Gearbox power losses

[ultiman]

Does anyone have any knowledge of the likely power loss in the G50, G50/50 or other such Porker gear box they might be using?
My local rolling road suggested 20%, others suggest a flat figure of 30bhp. Does anyone know the real answer.

[mondeoman]

It won't be a flat figure - there are loads of calculations that you'd need to do, based on gear diameters, tooth pitch, angle, contact patch sizes, contact forces, bearings, lubricant etc etc etc ..... and IIRC these figures are speed and load dependant, so if you are transmitting huge HP/torque then the losess are correspondingly bigger. You can turn a gearbox by hand remember.

20% is IMO a bit much - I'd've guessed at closer to 10%, but I'll ahppily bow to those with superior knowledge on this one.

[KenDoddsDadsdogs]

Hi there Ultiman. That was a very good question you asked there. Pity nobody knows the answer. Still at least you're back on page now!! Ken

[ultimaandy]

Who you trying to fool..........Got one of them split personallity things going on there

With the gearbox losses, my understanding is that it varies bepending on the efficiency of each gearbox, and that it's usually between 10-20% for a 2wd car more for a 4x4.

I suspect a Porsche unit will be on the more efficient side but I don't know any figures or facts (as usual)

[ultimaandy]

Who you trying to fool..........Got one of them split personallity things going on there

With the gearbox losses, my understanding is that it varies bepending on the efficiency of each gearbox, and that it's usually between 10-20% for a 2wd car more for a 4x4.

I suspect a Porsche unit will be on the more efficient side but I don't know any figures or facts (as usual)

[davefiddes]

Should be possible to find out in nauseating detail what the losses are if someone has a decent dyno plot from their engine builder and the same from a rolling road.

With very little work it should be possible to knock together a simple model that would allow you to predict what the losses are likely to be for other engines.

Yeah. I know that in absolute terms the values you get from dynos are never that accurate but I would have thought that getting within 5% wouldn't be too hard even with just one sample.

[james]

The other problem with this method is that a bench dyno is very unlikely to be using your exhaust system, so the bench result will be different from the installed engine result anyway. When you take into account all of the variables, you won't get an accurate answer by using your own engine for a comparison.

The best answer to this problem is to get into your car and drive it down the road instead of worrying how big a number your engine has popping out the back. You'll have lots more fun, and won't get so worried about it

James

[351cobra]

Don’t know about the g50 but typical losses in an American muscle car of around 450 hp run 25 to 28 percent, which is pretty typical. I would imagine the g50 would be more efficient due to the fact there is no drive shaft and the Germans tend to build great gearboxes but I would question 10% as this seems quite low. Remember as the Speed/Hp/Torque increases so does parasitic drive train loss with these cars capable of attaining speeds over 200 MPH it would be interesting to get some real data when running wide open.

[dannylt]

The Borg Warner T5 appears to have just over 25% loss looking at all Cerbera dyno print outs, i.e. about 100bhp with 300 at the wheels giving 400 at the flywheel. I would have thought the G50 is similar - I don't understand the comment about no driveshaft, and it has a notoriously steep hypoid angle.

I thought motorcycle gearboxes were closer to 10%.

danny

[davidy]

dannylt

Surely the driveline losses in the TVR should include the differential as well, therefore the gearbox is only part of the 15%??

davidy

[dannylt]

Ah, good point!

But how much power would really be consumed by a prop shaft? Extra inertia, sure, but a couple of universal joints and splines? Surely absolutely minimal?

danny

[ultimaandy]

I have a T5 in my cossie and would be amazed if it gives losses of 25%.

I was told by a cossie Guru that it would be about 15-20% losses from flywheel to wheels.

[ultiman]

james said:
The best answer to this problem is to get into your car and drive it down the road instead of worrying how big a number your engine has popping out the back. You'll have lots more fun, and won't get so worried about it

James

James, quite so, however when you are told by your engine builder 440+ and you think it is less than 300, you start to worry a bit that something is wrong and want to know the extent of it. lt is not an outright quest for big numbers as the cheaper option is to tell porkies as few will be able to disprove what you say. Just need to get what l paid for. lf l know what the gearbox losses are, l can subtract that from what l get on the rolling road, accommodating the difference in exhaust etc and that fact that the yanks test with no engine ancilleries and an optimistic view. So if l am loosing 10% gearbox and say another 10% for the above, l should see 360bhp at the wheels. lf not, l have a problem.


>> Edited by ultiman on Wednesday 23 October 14:21

[mondeoman]

Some rolling roads have a coast-down facility which measure the drivetrain losses from max engine speed down to idle, then add that figure (pro-rata) to the at-the-wheels HP to give a "true" engine HP.

[canam-phil]

----------------------------------------------------------
ultiman said:
.. accommodating the difference in exhaust etc and that fact that the yanks test with no engine ancilleries and an optimistic view. So if l am loosing 10% gearbox and say another 10% for the above, l should see 360bhp at the wheels. lf not, l have a problem.

----------------------------------------------------------

All the recent dyno photos I have seen show the testing being done with a fully dressed engine. The major difference will be in testing with the dyno exhaust system and headers. Look at any recent US website photos showing testing on a dyno and you will see fully dressed engines.

As a note, I have a dyno report that shows a performance exhaust header giving up to 30bhp difference when compared with a "run of the mill header".

Engine power was measured in USA as SAE gross hp until 1971 I think. Since then, generally, SAE net hp has been used. There are other differences between US and European measurement but this is not the thread to discuss these in.

Start shooting if you know different!!!

Phil

[ultiman]

Don't be coy Phil, you can tell me the differences between US and European measurements.

[canam-phil]

On the topic of geartrain power loss, you may find this interesting but not necessarily gospel!

www.sdsefi.com/techdyno.htm

[bigmack]

I'm sure a little surfing around the net will help satisfy your concerns regarding hp measurements of engines. Check this out for starters. http://kennedyp.iccom.com/pat/what_is_hp.htm
1 US HP=745.6999 Watts, 1 UK HP=745.7 Watts
I'm sure others will offer more input.
This should probably be discussed in a new thread though.

Cheers!
-Mack

[canam-phil]

Hi bigmac

You beat me to it... I was just going to quote this article using Watts as the conversion unit!!! (1 US HP=745.6999 Watts, 1 UK HP=745.7 Watts )

I agree a new thread is called for.

On the basis of this article, hp us and hp uk are very close. I always think differences are down to measurement conditions.

Has anyone got dyno results for the same engine in US and UK with a list of test setup and conditions?

Phil

[bigmack]

Sorry about that...As you pointed out, this is just an article of one persons research. He gives his source of information if that's not good enough for everyone

It satisfied my curiosity though.

Cheers!
-Mack