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Old 12-27-2009, 10:23 PM   #1
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Default What is the difference in short stoke to long stoke motor?

Ok ill give a couple of examples then go into my question

Motor A: has a stroke of 16.48mm and the bore of 16.44mm

Motor B: has a stroke of 17.40mm and the bore of 16.00mm

Ok now if both motors in comparison is it safe to say the one with the longer stroke and smaller bore would be quicker [motor B] and will the storke or bore affect the performance as far as better bottom end or better top end.
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Old 12-27-2009, 11:31 PM   #2
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In theory long stroke have more torque rev alittle slower. Short stroke big bore are fast reving high rpm engines
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Old 12-27-2009, 11:33 PM   #3
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Originally Posted by pdmustgt View Post
In theory long stroke have more torque rev alittle slower. Short stroke big bore are fast reving high rpm engines
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Old 12-28-2009, 02:05 AM   #4
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In theory long stroke have more torque rev alittle slower. Short stroke big bore are fast reving high rpm engines
That just about covers it.
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Old 12-28-2009, 02:33 AM   #5
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True but not the reason with 2-stroke I think.

In my eyes it has to do wit the combustion stroke. The combustion stroke is actually from the top down to the moment the exhaust opens. Buggy engines have a lower exhaust port compared with onroad giving a longer combustion stroke which is giving the torque. In the search for more RPM (RPM = Horsepower) you do need to make the exhaust port higher and that means shortening the combustion stroke.
With a longer stroke you have room to make the exhaust higher without shortening the combustion stroke you normally have with square stroke.

In most cases going from 16.4mm to 16.8mm means the exhaust can be made 0.4mm higher and that is a lot while the diameter from 16.4 to 16.2 is almost nothing.

Funny thing is that the RB WS7 models are square stroke and in theory they should perform less in an offroad compared with a long stroke and yet the WS7 models are the most used engines with many victories.
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Old 12-28-2009, 03:09 AM   #6
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Default so true...

the ws7 is a square stroke that is a high rpm motor, so that about smashes the theory. It's also a slowe reving engine with less torque. Slow reving usually means less torque. In off road I've seen square to long stroke engines all perform well with no real differences based on Stroke. If the stroke is longer than the bore, even by .oooooo1 it's a long stroke. Based on the theory, long stroke engines tend to have more torque in 2 stroke engines, and seems to be the standard. Some older engines had short strokes, but mostly, at least in off road, the long stroke is top stuff, like the Nova P5, plus-4, nero el bullo de flamo, hehe... and so on.. Yes the square stroke ws7 is a great engine, but does lack torque, but on a big track they ramp up to 38,000 rpm. Idle all day long, and never flame out, and run cool as a, well you know.....
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Old 01-04-2010, 04:21 AM   #7
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There is some info here that you might find helpful for this discussion...

http://nitrokb.netne.net/engines/reading.html
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