# Drive train loss on the dyno



## Spen123 (Feb 6, 2013)

What is the % used for the GTR from wheel to fly wheel ?


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## barry P. (May 9, 2010)

I think Dyno Dynamics calculates it at 21%


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## Spen123 (Feb 6, 2013)

Thanks Barry what about a hub dyno ?


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## Tim Radley (Aug 3, 2013)

Percentage should not be used. Majority of loss is rotating wheels and discs and that stays constant for the same car if you triple it's power


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## Tim Radley (Aug 3, 2013)

Spen123 said:


> Thanks Barry what about a hub dyno ?


See my previous comment. Wheels now removed so losses much less


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## Spen123 (Feb 6, 2013)

Wheels was removed Tim I have a wheel power and torque just wanted to know what it would be at the fly I was told around 15% ????


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## Spen123 (Feb 6, 2013)

Anymore input


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## Tim Radley (Aug 3, 2013)

Its not a fixed percentage. Its just a loss amount with a tiny bit of scaling of friction.


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## [email protected] M/S (Feb 16, 2002)

35GTR? Running in 2wd or 4wd?


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## Spen123 (Feb 6, 2013)

[email protected] M/S said:


> 35GTR? Running in 2wd or 4wd?


R35 4wd Mark


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## ACspeedtech (Aug 25, 2011)

Its 18% loss, beware on dyno dynamics as none of the shootout modes match this, make sure you get the very accurate and important wheels figures. There is a very long standing debate over the fixed or percentage method, both sides have valid points. If at all unsure I always just give the wheels figures as at the end of the day, that's what's being laid down to the tarmac.


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## Spen123 (Feb 6, 2013)

ACspeedtech said:


> Its 18% loss, beware on dyno dynamics as none of the shootout modes match this, make sure you get the very accurate and important wheels figures. There is a very long standing debate over the fixed or percentage method, both sides have valid points. If at all unsure I always just give the wheels figures as at the end of the day, that's what's being laid down to the tarmac.


Thanks For that mine was on a hub dyno and only gave me power/torque ATW.
Was just wondering what sort of drive loss from wheels to fly.


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## Conrad (Jul 29, 2004)

Spen, surely your figure from the Dynapack was At The Hubs which is different again to ATW?


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## thistle (Oct 27, 2007)

About 30lbft and 50HP IMHO which is as good as anyone else's as this is a hugely complex topic with Neanderthal thinking, incorrectly received wisdom and marketing contamination in most of the claims. At least I am not giving you a fake percentage which misrepresents the physics as Tim Ridley points out. Most of the losses are SPEED related.


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## Tim Radley (Aug 3, 2013)

Spen123 said:


> Thanks For that mine was on a hub dyno and only gave me power/torque ATW.
> Was just wondering what sort of drive loss from wheels to fly.


Hub dyno is at the hubs with wheels/tyres removed. You should be very close to the flywheel figure on a hub dyno.

Imagine a car with a transmission with a 200bhp loss on an 1000bhp engine through friction. This transmission has no water cooling circuit. Now imagine a 200bhp engine on the dyno and remove the cooling circuit. You have 200bhp of energy whatever way you want to look at it for both applications. If you do 5 pulls on both scenario's, how hot is the uncooled engine and how hot is the transmission? If both are generating 200bhp then surely the transmission would be hotter due to less mass in its casings. Answer - its not. You can put your hand on it.

The physics are quite simple and transmissions DO NOT GLOW IN THE DARK hence the validity of some methods. Calculate the inertia of 4 wheels and 4 tyres rotating at a given speed. Therein lies one's answer.

FWHP is an ego massager on a chassis dyno, nothing more.


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## [email protected] M/S (Feb 16, 2002)

R35GTR we have calculated that you loss around 75bhp from all 4 hubs to the flywheel on a Dynapack dyno.

Just on my way back from a tuning trip to Croatia will post some stock GTR Runs on our Dynapack when I am back in the office.


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## Conrad (Jul 29, 2004)

[email protected] M/S said:


> R35GTR we have calculated that you loss around 75bhp from all 4 hubs to the flywheel on a Dynapack dyno.
> 
> Just on my way back from a tuning trip to Croatia will post some stock GTR Runs on our Dynapack when I am back in the office.


