G50 Power Consumption

[builder]

Hi All,

Anyone made dyno runs on their engine before installation, then another on a chassis dyno? I am working with an engine builder now and want to get a close estimate of the power used by the transaxle. Published numbers range from 15-20%. Are there any first-hand, real-world examples?

Thanks,

-- Scott
Reno, NV

[Allen-GTR]

Hey Scott,

H I have some idea based on engine dyno/chassis dyno combination...

My estimates put the loss from transaxle and driveline/wheels to be about 45 hp.

Allen

[builder]

That's not bad at all! I was thinking -- how could it be 20%! That would be over 120 shaft HP!!! I can live with 45. Thanks, Allen.

[ultimacz]

My chassis dyno results were -15,3% (difference between engine power and rear wheel power)

[builder]

ultimacz said:

My chassis dyno results were -15,3% (difference between engine power and rear wheel power)

That's a bigger chunk than 45 rwhp, presuming you had more than 300 shaft hp. If building again, are there any steps you would take to reduce the loss?

[ultimacz]

builder said:

ultimacz said: My chassis dyno results were -15,3% (difference between engine power and rear wheel power) That's a bigger chunk than 45 rwhp, presuming you had more than 300 shaft hp. If building again, are there any steps you would take to reduce the loss?

Interesting question, but I don´t know which measures could improve that ratio. I have meanwhile upgraded the clutch but I doubt that this reduces the loss. BTW, my box is a 6-speed Getrag, don´t know whether this makes a difference. Would be interesting to know what the ratio is with 996 Porsches, using the same box...

[Allen-GTR]

Well, I am not 100% sure about that 45HP... but I believe its close. Several tuning changes were made to the engine, and I am trying to take that into account too. I suspect it has as much to do with torque and where it builds in the curve...

I don't know that a percentage of HP is a good measure of the loss. A 1000 HP motor would not lose 20% (200 HP) and a 100 HP would lose 20 HP... It would be ROUGHLY the same drop (parasidic drag) either way...

Just thinking out loud here...

Allen

[canam-phil]

Cz

Under what conditions was the engine dyno'ed and chassis dyno'ed?

Was output corrected for ambient conditions on both systems?
All auxillary system belts fitted?
Did it have the aircon pump (if fitted) running?
Your Ultima headers and exhaust system fitted?
Water pump?
etc etc

Was the chassis dyno just that or was it on rollers?

Phil

[ultimacz]

Hi Phil,
don´t know what the right English term is, maybe "rolling road"? We call it over here simply a "brake". I thought it is the same as a "chassis dyno", but maybe I´m wrong? (apologise for my weak English). Anyway, we dynoed the whole car on this brake, not the engine. This was in 2003, still with the AS engine in (383cui, 470 HP according to AS engine dyno). The car was strapped on to the rollers and they revved it up to the limiter. I think it was in 5th gear, but don´t remember. The printout I got then stated the rear wheel HP as well as the HP loss and the corrected engine HP. The difference was 15%, as I mentioned.
It is not the difference to the AS engine dyno sheet, this would be much bigger. Maybe because they use different norms in America (over here is used DIN 700 or so, but I can´t read that completely on my print-out). Or does AS the dynos without all auxilliary systems and with a different exhaust? If I would really compare the AS engine dyno figures with my chassis dyno figures, the loss would be around 30% for my engine and that is hardly possible.
Peter
Anyway, I did

[ikom]

builder said:

Hi All, Anyone made dyno runs on their engine before installation, then another on a chassis dyno? I am working with an engine builder now and want to get a close estimate of the power used by the transaxle. Published numbers range from 15-20%. Are there any first-hand, real-world examples? Thanks, -- Scott Reno, NV

Hi Scott,

Typical "Driveline loss" on my Porsches were calculated at 15%-16% on a dyno. I am assuming that the G50/XX mated to a small block would yield very similar results. If you really want to dig deep into the math, than go to the Pelican board where a lot of Porsche guys hang out and pontificate on this specific subject.

www.pelicanparts.com/techarticles/physics_racing/part26.htm

hope this helps.

[andygtt]

problem is that different drive shaft angles and the extra oil required to run the box inverted will have an effect on power loss.

[canam-phil]

Andy

I would have thought that any loss due to extra oil being present would cause appreciable oil temperature rise if the loss was a significant percentage.

The driveshaft loss would be a larger number than that due to oil volume. The other bigger loss is the wheel/tyre rolling road loss. But, OK, builder was asking for the transmission loss so this should be included.

15% was what my dyno bloke mentions but I always wonder whether this is just a guide figure that we all quote.

[builder]

ikom said:

Hi Scott, Typical "Driveline loss" on my Porsches were calculated at 15%-16% on a dyno. I am assuming that the G50/XX mated to a small block would yield very similar results. If you really want to dig deep into the math, than go to the Pelican board where a lot of Porsche guys hang out and pontificate on this specific subject. www.pelicanparts.com/techarticles/physics_racing/part26.htm hope this helps.

Thanks, Ike. I will check it out. That 15% keeps popping up. Must be somewhat close and time-tested. I will dyno my engine and then the rear wheels to compare when done. I don't know how else to test the transaxle for satisfactory through-put.

Anyone know if there is such a thing as a transaxle dyno? Do transaxle rebuilders have something like that?

-- Scott

[builder]

andygtt said:

problem is that different drive shaft angles and the extra oil required to run the box inverted will have an effect on power loss.

Sounds logical. I will be very happy the day I can test this.

[builder]

canam-phil said:

...15% was what my dyno bloke mentions but I always wonder whether this is just a guide figure that we all quote.

Attempting to discover the loss % for the purpose of validating a rebuilt transaxle. If the loss is much more than 16%, it sounds like the transaxle may be suspect.

[canam-phil]

Trouble is many loss factors are rev dependent.

There is a very good source so rather than precise it here it is

www.dynamometer.fsnet.co.uk/power-losses-flywheel-BHP.htm

[builder]

canam-phil said:

Trouble is many loss factors are rev dependent. There is a very good source so rather than precise it here it is www.dynamometer.fsnet.co.uk/power-losses-flywheel-BHP.htm

That's good info. Thanks, Phil. Very interesting site with reasonable conclusions.

[Allen-GTR]

Yes, there is kind-of such a thing as a transaxle dyno...

A dyno that attaches to the hubs instead of tires rolling on the rollers...

Upside is no slippage between rollers and tires. Downside is it does not take into account the weight/resistance of the wheel/tire combo...

These are a relativly new development I think...

I don't think this gives you quite the answer you were looking for, but interesting anyway....

Allen

[builder]

My best guess at an accurate procedure would have to include a dyno test at the crank. Then, with rollers hooked to the same dyno, test at the wheels. Subtract the known roller load and compare the curves.

If a known quantity of power (i.e. electric motor) were connected directly to the input shaft of the transaxle, then dyno'ed at the wheels, it seems these numbers would be somewhat accurate.

I will be speaking with some of the G50 rebuilders today and will find out if there is another method...

[arthurr]

600 hp on engine dyno and 486 at the rear wheels on a different dyno with a very strong G50/52