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Chevy 350 V8 Conversions
for sustained freeway use
Author - Jesse Ybarra
I talked to Scott on the phone, he will be searching for a complete 73- 85 Chevy
1/2 or 3/4 ton V8 TH-350/Np205 4x4 Let him know, if someone has one in Chicago
area, so we can end the 44 gears questions, I was getting lost with all the
replies.
This should help to explain a few things that hopefully will prevent terribly
wrong expensive conversions.
About costs, when building an FC Freeway Flyer, quit trying to think of economy,
and think of long time reliability, a lot of new people like Scott and a few
others are very new to FC's, Scott for example had never seen my #1 M-677 4 door
on Craig's Website. In past years, I have met a lot of people, that are really
new to all, that is automotive. Questions that seem to be common sense, to an FC
dinosaur like me, are really not the experience someone who has never driven an
FC can understand. Worse if you ask enough people that don't have an FC, about
what can sustain freeway speeds, it is easy to go in many directions. I have
enjoyed the benefits of driving my 4 door for many years as a daily driver on
freeways in hot AZ, so I want express a few FC-on the Freeway experience facts.
About the Small Block Chevrolet V8 350 or SBC, if you have you ever driven a 283
Chevy anything, you now it was reliable and had good power, well compared to a 6
cylinder, they were plentiful, but they were here before the freeways, they are
over 40 years old now. The 307 a longer stroke and the cool 327, these were good
motors, but short lived, then came the 350, like the original VW they were
unchanged everything was basically the same, until 87, the changes and
improvements made some problems, along the same time another short lived motor
the anti smog 305 came and went, it had a list of different issues. The pre 85
350 SBC remains as Chevrolet dealers most popular replacement, brand new motor
that is on the shelf. Here at the FC Roundup each year we only see a few FC's
that are actually capable of being on freeways, most can go for a few off-ramps
or miles, but can't or shouldn't go on the freeway, because of overheating or
handling. The FC is a big box, unlike a low to the ground sports car, as the FC
goes faster over 40 mph, it really pushes against the air, the faster it goes
the more the wind it fights against it, the more it pushes against the wind it
also looses stability, it is as heavy and requires about double the energy that
is required to push a regular Chevy pickup, maintaining constant freeway speeds,
this extra requirement, causes a lot of engine friction, that heats up the oil,
as the water gets hot the oil gets real hot. A larger motor does not mean you
can go faster, but it does the work with less effort, taller gears are what
makes them be able to go faster, the bigger the gear ratio, the more torque / HP
is required, again the 350 does the work with less effort.
Forget small cubic inch V6s and V8s, like I mentioned for example, the V6 225 or
283 motors, because they were last made over 40 years ago, it is impossible to
find one that is not going to need to be bored and they had small journal cast
cranks, they were made before unleaded gas, rebuilding a set of heads, and
changing the valve seats to hardened valve seats, can be a bunch of $. The 283s
are only good for when they are going in an original 58-66 Chevy.
4.3 made by Chevrolet, good but harder to maintain passing acceleration at over
60, without gaining overheat, working temp 195 degrees, 4.3 is a 5.7 (350) with
2 cylinders missing, Again more expensive to rebuild than the SBC.
SBC temp can run fine with 160 degree thermostat, this means cooler in the cab,
a large radiator is required and an oil cooler for the engine and trans are
needed.
Average cost on a band new SBC 350 crate motor is cheaper than the parts and
machine work to rebuild a tired motor. This applies to Ed Browning, just because
you have a motor taking up space don't assume it is less money to have it
redone. It will surprise most people how inexpensive it is to buy a band new
crate motor from the Chevy dealer. And it has a 2 year guarantee.
Question of Ed,
I have an intake from a 1978 z-28 also a friend gave me, don't know if would
help either.
Answer,
it is probably is for a 305, water crossover is restricted on some factory
aluminum manifolds but it may have the same size intake ports.
Question,
I have a transfer case out of a 1973 3spd/T-15, Jeepster/Commando I think is a
Dana 20. What do you think I would need to bolt all these together after I
overhaul the engine and rebuild everything? Can we do this upgrade and the back
drive shaft not bind up - FC-150?
Answer?
An inline 4.0 AMC motor and a 72-73 Jeepster, the bell housing will only fit an
AMC 232 six or 304 V8, that T-15 is a top shift. plus the Adapter that comes on
the Dana 20, makes it all pretty long for an FC-150. Even if someone is in the
bed shifting the gears. use a Chevy TH350/NP-205 or adapt the D-20 to the TH-350
Another question if you don't mind,
I have cut up a fc-170, if I put the spring hangers on one of my 1957 150 and I
know I can move the stands seat on the housing, I have Jeepster parts 1971-1973,
will any of this help make the upgraded 150 truck better on the highway 3.73
gears in Jeepster front and rear end? Should I look for a certain model of
housings to change to? Thanks Again and Again Ed your carefully planned insight.
Answer,
The 57 frame is tired fatigued and I am sure full of fractures, if not find
someone that really needs it. The frame on the FC-170 is very wide at the rear
and is tapered to the middle, the FC-150 frame is narrow front and rear, so the
hangers are not true 90 degree. Use the much better 73 Jeepster frame and the
Jeepster axles.
If you do use the Commando frame it probably has the mono leaf composite
springs, for sure the axle centering bolt will be to far forward in the wrong
place, so use the better FC-170 springs. After changing the springs, you will
have the centering holes in a new position, but upside down, use new ones and
put them in to match the perches, should be at less than 100" leave it, lengthen
the bed, or shorten it to 80". it will still be a spring under suspension but a
taller wide track. or cut off the spring under perches and add new ones on the
top. With the axles mounted, measure from the front axle on an FC-170, to where
the front cross member with the bell crank needs to be, then add on to the front
of the Commando frame, 2 feet of an FC-170 frame, to the Commando frame for the
steering. It sounds like a lot of work but it does have good resulting strength
benefits over the weaker narrow track frame.
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