Quote:
Originally Posted by Sid Squid
I don't prefer either, but technically speaking fours are better then twins. Technically twins don't make better power at the low end, they just run out of the necessary piston/valve area and thus their volumetric efficiency falls significantly when the revs rise, add to this that for a given capacity a twin's relatively heavy reciprocating parts reach their practical limits at a lower rotational speed and the piston speed limit, (which I understand is about 90m/s for a road engine about now), of the relatively longer stroke limits the max safe revs - racing twins spin much faster as their much reduced engine life is not important.
The suggestion that you need to rev the round things off a four to make it go is just plain wrong, they often make good power at the bottom and keep going when twins run out of puff. And even if they didn't it's just numbers on a dial, who cares where the needle is pointing? Pit your SV650 against a Panther and it would seem revvy, would this be a reasonable criticism of your SV?.
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You could apply same arguments against fours and for sixes, and look how well they lasted
Twins making better power at low end can be lots of things, geometry of intake tracts, cam profiles and timing, carburetion, allsorts of things most of which could be applied to a four.
Redlines and such, if you have a twin of similar ratio to a four and similar peak piston speed it will probably rev about the same.
Compare the 'busa to the SV...
One thing worth mentioning with twins is crankcase pumping loss, they have 2 fluctuations offset by 90 deg... where a four has two pairs of them offset by 180 degrees so they cancel out. Means less losses shipping gas in and out of crank breathers and hence more power/economy.