scania v8

You're right. I just remembered my uncle had a standard hood W9 with a Silver 92. Completely forgot about that.

 

That is what was in my A model originally, they are very compact engines, the transmission got moved back 14" when we put the 3406 in the truck.

 

Makes sense. You're adding 2 cylinders worth of length when swapping a V8 to a straight 6. The 3408 must be longer for some reason to warrant needing a long hood to fit it.

 

Turbo arrangement 3408 has the turbo hanging off the back end . 8v92ta turbo on top of engine

 

The air compressor is the biggest reason, if it weren't mounted into one of the gear ports on the back of the engine I believe everything would clear in a standard hood.

 

This is true but you can't ignore the heat factor of the turbo charger.
The manufacture can get away with a air compresor mounted close to the firewall, a turbo and up pipes is another story.

 

I got the chance to look at a 1995 Mack with their V8 in it. The frame was wide at the front to fit the engine in it by about 8 inches. Right after the frame came out from under the cab they went wider.

 

Here's a couple of pics of my 3408 in my KW cabover when I was doing a major job on it. As you can see the turbo and aftercooler take up a lot of room on top, that's without the intake and exhaust connected.
The engine is very wide, the exhaust manifolds actually overlap the frame rails. You can see the compressor at the back of the engine in the 2nd pic. It lays over on it's side there's so little room.