6V92 Tutorial

[mrkane1952]

Greetings:

There was a recent thread contrasting 6V, 8V, and series 60 engine
performance. In addition, I compared my fuel economy with a
spreadsheet kindly furnished me by the previous owner covering the
two years of his ownership. The difference between us is as much as
2 mpg, which makes me think I need a tutorial on best operation of
the 6V92.

Questions:

The 6V in our BBs is called "330 hp," but at what rpm? What is the
peak torque? (Peak torque and overall transmission ratio define the
GCWR.) Am I excessively overloaded at 39,000 lbs. gross plus the
7,000 lb toad? Is best economy achieved at the peak torque or peak
horsepower engine speed?

When climbing hills, I routinely use the cruise control until the
engine speed falls below 1650 rpm, then manually downshift the
Allison. When I find the gear which allows constant speed at an
engine rpm near 2100, I continue over the grade, feathering the
throttle as needed. Is this proper?

Differences in economy are related to variation in loading as well
as driver skill: The weight ticket I received from the former owner
indicated perhaps a 2000 lb greater load then, but his toad was
probably 3000 lbs lighter than mine. I've also added a Hydralift
motorcycle carrier. Formerly Lucas fuel additive was used but now
Schaeffer. Not sure about his typical road speed, but I stay around
5 mph below the posted limit. (Going slower seems to invite more
foolish driving by others, negating any potential safety gain.)

More bacground: Recently, I've been operating a Duramax pickup
which goes like a sports car: about 350 hp and 600 lb-ft peak. This
engine is fully computerized, with a useful operating range of
approximately 1600 to 3200 rpm. It's very easy to drive, basically
set the cruise at whatever speed you want.

My previous experience with a DD engine was a stationary application
on an offshore oilfield logging unit, where one set the engine rpm
at a constant value (about 1750 rpm.) Otherwise, I drove heavy
oilfield logging trucks, but not over the road. These were "old-
technology" engines without modern computerization, typified by
rather narrow useful rpm range (and LOTS of transmission speeds.)

Bottom line: Am I getting the best economy to be expected with my
setup, or is my technique substandard? Any experienced BB PT pilots
have pointers to share?

Thanks--
M.R.Kane
'85 PT40