| Dear reader, I
apologize
for neglecting to update my monthly saga. This April story has been
long
overdue. No, I haven't been resting on my laurels, but I quess I've
been
too busy, and also lacked suitable pictures. Please bear with me!
All the weekends seem to be filled with other stuff - weddings, bachelor parties, working on the boat and so on. Maybe I didn't mention but I had the bumpers stripped at the plating shop. We found the rear bumper to have been re-chromed in the past, without first removing all the old nickel layer and pitting as should have. Also, the front pieces were heavily rusted under the bumper guards. The plating shop wasn't really thrilled to start grinding and buffing it all, so I decided to save money and do it all myself. Well I finally forced myself to grind and buff the bumpers in the evenings, 25 hours of work in total. I had to gring extremely deep, and sometimes I felt that if I dug any deeper, I would end up in China! It's a dirty job but somebody's gotta do it. Now they are back at the plating shop. Now let's cut to the chase. It must be years ago when I got the idea of fabricating a dual-carb system to replace the modest one-carb system. Only the first round of intake manifolds I fabricated were too tall. I was so frustrated that I forgot the whole thing for a long while, but now they are ready - please enjoy the story. |
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| By 1946, Buick
had dropped
the dual-carb setup that was available before WW2, and it was never
again
available. The 1942 dual-carb 320 engine made some 165 HP while the
1946
single-carb engine only made 144 HP. The dual-carb setup worked
progressively
- at idle and cruise modes, only the front carb fed the engine, and
when
the pedal was pushed further, the rear carb cut in gradually. So it
worked
like a modern 4-barrel carb, but was made of two separate 2-barrel
carbs.
The secondary carb didn't feature an idle circuit at all.
The one-carb factory manifolds feature a few inherent problem areas, though. The runners to 1/2 and 7/8 cylinders are extremely long, while the runners to 3/4 and 5/6 cylinders are short. While hardly none of them are of ideal length, the biggest drawback is the huge difference between lengths, leading to uneven filling and mixture distribution between cylinders. Moreover, the 7/8 runner features two consecutive 90-degree bends that are very sharp and abrupt shape. Lastly, the heat riser valve get's stuck over time, boiling the carbs, causing the "hot start blues". Factory dual-carb manifolds may be of slightly better design, but I doubt it. I had a slightly different approach to the design. I decided to use two identical Stromberg AAV-26 carbs, which is the OE carb used in single-carb 320 engines. I fabricated two separate but identical manifols, one serving to cylinders 1-4 and the other to cylinders 5-8. The manifolds are made of stainless, and feature 1-5/8" runners that are slightly larger than original, and are of equal length. I used "chemical metal", which is an epoxy with metal filler, to form a smooth radius on the inside of plenum where the air enters the runners. |
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| People who have experience among V-8 intakes, know the difference between a dual-plane, divided plenum manifold, and a single plane, open plenum manifold. Now suppose you have a 4-barrel carb. With a divided plenum, each cylinder will draw from one primary and one secondary barrel, thus the signal to the venturi is strong at idle and low rpm, yielding better idle quality and low rpm torque. With an open plenum, each cylinder is allowed to drink from all 4 barrels, thus the signal to the venturi is weak at idle and low rpm, impairing low-rpm driveability, but yielding more horsepower at high rpm's due to increased airflow. |
 I
developed an adjustable plenum divider - I have no idea if it's ever
been
done before - which allows me to change the manners whenever I want to.
Inside the plenum, there's a trap door that can be adjusted manually
from
outside of the carb, either to shut the door to make it a divided
plenum,
or to open it to make it an open plenum manifold! When closed,
each
cylinder will drink from one barrel only, and when opened, each
cylinder
will drink from 2 barrels. In the picture above, you can see the
divider knob under the manifold. The stem is sealed with an O-ring, of
course. On the left is a view into the plenum, which is in open
position.
I can hardly wait getting to play with it! |
 |
 Above
and Right: Of course, all the vacuum lines and gas lines had to be
redone,
as well as the choke heater pipes and the whole linkage all the way to
the pedal! Also note Cool-Flex corrugated stainless radiator hose, and
a new aluminum full swivel thermostat housing. I found that the
original
cast iron thermostat housing was cracked, being one of the leakage
sources
I was able to identify. I also discovered that a common Chevy
thermostat
housing has exactly the same bolt spacing! While I found an affordable
full swivel housing on eBay, the same seller had a Cool-Flex hose kit,
which I coudn't resist, although it cost an arm and a leg. It sure
looks
cool.
The rear carb is a NOS item I was able to find in a nearby parts store! The front carb is the OE carb, that I disassembled, cleaned the internals in hot acid solution, and put back together with an overhaul kit from Bob's Automobilia. The NOS carb is actually a Bendix-made AAV-267, which is a replacement for the 1942-47 AAV-26 used in Buick models 60-70-90. I checked the main jets to be the same size as in the OE carb. I hope they are reasonably identical to make the engine run properly. The starter vacuum switch is slightly different on the Bendix unit. The wiper vacuum line is connected thru the vacuum pump to the front manifold. The brake booster is connected straight to the rear manifold. Distributor vacuum advance line is connected to the rear carb. Both the choke heat pipes and fuel lines are made of stainless tubing and Swagelok fittings. I didn't want any rubber lines above the headers. Speaking of safety, I also moved the fuel filter / glass strainer bowl, which is a sparepart for a Fordson tractor, on the other side of engine, just above the fuel pump. The throttle linkage between the carbs is made of two spherical rod ends, one with male threads and the other with female, allowing to synchronize the carbs by just turning the rod in between and lock it with jam nuts. Made of stainless of course. I also had to re-construct the linkage between the rear carb and gas pedal, stainless again. All and all, it required more work that I thought, and only time will tell if it was worth the effort. |