Why do American semi-trucks (18 wheelers etc) exclusively use inline 6-cylinder engines, no matter if it’s a Mack, Detroit Diesel, Cummins, or Volvo-built engine?

Question

I get why they are diesel, but why are they all of the inline 6-cylinder configuration? Why not V6 or straight 8 or freakin huge inline 4-cylinders?

In: 715

Answer 1

Typically it’s a simplicity/cost thing. Inline engines are cheaper to manufacture and easier to work on. In fact, an overhaul of an inline engine (especially on a tractor) can typically be performed with the engine in the frame of the vehicle. The inline 6 is inertly balanced where V engines typically aren’t thus they run extremely smoothly and tend to have very long service lives.

Just as a more practical example on simplicity. Since 1996 Ford has invested a ton of R&D resources into overhead valve engines especially with their V8’s. GM on the other hand stuck with the tried and true pushrod style (single camshaft). It’s simple and reliable such to the point when Ford was designing their new premier fleet engine about 5 years ago (the 7.3L Godzilla) they went back to the tried and true pushrod design. Inline 6 engines in the 12L to 16L displacement range have proven to be extremely effective, have lowest cost of ownership, and extremely reliable in the domestic (North American) market.