...and how exactly did you CALCULATE that Mark?


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## JamieP (Jun 5, 2006)

Ive been on a fair few dynos over the years and have always found hub dynos very close to the flywheel figures ive seen on a dyno dynamics, before i went crazy with the power my supra made 902bhp flywheel at SRR and the next day did 915 atw's on a dynapack hub dyno.


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## Conrad (Jul 29, 2004)

JamieP said:


> Ive been on a fair few dynos over the years and have always found hub dynos very close to the flywheel figures ive seen on a dyno dynamics, before i went crazy with the power my supra made 902bhp flywheel at SRR and the next day did 915 atw's on a dynapack hub dyno.


Jamie, 902 Flywheel on Dyno Dynamics is CALCULATED what was the Dyno Dynamics ATW figure which is measured ?(assuming no slip logged on dyno)


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## Tim Radley (Aug 3, 2013)

Conrad said:


> Jamie, 902 Flywheel on Dyno Dynamics is CALCULATED what was the Dyno Dynamics ATW figure which is measured ?(assuming no slip logged on dyno)


A lot of chassis dyno's use an assumed inertia value. If you put lightweight wheels and tyres on vs heavy ones the flywheel figure should not change but it does. Wheel should change in this scenario


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## ACspeedtech (Aug 25, 2011)

I agree its a long standing issue with chassis dynos, and it will clearly always be an estimation. Dyno dynamics had to design a system that gave an estimation relative to the drive line and engine configuration as they couldn't realistically construct a correct database for every vehicle, tyre and wheel combination on the market. It as always only a guide and why I stick to wheels figures. I used the number of 18% as the difference on a stock car between measured and flywheel factory quoted figures.
Specifically for the gtr, using a fixed number, and the benefit of the OP, I would estimate about 4%+100hp would be more correct? Tim? John? Mark? Thoughts?


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## Tim Radley (Aug 3, 2013)

ACspeedtech said:


> I agree its a long standing issue with chassis dynos, and it will clearly always be an estimation. Dyno dynamics had to design a system that gave an estimation relative to the drive line and engine configuration as they couldn't realistically construct a correct database for every vehicle, tyre and wheel combination on the market. It as always only a guide and why I stick to wheels figures. I used the number of 18% as the difference on a stock car between measured and flywheel factory quoted figures.
> Specifically for the gtr, using a fixed number, and the benefit of the OP, I would estimate about 4%+100hp would be more correct? Tim? John? Mark? Thoughts?


Yup that's more like what i'd expect. Problem i see is somebody measured the loss on a stock car and said "ah we have 20% here" then used that for any power level. Clearly if you take your stock gtr and double the power with new turbo's then you don't double your transmission loss. That's where their model fails badly.


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## [email protected] M/S (Feb 16, 2002)

As I said I have had a few stock GTR's (35) on our Dynapack , will post up a dyno graph's tomorrow.


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## [email protected] M/S (Feb 16, 2002)

Stock 09 GTR on our dyno




















12 sec runs.


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## Spen123 (Feb 6, 2013)

Some good information out of this thread


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## Conrad (Jul 29, 2004)

Spen123 said:


> Some good information out of this thread


....and an awful lot more nonsense mate!

The only way to tell what the true flywheel power is.... put it on an engine dyno.


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## [email protected] M/S (Feb 16, 2002)

But if you pull the motor and run it on a dyno you may well not have the same exhaust system and pipework fitted, the discussion will go on forever.

Main item is the lose from the wheels/hub to the flywheel isn't a percentage as people think, it is a set figure with a very small percentage for increased power maybe 1 to 2 % increase in relation to Torque.


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## Tim Radley (Aug 3, 2013)

[email protected] M/S said:


> But if you pull the motor and run it on a dyno you may well not have the same exhaust system and pipework fitted, the discussion will go on forever.
> 
> Main item is the lose from the wheels/hub to the flywheel isn't a percentage as people think, it is a set figure with a very small percentage for increased power maybe 1 to 2 % increase in relation to Torque.


Yup, also depends how the dyno operator runs the engine on any machine even an engine dyno.

Transient power and steady state power are not the same for an engine dyno or a chassis dyno. Different sweep rate, same engine, different power.

