This thread is a little stale but I thought I'd comment after returning
last night from a 3,000 mi. trip driving my 51 3800, loaded with camper and
weighing ~ 8200 lbs. Yes, wind is an issue.
261 Engine
A 261 engine would give you a welcome additional 10% torque over a 235.
This is a bolt-in swap from a 235 or 216 if you find one with the
high-mount water pump. If you use the 55-2 or later (low-mount water pump)
motor you have the usual long water pump hassles plus an additional one
that no one has mentioned. That is that the bottom of the fan extends below
the radiator and so some of its effort is wasted by pulling air under the
radiator rather than through it. Plus, if you use a big fan (more than
16") you have to drop the radiator in its mount so that the fan clears the
lower radiator outlet. Not a big deal but you do have to drill six extra
holes in the mount and get some j-nuts to remount the radiator. On the plus
side, the later 261 uses a full-flow oil filter, so you could plumb in a
useful oil cooler if you wanted.
Driveline
If you want to haul much with a 3800, you may have longevity problems with
the Saginaw five speed. My 3800 weighs 5100 lbs empty, lots more than an
S-10. The original Muncie is rated at 200 ft. lbs. but I think this is a
very conservative rating as GM used this transmission behind various
engines including V8s until 1966. Also, I doubt that you'll be able to use
a 30% overdrive except when running empty and even then probably not with a
stock 235. Using the stock 5.14 gear you'd have the equivalent of a 3.60
gear ratio. Mine will pull the equivalent of a 4.40 ratio loaded on flat
ground and up to about a 3% grade with no wind.
My 235 engine has an RV-type cam (220 deg @ 0.050 lift and .450 lift), twin
carbs, Fenton headers, 2-1/2" Flowmaster muffler, and MSD ignition and
7.5:1 comp. ratio. This setup will pull way above 3,000 RPM but in the
interest of engine life I don't run it above 3000 except occasionally 3400
to make the next gear. My experience with the rig loaded with camper, is
that turning 2750 at 60 MPH, I run at about 6 inches vacuum on flat ground
with no wind. The engine likes to pull right at 2800 RPM and will pull
down to about 2600 before it begins to fall off the cam. At 2400, it's time
to shift gears. I don't think I could pull 4:10 gears, much less 3:90. .
I'm running the stock 5.14 gear with a 17% overdrive and 255/85x16 rear tires.
In case you've never driven one with a tachometer, the stock setup will
turn 3367 RPM @ 60MPH with 7.50x17 tires.
With regards to the drive shaft, there is a limit to drive shaft length
that is related to RPM, as long ones will tend to whip at high RPM. This is
why you see drive shafts on long wheelbase trucks segmented with three of
even four sections. I'd stick with the stock 2-piece drive shaft setup and
match the transmission-end to the u-joint the transmission requires. There
are enough vibration problems on these things when stock.
I hope this information can be of help to you 3800 owners when considering
modifications.
Tom Allen
51- 3800
At 11:06 PM 12/28/01 -0500, Justin C. Earl wrote:
>Hi Phil:
>
>I also have a '51 3800. It came (non running) with a 235 that someone
>transplanted years ago. I had an old time car guy come into the store the
>other day and he says I should go with a 261 in my truck. He makes it sound
>simple, but I'm a little leary since everyone on the lists (and other
>sources) talk about the ease of a 235 conversion but I've never heard anyone
>talk about a 261.
>
>On the transmission, someone a while back on this list said a Chevy S-10 5
>speed will bolt right up to a 235. With that 5th overdrive gear it might be
>workable to keep the original rearend. The only thing I don't know is if
>this is truly a bolt up conversion. Anyone out there have any details on
>this?
>
>Good luck with your truck - I just got some air tools for Christmas so I'm
>hoping to make some progress in the coming new year.
>
>-Justin Earl
>Cartersville, GA
>'51 1 ton dually
>
>Hi Guys, been lurking for awhile, due to back trouble, but now am back at
>work on my 51 3800. Im going with a 235, and am condidering going with a
>3.90
>rear from art houser. Am contemplating a tranny change, anyone have any
>suggestions on this ?
>Phil Faircloth
>51 3800
>51 Burb
>53 3800
>oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>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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