I just returned from a long trip to Yukon and Alaska with my 51 one-ton. It
carried a camper and the gross was 8200 lbs. The motor is a 235 with dual
carbs and split manifold and a mild Howard's cam. Stock 7.5:1 compression.
The motor has about 50,000 miles on it since a major overhaul. The rear is
a 5.14 with 33'" tires. It has a four speed main transmission with a 3
speed auxillary.
With this setup I can pull a 7% grade in 4th and underdrive at 2200 RPM.
That gives 34 MPH. Any steeper and I have to drop to third and overdrive.
Except on some of the gravel "highways" in Alaska there are few highways
steeper than 7%. It'll pull about a 4% grade in fourth direct. At 2200 RPM
that's 42 MPH.
I have a 17% overdrive which yeilds an equivalent to an axle ratio of
4.26. With the camper on I can cruise at 60 at 2600 RPM. If there's a
strong headwind or more than about a 2% grade I have to drop to fourth
direct and run at about 2600 rpm which is about 50 MPH.
I try not to pull the motor hard below about 2200 because the fuel and oil
consumption go up considerably. It spends a lot of time pulling at 4 inches
of vacuum. That's actually only about 2/3 throttle but if you get lazy and
pull it at close to 0" vacuum down to 1800 or 1900 RPM for any length of
time, mileage goes from about 11.5 to about 8.5. Expensive! Oil consumption
also goes from 1 qt/1500mi to 1qt/300 mi. That must be why a lot of truck
engines had 4-ring pistons.
Based on my experience, if I had a straight 4-speed I would not go below a
4.56 axle ratio. If you have to drop to third gear on hills it knocks hell
out of your average speed and fuel economy. With a couple of old Nortons in
the back instead of a camper, you could probably get away with a 4.11 axle
and stay in high gear. But then I don't know how much load the AC might add.
You can use my figures and experience as a baseline but, of course your
mileage may vary, as they say.
-Tom Allen
'51 3800
> In my own case, I'm looking for an AD 3600 with a 65 - 70 mph cruise with
>the A/C on and enough power to climb Cajon Pass (a locally famous landmark
>enroute from L.A. to Las Vegas) at not less than 45 mph also with the A/C on
>and a couple of old motorcycles in the bed. Would anybody care to hazard a
>guess as to whether or not a stock 235 will have enough horses for that
>course?
>
>Paul O'Neil, Hudson29@aol.com
>1951 Chevrolet 3600 Pickup Project, See it at:
>The Poor Man's Advanced Design Tech Tips Page
>http://home.earthlink.net/~conntest47/
>Fullerton, California USA
>AEROMARK - Need Rubber Stamps or Signs? See:
>http://hometown.aol.com/hudson29/myhomepage/index.html
>oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
Tom Allen
Seattle, WA
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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