[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]

Re: bore/stroke (was Re: [T3] 74/78 crank?)

On 21 Nov 2003 at 22:33, Per Lindgren wrote:

> One thing is certain, longer stroke equals more torque.

That's true, but it's also true that more bore gives more torque.  

I don't know all the ins and outs, but one thing I hear talked about is peak or 
average piston speed, which relates to frictional power loss and ring wear. For 
a given RPM, piston speed goes up with stroke.  

OTOH, swept ring area goes up with bore, but I don't recall anyone ever 
bringing this factor up. Seems like it should be at least somewhat important.  

If piston speed is more inportant that ring swept area then it would make sense 
to make diesels with long strokes because they work best at low RPMs anyway, 
have large combustions pressures (giving rise to pistons forces that would only 
be achieved in a gas engine with larger bores), plus they really NEED the long 
stroke to get the compression ratios high enough for diesel operation. It's 
also true that once you reach a stroke long enough to get good diesel 
operation, you can then increase the bore to as much as the rod and main 
bearings will take.  

In the end, I suspect it's really hard to generalize about bore and stroke, 
because there have been so many combinations tried, and most of them have been 
done successfully by someone.  

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]