It is a function on a four-stroke engine of how many degrees off TDC each piston/con-rod is during the four cycles.
Multiples of three cylinders are naturally balanced; multiples of four need balancing weights. Multiples of four can be made “as smooth” with the addition of the mass necessary, but if we’re trying to maximize mileage, then we want to cut out any weight possible.
In V configuration engines, most of them are over-square and have sub-optimal short piston strokes. It is better to have an under-square cylinder dimension and have long power strokes to maximize the heat/pressure extraction. The latest IH/Ford Powerstroke is a V-8 and under-square and it still sucks in fuel efficiency compared to I-6’s. The 6.0L Powerstroke was a V-8 and has cost Ford and Navistar (ie, IH) a ton of money, not to mention pissed off a lot of Ford customers.
“Real” diesels in moderate power levels (say, up to 500, perhaps 600HP) are inline sixes. In the higher power levels (say, up to 2000HP) you see V-12’s (another multiple of three).
V-8 diesels have a very poor history, regardless of the manufacturer. Cat’s 3208, the Cummins 555 and 903, the IH/Navistar 6.9 and 7.3, etc, etc. At best, they’re “acceptable.” At worst, they’re steaming dung piles. Inline eights in medium speed diesels are rare, mostly because the torque levels would require a massively thick crankshaft to withstand the torque along the length of the shaft. You do see some inline eights (and more) in the low-speed diesels, ie, max operating speed is in the range of 600 to 900 RPM.
The best diesels, the ones that are “classic” for their reliability, fuel efficiency, etc are inline sixes - the Cummins 855’s, the NH 7.5L, Perkins 354, Deere 466, Cummins B5.9, Cat 3406, etc. And then there’s the whole line of I-6 Deutz diesels. Properly cared for, I-6’s can run 10K hours and more before tear-down. I’ve seen Deere 466’s run for 12K+ hours with no new bearings, no in-frame, no nothing and still be tight. Only thing needed was gapping the valves and regular maint. I’ve never seen a V-8 diesel make it to 10K hours without at least an in-frame. I’ve seen a couple of V-8’s in farming applications here go for a little too long without the rod bearings being replaced ventilate the blocks (ie, punch a rod).
Perhaps the only V-8 diesel to have a loyal following is the 8V92 Detroit two-stroke. Most people don’t want to put up with the downsides of the Detroit two-stroke design any more, from either a noise or pollution perspective, so it isn’t something we’re going to see a lot of going forward.
I’ve run a bunch of diesels on this farm and the only V-8 diesel we have is the 7.3L Powerstroke in the pickup. When it gets run out, I’ll pull the engine completely and replace it with a Cummins B5.9. And I won’t miss a thing about the way you can’t get a feeler gauge into the engine compartment of a V-8 diesel. I’d like to pimp-slap the engineers in Detroit who insist on pushing out these stupid V-6/V-8 diesel designs when everyone who knows diesel engines well knows what they want: an inline 4, 5 or 6 cylinder engine.
Even in gasoline engines, the I-6 configuration results in outstanding engines. Perhaps the single best work pickup gasoline engine I know of is the 300 cu in. Ford I-6 industrial engine. Absolutely reliable, very fuel efficient, very good low-end torque. I’d take a 300 over any mid-sized V-8 in a pickup any day. Every day. But does Ford offer this engine in pickups? Noooooo. They’re peddling their V-8 obsessions.
For efficiency, the best formula is larger displacement and fewer cylinders.
A 300 six banger is better than a 300 8 banger. A 300 4 banger is better than a 300 6 banger.
For smoothness, the opposite is true.
I don’t think I’m buying what you say about crankshafts in straight 8 motors. More main bearings equals less stiffness required in the crank. If the crank needs stiffening, just and a main or two. Of course more mains also equals more friction, greater expense, and less efficiency. The reason for the v8(instead of the straight 8) was to cut the mass of the crank in half, and the number of mains in half. Also the number of crank throws was cut in half. So the labor to construct the crankshaft was cut in half as well.
A 4 stroke engine has a 720 degree cycle(360x2). 720 is devided by 4 just as easily as it is by 3. A perfect firing interval 4 banger has the middle two pistons rising and falling together and the outside two pistons exactly opposite of the middle two. A 3 cylinder may have a slight edge over a 4 cylinder since none of it’s pistons are moving in unison, but a 3 cylinder is not going to have an edge over a straight 8 cylinder. And I would really doubt if a straight 6 would have an edge over a straight 8 either. I don’t believe a 6 banger does not need any counter weights on the crank.
I’m going to need more proof about your claim of straight 6 superiority.
I am a big fan of the ford 300-six. I also am a big fan of the old hudson hornet and it’s big six banger.
I have a ‘91 F-150 with the 300 in line 6. Great engine. The body will rust out before that engine gives out although I can’t vouch for your fuel mileage claim!
I have no idea what you’re talking. You obviously know more about the subject than I do. However I have owned a Dodge with a Cummins diesel and a Ford with the Powerstroke took both up Monarch Pass and the Powerstroke put the Cummins to shame. i wasn’t even close I had to pass my brothers Dodge going up the pass because I was losing RPMs staying behind him. He traded for a Powerstroke as soon as we got back. I don’t know the Physics of all this but I know which vehicle out performed the other.