Horsepower measurement

[Ascalon]

So, I think I remember reading that on average a rear wheel horsepower measurement is down something like 10-15% on crank figures.

This may have been from an old dyno and power measurement article from the Most Reverend John Robinson himself some years ago in PB.

Is this still valid? Or have improvements in gear box design, oil, chain and bearing technology reduced this?

Cheers all,

A

[David W]

If you ask me, the only power measurement should be what is measured at the rear wheel on a dyno. The rest is bollocks because if you reverse engineer heat losses, gearbox losses, friction losses, you end up with the calorific value of the petrol which is several hundred horsepower more than the engine can actually convert.

[porter_jamie]

he's kinda got a point there!

[Ascalon]

Cheers guys, just wondering ina blue sky sort of way.

A

[Tigger]

reminds me of a conversation with an engine tuner..... "you not get any ,ore power out of this" why? "because the injectors are at full flow for 2000rpm" ahhh I see, bar reducing frictional losses that's about your lot unless you can get somthing extra in efficiency from higher compression.

[Guest]

he's kinda got a point there!

Yes. Yes he has.

[wavydavy]

reminds me of a conversation with an engine tuner..... "you not get any ,ore power out of this" why? "because the injectors are at full flow for 2000rpm" ahhh I see, bar reducing frictional losses that's about your lot unless you can get somthing extra in efficiency from higher compression.

Ummmmmmm..... Air flow in? Exhaust gas flow out? Combustion efficiency? Valve timing? Ignition timing?

I can see what you are getting at, but injectors operating at 'full flow' on their own doesn't mean there's nothing more to come from the motor.

[kaighn80]

well yes if you phisically cant get any more fuel in then increasing the capacity of air in or exhaust out wont help you'll end up running lean and putting vents into pistons, although valve timing and ignition timing may help depending on wether or not they are right anyway. as far as things like injectors and fuel pump capacity (and most everything else) im a firm believer of the phrase "its better to have it and not need it than to need it and not have it" after all you can always turn it down if you need to (sometimes) was it the rs500 that had 8 injectors and had them wired so that the second bank of four came in when the first ran out of adjustment? or maybe one of the honda racers?

[Spartacus]

Ummmmmmm..... Air flow in? Exhaust gas flow out? Combustion efficiency? Valve timing? Ignition timing?

I can see what you are getting at, but injectors operating at 'full flow' on their own doesn't mean there's nothing more to come from the motor.

You could have them open a bit longer? Wouldn't take much to get the extra fuel in?

[kaighn80]

but if the injectors are flat out and its having all the fuel in the bore then all that will happen is the piston will start to come up before the valve closes and then the fuel air mix will be pushed out the valve and its no better off. infact its worse off as it will be running like its restricted. if the injectors are maxed out get biggerones or fit another set so you can turn it down and start from there again. milliemillie knows im sure he's faffed around with this kind of setup before i seem to remember a single that needed more fuel. pick his brains advice costs nothing.