ynotink wrote:
>> Long-stroke doesn't mean low-speed torque, got nothing to do with it
>> at all actually.
> Actually it does for the reason stated. The force on the piston (BMEP)
> multiplied by the additional stroke length determines the additional
> torque to be expected from a longer stroke.
Other things come into play there my friend, take a look at that miniguide.
> I don't think the size of the ports in itself affects the potential
> torque. The tendency to combine greater valve overlaps with larger
> ports to improve cylinder filling and increase horsepower output
> works to decrease torque capacity. This is because opening the intake
> earlier and closing the exhaust later decreases the duration of the
> power stroke.
>
> There are several other factors in the torque/power interaction that
> are lost in the mists of my mind.
Well go find them before you say what does and does not affect torque...
torque = cylinder filling. Get more air and fuel into the engine and you'll
get mroe torque. The difference betweeen a low-rev torque monster and a
high-rev power-monster is where the engine is 'tuned' for torque. The cam
profile, the valve and port sizes, and the manifolding arrangments determine
this. Long 'runners' on manifolds, narrow ports, small valves, mild cam with
little overlap all mean a torque peak at low revs. Short runners, big ports,
big valves, bonkers cam mean high-rev torque.
As it happens, most long-stroke engines do tend to have small-valves, small
ports, long runners and mild cams, which is why the make low-rev torque; but
if you were to put those same small valves, small ports, long runner, mild
cams onto a short-stroke wide-bore engine you would make exactly the same
low-rev torque. So square or over-square has 'owt to do with where it makes
its peak torque.
"The tendency to combine greater valve overlaps with larger ports to improve
cylinder filling and increase horsepower output works to decrease torque
capacity."
It moves the torque-peak up the rev-range, so the smae torque moved higher
up makes more power. Honda S2000, THE bonkers high-revving road car, 240bhp
from 2 litres, 140something lbft peak torque. Land-Rover Discovery
pi (a 2 litre petrol version we got in the UK), 131bhp from 2 litres,
136lbft peak torque. Torque is basically the same, not decreased, just in a
different place..
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This archive was generated by hypermail 2b30 : Sat Mar 29 2003 - 06:27:47 EST