(14 Aug 2020, 2:29 pm)streetdeckfan wrote Either way, regardless of the engine, it'll still be spinning at the same RPM if the gearing is the same, so say the StreetDeck is sitting at 2000RMP at 50mph, so would the B9.
It's not really about the stress put on the engine, but the fact that the gearing just isn't suitable for higher speeds.
Yes, but the point is if you have 2 more cylinders, that's 6 cylinders producing the same revolutions as a 4 cylinder engine.
Therefore the 6 cylinder engine will be under less strain at the same given RPM. This is mechanics for you, not opinion.
There's also factors like differential (final) gear ratios and tyre size that affect true speed. The gearing is fine on those 4 speed gearboxes. Voith's approach is less gears = less gear changing = more stable. Voith don't make a gearbox for buses with more than 4 speed, and this technology serves well in Pulsars, Cadets, some Citaros and some older B7s, a variety of 4 and 6 pot engines.
In this case, it has less to do with the gearing, more to do with cost to engine health over a prolonged time. This is why 4 pot coaches aren't a thing, even with advanced systems such as i-Shift. They aren't suitable for that sort of work over a large period of time due to the lacklustre properties of using less cylinders.