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Discussion Starter #1
Hello to all knowledgeable folk.

A minor question that could possible spark some debate :

If a car is stated as haveing 420bhp at the Flywheel, what would be the typical losses in power to the running gear on an R32 GT-R.

In fact, for any Skyline as this information would be interested from a tuning point of view as to how much realistic power is going to be achieved.

Cheers,

Alex
 

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25-35% or more is typical for 4wd. (more for auto's I would think)
8-20% RWD (Manual and Auto's covered.
Less on FWD but I am not really sure of the range think is can be as low as 6%...

All figures are based on what I've heard....

You are best off, though, getting a reading for your car via a HUB based dyno.

Abbey and Thor have hub based dyno's which remove tyre slip from the equation - this will get you a reliable MECHANICAL power loss figure to which you will have to add a %age of loss when back on the road to take into account the the wheels and tyres. Different tyres will cost you varying amounts of power.
 

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power losses

GTRs when driven on the road are in 2wd most of the time
they only go into 4wd when the electronics sense that there is need for 4wd.

on a dyno they run in 4wd all the time

on the road they don't

more power on the road than what you see when on a dyno ???????


Keith
 

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Why hubs

Why ? are you best off getting a power reading from the hubs alex, what does this mean, it is just another way of measuring power,
Road wheels are what transmit the power to the road, why should if you prepare the base and perform the test should you not be able to get a reading without slip.
We had a car slip the clutch BEFORE it lost traction from the tyres to the roller.
Power measurement is just what you get at the time of the test and whilst you are testing all you want is the higest figure throught the rev range regardless how it is measured
Gary
GT
ART
 

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Discussion Starter #6
i was just after rough guideline fgures really.

See, I think that a power rating should be given at the wheels / hubs, because that is the force you are delivering to the road to propel the vehicle.

When looking to buy a car or looking at peoples stats, they tend to state at the fly, which in my mind (and is my taste I guess) is not the true figure, for me the true figure is the delvery power.

Not to say that everyone should think like that, it is just my preference.

Cheers,

Alex
 

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I assume that Gary was asking me...'tother Alex...

The question was about mechanical losses. I was giving a way of getting pure gearbox and drive train losses.
 

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I am curiuos when people say the Skyline doesn' have the normal drag of a a 4wd car as the system runs in 2wd mode. Unless the skyline uses freehubs on the front, this is not correct at all.

Much of the drive line loses are viscous and do not depend on load. So while the front wheels may not have significant torque applied to them, they still sap power from the centre diff all the way to the front wheels. The driveshafts are still turning as is the propshaft, etc. All the losses in the bearings are still there.

Paul
 

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Discussion Starter #10
I think it is the fact that at the hub and at the wheel there is not much loss, due to the elasticity of the tyre the power will be transfered in most cases at some point during a revolution.

Most of the mechanical loss is through drive shafts diffs, gearboxes etc etc.
 

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I'm sure part of it probably also comes down to ease and convenience.. When the cars start getting up to very high power, it gets harder and harder to keep them strapped down to the rollers and the slip under control..

Not to mention that if anyone makes a mistake strapping the car down, you can have a nasty mess of a car & workshop.. no such problem with the hub dyno..

I think personally I'd feel safer with my car on a hub dyno than a roller dyno :)

(I'm sure you knew all that already though Nismo_Freak.. I'm just bored and looking for excuses to post!)

Aaron
 

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Nismo_Freak said:
Power at the wheels is the true output of the vehicle. You can't drive around on all four hubs with your GTR, so why bother using a hub dyno to predict actual horsepower output?
they are designed for acurate, repeatable, mapping not power runs....but they can do power runs...

Why are you so hostile to Hub dyno's? Abbey thought they were a good idea and by all accounts you lot think a lot of Abbey's opinion.

:( :confused:

:)
 

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LOSSSES

Posted with no disrespect for HUB tuners,its all the same or is it ?
Power should be measured at the wheels,
The hubs is a totally different thing, what is power at the hubs ?come on it is just a different way of measurement, It will show higer output as you have taken away the wheel and tyre, in reality it is important as you dont drive your car on the hubs do you.
This is not intended as a slur for the hub dynos but will probably be taken as one if so Sorry
I was told the other day that dyno pac was water based is this true as i thought it was oil based,
I wont write anymore but i am glad i have my dyno dynamics dyno on its way:D
 

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I don't know why people get so 'precious' about this subject. It can only be down down to either vested interests or personal preference I suppose.

As far as I can see, each system has it's advantages and disadvantages. Why people say that hub dynos aren't any good because you don't drive around on your hubs makes me laugh, why produce engine dynos then because you don't drive around on your engine either do you...?

It all seems to come back to the power issue and which system is more accurate. More accurate for what? Measuring the power at the flywheel? If so, clearly the engine dyno wins. The further you move away from the engine, the greater the losses so in theory, a chassis dyno will be furthest from actual engine output and as such require the greatest amount of interpolation of the result to get back to flywheel figures. Sure power at the wheels is the true measure of performance but if anybody truly believes that this method of expressing power will catch on, then they are living in cloud cuckoo land. Flywheel power will always be quoted because that's the most and we all want the most don't we.

There are inaccuracies in all systems, all systems can be manipulated to produce better or worse figures, I've seen it demonstrated to me, I've been, for want of a better word, a victim of 'massaged' figures. There will never be universal agreement on the best and most accurate system so why not just use them for what they should be used for, tuning. And for that purpose, I cannot see much difference between a hub dyno and a chassis dyno. Personally, the hub dyno felt much more secure to me but I wouldn't advocate either personally as the final means of tuning, OK for good intermediate means of setting up but the black stuff is the ONLY place where you can finish it all off, end of. IMHO of course. :D
 

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Totally agree

I tried measuring at the flywheel but sitting on the plenum got totally dizzy counting how many times i went round, then holding on to the scales was just impossible, but then so is driving on your hubs,
driving on your wheels is possible, but all said and done
Peter you are correct and you worded it perfectly,
just use the things for tuning
regards
Gary
GT
ART
 

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alex h said:
they are designed for acurate, repeatable, mapping not power runs....but they can do power runs...

Why are you so hostile to Hub dyno's? Abbey thought they were a good idea and by all accounts you lot think a lot of Abbey's opinion.

:( :confused:

:)
I don't know why you singled out my post. I'm 3000+ miles away from Abbey and have never spoken, talked, chatted, or as much as seen anything they have done, nor have I ever said anything good or bad about them.

Plus I'm not hostile towards the hub dyno...
 

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Alexb said:
I think it is the fact that at the hub and at the wheel there is not much loss, due to the elasticity of the tyre the power will be transfered in most cases at some point during a revolution.

Most of the mechanical loss is through drive shafts diffs, gearboxes etc etc.
By all accounts, you're quite wrong there Alex. The tyres contribute considerably to the 'transmission' losses. As an approximate estimate, on a stage 1 ish car, you'll suffer around 120 - 130bhp losses from flywheel to road and around 50 - 60bhp from flywheel to hubs, I think... :)

On the question raised by Pavlo about 2/4wd losses, as far as I can understand it, losses also occur at bearings and the like so I'm sure that there is a fairly substantial difference when a GTR is dynoed in 2wd and 4wd. I'm sure this has been done back to back and proved somewhere...?
 

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.

:)
 
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