|
Back in the mid 1960s Gordon Jennings wrote in his technical column in Cycle World about the oversquare/revver vs undersquare/torque issue, and found it to be somewhat bogus.
Keep in mind that undersquare bikes are often mildly tuned bikes, and thalso don't have much room for big valves, nor doa they rev very high and so friction losses are low. They also will tend to have bigger diameter flywheels (for a bike of the same size that is oversquare) and so will have more flywheel mass/rotating moment in the crankshaft, which will also make them seem "more torquey". So even a hopped up "long stroker" doesn't have as much potential for "hopping up" as a big bore/short stroke engine. GJ's example in the article was the English Ford 105E (Anglia IIRC) engine, which was a fairly oversquare car engine, but that he thought was very "torquey" when compared to the longer-stroke competition.
My Bultaco 326cc vintage trials bike has the same 60mm stroke as the 250 (83.2x60 vs 72x60) so it is pretty oversquare. Yet it makes less claimed HP than some of the earlier 250 trials bikes and with the very mild tuning and massive flywheels it is a LOT more difficult to stall.
Bore/stroke ratio is more of a concern when you are looking to develop maximum power. For the street porting/cam timing/valve sizes/exhaust/intake/effective flywheel mass is what will determine slogger vs revver.
Look at what niche the bike was built to fill. If it was very sporting, then a more plebian "commuter" version will probably give you what you want.
On the other hand, I rode an early 748 Ducati (stock but for exhausts/wheels, maybe a chip) a few laps around Sears Point, and for a sport bike my thought was "what a great street bike this engine would make". It was so smooth/torquey/linear, yet it was still very powerful/fast when pushed.
cheers,
Michael
|