doesn't make a lot of sense to build an I5 when an I6 makes a lot more power/torque, is smoother, cheaper to manufacture, and most of the time fits in the same place an I5 would
I4's are a little buzzy without a counterbalancer. All of the M series have counterbalance. Most of the L's do not. On the B3350, B3300, B2900, etc (4 cylinders), you will notice it a lot more because of the little bitty frame, it doesn't really absorb the vibration like the L's do
MX's, I am not sure about--I bet they ain't balanced either but it's been a minute since I been into an MX engine of any type
Kubota likes inline 4's, they use them all the up to the M8 which is an I6. M4000 was also an I6, oddly enough. They didn't use the I6 very much. I5's of course were used some. It is counterbalanced (has to be).
Inline 3 Kubota's generally don't have counterbalancers. They're cheap little engines, that's why they use them so much. But you will notice some vibration, some machines it's not much others....it's obvious (mowers are a good example). They mount them on rubber mounts to isolate it if possible (BX'x and lawn mowers). They are very cheap to make in comparison to I-4 but once they start getting "bigger" (more displacement) the weights of the reciprocating and rotating parts start to become an issue (vibration). Then adding a turbocharger, it will need a surge tank of some sorts to help dampen the pulsing in the intake manifold. At that point, it's cheaper to put a normally aspirated 4 cylinder on the machine, which runs a little smoother and makes more torque given the same displacement.
Emissions is also an issue.....won't even begin to get into that. There are more kinds of emissions than exhaust....
used to be a website that went into the basic engineering details of internal combustion otto-cycle multicylinder piston engines and why they were chosen, their pros, cons, and a ton of other stuff. Excellent read if you have a day or two to soak up all the information. IIRC it went into everything from single cylinder all the way to I think 20 cylinder, both inline, vee, H, and IIRC radial. Going off of memory, I found it by googling the firing order for Viper V-10 since I was helping a man change plug wires and plugs on his 97 GTS. Has to be the worst sounding engine of all time. Scratch that, any V6 is and 90 deg V6's worse than 60 deg. Viper V-10 close second with it's stupid odd firing order (google it you'll see what I mean, they used the old Dauntless V6 "shaker" style firing strategy)
en.m.wikipedia.org
