at the risk of re-igniting a flame war....
BHP basically = RPM, if you want more BHP you need more RPM, more RPM = exponentially more load on every single component, putting that in human terms is making you walk up the stairs with your wife and kids on your shoulders, you'll likely pop an artery
Well since you asked.
Let me rewrite that so it is a little more accurate.
BHP basically = RPM * Torque, if you want more BHP you need more RPM or more Torque or both, more of either = .....
Of the rest anything else I may not agree with is open to different interpretations or too trivial to bring up.
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Andre' B.
BHP is a pretty good guide to fuel consumption, there is a very close correlation.
BHP can be expressed as energy.
Fuel can be expressed as energy.
more ROM = more air/fuel mixture pumped per second, so RPM is the energy control device
torque is a different thing entirely, except it is related, so people claim it isn't different.
BHP = Torque at 5252 RPM on every engine ever made, that alone tells you all you need to know, eg it is a semi arbitrary formula.
Torque @ various given RPM is all the engineer cares about, whether it's running low nines on a drag strip or building an economical and reliable engine like a lister.
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Analogies are drawn between BHP/Torque/RPM and between V/I/R
These analogies are as bogus as the claims made about BHP, I don't know how many times I've pulled 400 amperes DC on a welding cable and I have never seen that cable display any torque, ever, because there is a complete lack of mention of cutting lines of magnetic force.
6 bhp tell you nothing about an engine except its fuel consumption and thermal rejection.
50 ft/lbs tell you nothing about an engine except its ability to do some sort of work
6 bhp at 650 rpm tell you nothing about the power range of an engine, it could be on tickover.
50 ft/lbs at 650 rpm tell you nothing about an engine except its approximate swept volume per cylinder, it could be on tickover
50 ft/lbs and 6 bhp @ 650 rpm tells you something about the efficiency of the engine in converting fuel into work, if you look at the flat torque graph of a 6/1 it tells you you get 50 ft/lbs @ 650 rpm from a minute (6 bhp worth) rate of fuel consumption and thermal rejection.
Electric to IC analogies
Electric RPM = IC RPM
Electric KVA = IC BHP (which = IC fuel consumption)
Electric Torque = IC Torque
Electric KVA*** is a whole lot of things stuck together, 100 VDC @ 400 Amperes in a bus bar = no work done.
*** We need to specify is this motor or dynamo KVA? or just power in a conductor, not cutting lines of magnetic force.
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your original comment was "if you want more BHP you need more RPM or more Torque", which is true enough as far as a formula on paper goes.
In the real world more RPM can be done, within pretty severe limits, I know of no economic engine mod that can take double rpm, 10% is often doable, beyond that is diminishing returns and "if I was going there, I wouldn't start from here"
In creasing the RPM increases the number of times per minute the engine takes a fuel air charge, double rpm = double fuel usage rate and double thermal rejection (simplified to exclude lower efficiency at higher rpm)
In the real world more torque can't be done, sure you can blow it at 15 pounds boost, but you just doubled the fuel, same as if you doubled the rpm, that's about it as far as torque goes.
to re-ignite a previous example
A modern 600 cc japanese motorcycle engine and a 10 litre Gardner diesel both produce around 100 bhp, which means both consume fuel at about the same rate (albeit one burns diesel and one petrol, which have different calorific values) and both reject heat at about the same rate, but at the end of the day you will never ever ever drive a fully laden 40 ton truck with a 600 cc japanese motorcycle engine, no matter what gearbox you use, because as I keep saying, bhp is just revs, think about it, for a 600 cc engine to burn as much fuel, eg pump as much air, per minute as a 10 litre engine, it HAS to rev its bloody tits off...
there is only so much oxygen in 1000 litres of air, the MOST power you can get is by burning all of it, if you have a 1 litre engine it will HAVE to spin ten times as fast as a ten litre engine to consume that amount of air, and therefore oxygen, in any given time period.
Since oxygen in air is fixed, the only way to produce more "power" (eg bhp) is to burn fuel at a faster rate, and that means pump more air per second, so you either run a small pump fast or a big pump slow, either way you pump the SAME amount of air, use the SAME amount of fuel, and RPM related losses aside reject the SAME amount of heat.
Look into the ACTUAL thermal rejection of a 6 BHP lister as opposed to a 6 bhp @ 2600 rpm or 6 bhp @ 3900 rpm small diesel, and the lister rejects a significantly lower proportion of that SAME FUEL CONSUMED as heat, and that, my friends, is your torque.
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compressing gases and liquids* is not a joke, and it certainly is not a spring or elastic, it doesn't just pop back with no losses, the harder and faster you work it the greater the losses.... (liquids compress about 1% per 100 bar)
nobody seems to get this, meanwhile everyone is wondering why loads that are apparently within the capacity of generator X won't start, because your air compressor is a compressor, so is your Air Con, so is your well pump....
years ago we had to build a 4 stage pump to pipe water 1000 foot up a hill, 2" pipe, in summer that water came out hot enough to scald your skin, while we were doing it I got talking to a civil engineer, he said on big stuff like bridges it was a real problem to pump concrete to large heads and not steam cook it in the delivery pipe
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aero engines make about 2000-2500 rpm, why? smaller lighter engines could produce the same "power" at higher revs...
but it doesn't take power, eg fuel consumption or energy production at a specific rate, to get a plane off the ground, it takes torque, and that takes efficiency, and that means low rpm, which is why you has (relatively small for a fighter plane) 27 litre merlin engines putting out less than 1000 bhp....
fuel capacity = weight to get off the ground, burning fuel at the rate of 1000 bhp gave enough range and endurance to make the plane usable, more bhp = less range
but
a half size and weight engine would also mean more range, so it was never about bhp, only torque, which is why the dorniers etc had diesel engines
bhp + fuel tank size will give you the range of a car
torque + kerb weight will give you the standing quarter
torque + resistance will give you top speed
