FAO: Those who know about dynos...

[Flukester]

Personally I'd ignore anyone who quotes "crank hp" or "flywheel hp", it's different for every car, and that includes the same car at any given time.

imo they should give you whp and leave it at that, then people can properly compare hp.

Fantastic example of this is my mates ex-paseo, 89hp stock. He put a cone filter and a chav can on and some douche bags with a rolling road and an equation said it suddenly produced 114hp.

Also his MR2 apparently makes nearly 200hp (same place) even though it's a virtually stock GT T-bar.

no one should really being quoting or comparing anything tbh, yeah you get a VERY rough idea of power outputs but dynos should be seen as a tuning tool for 'before and after' nothing more.

I know my bike before tuning put out 157, and after 166 at wheel... not sure on the accuracy, but don't really care as felt it and the engine was much more responsive throughout rev range which is what I really wanted.

 

[siztenboots]

Yes, they have got something wrong on the power calculation. There are several standards for corrected dyno horse power, SAE , DIN , but you should always get the cross point at 5252 on the same scales

 

[Lashout_UK]

Not if they measure torque in Nm, or power in kW - and so on.

For example.

 

[Dogbreath]

Not if they measure torque in Nm, or power in kW - and so on.

True, but in the OPs case it clearly shows torque in lbft and power in horse power.

 

[Lashout_UK]

Yea I know, wasn't referring to that - should have quoted siztenboots really

 

[scratch]

I emailed the garage in the end, who came back with the following response to the dodgy graph:

Sorry for the error Andy, The graphs don't cross because the bhp is at the
flywheel and the torque figure is at the wheels, very sorry it was my fault
I just printed the graphs out wrong. Correct flywheel graph attached

Here's the corrected graph:

 

[BigglesPiP]

I thought that the curves should always cross at that point?

What idiot told you that?

The point/s they cross depends on the scales, so it is irrelevant.

 

[SpeedFreak]

Power of the vehicle as a function of torque and is used to normalise for the transmition. Power is used to compare two different vehicles with different transmitions, but if you are looking to compare improvements in your own vehicle, torque should be all that matters.

 

[Dogbreath]

The graphs don't cross because the bhp is at the
flywheel and the torque figure is at the wheels

It could be that the power curve has been corrected from the coast down run, but the displayed torque data has not.

What do I win?

 

[( |-| |2 ][ $]

What happens if you dyno a diesel that doesn't do 5252rpm?
Are you saying the graphs won't cross?

 

[mattyprice4004]

Changing the scales on a graph wouldn't alter the point at which they cross, it'd still cross at 5250rpm (?) or whatever other point they do. The graph would just look different.

Simple maths and obviousness, really

 

[Jonnycoupe]

Changing the scales on a graph wouldn't alter the point at which they cross, it'd still cross at 5250rpm (?) or whatever other point they do. The graph would just look different.

Simple maths and obviousness, really

It wouldn't if bhp and lbft had their own Y-axis with different values, nor if you have a graph showing bhp and Nm.

 

[Jonnycoupe]

What happens if you dyno a diesel that doesn't do 5252rpm?
Are you saying the graphs won't cross?

Yes they won't cross, its impossible.

Power = torque/5252 x rpm*

Here clearly an rpm of 5252 gives you a factor of 1 to apply to the torque, hence they cross as that have the same value here.

*Power in bhp, torque in lbft.

 

[Jonnycoupe]

What idiot told you that?

Someone using imperial units no doubt.

 

[howler]

here is my dyno dynamics rolling road graph after mapping to add some fuel to your discussion

Dyno Dynamics rolling roads are very reputable

 

[Dogbreath]

How come the plot goes "backwards" above a certain RPM? Is that part of the coast down that's been recorded?