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Bob,
I agree with earlier comments regarding changing your rear end
ratio. It would not be worth the cost and those old trucks were equipped
with 4.10:1 gears to give them adequate power to tow. You could probably
realize a small increase in fuel mileage while not towing if you changed all the
way to a ratio around 3:1 but then towing performance would suffer. Newer
trucks with overdrive transmissions can make the compromise better because many
of them enjoy the pulling power of gears in the 4:1 range for starting the load
rolling but then overdrive reduces the final drive ratio by 25% to 30%. In
other words, multiply 4.10 by .70 (30% overdrive) and you have a final drive
ratio of 2.87:1.
Dual exhaust systems will improve high rpm horsepower, but in
some cases, will reduce low speed torque. Most stock engines have
adequate exhaust flow at low engine speeds, it is only at high rpm when flow is
restricted by the old single exhaust with a restrictive factory (quiet)
muffler. Most towing is done at lower engine speed where torque, not
horsepower is important.
Installation of a dual exhaust system will have no effect
on engine braking. Engine braking in a gasoline engine results from the
retarding effect of compression on the compression stroke and a similar
retarding effect of restricting intake of air on the intake stroke.
Dumping exhaust tail pipes in front of the rear wheels will
cause no problems, that method was once pretty common. It will possibly
increase the noise heard by the driver in the cab.
I hate to rain on your enthusiasm but if you can find old back
issues of Trailer Life or some of the other RV industry magazines of the '60s
and review the test reports, I think you'll find that the carbureted gas engines
of the day typically returned around 10 mpg empty and 6 or 8 mpg towing.
Sometimes worse depending on weight and frontal area. Fuel mileage of that
period led Detroit and Dearborn to develop and install fuel injections
systems.
However, your original '66 Ford F250 Camper Special and
original Airstream Safari are going to make a great looking and perfectly
satisfactory rig. Unless you are going to tow 50k miles per year, a few
mpg is not really going to be very important in the overall scheme of
things. Just enjoy it and watch the heads turn and the "thumbs up" flash
as you pass. You'll have to answer a dozen questions every time you
stop. I'm looking forward to seeing the photos when you post
them.
Harvey
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