The Stovebolt Site Forums The Shop Area The HiPo Shop multi carbs on a 6 cylinder

From a pratical standpoint, is it eazier to run a 2 or 3 carb set up on our old sixes?

It seems to me that the 3 carb set up would have more even fuel distribution if it was adjusted correctly. The drawback seems to be the slower fuel velocity at low rpms.

The 2 carb is an improvement over stock, but doesen't seem to give an even distribution of fuel to all cylinders. I can't help thinking that the #3 and 4 cylinders are getting twice as much fuel as the rest.

Anybody running one of these setups have any practical insight?

Anybody else have an opinion?

I had a hot rod 235 with three single barrels on it. It had tons of other stuff done to it to support that amount of carburetion.

Without the additional modifications, I think the general consensus is that two carburetors is optimum...three is too many.

Fuel distribution certainly is a big part of the multiple carbs. The spacing of two would seem better than the single, and the spacing of three would seem better yet.

Every time you open a 'hole' to atmosphere your flow is divided proportionately.

With three 'holes' you have less velocity, and usually more fuel...this is probably too much for the little old 235 in stock form.

My unprofessional opinion is that two carburetors would be fine on a stock engine, but three would be too many.

Although this subject has been beaten to a bloody pulp on many occasions, it remains a interesting topic.

Stuart

The real practicality of two or more carbs is the cool factor. The less is better rule applies to functionality and horsepower.

Oh yeah, forgot to mention its for a 302 with cam, headers, 9:1 pistons and balanced, also using HEI ignition. Not sure if that'll change any recomendations. 2 carbs look good, 3 carbs look great, 5 carbs on a polished Howard manifold...

There probably is not a "one answer for all"; but in general properly SIZED AND TUNED multiple carbs will be marginally better than a properly sized and tuned single carb due to better fuel distribution to all cylinders.

So how much is "marginally better"??? Lets say that the "perfect" multiple carb setup is 100 percent; then the "perfect" single carb setup will probably be at 96~98 percent. So while measurable on a dynomometer, can you measure 2 percent HP increase by the "seat of the pants"? Can you measure a 2 percent increase in fuel economy?

The key in all of the above is properly sized and tuned.

As to whether 2 or 3 or 5 or ??? carburetors??? Much depends on head design (individual ports, siamesed ports, triple ports, etc.) and whether the carbs will be run simultaneously or progressive. I personally am a firm believer that the number of "barrels" should be an even divisor of the number of cylinders; so for a six-cylinder engine, that means 1, 2, 3, or 6 1-barrel carburetors; or maybe 1 or 3 two-barrel carburetors. A single four-barrel with primaries and secondaries feeding a common plenum is also a possibility.

The theory AND practice remain the same, regardless of the displacement, assuming that carburetors of sufficient size may be obtained.

Again, and it cannot be over-stated: the initial selection of the carburetors, and tuning on the engine is the key.

Jon.

bigbadswingdaddy,

If you are serious about the info in your last post, you are more than likely running more than one carburetor already.

If you aren't running more than one carb, you are selling all that engine work WAY short.

Stuart

Haven't put it together yet. I flinched at the cost of all those carbs. I'm still running with my 228, but plan to switch out to that 302 soon.

Back in the early'50's I had a 270 GMC in a '39 Chevy sedan with a Howard 5 carb manifold. It ran great and was never beat on the street by a F**d of any description. The 5 carbs were 81's came off a v-8 60 engine, it was not over carbureted, had progressive linkage with the middle 2 opening first, the end and center 3 came at about 1/2 throttle, it really came on hard at full throttle. Way before e.t. clocks it ran 98 MPH at Santa Ana drags. I drove it on the street every day, only problem was it had way too much torque for the stock Chevy 3 speed and I broke a lot of transmissions, sometimes even carried a spare in the trunk and changed the trans at the curb several times. (Oh for the good old days)

Chevman Thats exactly the setup I want to use! I was thinking bout running on the 2nd and 4th carbs, and progressing the 1st, 3rd, and 5th in. I know there are other setups that may work better, but what would look better than 5 strombergs? Definetely not something you see everyday.