Transmission Power Loss

[bonob]

Does anybody know what the typical transmission power loss is for a Golf TDI, I’m guessing about 15 to 20%.

I’ve been told that the original figures normally quoted (90bhp in this case) are at the flywheel. After I made a few mod’s to the engine, I had it dyno’d and they gave me ‘on the road’ figures, and am now trying to compare them.

Any intellectuals out there?

 

[mickey]

Intellectuals? You've definitely come to the wrong place, my friend. We're all overcome by diesel exhaust.

-mickey

 

[Dieselworld]

I am pretty sure that the 90hp is at the rear wheels.

 

[mickey]

According to Wetterauer's web site, they compare the stock power to the "chipped" power on a chassis dyno. The stock power they list for the NB is the same as the factory number. I'd say the 90 hp is "on the ground", not at the flywheel. By the way, Russell, there's only torque at the REAR wheels if you're driving backwards.

-mickey

 

[bonob]

Not that I’m a cynic, but, I always thought that the manufacturers quoted the power at the crank/flywheel as its always a higher figure, and more likely to sell a car, OK I am a cynic.

When I recently read the article about the ‘Allard Engineering’ 148bhp TDI, I noticed that it quoted 117bhp @ the wheels and 148bhp @ crank, so I wondered where this 126% conversion figure came from. 26% allowance for transmission loss seems a little high to me, I’m sure that the VW transmission isn’t that inefficient, is it?

I know that most dyno’s compensate for the transmission, and the figures quoted contain a % to allow to transmission loss. Most people would be very upset if they where told that the car that they bought thinking it had 90bhp(crank) only had 71bhp at the wheels (assuming 26% is correct)

As in my car a new and healthy ‘red eye’ (110bhp) Golf pre mod’s managed to muster 91bhp at the wheels as standard, but with the mod’s ran up to 121bhp with 246lb/ft.

In case your thinking that the rolling road was out, it was a pro one as used by a certain F1 team in Oxford, I can’t say which else I’ll get my mate who let me in the sack.



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[RabbitGTI]

Quoted power figures for cars are usually engine output, not road horsepower. A loss of 20 % or so in a roadcar is normal. Power is lost not only in drivetrain friction (transmission, bearings, etc...), lots is lost torquing the chassis and squashing motor mounts.

 

[Keith]

According to HPA Motorsport, the VW trans. in stock form soaks up 14%, and installing a Quaiffe diff. causes almost no power to be lost from the flywheel to the wheels. Can anyone confirm this from another source?

Bonob: What are your mods for 121hp at the wheels?

Keith

 

[Lug_Nut]

I suspect that the manufacturer's HP numbers are determined by engine dynamometer testing an engine or three, putting those engines into cars, then chassis dyno testing the same to determine the percentage of loss. From that point on, all the chassis dyno tests have this calculated loss figured back in. My 96 Passat TDI produced 90.3 peak HP at the wheels on a chassis dyno that has an approximate loss factor of 15%. Stock 2.0 VW engines, rated at 115 HP, were producing 95 to 98 HP that same day I tested mine. There were no stock 2.8 VR6 cars this day. Even the chipped and modified ones did not produce over 172 HP at the wheels.

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Jonathan Bartlett

 

[bonob]

Thanks for the info, all.

So I reckon that 20% is a safe assumption, 14% gearbox & 6% suspension, chassis etc.

Yippee I’ve got 145 hp
Keith, So far it has been chipped with a Modem Superchip and a K&N replacement filter has also been fitted. Next stage is to get a little extra air in. I’ve been speaking to Sooty who has a weird air intake system, but it works! I may try some of his tricks. Once I get the air sorted the next stage will be a new intercooler, my mate say’s that he should be able to knock something together for me.


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[This message has been edited by bonob (edited May 22, 1999).]