On 28/03/2016 00:29, Dave Plowman (News) wrote:
In article ,
Vir Campestris wrote:
On 26/03/2016 14:53, Dave Plowman (News) wrote:
In article ,
Vir Campestris wrote:
Easy to remember. Two pies 'n' tea.

So:-
2 x pi x RPM x torque(lb.ft)
---------------------------- = BHP
33,000

Result is approx 112 bhp.


OK, now if it's generating 200BHP at 5000RPM, what's the torque? (I'd
have stuck with kW, about 84, with fewer conversions but that's not
important)

Think you may need to get your maths books out and revise. ;-)

Well, if it's too hard for you...

I'm not the one asking. And I've given you the means to calculate BHP or
torque at a given RPM. Which is why I suggested you revise your maths.

400nM at 2000RPM = 84kW (to the nearest integer) ~= 112HP.

Be better if you stuck to the same units.

I didn't choose to insert imperial. You did.

Reverse the transformation, and from 200HP you get 210lb-ft, or 284nM. A
little over half. Right?

You are the one doing the calcs.

Now, if you have a gearbox attached to this engine, and you set it to
reduce the output shaft to 1000RPM, what is the resultant torque at
those two engine speeds?

What is the point of all this? A gearbox multiplies the torque in
relationship to the ratio of the gears, less any friction.


The point is, Dave, that you are unable to apply these calculations to
real world situations when they disagree with your prejudices. I'd hoped
to be able to talk you through it.

112BHP / 400nM at 2000 RPM geared down to 1000 RPM gives a little under
(because of friction) 800nM at the output.

200 BHP / 284nM at 5000 RPM geared down to 1000 RPM gives a little under
1420nM at the output.

This clearly shows you get more force by choosing peak power in a low
gear over peak torque in a higher one.

But, hey, if you want to believe otherwise when you've got the
mathematical skills to prove to yourself that your long held prejudice
is wrong - I'm not going to argue with you any more.

Andy