mfg Posted March 27, 2014 Report Share Posted March 27, 2014 I have a dual four barrel carb setup that I'm thinking of installing on My '63 R2 Avanti. It has two rebuilt sealed carbs and a custom 'Y' splitter for ducting pressurized air from the Paxton supercharger. I'll be using progressive linkage with this setup. Wondering if anyone has tried a setup like this on their stock R2 avanti....and if so, how did it work out? More trouble than its worth? Link to comment Share on other sites More sharing options...
PackardV8 Posted March 27, 2014 Report Share Posted March 27, 2014 Yes, it's more trouble than it's worth. Idle becomes problematic. Fuel mileage will be dramatically lessened. The extra power will only be at the very top end. No, there won't be another one like it at most any show. Many OOHHs and AAHHs. Maybe, decide what you're trying to accomplish and what you're willing to do to get it. And are you sure the hood will close over that setup? jack vines Link to comment Share on other sites More sharing options...
mfg Posted March 27, 2014 Author Report Share Posted March 27, 2014 That's what Im expecting, but at least with a Stude there's no coolant flow through the manifold so as You know intake swaps are not a big deal save for a new set of gaskets. The hood may clear with stock front engine mounts, but definitely will clear with those short R3 types, which I bought last year. Thanks. Link to comment Share on other sites More sharing options...
brad Posted March 28, 2014 Report Share Posted March 28, 2014 Originally the dual quads only had one carburetor with an idle circuit (the rear carb). I am using a Novi blower with much higher boost (up to 15 lbs). Just be sure your progressive linkage is set right, and you will have to lighten the secondary auxilliary throttle so the actually open with less airflow (because it is split between two carbs now) I drastically modify the venturi cross sections to get back a strong metering signal. Too much carburetion will make any engine fall flat on it's face.......1250 cfm on 304 cubic inches (for the R4) was not conducive for street driving. It was set up for WOT flat out, with no concern for streeability. Link to comment Share on other sites More sharing options...
Devildog Posted March 28, 2014 Report Share Posted March 28, 2014 (edited) I have a 61 Corvette with the original 2 x 4 WCFB carbs. I have driven it for 45 years and over 200,000 miles. As others have indicated, ned to have smaller carbs. These WCFB's are about 350 cfm each. Both have an idle circuit, and the car is quite streetable and gets good mileage. What size carbs do you have ? If you had 400-500 cfm carbs would work OK. I do not think it would be too difficult to set-up, but I doubt you would notice any significant performance increase. But, 2 x 4's are a big WOW facto which people enjoy Joe Edited March 28, 2014 by Devildog Link to comment Share on other sites More sharing options...
mfg Posted March 28, 2014 Author Report Share Posted March 28, 2014 Thanks for the replies. The carbs I intended to use are twin R2 sealed type, which probably have at least 625 cfm capacity each. Link to comment Share on other sites More sharing options...
mfg Posted March 29, 2014 Author Report Share Posted March 29, 2014 The twin Carter AFB's on this setup both have working automatic chokes with hot air delivered to both choke housings from a 'Y' connection at the manifold. Using progressive throttle linkage, would it be better to disable the choke in the front carb (leave wide open), and just rely on the choke in the rear carb for warmup....or leave it the way it is? Opinions? Link to comment Share on other sites More sharing options...
Devildog Posted March 29, 2014 Report Share Posted March 29, 2014 The twin Carter AFB's on this setup both have working automatic chokes with hot air delivered to both choke housings from a 'Y' connection at the manifold. Using progressive throttle linkage, would it be better to disable the choke in the front carb (leave wide open), and just rely on the choke in the rear carb for warmup....or leave it the way it is? Opinions? Yes, I think on an AFB there are two small screws that hold the choke plate on the shaft...just remove plate. To initially tune the car, just disconnect the linkage to the secondary AFB, get the primary AFB performing as you want. Then set linkage to bring in the secondary. It will run OK Joe Link to comment Share on other sites More sharing options...
brad Posted March 29, 2014 Report Share Posted March 29, 2014 Don't forget the secondary carb is the front one. The reason being the idle circuit on the rear carb is closer to the center(of the manifold) for better distribution Link to comment Share on other sites More sharing options...
mfg Posted March 29, 2014 Author Report Share Posted March 29, 2014 I have a 61 Corvette with the original 2 x 4 WCFB carbs. I have driven it for 45 years and over 200,000 miles. As others have indicated, ned to have smaller carbs. These WCFB's are about 350 cfm each. Both have an idle circuit, and the car is quite streetable and gets good mileage. What size carbs do you have ? If you had 400-500 cfm carbs would work OK. I do not think it would be too difficult to set-up, but I doubt you would notice any significant performance increase. But, 2 x 4's are a big WOW facto which people enjoy Joe A 1961 Corvette with factory dual fours...You own a great car! Question...On You Corvette, is the front carb working at all at idle speed..or is it completely shut down? I'm guessing that Chevrolet used progressive throttle linkage to control these carbs...true? Thanks. Link to comment Share on other sites More sharing options...
