Cranky V6 v Inline 6

[C M Smith <cmsmith@domain.elided>]

Theoretically an inline 6 should be capable of generating more power than a 
V6 because of the virtual perfection of balance, both first and second 
order vibrations (harmonics) are excellent. Only  a 12 or a flat 8 compares.

However, the real world intrudes in the form of crankshaft harmonics. An 
inline 6 has a crank almost twice as long as the equivalent sized V6 (big 
bore V6 have longer cranks than small bore BTW). This increases the total 
bending moments that the engineers have to deal with. Heavier cranks with 
bigger bearings are the result.

Street engines built of modern materials and with modern engineering could 
care less. BMW latest inline 6 in the M3 is a fantastic street motor, 
better than any V6 I can think of. With over 330 hp on tap, it is also 
extremely powerful for an engine which must idle docilely and trickle along 
in traffic for 95% of its operating life, punctuated by rip roaring bursts 
of full torque and the very occasional production of full power.


A 60 degree or 120 degree V6 is the best version for balance in the V 
format, though slightly narrower angle V6 are becoming popular. I suspect 
there may be some advantage in firing order imbalance correction to a 
narrower angle. Also, VW has done some very interesting work with their VR6 
and related short crank motors utilizing one head for 4,5 or 6 staggered 
cylinders. The latest iteration is a truly fascinating W 8 with two heads 
and four cams covering two interleaved narrow angle V4 engines cast in one 
piece.

Still, the compact shape of a 60 degree V6 has such huge advantages in 
packaging and vibration damping that it is still the preferred option IMHO. 
I just wish we could get the latest iteration of the 4 cam 24 valve Alfa 
V6.....with a Selespeed.... awd....under US$35,0000   Ha.


Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner

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