The Stovebolt Site Forums The Shop Area Engine Shop 261 multi-carb basic questions

Forgive my ignorance, but....

How do you match a carburetor's CFM rating to the engine when you want to use a dual carb setup?

For example, I have a '54 261 engine. I didn't want to use the original Rochester "B", so I went to the Carter YF 2100S. I knew that this carb was too small for the 261, but I used it until I found a Zenith from a GMC 270 that had a higher CFM rating.

Now, if I went to a dual carb setup, would I still be pulling in the same amount of air through two carbs as I did with only one? Or, would a dual carb pull in more air? That doesn't seem likely since it would also pull in more fuel, thus decreasing mileage...right?

So, to go to a dual carb setup on a 261, should I have two carbs that have a high enough CFM rating to be used alone for the engine? (such as the Zenith's) Or, can I use two lower CFM rated carbs (such as the Carter YF's)?

As I understand it, multi-carb setups (when done properly)can provide better fuel economy and more even aspiration, thus giving more power, right?What about a triple carb setup? Any advantage over a dual? Or,does that become a nightmare to tune?

Thanks for your help,
Steve

Chevy under-carbed the six through the years. Using larger (or more) carburetors moves the power curves higher on the rpm scale. You will lose some of the grunt at low rpm, but you will also have more power at the top end.

How much carb is needed depends on what else you have done to the engine. What goes in must go out, so a split exhaust of some sort is helpful with dual carbs. Also, a camshaft with more valve lift and duration is another plus. Neither of these is mandatory, but they help to use the added airflow. If your engine is otherwise stock, a pair of the YFs would be a good start. If you have the split exhaust and cam, consider dual Zeniths or even triple YFs.

I doubt if you will see an increase in gas milage, unless you have a horribly inefficent carburetor. Tuning multiples isn't that difficult, but they do need to be matched with the proper size jets. It is the jetting that determines your air/fuel ratio.

Another option that will increase milage and performance is an HEI distributor.

For more info on carbs, search this forum for posts by Jon, aka carbking, bolter #2929. He rebuilds antique carbs for a living.