Dyno fail. FAO: Scubascorpion

[TW]Fox;15845108 said:
Are you the same guy who said the Vauxhall Corsa was the best all round car on sale?
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Kind of, I said I thought it was the best all round car for the money - at the time, it was the perfect compromise of everything I wanted out of a car.

Why is that relevant?
 
Scuzi said:
I did but I never got a satisfactory answer. I don't know about anyone else but the flywheel figure is irrelevant to me. I'd much rather have an accurate at the wheel figure since it is more relevant when comparing to other cars.
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Only if its the same dyno.

They should call it roller power rather than wheel, as the wheel figure you see on the road is different.

For a start for the dyno to measure the resisting power, it would need to apply it to the car which would mean a fixed rpm.... that doesnt happen on a power run ;)
 
L0rdMike said:
Im not really bothered about the wheel figure too much, every thing is quoted at the fly more or less all the time.
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That's true, but what if you want to compare, a FWD car, a RWD car and an AWD car? At the fly means less than at the wheels with varying drivetrain losses. If you don't have at the wheels figures for the other car at the fly is more useful. I'd rather have at the wheels for all of them.
 
MikeHiow, quick brief for you.

1 contact Patch rolling road creates a flywheel figure of say 300bhp. It's ATW figure was 225bhp and therefore, on it's "run down" it created 75bhp DRAG LOSSES.

Do you deem this inaccurate ? Or is this right because it only has one contact patch?

2 contact patch rollling road creates a flywheel figure of 300bhp. It's ATW figure was 185bhp and therefore, on it's "run down" it created 115bhp DRAG LOSSES.

Now can you tell me the difference?

Wait, I can! The 2 contact patch has more resistance, due to a larger part of the tyre being in contact with said rollers, therefore there was more drag. However, both then use the roller BHP + the roller drag losses to create the ATF bhp.

Theeeerefore, they come out with similar results, based on the condition of the tyres, inflation, gearbox oil blah blah. Just done slightly differently, but actually done the same way..

Maketh senseth?
 
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ScoobyDoo69 said:
MikeHiow, quick brief for you.

1 contact Patch rolling road creates a flywheel figure of say 300bhp. It's ATW figure was 225bhp and therefore, on it's "run down" it created 75bhp DRAG LOSSES.

Do you deem this inaccurate ? Or is this right because it only has one contact patch?

2 contact patch rollling road creates a flywheel figure of 300bhp. It's ATW figure was 185bhp and therefore, on it's "run down" it created 115bhp DRAG LOSSES.

Now can you tell me the difference?

Wait, I can! The 2 contact patch has more resistance, due to a larger part of the tyre being in contact with said rollers, therefore there was more drag. However, both then use the roller BHP + the roller drag losses to create the ATF bhp

Maketh senseth?
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That would make sense, IF and that's a huge if, coast down was a reliable gauge of drivetrain losses - except it isn't.
 
burns said:
That's true, but what if you want to compare, a FWD car, a RWD car and an AWD car? At the fly means less than at the wheels with varying drivetrain losses. If you don't have at the wheels figures for the other car at the fly is more useful. I'd rather have at the wheels for all of them.
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You would but I couldnt give a toss what it is at the wheels.
 
Just to clarify, I don't believe any dyno bar an engine dyno is ever going to be 100% accurate, they do however make for a great idea of what power you're making, where in the rev range, and make for amazing tuning tools, and can give pretty damn accurate results at times.
 
Besides if you have work done on your car you should go to the same dyno. My MR2 ran on 3 different dynos making all sorts of power.
 
ScoobyDoo69 said:
So where do YOU get your 275bhp / 324lbft figure from?
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From the tuner who makes before and after runs, and gives figures in BHP increases rather than the resulting power figure, so given that the actual figures are irrelevant, and all that mattered in this measurement was consistency, I can put reasonable trust in the figures given to me. As I can in the manufacturer stated figure.

That said, you'll notice in the couple of times I've mentioned the power of my car in a post, I've stated an estimated 275bhp.

I'm not sure how that is a relevant retort to the fact that coast downs are not a reliable means to gauge transmission losses.
 
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