I'm in the process of building a 355 SBC and I want to run traditional Tri power with Rochester 2 GC's. I've had 3x2 set ups in the past on Pontiac's and on my 409 and have never had a single issue, and just really like the way they look so my questions are I know some guys op for the center carb primary and outer carbs secondaries but has or does anyone run all 3 as primary carbs? Is this more trouble than its worth or would it be to some advantage, I plan on a pretty hot cam and have flat top pistons on a fully balanced lower end. I would also appreciate any input on what cams you guys have run also.
..I am no expert but from what I have read if the wrong carbs are used,( all primaries )... problems are sure to come along with a possible engine fire....also how would you get the engine to idle?...miller
With all three Rochesters set up as primary carbs running straight up linkage, you will probably have way to much fuel dumpin into it. I have never done it with 2GC's but have done three 94's running a straight linkage on a 327 and i thought it worked pretty well. It ran a bit rich but not much. If your considering using 3 primary carbs and modifying the outers to be dumpers, that can be done. I think Vintage speed was selling kits that included new base plates the to convert primary carbs to secondary.
I've seen a car that idled on all 3 and up to half throttle opened only center, then above half throttle opened all 3. Owner said it resolved problem where outer carbs ran or leaked dry under prolonged low power use. Sent from my iPhone using The H.A.M.B. mobile app
3-2's and dual quad engines have special needs. If driven like a little old lady you may need to try something different. Fuel pumps will keep them full but the continuous shaking of a typical engine will cause the unused ones to over fill. You need to open them up every so often. On my dual quads I need to use both idle circuits and with it cold to floor the foot feed to not only set the choke on the rear lead carb but to squirt fuel at the front ports so it will start but only when cold... Good Luck.
I have set up lots of 3-2 setups and I am a fan of all 3 carbs using idle curcuits which a lot of guys don't like. So here is my belief set the carbs up progressive so that when you are going slow like parking or going through a show your not over fueling with 3 accelerator pumps squirting or 3 carbs dumping fuel.You can adjust how soon they come in depend on what ratio you use on the linkage. Just remember one important thing the carbs must all be jetted the same way and all idle screws must be out the same amount also you must use the same power valve spring and jet. I like idling on all 3 carbs so that you have even fuel distribution. Good luck if you need more info get in touch with me
The key to running them all at one time is throttle blade to bore sealing and shaft sealing. the power valve springs will have to be modified so they don't open too soon and bog the engine with fuel. Some of the problem will be with the ignition system that will also have to be modified with quicker advance and a low vacuum canister. ^ you have to use three "center" carbs and use their idle circuits......
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