Any reason why there are no small 6/8 cylinder engines?

alexthecheese said:
Why is a V6 unbalanced compared to an inline 4?
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Because its essentially 2x 3 cylinder engines, its all to do with they way they fire and the rotating masses. you need ballancing shafts etc in a V6 to make it smooth. But like i said an inline 4 isn't perfectly balanced either as it has secondary vibrations. However an Inline 6 is in perfect balance which is why BMW's are so lovely and smooth.
 
acemastr said:
Apart from a V5, all V engines are balanced, the same number of cylinders on each bank in a V configuration.

No where near as smooth as a straight 6 though, mine is sexual when it's revving.
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No, a V6 does not have naturally perfect balance as sovietbobspy correctly states. They require one or two balance shafts depending on the V angle to fully balance them.
 
The thing you gain in a V6, despite its unbalanced nature is overlapping power strokes. So it can have a smoother power delivery despite the vibrations.

Ideally you want a V12 for perfect smoothness :D
 
Dogbreath said:
No, a V6 does not have naturally perfect balance as sovietbobspy correctly states. They require one or two balance shafts depending on the V angle to fully balance them.
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A flat six - a boxer engine, like Porsche use - is also perfectly balanced.

Also, as a V12 is essentially two straight sixes stuck together, that too is perfectly balanced.

W configurations, like the Veyron uses, can also be perfectly balanced, depending on how they're set up, but I don't know if the Veyron's engine is.
 
So the answer to the original question "why aren't there small V6s" is "there are plenty small V6/I6s"

What's the smallest diesel with 6 or more cylinders then?
 
[TW]Fox;23628636 said:
2.5 V6 isn't small, its also one of the most common 6 cylinder sizes.
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Location relevant surely? Would be considered small in Oz, and tiny in the USA! :) But for Europe averageish.

Manufacturing costs play a big part, Ford moving to their new 3cyl is a good example, less can be more if done right!
 
Dogbreath said:
No, a V6 does not have naturally perfect balance as sovietbobspy correctly states. They require one or two balance shafts depending on the V angle to fully balance them.
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That's perfectly true, but also worth pointing out that despite that fact, virtually no modern V6s actually have balance shafts!:) You can reduce vibrations to acceptable levels with clever crankshafts (with offset crank journals, flying arms, counterweights, all that stuff) and engine mounts. I've never come accross a 60-degree V6 with balance shafts as they are easiest to make acceptable. I have come accross 2 90-degree V6s with shafts though - a Mercedes and a 3.5l Honda Legend as they are more troublesome. On the other hand there are quite a lot of straight-4s with a balance shaft.
 
The optimum size for a cylinder is around 500cc so you start losing out if the engine is too small.

V8s with 90° cranks are also perfectly balanced but do need counter balance weights on the crank.
 
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