Mike - glad you posted the article so that everyone can read it. I have a copy in my files, and obviously have read it before.
Points that I would like to suggest about the article:
(1) My guess is the ability of the person doing this test is above most of us as far as what he can accomplish; so we can say that his results were maybe 99 percent of optimal for available parts at the time.
(2) The Stromberg carbs used (wonder how many OTHER carbs were tried before he settled on the Strombergs) were 216 carbs; two of which he considered optimal for for the 261. NOT a pair of 235 carbs on a 235. If a pair of 216 carbs is optimal, does anyone not believe that larger carbs on a smaller engine are going to be over-carbureted?
(3) Incidentally, he listed the Stromberg sales number 380269 which is not found on any Stromberg carburetor. For any wishing to duplicate the test, the Stromberg code number for 380269 that is STAMPED on the top cover of the carburetor is 14-22. There may be an engineering "status code" appended to the 14-22. So one might find a 14-22A or 14-22B. Same carburetor with a "tweak".
(4) It would have been nice had a test also been done where dual carbs were added with the stock manifold, but we don't have that so we have to draw conclusions from what we have. The addition of the Corvette exhaust manifold gives approximately a 5 percent increase alone, where the addition of the both the Corvette exhaust AND the dual carbs give approximately a 16 percent increase. Since we don't have the test results, I would GUESS that the additional of the dual carbs alone would give approximately the same 5 percent increase as the Corvette exhaust; and the 16 percent was the combination of both, as they complement each other.
The article does prove that some modest improvement IS POSSIBLE; but it does NOT follow that all of us are going to obtain the exact same results as the gentleman doing this test, even if we use the same parts!
For a number of years, I have been suggesting to those that wish to use dual carbs, to use the 216 carbs on the 235 (or the 261), but they are many more running 235's than 261's. I have been suggesting Carter W-1's for the reason that they are MUCH more readily available AND less expensive than the Strombergs. Also parts are much more readily available for the W-1's than the Strombergs. I have also suggested for many years that the Stromberg type B and the Zenith type 228 are very slightly better than the Carters, and significantly better than the Rochester B's.
So what is the bottom line for this part of the post? Placing dual carbs on the Chevrolet six (216, 235, 261) is NOT the BEST configuration, because of the cylinder head intake port configuration, for MAXIMUM improvement. Yes, the article did prove some improvement is possible on an otherwise stock engine (and Corvette exhaust) IF THE CARBS ARE CHOSEN WITH CARE AND INSTALLED AND ADJUSTED BY A PROFESSIONAL! I would submit that if the carbs are NOT chosen with care, and professionally adjusted, it is quite possible to actually LOSE power with the dual carb installation!
The one issue many do not consider, and this is true, when replacing anything that is defective with something new: just because whatever is new performs better than a defective original does not mean whatever is new is better than the original IF the original is in perfect working order.
As to the question about linkage:
Depending on the manifold and carburetors used, the carburetor throttle throw will either be parallel to, or perpendicular to, the length of the engine.
If the throttle throws are parallel to the engine:
(1) assemble materials (A) a 1/4 inch steel rod approximately 2 inches longer than the centerline distance of the two carburetors, (B) a piece of 1/2 inch brass rod maybe 12 inches or so (too much unless you make mistakes).
(2) Measure the inside diameter of the holes in the throttle arm for carburetor linkage, AND the thickness of the throttle arm.
(3) chuck the 1/2 inch brass bar in your lathe, and turn a diameter 0.005 (5 thousandths) less than the inner diameter of the hole. This diameter should be long enough to include (A) the thickness of the arm, a retaining washer, and a space to drill a hole for a cotter pin. Cut the 1/2 inch bar so that the 1/2 inch diameter is 1/2 inch long. Drill a hole in the small diameter for the cotter pin of your choice. Drill a hole through the center of the 1/2 inch portion of the brass perpendicular to the diamter that is 0.228 inch (#1 drill bit). Now drill another hole perpendicular to the first. This hole should be 0.133 (#36 drill bit), and tap for a 6 x 32 set screw.
(4) repeat step (3) as you need one for each carburetor.
(5) make a similar piece for the approximate center of the rod to hook up the linkage from the footfeed.
(6) Assemble the two fittings into the throttle arms of the carburetors, assemble the rod through the large holes in the fittings, with the third fitting also on the rod.
(7) Start the engine, synchronize the carburetors, and THEN tighten the set screws on the bottom of the fittings.
Once you have done a few, you will be able to machine the fittings in 10~15 minutes each.
If the throttle throws are perpendicular to the engine, the procedure is a bit more complicate, but certainly within the ability of any enthusiast with a few tools. The idea is to fabricate two brackets, one for the front of the front carburetor and the rear of the rear carburetor to hold a rotating rod. Make the necessary fittings to hook the rod to the carburetor throws, and adjust.
Since the above is "eye candy" by all means, send the parts off to be chrome plated, but if you do, adjust the clearances I have mentioned to allow for the thickness of the plating. Ask your plater the average thickness of the plating.
And if space in the engine compartment permits, I will continue to suggest 3 carbs on any of these 6 cylinders, because of the cylinder head intake port configuration.
Take a look at the post by panic, suggesting 3 short intakes rather than a log intake with 3 holes. Agree completely, but remember the choice of carburetors will be significantly different for the two different intake configurations.
Jon.
