Crossplane
Crossplane crankshafts could feasibly be used with a great many other cylinder configurations, but the advantages and disadvantages described below may not apply to any or all of them and must be considered on a case-by-case basis.
Because four pistons stop and start together in the same plane in both banks, the second-order forces inherent to the flatplane design stack up and become noticeable in large displacement engines.
Each bank of the crossplane engine has four distinct piston phases that cancel the second-order free forces entirely, leaving only minor vibrations due to variation in masses of components during manufacture.
In later years, first Indee and later F1 engine developers took notice in the high revving potential of flat plane crank V8s.
Four stroke crossplane V8 engines have even 90 degree ignition intervals, but unevenly spaced firing patterns within each cylinder bank.
As can be seen by counting four characters to the right of each 'L' or 'R' (4 x 90° = 360°), the cylinders that fire (and thus exhaust) at 360° phase difference reside in opposite banks in a crossplane V8.
The specific firing order of the engine and the exhaust configuration can lead to subtle variations which may or may not be noticeable to enthusiasts.
Other sounds are possible by careful grouping of the exhaust pulses, but the packaging (space) requirements generally make this unfeasible in road-going machines.
[4] The Ford GT40 made the concept on production-based V8s famous with an elaborate arrangement of long exhaust pipes nicknamed "Bundle of Snakes".
Prior to this, straight individual "stack pipes", or "zoomies", were sometimes used (e.g. BRM[5]) to avoid the negative impact of uneven exhaust pulse interference on scavenging, at the cost of not benefiting from the positive extraction effects of merging, as above.
This was inspired by Yamaha's M1 MotoGP racing models, which continue to use crossplane cranks to this date because of their significant inertial torque advantage at the extreme high rpm operation these engines see.
The different layout was primarily chosen to reduce the impact of the inertial torsion inherent with crank throws spaced 90° apart due to the pistons being accelerated (start-stop motion), given this engine was meant to be high revving and inertial forces scale as to the square of engine speed.
The reduction in torsion was achieved by splitting the crank into two separate parts, geared together, from their respective midpoints, via a counter-shaft, from which power was delivered to the gearbox.
[citation needed] In 1995, Yamaha fitted 270° crankshaft to its TRX850 and in 1996 to the TDM850 MK2, plus a balance shaft to counter the resulting combination of free forces and rocking couples.
The 270° configuration represents a successful compromise and has been adopted for Honda's NC700 and 2016 Africa Twin, Hinckley Triumph's Scrambler and Thunderbird cruiser, Yamaha's MT-07 / FZ-07 and a number of others.