Gunslinger Posted March 29, 2014 Report Share Posted March 29, 2014 Please correct me if my thinking is wrong, but wouldn't splitting the boost hose from a single Paxton cut the boost in half to each carburetor? I don't know the exact proportions but it seems like total boost would be halved. When Paxton built the colloquially referred to R5 engine, they installed two superchargers...one for each carburetor to maintain desired boost. While there definitely be a lot of bling appearance-wise, I'm not sure a boost in performance commensurate with the effort will be there. A well setup and tuned R2 will likely be more streetable than a split hose R2 with two carbs...plus get better fuel economy. Link to comment Share on other sites More sharing options...
mfg Posted March 30, 2014 Author Report Share Posted March 30, 2014 Never considered that. But in thinking about it, I would guess that boost would not fall off unless the cylinders were made bigger (increased cubic inches). An air box on an R3 engine, for example, probably has more interior volume to fill than what I'm thinking of doing.. I don't think that the extra 'pre-cylinder' volume of an R3 air box effects boost on those engines. Opinions? Link to comment Share on other sites More sharing options...
Gunslinger Posted March 30, 2014 Report Share Posted March 30, 2014 R3 engines have a higher compression ratio (9.75:1) as opposed to the 9:1 of an R2, a little higher boost plus a different cam profile and bigger valves for better breathing so the whole integrated system has to be considered when making comparisons...not just adding a carburetor or a pressure box. Changing one item affects the whole...maybe positively, maybe negatively. Everything has to complement each other in unison. I've often seen guys...doesn't matter whether Chevy, Ford, Mopar, etc., add high quality performance parts to their engines and not get the best results because those parts...no matter the brand or how well made...weren't engineered to work together. They were simply a bunch of quality parts bolted on without regard for compatibility or to achieve a specific goal. I'm not saying this is what you're trying to do. I'm not denying visual appeal can't be justified...we all enjoy eye candy. I simply think we need to individually define our goals and make a reasonable plan to achieve that. Link to comment Share on other sites More sharing options...
mfg Posted March 30, 2014 Author Report Share Posted March 30, 2014 I agree with Your comments. What really started Me thinking about adding the extra carb was an e-bay auction. Someone had a blue '63 Avanti for sale which had the nicest looking R2, with two four barrels added, that I've ever seen. The seller went all out on the boost splitter piping to the carbs, which was either highly polished aluminum or chrome plated steel...a real nice install that definitely qualified as eye candy! Link to comment Share on other sites More sharing options...
Gunslinger Posted March 30, 2014 Report Share Posted March 30, 2014 I remember seeing that Avanti. It was stunning...the engine was very impressive. Link to comment Share on other sites More sharing options...
brad Posted March 31, 2014 Report Share Posted March 31, 2014 There wasn't a carburetor to be found on the R5! they used an experimental fuel injection system from Bendix. It won't matter how many "branches " the boost travels through, unless the displacement changes, boost will remain the same. Boost is volume in vs volume used. Link to comment Share on other sites More sharing options...
PackardV8 Posted March 31, 2014 Report Share Posted March 31, 2014 Remember, boost pressure is what the supercharger generated which could not get past the intake manifold, ports and valves. No matter how large the carbs or how many, it's the intake ports and valves which are the choke point. The boost will be very nearly the same with one or with two AFBs. As previously mentioned, the 2x4 will probably make a bit more horsepower above 5,000 RPMs just because the intake manifold has less restriction than the single 4-bbl manifold. jack vines Link to comment Share on other sites More sharing options...
Gunslinger Posted March 31, 2014 Report Share Posted March 31, 2014 You guys are correct...I completely forgot the R5 used a fuel injection unit adapted from the Novi engines. Thanks for the correction about boost pressure. Link to comment Share on other sites More sharing options...
Devildog Posted March 31, 2014 Report Share Posted March 31, 2014 A 1961 Corvette with factory dual fours...You own a great car! Question...On You Corvette, is the front carb working at all at idle speed..or is it completely shut down? I'm guessing that Chevrolet used progressive throttle linkage to control these carbs...true? Thanks. The front carb has both primary and secondary throttle plates closed most of the time; however, the front carb idle circuit is adjusted make a smooth idle. Yes, the linkage is progressive and adjustable. Most of the time you are drive just on the rear primary barrels. Contrary to what most think, if you do not 'put your foot in to it' the mileage is quite good because with the small primary barrel you have a more controllable air/fuel management than a larger single carb. With a 270hp/283 cu in solid lifter Duntov cam (factory set-up) and 4 speed with 3:36 differential, routinely got 20 mpg at 70 mph. I take it to the Nostalgic Drag Races once or twice a year. I shorten the linkage to the front carb so the front barrels activate earlier ('shotgun' is the terminology). Makes the car a bit quicker, but I do not push as hard as I could. A few years ago put a DART 400 SBC and DART heads in the 61. I used ALL the original ignition, carbs, intake (hand enlarged runner), etc. It looks just the same as the original 283. It dyno 496 hp and 440 ft lb torque with same 2 x 4 WCFB carbs (350 cfm each) I am not familiar with the manifold you are using, but heads and manifold flow have a heck of a lot more effect on power than just sticking and another carb on the engine. Do it, an interesting project. Link to comment Share on other sites More sharing options...
mfg Posted April 2, 2014 Author Report Share Posted April 2, 2014 Well, I went ahead and ordered a set of composite intake manifold gaskets. (New style) We'll see what happens! Link to comment Share on other sites More sharing options...
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