"Mike Marron" wrote in message
...
(Peter Stickney) wrote:

Allison also Diesel engines for use in tractor-trailers & other such
applications. You can easily pick 'em out by ear, they've got a
distinctive high-frequency scream in their engine note.

I'm not aware of any Allison diesel engines used in semis. The Big
Three truck engine manufacturers are Caterpillar, Cummins and Detroit
Diesel. Going down the road, you can't differentiate between the three
by the sound alone and I suspect the high-freqency scream you're
referring to is simply the turbo.

They are in a lot of school buses, some semi-tractors & heavy equipment
but they're not as popular in semis as some of the others.
I've even seen turboed Allison V-8 diesels on pulling tractors; like
a bomb going off when they snapped the throttle open and shut.