Why does a bigger engine make more torque, but not necessarily more bhp?
23 May 2010, 10:37 AM
#4
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torque is the amount of work done, BHP is the speed in which that work is done.
in an engine and put very simply, it's because the bigger the displacement, the more work is carried out per cycle because the amount of fuel is greater in each cylinder or in a combination of cylinders generating more energy per cycle .................easiest comparison is a shovel, the bigger the shovel, the more work can be done per shovelfull, but more energy (fuel) is required to maintain a similar shovelling speed to a small shovel.
there is a comprimise though, the bigger the displacement, the slower the burn, per cylinder. (which is why bikes redline so high, and muscle cars redline so low)
not quite as simple as that, but you get the idea.
in an engine and put very simply, it's because the bigger the displacement, the more work is carried out per cycle because the amount of fuel is greater in each cylinder or in a combination of cylinders generating more energy per cycle .................easiest comparison is a shovel, the bigger the shovel, the more work can be done per shovelfull, but more energy (fuel) is required to maintain a similar shovelling speed to a small shovel.
there is a comprimise though, the bigger the displacement, the slower the burn, per cylinder. (which is why bikes redline so high, and muscle cars redline so low)
not quite as simple as that, but you get the idea.
23 May 2010, 10:52 AM
#6
I think it's something to do with area of displacement over length of stoke. APIDavid posted something about the relation of the two being over square in the bigger engine i.e 2.5 verses 2.0.
To get more power you need good torque x high revs, the bigger engine spools up quicker but doesn't produce as much torque higher up.
bin this if it sounds like crap.
Trev
To get more power you need good torque x high revs, the bigger engine spools up quicker but doesn't produce as much torque higher up.
bin this if it sounds like crap.
Trev
23 May 2010, 11:01 AM
#7
Don't forget that it's just a coincidence that bhp is a measuring unit that just happens to end up being a similar arbitary figure as the lb ft torque figure - at least in a forced induction and/or high displacement engine,
I'm sure you know this, but torque is a twisting force expressed as a function of force x distance - in this case expressed as the force of the weight unit of pounds, bearing down on the end of a 1 foot long bar, with the opposite end of the bar being the where the fulcrum (rotational axis) goes through.
bhp is a power unit which is the rate of that work done i.e. torque x rpm (amount of events over a measured time interval) = power
The less revvy and/or the greater displacement an engine is, will invariably yield greater peak lb ft torque number than its peak bhp power number.
I'm sure you know this, but torque is a twisting force expressed as a function of force x distance - in this case expressed as the force of the weight unit of pounds, bearing down on the end of a 1 foot long bar, with the opposite end of the bar being the where the fulcrum (rotational axis) goes through.
bhp is a power unit which is the rate of that work done i.e. torque x rpm (amount of events over a measured time interval) = power
The less revvy and/or the greater displacement an engine is, will invariably yield greater peak lb ft torque number than its peak bhp power number.
Last edited by joz8968; 23 May 2010 at 01:11 PM.
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23 May 2010, 01:47 PM
#12
lol, yeah coincidentally I watched, back to back, Chris Barrie's Massive Machines yesterday, and the one on the supertankers' turbo-diesel engines was mental. They showed that 12 cylinder one and the crank's massive bottom ends.... and the four turbos, each the size of a supermini car!!!
Utterly bonkers!
Utterly bonkers!
Last edited by joz8968; 23 May 2010 at 01:53 PM.
24 May 2010, 12:07 AM
#17
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The difference is that your 2.5 will spin all four wheels if you aren't wide awake !
Whilst a 2.0 won't.
Simples !
dunx
Whilst a 2.0 won't.
Simples !
dunx
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