I've owned both types of dyno and spent so much time chasing repeatability to still find there are issues such as weather correction, load profile, etc.

That is being really anal though. What is not good is when you have a 300+bhp error in estimation as often see on dyno charts on the interweb.


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## Tim Radley (Aug 3, 2013)

Oh and we didn't even get onto wheel slip yet on the rollers or 'ratio-based rpm' based off tacho's with a 600rpm error in display.


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## [email protected] M/S (Feb 16, 2002)

STAGE 1.5 CAR , Y pipe and Tune (using Cobb) stock airboxes 





















shows you the gain running a little more boost and a tune on these awesome cars


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## Conrad (Jul 29, 2004)

[email protected] M/S said:


> STAGE 1.5 CAR , Y pipe and Tune (using Cobb) stock airboxes
> 
> 
> 
> ...


Mark, that graph is nonsense, there is other issues going on there??

After the tune the torque Graph is wavey as hell? Makes torque, loses some, make some more, loses again then tails off and at 4600 makes some more back to 4800rpm before falling away??? 

Power peaks at 4900rpm, drops away, climbs again at 5700rpm, falls away, 
climbs again from 6100rpm to 6500rpm????

That doesnt look right to me... was that the finished article?


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## [email protected] M/S (Feb 16, 2002)

torque curve was wavy in stock tune , Dynapck doesnt have any big rollers to smooth the plot, a lot of cars produce wavy runs on the dyno;


The answer is in the boost curve thou.

does this look any better


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## Conrad (Jul 29, 2004)

Not half as wavy as it was after you had finished with it......

I suspected the boost control or the Dynapacks inabillity to apply the load smoothly throughout the run. Adding smoothing filters doesnt really help, it just masks the problem


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## Tim Radley (Aug 3, 2013)

Conrad said:


> Not half as wavy as it was after you had finished with it......
> 
> I suspected the boost control or the Dynapacks inabillity to apply the load smoothly throughout the run. Adding smoothing filters doesnt really help, it just masks the problem


Smoothed, unsmoothed.


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## Conrad (Jul 29, 2004)

Tim Radley said:


> Smoothed, unsmoothed.


On the the graphs that Mark posted it isnt a smoothing issue, its a control issue.


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## Tim Radley (Aug 3, 2013)

Conrad said:


> On the the graphs that Mark posted it isnt a smoothing issue, its a control issue.


Does the dynapack use a closed loop PID? Dynojet does and you can change the values but the PPR on the roller pickup I think causes a further issue. All dyno's I've used have flaws


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## Spen123 (Feb 6, 2013)

I suppose it comes down to what the v box data says, real world performace not a dyno graph


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## [email protected] M/S (Feb 16, 2002)

No smoothing on a Dynapack I just changed the DYNO plots from auto axis plots to chosen axis's. 

We have no trouble with control, hold control rpm +/- 15 rpm under full load,no wheel spin no tyres to over heat.


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## Tim Radley (Aug 3, 2013)

[email protected] M/S said:


> No smoothing on a Dynapack I just changed the DYNO plots from auto axis plots to chosen axis's.
> 
> We have no trouble with control, hold control rpm +/- 15 rpm under full load,no wheel spin no tyres to over heat.


The dyno geeks among you should read this
DEPAC Method of Physics


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## thistle (Oct 27, 2007)

Can't find the patent, but would like to read. Integrating over a time base that is synchronised to the rotation of the crank is interesting, but what about resonance in the dyno itself which will not be at an integer multiple or divisor of engine speed due to gearing and contacting rotating surfaces of different diameters? Is correcting sampling to engine rotation speed reducing a real world significant source of error or is it marketing? Seems like it would be quite easy to do in software using a fast high rest ADC with thousands of samples per engine revolution?


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## Tim Radley (Aug 3, 2013)

thistle said:


> Can't find the patent, but would like to read. Integrating over a time base that is synchronised to the rotation of the crank is interesting, but what about resonance in the dyno itself which will not be at an integer multiple or divisor of engine speed due to gearing and contacting rotating surfaces of different diameters? Is correcting sampling to engine rotation speed reducing a real world significant source of error or is it marketing? Seems like it would be quite easy to do in software using a fast high rest ADC with thousands of samples per engine revolution?


