tuj wrote: .... Porsche is developing a V4 turbo engine for Le Mans which has worse balance issues than the V6's. If they can make a structural 90 degreeV4 winner
..... Also, has anyone thought about what they did in MotoGP to manage the torque/traction events, ie. the 'big bang' firing order engines? They moved the power pulses from being evenly spaced to a more 'clustered' pattern to give the tires more time to recover from the initial traction event.
in another thread I wrote IIRC that the suggested Porsche V4 would not make a good road car, because of the uneven firing intervals
though the twin clutch 'manual' transmission may manage the gear selection to avoid a transmission snatch issue ?
(a 2 throw 3 main bearing 180 deg crank seemed plausible in the racer, though a 1 throw 2 main bearing crank is conceivable)
now the rumour mill says that the V angle would be a lot more than 90 deg (for aesthetic continuity with flat engine tradition ?)
that would make the firing intervals closer to even, but introduce some uneveness in the inertial intervals
so a 2 split-throw crank could be good in the road version, directly substituting the race crank and giving near-equal firing intervals
the resulting uneven inertial intervals being unimportant for road use, it would be much like a flat 4 (but more compact etc ?)
IMO the 'big bang' is a myth, because .......
the late Prof Dr Blair implied that it was
and said that firing interval choice determined the power band etc due to induction system effects (his speciality)
the frequency of the torque ripple at eg 10000rpm is higher than could be transmitted to the road through the pneumatic tyre ?
square 4 cyl 2 strokes (1965 on) anyway had paired firing for balance and a simpler ignition system, so were naturally 'big bang'
the Doohan era Honda was a 76 ? deg V4, like the 60s Yamahas it would naturally have worse balance and rather even firing ie 'screamer'
(ie if the cranks were set in phase as in the square 4s)
but if the cranks were set out of phase eg by the V angle the firing would be paired ie 'big bang'
in principle it is possible to obtain any firing interval, even to have all 4 cylinders firing together
110 deg cranks are conceivable, and such, suitably phased, seem necessary to get 3 firings in 110 deg (the rumoured 'big bang')
so-called 'big bang' inline 4 cyl 4 strokes have cross-plane cranks giving even-spaced inertia (reciprocation) loads
(ie pistons take turns to stop eg at tdc) and uneven-spaced firing loads
this is the opposite of the conventional arrangement (uneven inertial intervals ie 2 pistons stop at tdc together etc)
and allows a lighter crank with smaller main and rod bearings (reducing friction) by helping keep the torsional natural frequency high
reciprocation loads become large at high rpm and are then more important than the firing loads, being at twice the frequency
the cross-plane crank also still causes vibration at double the 'rpm frequency' but this vibration is more evenly spread