Topic: Motoring Memories: The V6 engine

[ktm525]

I didn't know about the odd cylinder engine rocking. I can tell you that the inline 5 cylinder in the Volvo is not a refined operator and it has an odd exhaust note.

And having had one in the family for over 7 years, I can also tell u it's a thirsty piece of garbage.

Garbage in what way? The 5 cylinder has it's own personality for sure but I wouldn't call a 2.5L engine that can produce 300HP (R version) and return 25 mpg at 80 mph garbage.    Volvo's have their issues but the 2.5 is a rock solid little motor. I hope you are not one of the red-block huggers daydreaming about the last of the 240s.

[Sir Osis of Liver]

Inline 6, 60 and 120 degree V6s all have primary balance. 90 degree V4s and V8s do too.
The problem with many of the older V6s was that they were derived from 90 degree V8s, thus an odd firing sequence.

Not quite.  I always thought that 60 and 120 deg V6s were good but... From Wiki V6

"Due to the odd number of cylinders in each bank, V6 designs are inherently unbalanced, regardless of their V-angle. All straight engines with an odd number of cylinders suffer from primary dynamic imbalance, which causes an end-to-end rocking motion. Each cylinder bank in a V6 has an odd number of pistons, so the V6 also suffers from the same problem unless steps are taken to mitigate it. In the horizontally-opposed flat-6 layout the rocking motions of the two straight cylinder banks offset each other, while in the inline-6 layout, the two ends of engine are mirror images of each other and compensate every rocking motion. Concentrating on the first order rocking motion, the V6 can be assumed to consist of two separate straight-3 where counterweights on the crankshaft and a counter rotating balancer shaft compensate the first order rocking motion. At mating, the angle between the banks and the angle between the crankshafts can be varied so that the balancer shafts cancel each other 90° V6 (larger counter weights) and the even firing 60° V6 with 60° flying arms (smaller counter weights. The second order rocking motion can be balanced by a single co-rotating balancer shaft.).
...
"

That's what I get for going from memory!
They also say the following about the 60 degree V6:

60 degrees
The most efficient cylinder bank angle for a V6 is 60 degrees, minimizing size and vibration. While 60° V6 engines are not as well balanced as inline-6 and flat-6 engines, modern techniques for designing and mounting engines have largely disguised their vibrations. Unlike most other angles, 60 degree V6 engines can be made acceptably smooth without the need for balance shafts. When Lancia pioneered the 60° V6 in 1950, a 6-throw crankshaft was used to give equal firing intervals of 120°. However, more modern designs often use a 3-throw crankshaft with what are termed flying arms between the crankpins, which not only give the required 120° separation but also can be used for balancing purposes. Combined with a pair of heavy counterweights on the crankshaft ends, these can eliminate all but a modest secondary imbalance which can easily be damped out by the engine mounts.[1]

This configuration is a good fit in cars which are too big to be powered by four-cylinder engines, but for which compactness and low cost are important. The most common 60° V6s were built by General Motors (the heavy duty commercial models, as well as a design used in many GM front wheel drive cars) and Ford European subsidiaries (Essex V6, Cologne V6 and the more recent Duratec V6). Other 60° V6 engines are the Chrysler 3.3 V6 engine, Nissan VQ engine and the Alfa Romeo V6 engine.

[Sir Osis of Liver]

Wiki also mentions this:

Although it is more complicated and not as smooth as the inline 6, the V6 is more compact, more rigid, and less prone to torsional vibrations in the crankshaft.

Wasn't that last bit one of the reasons BMW switched to a V8 in the last M3? It struck me as familiar when I read it.

I know that torsion, weight and physical size lead to the downfall of the old straight 8.