Talk:Flat-6
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Corvair section isn't all that accurate.
66.56.28.232 11:22, 29 September 2007 (UTC)
[edit] Balance and Vibration
"The movement of the pistons in a horizontal engine is all in the same plane, so it creates less vibration than in a V-configuration engine; particularly one with an odd number of cylinders on each side of the engine, like a V6. Unlike the V6 but like the inline-6, the flat-6 is a fully balanced configuration which is in perfect primary and secondary balance. The three cylinders on each side of the crankcase tend to have an end-to-end rocking motion, like a pair of straight-3 engines, but in the usual boxer engine configuration, the imbalances on each side cancel each other, resulting in a perfectly smooth engine.""
That is nonsense. For starters, the terms "primary balance" and "secondary balance" have no universal definition, and whenever anyone uses these terms, it is a dead giveaway that they don't really understand anything about this stuff, and are merely regurgitating some nonsense that they read somewhere else. It is not possible for the three cylinders on one side to cancel the end-over-end rotation of the crankcase that is caused by the three cylinders on the other side. The only way that would be possible would be if there were four cylinders on each side, in which case the rocking motion is cancelled on each side independently of the other side. —Preceding unsigned comment added by Princesscheetah (talk • contribs) 18:59, 13 April 2008 (UTC)
- It's not nonsense, nor does it suffer from lack of definitions. Primary imbalances tend to cause vibration at engine speed, secondary imbalances tend cause vibrations at twice engine speed, and tertiary imbalances cause vibrations at three times engine speed. Higher order balances tend to cause much less vibration than lower order balances. Hence, primary imbalances are very serious, secondary imbalances are considerably less so, and tertiary imbalances not much of a concern at all. Straight-3 engines have a primary imbalance that causes an end-to-end rocking motion at engine speed that is very annoying unless canceled by a balancing shaft. Straight-4 engines are in primary balance but have a secondary up-and-down vibration at twice engine speed that only needs balance shafts in the larger displacements.
- Now, a flat-6 configuration consists of two straight-3 engines laying on their side and connected to the same crankshaft. In the horizontally-opposed or boxer configuration, the two halves are mirror images of each other and the directly opposing pistons are moving toward each other or away from each other at the same time. So, while one three-cylinder bank is trying to rock clockwise, the other other bank is trying to rock counterclockwise, and the two motions cancel each other. Hence the engine is in perfect primary balance. Straight-3 engines have no secondary imbalances, so all you are left with is an intrinsic tertiary vibration caused by the fact there are only three cylinders firing per crankshaft revolution, and as I said, tertiary vibrations are not much of a problem.
- Flat-8 engines would be even better, because in the boxer configuration the secondary vibrations of the two straight-4 banks will cancel each other, there are no tertiary vibrations, and all you are left with is an intrinsic quaternary vibration which should be insignificant. But nobody has a problem with the tertiary vibrations of the flat-6 (which are themselves very expensive to build), so nobody bothers with flat-8s. They are sometimes used in racing engines, but racers are not concerned with a few vibrations, so they usually use the non-boxer or 180° V8 layout in which opposing pistons share crank journals. In this case the two banks reinforce rather than cancel the secondary imbalances, and the engine has a rather nasty side-to-side vibration at twice crankshaft speed. They just use lots of lock washers, secure all the fasteners very well, and hope the engine doesn't shake the car to pieces at high speed.RockyMtnGuy (talk) 02:45, 14 April 2008 (UTC)
