Quote:
Originally Posted by mkoesel
And? The original hypothesis was that for a given displacement a longer stroke yields more torque. No one said anything about an RPM limitation on that claim. If the long stroke ultimately limits the engine in ways that keep it from being physically capable of making as much torque as an engine with the shorter stroke then we simply conclude the original hypothesis is invalid and move on.
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See my edited post with comparison of two similar engines, one oversquare the other undersquare (Kawasaki vs Honda CBX).
Wasn't the "original hypothesis" about two
comparable engines?
If not, the discussion would be meaningless, as we could have said the same about boost pressure as you just did about rpm (undersquare generally tolerates higher boost easier). Just using displacement would make a unusable comparison. CR, RPM, cam timing, ign timing, fuelling, exhaust and intake systems make a HUGE impact. Not just displacement...
You are not seriously suggesting it is fair to compare, say, a 60hp/l engine with a 120hp/l engine? There are many other different factors beside bore/stroke ratio between two such engines
We are talking of a 7500+rpm engine, one which would also be possible with a long stroke (like S54). If you are looking for a 9000rpm NA engine, oversquare is the preferable way to go. BECAUSE of that ability to rev to 9000rpm the engine makes more power and torque than a engine that revs to 6000rpm. But look at the dyno chart and you would see which one would be stronger low down...
I have thought that we discussed apples to apples, ie a engine that could be either over- or undersquare and what advantages either design has.
On the grounds you claimed, I cannot agree that the hypothesis is invalid. The only thing you have established is that a engine that revs to 9000rpm makes more power than a engine that revs to 6000rpm. And that if you want to rev to 9000rpm, you generally want a oversquare engine.
Displacement is just ONE factor. If you really want to know whether over- or undersquare makes more torque, you need to compare two similar engines. Similar as in more than just similar displacement...