I remember reading somewhere that an inline engine is 'inherently more efficient' (or similar words to that effect) than a V type engine. I don't know if its true or not, but I'd like it to be because I prefer the simplicity of the inline type engine. I'd sure rather have a 6bt than any of the current crop of american V8 diesels.

Anyway I see that major manufacturers like cummins are moving into the v6 and v8 light duty diesel realm, and it seems to be a trend.

http://www.dieselpowermag.com/tech/dodge/0612dp_new_cummins_v6_and_v8/index.html

There are obviously more transaxle possibilities w/ a V type engine, what with the transverse mounting possibilities, and maybe vibration mitigation posibilities as well.

thoughts?

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Cheers,
Robert

Well, you can get into some serious harmonic and balance issues with straight engines as the displacement and/or length of the crank increases. 90-degree V-8s have inherent harmonic and balance advantages. Yes, lots of old cars used straight-eight engines, but even with large displacements, they didn't have much power and operated at fairly low RPM. The very large diesel inline engines that are used in ships operate at really low RPM.

this is like comparing a ford 289 to a mercedes diesel inline.. THe ford 289 is a very solid engine long lasting been around forever. A v8 is simply two four cylinders on the same crank.. so if a 616 engine would get 25mpg then two of them together would make half that, (About 12.5) And thats what you would expect with a v8. But.. then there are many diffrences with the way the power is managed, in a v8 engine you can have a full blown miss on a cylinder, and you may never know it. Where as if a mercedes diesel had a miss you would know it for sure. And alot of these v8s are pushrod engines, Beautifull thought whoever made this really. It makes it so simple..

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Given two diesel engines of the same type (family), one in-line and one Vee type, the Vee type is in fact fractionally more efficient than the in-line engine, due to fractionally less friction losses on moving parts, etc. The difference is very minor.

In the marine industry, marine engineers have traditionally preferred in-line engines to Vee types, not due to efficiency, but due to the fact that to pull a piston the lifting angle is vertical (hence easier to obtain in a tight engine room) as opposed to pulling a piston from a Vee configuration at an angle. There are also long standing (but not necessarily accurate, today) beliefs regarding the robustness of Vee engines with two big-end bearings on one crank throw, etc. compared to an in-line engine with one per throw.

Balance issues are not related to efficiency at all, strictly engine geometry. V-8 engines are technically not great from the balance perspective, but there are plenty of them out there. Same for in-line four cylinder units. There are 4's out there with counterbalance shafts, and some (most?) without. It's all relative, and today virtually all engines are designed well from the balance point of view, no matter what the configuration.

Rgds,
Chris W.
in the large diesel business

Agree on all points.

I'll also add that the I-6 is perfectly balanced both for static and rocking couples. No additional counterbalance weights are needed on the crankshaft (as in a V8) and no counterbalance shafts are required (as in an I-4).

The straight six is a lot simpler to work on than a v8, with one head and easier access to accessories too.


Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Inline engines are preferred for many reasons, smoother operation, main bearings between each rod is common, the forces on the main bearings being more normal, the air intake/exhaust packaging, casting and design efficiency of the block, and cooling efficiency.

Vee engines are preferred for other reasons, less casting weight per cylinder, smaller package, saving both money and space, the two most important things in high-volume automobiles (cars and light trucks).

For larger engines? The 92 CID per cylinder V-8 and V-6 (and 71series before it) Detroit diesels gave way to the 60-series inline sixes etc., the medium-duty Caterpillar 3208 gave way to the C-10 and other inline sixes, for truck, industrial, marine, etc. The inline arrangement is superior for pretty much everything except packaging size.

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I prefer an I6 but they are so rare these days, you have to buy a BMW to get one. I6's are nice, lots of torque, smooth as silk, and they return better mileage than a V8. The new BMW I6's are amazing, electric engine smooth and they rev sky high with no effort, truely very mature techonligy.

V8's are nice because of the torque. I really prefer European V8's because they will rev as high as most 4 bangers. The M119 and latest MB 5.5L offering are my two favorites.

V12's are amazing sexy beasts that are not only silky smooth but scream up to a wonderfull red line. MB V12's really have jekyll and hyde personality. Keep the rev's down and they will waft you around with no effort, in perfect silence, all noise and engine vibrations are absent. But if you get on it and go above 4kish and she will get on her cams and scream, and the progress becomes quite rapid.

I hate I4's, not enough cylinders to rough. V6's don't really do anything for me either. Nissan has a nice one in the G35 and 350Z, its a great engine for sure but it falls short of BMW's I6's.

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I must be biased b/c my first engine was an AMC jeep 258ci straight 6, ez to work on, almost impossible to kill... it basically ruined me for working V type engines. I'm still ok w/ boxers tho

I don't necessarily want to focus entirely on balance issues, but here goes...

I'm not disputing the facts or accuracy of any of the previous posters, but my personal version of common sense tells me that an engine that requires extra rotating mass for balancing OR transfers some of its energy into a vibration ought to be less efficient.


Someone please straighten me out.

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Cheers,
Robert

You are correct. The actual cost associated with the less efficient engine is probably small in terms of miles per gallon or however you wish to measure it. Comfort for the occupants is likely to be a more important argument. As has been said, the engineers have gotten pretty good at designing engines that are smooth regardless of configuration.

The buying public really doesn't care if the engine has balance shafts or flying squirrels -- if it is smooth and powerful and (third or fourth place) gets reasonable fuel economy, they're happy. That an I-6 can do the same thing a little simpler affects only people like us.

I'm still surprised that Mercedes built an I-5 diesel -- it's inherently unbalanced and definitely not as smooth as the I-6 that succeeded it. But it's otherwise a nice engine. We can only wonder what an I-6 version of the 617 would have been like, cast iron head and all -- combining 617 durability and serviceability with 603 smoothness. Mmmmmmm!

Jeremy

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Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
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Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
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It was a packaging decision to build the five inline. There simply was not room in the 123 chassis for a six diesel.

INterestingly Henry Ford built an inline five back in the thirties but never put it into production. They went to inline sixes. In the thirties they went from I4s to v8s for packaging reasons, only later when they built their cars larger did they provide the room for the I6.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The addition of a balancing weight doesn't affect the efficiency of the engine. The weight adds a small bit to the rotating mass, which is negligible in terms of the torque required to rotate the engine. Friction of rings and bearings create 99.99% of the resistance to rotation. The actual work required to accelerate the rotating mass is not significant.

You could make the case that the additional balance shafts on the I-4 and the associated gear required to rotate those shafts would lessen the efficiency of that engine very slightly.

I think you might find that this is not correct. The six could probably fit in the W-123 with some effort in the front. There's quite a bit of wasted space in front of the 617.

What was more likely is that the Germans decided they needed a bit more power from the four cylinder and, clearly, did not need to go to a six cylinder. So, they would design and get a five cylinder to work. Typical teutonic thinking.

Exactly.

Also, both Volvo, VW, and even GM also have a number of current production vehicles using a 5 cylinder gasser.

The Jetta "2.5" sedan has a 5 cylinder.

The chevy "colorado" pickup has a 5 cylinder. Both companies bill it as having the "power of a 6 with the economy of a 4"

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Yep, thats how they think! And God help you if you tell a German engineer that he is wrong, or his design is less than perfect!

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