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Old 02-06-2012, 12:36 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by blight
I happen to be doing some reading recently on (ferrari, datsun L6 motors etc) v12s and L6s and angle of crankshafts etc. I came across some info on why v12s and L6 motors are "naturally balanced". Apparently aside from crankshaft angles uses of flat plane crankshafts, one of the biggest factors was the firing order of the engines and how that then affects the throw of each cylinder balance the other piston throws (in basic terms).

So - that being said, theoretically, what firing order would a sbc need to have to be balance like these motors?


on a side note
Has nothing to do with firing order, the issue is of secondary balance which is having a cylinder's parts in motion off setting the actions of another. In this case an inline 6 or a 60, 120,180 degree V12 have such a situation because of block and crankshaft configuration.

A 90 degree V8 always has a little secondary vib, there's no way around it by juggling firing orders or anything else short of a counter balance shaft.

The I6, V12 and V8 have primary balance which is the rotational masses in balance. The secondary balance the is motion of the reciprocating parts. Their motions are not linear with crankshaft degrees. Each piston with the rod small ends and some amount of shank have different rates of acceleration as the crankshaft turns and the reciprocating parts move up and down rather than round and round as the crank and big end of the rod do. For secondary balance there needs to be a combination of two cylinders worth of rods and pistons that are doing exactly the same acceleration but in reverse directions of motion to each other.

By "acceleration" I'm talking the different speeds the piston and upper rod travel at even when the engine itself is held to a constant RPM. This has nothing to do with speeding or slowing the crankshaft.

It's all in high school trigonometry class. Think how much more fun it would be with engines for examples instead of dry memorization of trig functions and the doing of inane problems. The SAE keeps bugging me to become a math mentor, maybe I should. That would be one bizarre math class.