno is wheel BHP,yhey the "calculate" you engine bhp from there, T

 

he average transmition loss is around 10% for a FWD car and closer to 15-20 for a 4WD car, so if your engine is 155bhp you should see around 140 through the wheels on the dyno, if your wheels are showing 110bho your engine is only giving out 120 ish,

 

Paul.

 

10% is overly optimistic in my experience, but entirely possible. but there are definitely dynos out there showing 30% loss, we have recently seen this on some dyno printouts on this site. It is common with one particular dyno printout, the one that mixes nm and BHP

 

The point is, coastdown losses are inaccurate, and when you see huge coastdown losses, it is usually because the dyno itself has some inherrent issues that have been "calculated" out.

 

This dos not make them any less accurate with flywheel figures, if they are properly calibrated and operated, however, it usually results in a very low wheel torque/bhp figure.

 

I will try to find a sample printout to post here.

 

In theory, the minimum a rolling road should get right is the figures at the wheel, my experience shows that some simply don't.

 

 

Here are some graphs...

 

 

 

 

Edited November 2, 2009 by Galifrey

[sub205 5]

(...)

 

thanks for the infos, exactly what i thought.

maybe the only way to get a reliable wheel-bhp is to drive the car to topspeed and compary it with aerodynamics (cw) ;-)

[Galifrey 1]

thanks for the infos, exactly what i thought.

maybe the only way to get a reliable wheel-bhp is to drive the car to topspeed and compary it with aerodynamics (cw) ;-)

 

First try and find an accurate speedo you will have as much luck with that as an accurate dyno!

[Sandy 191]

On long journeys you can entertain yourself by setting the cruise control and comparing the speed with elapsed time against the km markers at the side of main roads My Honda reads 3mph over at almost all legal speeds!

 

Anyway.... There's alot of discussion about Powerstation (and the latest MAHA LPS 3000 package on the whole), but looking at all the above flywheel figures, you have to say they're looking good. Take any of those cars to a Dyno Dynamics RR though and you'll almost certainly see less, but probably not consistently so. Both operators will of course argu they're accurate.

 

I've had access to alot of Dyno to Hub-dyno results lately and the transmission loss on them it literal (ie no tyre losses). What's interesting about that, is you get almost linear 8-10% loss on tranverse units and 10-12% on in line, slightly less with straight cut gears and it seems very proportional to the power output, which proves that losses under load will be greater than running free. I also recently saw the "wheels" figures improved by 10bhp peak, from changing a worn CWP on a stock car! We know that the tyres account for a substantial portion of the overall loss, so any claims of 10% overall, are definitely optimistic. The tyre losses seem to rise very dramatically over about 70mph roller speed and the curve isn't very predictable, certainly not formulaic. Add onto that, that engines almost always perform a little different installed to on an engine dyno and you have a minefield for potential errors!

Edited November 3, 2009 by Sandy