Re: Max RPM

[Tom Harais <tjhemh@domain.elided>]

John:

Your point about the torque curve is well taken.

So is the "screaming".

We must remember that a 350 Chevy (a typical example) has a 4" bore with
a 3.48" stroke, while the IH 345 has "only" a 3.875" bore with a 3.656"
stroke. The Chevy is "more oversquare" (bore larger than stroke) than
the IH. This is the way truck engines were built for many years. Longer
strokes, less bore than a car engine. The trade off was higher torque
across the band but lower top RPM and not as good of fuel economy, and a
lower HP due to the more limited RPM (HP is torque per unit of time).

Another way to look at this is the IH 345 is more like a "stroked" Chevy
307 than it is the 350. For comparison to the 350, use the IH 392 which
is a "stroked" 350. That is closer to reality than 345 to 350 or 392 to
400.

Bottom line. IH was still using truck motors when everyone else had gone
to car motors in their trucks, with cam changes to bring more torque to
the lower RPMS. You can throw the "big block" IH issue to the "small"
block Ford, Chevy or Dodge as additional support.

Question remains, how fast do you want a truck motor to turn? My
neighbor's new Dodge/Cummins redlines at 3500 RPM. And that is
considered a "light duty" diesel. A true "heavy duty" diesel winds out a
mere 2000 or 2200 RPM. They also make something like 600 to  800 ft/lbs
of torque at idle speed!

Tom H.