No life (a.k.a. DattoMaster)
Joined: 2008/10/10 22:02
From Melbourne Australia (and likely under the car)
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David Vizard spelt out the maths about light flywheels in one of his books about either minis or mini/bmc A-series engines. Basically with such small and relatively underpowered engines, esp with really outrageous gearing stuff approaching 5:1 diff gears with smaller tyre diameter than a datto, and that combined with the multiplication ratio of 1st gear as well and you're actually to the point that in first gear (and to a much lesser extent 2nd gear, and almost negligible in the higher gears) that flywheel weight actually 'appears' to the engine at full throttle to be a relevant weight/mass to be accelerated, since the torque multiplication of the diff/1st gear combined makes the engine 'think' the car is a lot lighter (sort of) vs if it had to accelerate it with 1:1 gearing and say a 3.7 diff. So in that first gear and with very low diff gears (higher numerical ratio) you can actually gain something like (traction willing) perhaps a 5% acceleration advantage with a lighter flywheel. I foget the exact figure quoted and obviously it would be different with different engines/cars and their specific gear/diff gear ratios, but the point is, traction willing it can have an effect in first gear.
But keep in mind just how little time the car will be in first gear at all before it hits the redline and the advantage is less than that '5%' approximate figure might otherwise suggest. Still, if you were in a very hotly contested and tightly restricted racing class and flywheel weight wasn't restricted to the lightest factory stock flywheel, well every little bit helps.
As already mentioned, it'd be an absolute abomination in gridlock traffic, also a little more 'fussy' if you were leaving from a standstill, when parked uphill somewhere and wanted to take off at a normal/sedate pace (if it's a racing takeoff, hillclimb, well you can give it all the rpms you want I guess. I'd probably suggest that for a street driven car, a pretty decent compromise would be running an a14/15 with an a12 flywheel. Personally I'm a bit of a masochist, and have always loved race cammed engines (don't even get me started on highly modified 2 stroke bikes, I think there's nothing more enjoyable to ride) and the lighter flywheel and all that. In a strange way the more difficult they are to get into the groove with and drive optimally the more satisfaction that comes from mastering their idiosynchrasies.
NOt suggesting I'd take that sort of car to work and back, but would have no reservations about street driving it on weekends in that state of tune :) .
Posted on: 2015/6/18 10:42
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