A decent engine dyno should have sufficient damping in the connection to the engine in 'order' (no pun intended) to avoid breaking the absorber with that resonance.
A chassis dyno does suffer from resonance but then tyres and suspension have an effect.
If you sample the torque thousands of time per engine revolution you'd end up with a really funny looking chart as torque is constantly varying with crank angle.


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## Tim Radley (Aug 3, 2013)

Here is a dyno made in Greece
http://www.howstuffworks.com/etch-a-sketch-pictures.htm


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## thistle (Oct 27, 2007)

If you sample thousands of times per engine revolution couldn't you just add them together to integrate between trigger events? It would give you some flexibility after the event to analyse, and a 16 bit 44.1kHz ADC (which costs pennies) that would give you over 350 samples for each revolution of most car engines at red line.


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## Tim Radley (Aug 3, 2013)

thistle said:


> If you sample thousands of times per engine revolution couldn't you just add them together to integrate between trigger events? It would give you some flexibility after the event to analyse, and a 16 bit 44.1kHz ADC (which costs pennies) that would give you over 350 samples for each revolution of most car engines at red line.


Yes you could depends the level of accuracy you want. There is also a case for too much accuracy is not required in some instances! It would be nice to know how most of the dyno manufacturers actually derive their torque readings.

My view is all rolling roads needs to be able to do a coastdown loss test. The inertia of the drum is a given so anything else is combined rolling inertia of the drivetrain which can then be added. The motoring loss friction won't be the same as decel loss friction inside the drivetrain though but again what that is won't be a fixed amount for every vehicle - if i superfinish diff and box internals the friction just by hand is massively reduced let alone with 1800ftlb torque on it. Assuming a percentage loss is wrong on so many levels.

Often I have to test the same engine repeatedly during engine development and on a chassis dyno if you don't have absolute control (or near as damn it) over all these factors then you may as well not bother as you can end up throwing good parts away. Imagine the chart in this post http://www.gtr.co.uk/forum/2175441-post24.html If you'd done that on two different days with a 70bhp error due to dyno setup then how on earth could you be testing a modification with regards to spool for example? The same engine reaches 220lbft 500rpm earlier with no changes.


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## thistle (Oct 27, 2007)

Thanks. The coastdown losses are greater than the "drivetrain" + single contact patch losses on the road because they include double compressed/tied down contact patch and losses in the dyno itself? This simplistic understanding has always made me a fan of the coastdown correction because whilst not perfect it does remove some difficult to control variables, and I often feel the differences between modification gains/losses is less than dyno bias.


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## Adamantium (Jun 24, 2002)

John, 

I know that not dynodynamics are but not all dynos have twin rollers. Personally I don't like the fact that on dyno dynamics the axles are not connected to one another, and so coast down losses, if measured are again not comparable to the road.

I hate to say it, but the american convention of quoting power at the wheels though not perfect, does have its advantages.

For crank horsepower we really should only be relying on engine dyno numbers.


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## Tim Radley (Aug 3, 2013)

Adamantium said:


> John,
> 
> I know that not dynodynamics are but not all dynos have twin rollers. Personally I don't like the fact that on dyno dynamics the axles are not connected to one another, and so coast down losses, if measured are again not comparable to the road.
> 
> ...


Only problem there is the DYNOJET AWHP is not actually wheel power its estimated flywheel.:thumbsup:


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## Conrad (Jul 29, 2004)

Adamantium said:


> John,
> 
> I know that not dynodynamics are but not all dynos have twin rollers. Personally I don't like the fact that on dyno dynamics the axles are not connected to one another, and so coast down losses, if measured are again not comparable to the road.
> 
> ...


Adam, coast down losses are not measured on Dyno Dynamics. The "estimated" flywheel figure is derived from a % calculation and a value in a look up table based on the transmission type selected for the run.


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## thistle (Oct 27, 2007)

On our funny asymmetric drivetrain with shuffling torque, the coastdown could indeed be weird without the rollers rotating together.

An appropriate coastdown technique I think solves far more issues than it creates though and an engine dyno not just with different exhaust/intercooler/airflow also presents different loading so is no panacea either. If it was, you wouldn't need to finish off an engine dyno tune on the road.

