MarkoNTL 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.
>
>
> The actual reason is that long-stroke engines tend to have smaller ports and
> valves (do favour low speed torque) due to the smaller bore and reduced
> room, whereas short-stroke engines tend to have bigger ports and valves
> ('cos they can fit 'em in the bigger bore space available). Put small ports
> and valves on a large-bore, short-stroke engine and it'll be a low-revving
> torque monster too, everything else being equal.
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.
Bill Lawrence
>
>
> Some interesting stuff, "debunks" a lot of mis-information out there.
> http://www.motionsoftware.com/minigide.htm
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