Editorial: Ruminations On the V6

Featured Posts, Interesting | October 10th, 2011 by 44
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A curious thing is the V6 – it’s either half an engine or three quarters of an engine. It isn’t as smooth as an in-line six, and it requires more individual parts. Based on its V angle it can sound as coarse as a cob at higher RPMs or sound nigh on perfect given individual exhausts for each bank.

The first appearance of the V6 configuration is probably the Delahaye design from 1911 mentioned in Jan Norbye’s book, “The Complete Handbook of Automotive Power Trains”. The V6 then reappears in a 1950 Lancia Aurelia. But it became a popular engine configuration with the advent of mainstream front wheel drive vehicles and the need to minimize engine length in transverse applications.

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Of course the V6 most Americans are familiar with is the Buick 3800 – derived initially from the 3.5L V8 (which became a Rover staple – and there is your BMW connection). It was known as the Fireball V6 and grew in size and applications soon thereafter. At the end of it’s life, over 25 million units were built and they had infested everything (with the exception of Cadillac) in GM’s lineup. Often a member of Ward’s Best Engine lists it was a workhorse. It’s biggest drawback was the uninspiring nature of its exhaust note. Something akin to mechanical flatulence, it was a victim of its pedigree – its derivation from a V8 and subsequent 90 degree V angle.

The 60 degree V6, on the other hand has an even firing order and can be derived from a V12. Ferrari did that with the 246 Dino, a car that many still lust after. Alfa Romeo built a number of very fine 60 degree V6 engines, and Ford had a really nice small 2.5L V6 in the 1990s known as a Duratec. What’s interesting to note is that in most cases V6 engines are synonymous with transverse engine placement.

The question for BMW is what do they stand to gain by introducing a V6 in the next M3. For one thing there is less of a nose heavy weight penalty for a V6 than an in-line six. You give up the smoothness of the in-line 6 in either 60 or 90 degree V implementations. And you create additional work for audio engineers with a 90 degree V.

A 60 degree V6 can be derived from the existing V12. Because of the narrow V angle it would probably use a turbo on each bank with conventional exhaust. It would be smoother sounding than the 90 degree V6, but would have two hot zones in the engine compartment.

A 90 degree V6 makes some sense if you want to use a twin scroll turbo. It would be placed in the V and take exhaust from either bank of cylinders much like the current M V8s. It’s drawbacks are the need for a crankshaft with offset journals (to even the firing impulses) and of
course the less than pleasing sound emitted.

Frankly – BMW has taken pains over the years to emphasize the long hood that speaks of an in-line six and rear wheel drive. I believe there are only two mainstream auto manufacturers of in-line six engines left, BMW and Volvo (I don’t want to count the massive in-line six marine diesels still being built). I do not know why BMW would want to introduce a V6 – it would be a bespoke engine for the M3 initially, if the rumors are accurate. If it’s a 90 degree V6 it will require more development time to get it ‘just right’. And the primary purpose of a V6, extending the power options for FWD cars into C and D class ranges, is outside the scope of where BMW wants to take FWD cars from what I understand.

So why introduce what will be an exceptionally controversial power train into the very heart of the M brand? Are they daft or are they just stirring the pot and enjoying the ranting and ravings on the intertubes. Stay tuned, we’ll find out for sure eventually.