With wheel figures, how do you correct/control for:

Tyre size/temperature/pressure/type/condition/deformation due to tie down force
Axle spacing
Gear oil temperature/viscosity
Gearing

The coastdown run attempts to correct for all these factors.

The "use wheel figures because that is what it puts down to the asphalt" hides a multitude of sins. I like ********, but it is just a bit too *******.


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## Adamantium (Jun 24, 2002)

At sema in 2011 they had a road dyno that involved disconnection of the prop from the rear diff and connecting it direct to the dyno.

It gave engine dyno readouts but utilised the car's systems and ecu.

Sure it wasn't a quick installation rolling road type affair but it did solve a lot of problems. Not taken off though!

Conrad, for coastdown, I recall that DD calculates which as stated must be nonsense, but I do recall seeing a coastdown graph generated after each run, perhaps I am thinking of the maha at power engineering, or Rob's dastek at perfect touch.


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## Conrad (Jul 29, 2004)

Adamantium said:


> At sema in 2011 they had a road dyno that involved disconnection of the prop from the rear diff and connecting it direct to the dyno.
> 
> It gave engine dyno readouts but utilised the car's systems and ecu.
> 
> ...


Adam, definately not the Dyno Dynamics


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## Adamantium (Jun 24, 2002)

Conrad, what would you know about DD, it's not as if you have owned one!


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## Conrad (Jul 29, 2004)

Adamantium said:


> Conrad, what would you know about DD, it's not as if you have owned one!


A long time ago mate


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## [email protected] (Sep 7, 2006)

I had 2 GTR's on the dyno on Saturday and I coast tested both and there was a 10bhp difference in losses.

Differences in the cars were

Car 1 - Stock Tyre sizes
Car 2 - 285/305 Tyre widths

Car 1 - Stock Size Alcon Front Rotors
Car 2 - 400mm Alcon Front Rotors

The wheel horse power would therefore be a poor indication of the comparison as there was only 20bhp difference at the wheels but 30bhp ATF between the cars.


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## [email protected] M/S (Feb 16, 2002)

car runs in 4wd on power but 2wd on coast, so I never take any notice of coast down figures.


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## Conrad (Jul 29, 2004)

[email protected] M/S said:


> car runs in 4wd on power but 2wd on coast, so I never take any notice of coast down figures.


Why on earth would you do that?


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## [email protected] M/S (Feb 16, 2002)

It how the car run, when you have the throttle pedal down on the dyno pull , it runs full 4wd , when you lift at the end of the run it release's the drive to the front wheels via the transfer clutch so the coast down figure arent correct and if you blip the throttle on the run down it flicks torque to the front wheels so the coast down figure would be in correct any way.

Still running all the transmission like normal.


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## [email protected] (Sep 7, 2006)

How are you running a coast down?


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## [email protected] M/S (Feb 16, 2002)

I don't but I have used another roller dyno's I'm my time to know what they do and don't.


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## Conrad (Jul 29, 2004)

[email protected] M/S said:


> It how the car run, when you have the throttle pedal down on the dyno pull , it runs full 4wd , when you lift at the end of the run it release's the drive to the front wheels via the transfer clutch so the coast down figure arent correct and if you blip the throttle on the run down it flicks torque to the front wheels so the coast down figure would be in correct any way.
> 
> Still running all the transmission like normal.


But there is still some drive to the front diff? Unless you have an ETS pro or something like that then there is still pressure on the transfer clutches as it never goes to zero?


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## [email protected] M/S (Feb 16, 2002)

Aren't we taking about 35GTR's?


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## Tim Radley (Aug 3, 2013)

All four wheels will have a bunch of inertia (losses) regardless of whether they are driven or coasting.


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## [email protected] M/S (Feb 16, 2002)

Yes I agree Tim, but blipping the throttle on the coast down increase the losses so bumping the flywheel figure.


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## Tim Radley (Aug 3, 2013)

[email protected] M/S said:


> Yes I agree Tim, but blipping the throttle on the coast down increase the losses so bumping the flywheel figure.


I dip the clutch on coast down test so whether its shut or at full throttle for 20 seconds makes no difference to the loss measurement. Maybe others do it differently???


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