Flat Plane Crankshaft V8 engines can be balanced ?
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Teching In
Joined: Dec 2004
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Flat Plane Crankshaft V8 engines can be balanced ? Mitsubishi I4 has a balance shaft and Buik V6 also has a balance shaft too so can this be done to Flat Plane Crankshaft V8 engines for vibration cure ?
Last edited by aboadnan; Aug 30, 2019 at 02:02 AM. Reason: adding
Staging Lane
Joined: Mar 2011
Posts: 55
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From: SoCal
You would need 4 balance shafts, spinning at 2x crank speed to cancel out the 2nd order vibrations. Can be done, but I haven't seen it implemented before. Keeping the stroke short is the typical workaround.
On The Tree
Joined: Jan 2008
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From: Where you least expect me
A 4 cylinder's "secondary" mode is vertical at twice crankshaft speed. Since a single balance shaft produces a rotating couple, you have to have two counter-rotating balance shafts so that the lateral components cancel and only the vertical components remain to offset the engine's vertical vibration.
When you put two 4 cylinder engines together to make a V8, you get the two vibrations 90 degrees out from each other, which creates a rotating couple which can be offset by a single balance shaft.
More to the point... why? The basic purpose of the single plane V8 is better exhaust tuning for high RPM power. The balance shaft adds weight and rotating inertia that slows the engine's trips up and down the tachometer... If high RPM power and fast revving are not a requirement, just build a cross-plane V8.
When you put two 4 cylinder engines together to make a V8, you get the two vibrations 90 degrees out from each other, which creates a rotating couple which can be offset by a single balance shaft.
More to the point... why? The basic purpose of the single plane V8 is better exhaust tuning for high RPM power. The balance shaft adds weight and rotating inertia that slows the engine's trips up and down the tachometer... If high RPM power and fast revving are not a requirement, just build a cross-plane V8.
Teching In
Joined: Jun 2008
Posts: 9
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From: Columbus, Ohio
To balance perfectly, that single balance shaft has to be in the same place as the crankshaft. Anywhere else and it creates a moment. Two shafts, one on each side of the crank should work. But as others have said, why? The even firing of a flat plane, and the improved tuning only help with very long duration cams. Exhaust pulses on a bank can be separated in a tri-y, since firing pulses in each group of a tri-y on a bank of a two plane crank V-8 are 270-540. That isn't perfect, but pretty good.
