I'm planning on running a 3x2 set up on my 355 cid small block Chevy in my 48 Plymouth custom that I'm currently building. I have perfect Rochester 2Gc carbs a few dozen actually most likely I could bolt em right up with no issue but I plan on tearing them down and giving each one a freshen up. My question to you guys is this would you run all three as primary carbs or would you run the outer two secondary and just a single center primary? I've had many 3x2 intake setups over the years and both the 348 and 409 had three primary carbs, but they were hotrods not cruisers. Your thoughts are always appreciated
Unless you have the correct or correctly modified end carbs. and can use progressive linkage. You only option is to let it idle on all three. Then you have a very (touchy) throttle. So you need a bellcrank arrangement to reduce throttle movement versus gas pedal movement. Or you can just make the end carbs dummies LOL
I cannot see any good reason to not run them progressive. I've had many, all were running mechanical progressive linkages, and all were genuine tri-power carbs where the outboard carbs have thicker throttle plates that seal perfectly for a mint idle on a driver.
You can get bases from Charlie Price, Vintage Speed which eliminate idle mixture screws like the ones on 348 Chevs.
Yes, set it up to idle and drive at low and normal speeds on the center carburetor alone, the outboard carbs opening progressively via an adjustable linkage. Unless you want to be tinkering with it all the time and using a lot of fuel, set the outboard carbs to open when the throttle linkage position is beyond what it would be at normal cruising speed - like above 70 mph. Think of it like a non-vacuum secondary 4-barrel carburetor which runs on the two primary barrels most of the time, the other two open manually only when you want a burst of power. If the end carbs kick open too soon you'll get a bog that makes the car annoying to drive. It'll take a bit of tinkering to get the adjustment just right but it's better to have the two outer carbs kick in too late than too early. Be aware also that the bases of the end carburetors should have the idle and intermediate circuits deactivated with only the primary circuits active. I don't know who makes them but I'm sure these 3x2 end carb bases for 2GC's are available in the aftermarket. Oh...and the linkage should be designed so that the end carburetors open at a faster rate than the center carb. So the end carbs begin to open later but all three achieve WOT at the same time. Good luck!
Its odd to me. when it comes to a tri power everyone thinks you gotta have progressive linkage and modified end carbs. Yet I had a factory dual carb engine in a corvair and both carbs where fully functional and it never had any bog. it idled on both carbs. many 6 cyl engines have been converted to dual or triple carbs and all of then fully functioning. The Man A Free intake that came out in the 1950,s mounted 4 two bbl carbs all fully functioning on a 265. No reason why you cant successfully use 3 fully functioning two BBL carbs on a 283. The accelerator pump and idle and intermediate cover up the bog. Holley developed the Double pumper 4 bbl for the same reason. Ive run dual and multiple carbs with them all functioning. It simply takes more effort to properly synchronize and tune them. You got to fiddle with jet size ect. on the idle a single two bbl you adjust the screws out 1&1/2 turns yo start. so with three carbs you adjust 1/2 turn to start. if the plugs are sooty and black you reduce jet size. keep reading plugs and adjust as needed. I know the factory used progressive linkage and sometimes vacuum operated end carbs. However the factory has certain parameters they must adhere to and must make it lean more toward the user friendly engineered rather than optimal performance.
I tried it both ways on my flatty and it runs better in my application with the progressive linkage. What is nice about the Stromberg progressive linkage is that you can quickly change it with an Allen wrench if you want to go with all three.
ok on another thread here receintly there is a member who just scored a factory chevy tri power intake that all three carbs are the same and does not use progressive linkage! He has a intake with three weber side draft carbs for a 235 chevy.
Probably hard/expensive to find today, but the stock 348 Chevy 3x2 setup has secondary carbs with the non-idle bases. I managed to find a set back in the 80's and still have them on my roadster's SBC.
Hello: would you consider a turn-key system ready to go! It is an Offenhauser four deuce system. I build these systems here in Lincoln, Nebraska. I build the Man-A-Fre four deuce too. I worked alongside the owner, Harold Graves, in the sixties. The Offy4x2’s are a popular alternative to he Man-A-Fre. Please check out my four deuce units at oldschoolinduction.com. [email protected]. Thank you, Tim Bowman.
I would be interested in looking at your Rochesters. Can you contact me and offer some pics and more for?
I have three Strombergs on a 327 SBC. Not progressive linkage. I don’t know exactly why anyone would want that. I can get a nice spray of fuel in the windshield if I stomp it just right.
Mine's the same setup as you are planning-355 etc. I've tried a lot of different ways over the years, finally settled on large base pontiac's (a factory tri power) setup with progressive. I run on just the stock center with no mods, does fine on idle, cruise, and stoplights. Ends are only "dumpers" when called upon. I can relay this to you-absolute Must have no vacuum loss anywhere, that means the end bflys. The center has to be setup to run alone (block off the ends) with no problem. As some others mentioned, Speedway and Vintage (mine) sell the end bases that seal-the way to go. Finally, a regulator should help, i didn't run one for a long time and did have some flooding problems, the regulator solved that. They are not trouble free but multiple anything normally isn't.
I do not recommend non-progressive linkage for any street driven vehicle. I was making a joke, because all that extra fuel proves my point. The best setup would never give the engine more than it wants at any given time.
The Jalopy Journal
