I am considering either a dual or triple intake manifold for my 235 engine. Does anybody have any comments either way? I would like to go with 3 carbs. I like the look better but heard that there might be a behavier issue. I would appreciate any comments guys. Thank you, Scott
Multiple carbs are fine if one is knowledgeable and skilled. GM had no problem on the 54 Corvette but it used a side draft manifold and carbs specifically designed for the job. I like to use 1" or so spacer with a 1/2" tube in the side under each carb. The end spacers tubes face the center carb and it has a tube out each side so short rubber hose connects the bases of all three carbs. This "balance tube" really helps low rpm running and driveability. A 235 at 3500 rpm uses about 250 cfm of air so it is easy to use too big of carbs which guarantees a miserable running engine. Progressive linkage is a must. This lets the engine run off the center carb till an engine speed is reached that can use the extra air without dropping the vacuum and causing it to stumble. Years ago there were foreign cars with 1200 or 1300 cc engines that had down draft carbs and I've often wondered if three of these would have worked well since each pair of 235 cylinders that they would have been feeding comes to 1280 cc's. Probably just another entry into my dictionary of useless facts.
I think more is always better on these engines but there are a few things to consider when running multiple Carbs. First thing is air fuel ratio. If you are running multiple Carbs you have to make sure that your manifold has enough air volume to atomize the amount of fuel you are dumping into your engine. I think 2 Carbs are fine with the Fenton or Offy. manifolds 3 Carbs are going to cause you a few problems in the low end with stumbling and flooding. You also need to consider upgrading your ignition, a coil is good but an MSD box is better. You can go with a duel point distributor but keep in mind that if you use an MSD box the only thing the distributor does is trigger the box so a good stock distributor should be fine. When running an MSD box you can also increase your plug gap .038-.040. The MSD box will fire each plug 4times and burn all that extra fuel better than a stock ignition. Now that you have dumped all that fuel in to your engine and figured out how to burn it you have to be able to get the engine to exhaust the spent gasses in a hurry So you will probably need a set of headers. Cliffords makes a couple different kinds and there are Fenton cast iron headers too. Once you open this can of worms it can become an addiction and there is no end to what you can do. I've been playing with my "54" for over 30 years now and I am always thinking of something new I can do to make that 261 run better. Here's a link about A/F ratios and a couple of pix....Have fun.. http://www.know-yourcar.com/Air-Fuel-ratio-Engine-Power.html 261 chevy .030 over with 9.5-1 Jans pistons .125 shaved off the head with resesed valves, porting and .08 decked off the top of the block with head studs installed. The center weight was chopped of the crank and the crank was balanced Custom 4 bolt main caps were made and the rods were shot peen and I beam ground with ARP rod bolts installed. A custom Crowler cam shaft was made and Clifford made an Alum. fly wheel. A custom tunnel ram was made by me as well as a set of S.S. fender well headers. Two Holly 350 CFM Carbs with 50 CC accelerator pumps, Mallory (YC) type distributor, Mallory coil, and Accel 8.8 mm wires were used with an MSD 6A ignition box with timing control. Borg Warner super T 10 4 SPD with a vertical gate shifter, narrowed 9 In., Strange billet carrier, Detroit Locker with 456 gears. All machine work was done by Bell & Gains Service and assembled by Larry Neville of Neville Bros. Automotive Modesto Ca. and myself This thing will smoke them 31x18.50x15 Micky's through 2 gears, rip 3Rd. and bark 4TH OH YEAH...
Multi Carburation In general , one carby per intake port gives maximum power through more precise fuel metering . As Evan said , three pots can be a handful on these old tech , long stroke engines . Most folks want good bottom end power , tractable so the take off from a red light or loaded up , is still smooth . For this , two stock carbys on a intake manifold is best . Also , the balance tubes are not really necessary as the intake manifold is a "log typ " ~ open internally so the intake pulses tend to self balance . If you want a smooth running , powerful and fun to drive engine , use two carbys . If you're a Hot Rodder and are looking to spin the tires and so on , use three carbys but don't complain when you blow the engine in under 10,000 miles . Basically , you pays your moneys and makes your choice . Choose wisely .
That engine I am jealous of!!!!! That looks like 30 years of tinkering... That for the advice. Scottys54
Thanks Nate..... i would love to hot rod kind of old school style as i am tring to keep it as stock as I can. But I was looking for a little more from the engine. I will probably go your 2 carb route. I much rather have the reliability than a few more horses..... Scottys54
For me personally two was enough. It looks in proportion to the engine compartment. There are other peripheral considerations. The diagonal brace from the firewall to the left fender was hard enough to re-fashion around the rear carb with two, three might not be do-able. Like I was asking the guys about earlier this week, the in-line glass fuel filter also has to fit somewhere. I had to tap holes in the intake manifold to mount my remote Oil filter. One of the manifolds (Edelbrock?) comes factory with Oil filter mounting holes or brackets. I had already bought the Fenton so did my own mods. Flashlight
Multi Carburation Onbe important thing to remember : once you have them balanced and dialed in , LEAVE THEM ALONE ! " Carburator is a French word meaning LEAVE IT ALONE " Carburators DO NOT go out of adjustment ! other things do but not them . Resist the urge to constantly fiddle with and tweak them , beware the person who insists they always need touching ~ he knows not whereof he speaks . You'll need two glass bowl filters , one for each carby , mounted right at the inlet . simple & easy to do , I see lots of repop glass bowl fuel filters out there . AC & WIX (NAPA) both still make replacement filters and gaskets for these . DO NOT usethose tiny 3" chrome air filters and expect it to run well . use two matching air filters as you'll be passing serious CFM's of air. You'll find that two matching stock carbies will be sufficient to splinter the ring gear and spin the tires too , your old wheezy 216/235 smoker will really come alive . beware of this .
