# % drivetrain losses on GTR



## R33_GTS-t (Apr 27, 2005)

What sort of percentage drivetrain losses does the GTR get in RWD and 4WD mode? I know there have been several threads on this but no definitive answer. Is there one now? I'm guessing at 25% loss in 4WD mode.


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## wilfsp1 (Sep 27, 2004)

I was told by Abbey it's 70 BHP and nothing more or less


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## R33_GTS-t (Apr 27, 2005)

Is that when measuring at all 4 wheels?


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## dan0h (Jul 26, 2002)

That is our quoted figure from all four hubs to the flywheel, and that figure wasnt plucked from thin air, it mates up with known specification cars, and standard cars to give a perfect match to flywheel in 99% of cases, it has been confirmed with a number of well plugged in people also. You can add another 1-2% to it, as you edge over say 650hp. Guesstimated.

As for percentage-based losses (as opposed to fixed loss with small percentage correction for crownwheel distortion etc) 25% seems an excessive loss figure for a GTR, by that theory the following would be true:

* A 300hp flywheel Skyline would loose 75hp to the drivetrain, probably not a bad benchmark for a standard car.

* However, the same drivetrain and wheels but with 650hp would loose 162.5hp.

So another 87.5hp is needed to turn the same wheels, the same gearbox, the same tyres? I think not. Thats over another 100% on top of a factory car!

For us hub-dyno bods we stick to our hub figures for comparison work, and generally speaking the respectable wheel-based tuners stick to their wheel figures to perform comparisons. Keeping flywheel guesstimates and crystal-ball predictions strictly for pub talk.

Obviously using a wheel based system however, frictional properties of the tyres, or thermodynamic changes in the tyre carcass during the entire testing cycle cannot be taken into consideration, but its figures are most likely near enough for most purposes. But take the tyres out of the mix and you have a much more precise base to work with.

Merely of course, my opinion


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## Guy (Jun 27, 2001)

wilfsp1 said:


> I was told by Abbey it's 70 BHP and nothing more or less


So if you took a stock car, turned off the turbos (zero-boost), ran the car on really poor fuel and retarded the ignition sufficiently to ensure that it was only able to make precisely 70bhp at the engine, then your saying that it would not be able to turn the wheels at all......? I think not, so loss is at least partially a function of power.

Simple logic and physics suggest that drivetrain-loss if a non-linear percentage function. A 100bhp will lose less overall power than a 500bhp engine, than a 1000bhp engine, as the losses are created by the shear forces operating on the surfaces, creating heat (which is why more powerful cars need extra gearbox and diff coolers etc). This will increase as power increases. However it is not linear with power ie losses do not double as power doubles, so the percentage lost drops as power increases.


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## Paul Hackley (Jan 3, 2003)

How about some recorded comparisons,
G-Force 482 at the wheels
Thor 549.5 at the hubs
But heres the the rub, how often is the equipment calibrated or what percentage tolerance is allowed?


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## AJFleming (Feb 25, 2003)

If you want to know flywheel figure get an engine dyno. Its atw/h bhp that counts, transmission loss is very subjective IMHO although I agree some of the figures when a percentage is used are ridiculous. My RX7 has 527 BHP at the rear wheels, I would say thats 600+ bhp as an estimate but I am not a believer in losses of 160+ bhp as Dan rightly says.


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## -C- (Oct 16, 2003)

25% would be excessively high IMO.

The only true way to do it, would be to have the engine on an engine dyno, run it, put it in the car, run it again.

FYI, the Evo lot with standard cars lose approximately 24% from flywheel to the wheels, this was also the same with Simon Norris's high powered Evo when running on an engine dyno, then on a RR


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## skyline69_uk (Jan 6, 2005)

As with all things automotive the formula tends to be of the 

x = C + ab(etc) + cd^2(etc) + ef^3 (etc) ...... etc type with the bhp to whp formula being more like

x = C + ab + cd + ef ... etc

there are set losses that change with gear selected (4th is normally the least losses), rpm of engine etc. For the most part the losses vary greatly as I have seen figures that suggest a standard GT-R losses about 70 to 90 hp from engine to wheels but seen one figure (Australia) that tested from wheel dyno to engine dyno a loss of 105bhp for a standard R32 GT-R in 4wd mode. The losses do increase for bigger bhp but remember a lot of the bigger bhp cars use lightweight parts and these greatly reduce the loss!


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## R33_GTS-t (Apr 27, 2005)

skyline69_uk said:


> there are set losses that change with gear selected (4th is normally the least losses), rpm of engine etc. For the most part the losses vary greatly as I have seen figures that suggest a standard GT-R losses about 70 to 90 hp from engine to wheels but seen one figure (Australia) that tested from wheel dyno to engine dyno a loss of 105bhp for a standard R32 GT-R in 4wd mode.


Yeah, I've heard the Australian's tend to use dyno dynamics which measure more power loss than Dynojets. How, I don't know?


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