Re: 3 cyls vs 4

[Alex Jenner <alexj@domain.elided>]

Ron Ewing asked:
> For small displacement engines, why don't automakers go with
> 3 cyl engines more often?
> Cheaper and lighter than a complarable 4 - right?  Smooth and
> revvy from memories of being ferried around in 3 cyl 2 cycle
> Saabs in my youth.

I think for a given size, a four cyl engine is smoother than 3. Most
small (say 0-1400cc) car engines don't need/use a balancer shaft, while
it seems to be needed in 3 cyl examples (at least in modern 4 stroke
engines - Daihatsu is one that springs to mind). This negates some of
the savings of the 3 cyl engine. I guess you could also speculate that
it might be 	nessesary to go to a 12 valve DOHC design for a 3 cyl
(valve area/performance issues), while for a 4 cyl, a 8 valve SOHC
design might be adequate.

However I think it probably has a lot more to do with tooling and design
issues. If you already produce a 1600cc 4 cyl, then building a 1200cc
version is quite straighforward compared with designing a totally new 3
cyl engine (even if you can share some components).

Trivia question: Name an Alfa that was sold with a 3 cylinder engine
(misfiring 4's don't count).

Regards
Lex Jenner
Auckland/New Zealand

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