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Dyno Differences

JH32

By JH32,
in General Automotive Discussion

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Guest Nismo_Freak

Guest Nismo_Freak

Posted
Posted

No shit mate... Im in the US and just realized that the standard KW --> HP doesnt work on you Aussies #s. That blue GTR that put out 440rwkw comes out to 600rwhp ... however they later ran it in the hp figure and it came out to 800+!! All this time I was thinking the RB25 was making 250rwhp on full bolt ons when its really pushing the 300rwhp mark.

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blind_elk Grand Master

blind_elk

Posted
Posted

They still have to be calibrated against something, same as scales are calibrated against known weights. If the calibration 'standard' is wrong, then the dyno is wrong.

Also, depends on the ramping they use to release the load, and the gear its run in, temperature compensation, and other variables.

Nismo_Freak,

The 800hp would have to be flywheel HP. kw -> hp is a constant. so it puts out 440 rwkW and it puts out 600 rwHP, because the conversion factor is constant. (There are some dynos claiming to be able to calculate drive-train losses).

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Guest air

Guest air

Posted
Posted
Originally posted by JiMiH

If a dyno is essentially an instrument for measuring power output, then why can't they all be standardised?

Like a set of scales, or a temperature guage??

Its hard to standardise it because unlike scales working directly off an known quantity, it is equating a known quantity (torque) with an "assumed" or "projected" (insert preverbial!) quantity (RPM) and calculating your horsepower from it.

The dyno measures the torque... but to calculate the hp you have to be sure of the RPM... thus these factors can contribute:

- Tyre sizes! (affect RPM <-> speedo)

- Gear Ratio (Sometimes not the actual ratio ... affects speed)

- Wheel slippage (get ppl in the trunk!!!!)

- Drivetrain losses (where do you start?!)

Thus you can correct the figures to reflect the conditions.

The only thing you can measure is the twisting force or torque. That can be calibrated directly from, say, a set of rollers that can produce a certain level of resistance (voici le dyno!). But how do you work out horsepower from torque?!?! Its hp = torque * rpm / 5252... and the only other variable in that equation is RPM.... and all those "other" factors I outlined above can affect RPM...... which can affect the equation.... which can affect your HP reading.... and whether the dyno can correct itself or not is still not going to be as accurate as, say, a scale which can be calibrated to a known weight.

Yeah.

:burnout:

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