Jac - I would think vibration would still be worse in the flat plane mode.I remember my friends Chevy Monza which ,early on, came through with a 180 crank.The engine(V6) seemed to have more torque than the comparable motor with the conventional crank - it felt quicker but you definitely knew when the engine was pulling as it was noticeably rougher and for some reason,louder.Also,I had thought that the Sprint car boys went the flat plane route in their Chevy's to get more torque off the corner and to allow more time between power pulses so the tires could get more bite in the dirt.As for less rotating mass,you could get the same benefit for a lot less dough by using a smaller diameter and lighter flywheel and smaller multi disc clutch. Your opinion? A.J.
I’m more or less parroting what Jac Mac stated. I think you might be confusing common pin crank for a flat plane. The v-6 by design realistically can’t be had in a flat plane config, though I guess it could if one really really wanted that. A 90 degree V-6 block with common pin would be odd fire and would have vibrations induced from the odd firing times.
Below are a couple illustrations for the common crank configuration for single and dual plane V-8 cranks,
(inline 4’s and flat 4’s are also flat plane).
Left is "
Single Plane", right is "
Dual Plane"
Note the crank pin configuration. When looking down the front of the crank, there is a crank pin every 90 degrees, on two planes, hence the name Dual plane, or 90 degree crank.
Here is how the dual plane/90 degree crank looks;
DUAL PLANE
Here is
Dual Plane LS1 crank and CAD rendering of a
Dual Plane SBC 350 crank;
Here is how the single plane/180 degree crank looks;
SINGLE PLANE
And here is a Ferrari 355
Single Plane V-8 crank;
…and here is a SBC
Single Plane Crankshaft
(two piece rear main seal)!
As for power/torque differences between the two crankshaft designs for a given displacement and comparable builds? Here is a partial list of the pros and cons for single plane and dual pane V-8 crankshafts, as I understand them.
Single Plane;
Pros;
1) Exhaust pipe length tuning due to the even pulses per bank of cylinders, (
on a 400 HP engine could be worth 5-10 HP).
2) Exhaust note, (
this is more of a personal taste thing)
3) Lighter weight crank due to less mass needed in the counterweights for a given stroke. Faster revs, though not as smooth.
4) It’s different!
Cons;
1) 2nd order harmonics. Those harmonics are exaggerated with displacement, rod to stroke ratio determining how much 2nd order vibration, as well as how much stroke impacting the amplitude of those harmonics, (
buzzy like big displacement four cylinder engines).
2) Cost of the crank and slightly more cost for the custom cam.
3) Complexity added to the project.
Dual Plane;
Pros;
1) Much smoother from a vibration/harmonics standpoint.
2) Readily available.
3) Exhaust note, (
this is more of a personal taste thing)
4) Longer stroke/larger displacements without added buzziness.
Cons;
1) For given stroke, has more mass in the counterweights. Slower revs, but smoother.
2) For me anyhow, the exhaust note is a con. (
Again, this is more of a personal taste than a performance aspect)
I apologize if I'm boring you guys or spewing too much...