PS has been creeping out for years. It is no longer the EU "legal" definition of power, and despite representing a German Horse Power, German horses are less powerful than British ones so causing all the more confusion. Perhaps the feeling they are "creeping in" is more a reflection of the cars you buy, or for cars where power is seen as so crucial, or even marketing where you get more PSs for your money?
kW is an international unit with no local variation, so perhaps best to stick to that?
He could also try studying basic mechanics. ;-)
It's like many things. One tends to stick to units you are familiar with - unless for professional reasons. Same way as many still give a person's height in feet. Know the price of a pint of milk. And so on.
A colleague of mine at Rover studied this is some detail, and plotted a graph of 0 - 30 times (admittedly not 0 - 60) against power to weight ratio for a wide range of vehicles. He found a very strong correlation.
Why compare a bike engine with V8 car engine?
If you take the same car and equip it with a high revving petrol engine, and then swap the engine for diesel which produces the same power but at a lower speed (with a suitable matching gearbox in each case) there will be very little difference in the accelerative performance - even though the level of drama may be different.
It depends on the amounts of inertia in the engines relative to the whole vehicle's inertia. The typical diesel equivalent to its petrol counterpart will have more inertia, reducing the overall acceleration performance despite providing the same top speed performance. This assumes the overall mass of the vehicles remain identical. In practice, the diesel variant tends to weigh a few pounds more than its petrol engined counterpart.
Of course, the ratios available in the gearbox along with clutch technique used when maximising acceleration performance will modify this, with full throttle change up and abuse of of the clutch even reversing this trend. An automatic box with continuously variable ratio configured to allow the engine to run at its peak BHP revs will eliminate such a difference.
You still can't grasp that "Full Throttle" does NOT equate to "Full Power"; it only equates to "Full Power" at Full Power" engine RPMs. Which means that you cannot accelerate AT "Full Power"; you can only accelerate UP TO "Full Power"
Well yes. Since most makers aim for the same sort of engine output curve.
Because you've singled out power to weight as some sort of benchmark. And it would be easy enough to find a small capacity high revving bike engine with the same sort of peak BHP as a lazy V8. Put them in vehicles so the power to weight ratio is the same, and see which one accelerates faster. It will be the one with the flatter torque curve.
I doubt it. Most modern diesel engines seem to produce near constant power over a very large range of revs. Bike engines don't.
Are you suggesting that it isn't power that accelerates a car and towed trailer to a desired speed?
If you regard torque as the single indicator of performance, you have a strange sense of performance.
No they dont. Perhaps more constant torque, but not power
e.g.
Torque flat to 3000, then tails away to peak power at 4500.
I mentioned in an earlier post that you needed to consider the effective mass of the engine in each gear and add it to the vehicle mass when calculating acceleration. The diesel engine will have a higher moment of inertia in absolute terms, but the diesel car will be higher geared - so the 'effective' mass of the engine probably won't be any greater than that of the petrol. [And no, I don't have any specific figures in order to verify that, but that is my hunch.]
Well, it seemed to apply to everything from a Fiat 500 to a V12 Jaguar.
It's not a practical thing to do - and you'd *have* to do it to prove whether or not your statement is true.
I'm not comparing it with a bike engine - that was Dave's idea!
But you haven't read what I wrote! I have never once asserted that full throttle equates to full power under all conditions - it clearly doesn't
- just look at an engine power curve, showing that max power only occurs at one specific engine speed.
What I actually said was that you needed to run the engine as close to max power as possible. Naturally *how* close to max power you can keep it as the car accelerates depends on how many gears you've got, and how they're spaced.
As I have said before, if you had a continuously variable transmission rather than a stepped gearbox, you *could* actually hold the engine at max power and continuously change the ratios to match the road speed.
So you stick the pedal to the metal at 40mph - full power and the car doesn't accelerate any further.
I've read everything that you written on this thread. All through it you've been using the words "Max Power" when you should have used the words "Full Throttle". The confusion is your fault. Now go and stick your head up a dead bear's bum.
You are the only one who's confused!
Whenever I've referred to max power I've meant just that - namely operating the engine at full throttle at the speed at which it produces its maximum power.
That's nice and friendly! How about trying to have a civilised discussion?
See what I mean about the misuse of 'power'?
Actually, quite easy to do.
But are you then saying power to weight isn't the be all and end all of acceleration?
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