Why run dual quads?
I was doing a little thinking-over-coffee this morning, and while perusing some threads where dual quads were a topic I came up with more questions than answers. In a nutshell, why would a person want to run dual quads instead of a single carb? For sure there is the coolness factor and visual appeal but otherwise what's the benefit? If running a pair of 600 CFM (or whatever size) carbs why not just run a big single 4-barrel?
Enquiring minds want to know...:)
Back in another lifetime, there was only 1 barrel carbs. So to get more airflow people built 2, 3, 4 and 6 carb manifolds.
Will Carter was an early tinkerer and inventor when fuels were of questionable quality at best and many carburetors no better. He designed and built a 1 barrel updraft carb that worked better. A great inventor but not so goox at looking after the finances, he sold out but stayed working for the company.
In the 1950's, engine displacements were getting larger and roads better quality. To supply that required more air and fuel. Thus the Carter WCFB, Will Carter Four Barrel, carb was developed. Shortly later Rochester introduced the 4G and 4GC carbs. The WCFB's were rated at 385CFM. On the Chevy Corvette 283 they wanted more, so installing 2 x 4 carbs was the hot ticket. Then engine dislpacements went to 400+ CID. For the bread and butter engines a 2 barrel carb was good enough but the next step up was a 4 barrel.
Then we got the 389 Pontiac GTO's and Ford 390's with 3 2 barrel carbs that ran most of the time on just the center carb and with progressive linkage opened up the front and rear carbs. Then with the 427 or 7 liter engines dual 4 barrels with progressive linkage provided the airflow. With this there is a primary and secondary carb. So putzing around town you are probably running on the primary carb primary throttle bores only. With the fairly small throttle bores and venturis, the air is moving quickly which promotes atomization. As you want a bit more speed or power, the secondary carb primaries start to open. The airflow remains high and fuel economy is still pretty good. As you request more the primary secondaries open and then the secondary secondary throttles open. This is all mechanical linkage.
With vacuum operated secondaries, the primaries are probably progressive to give that goid fuel economy and easy staged application of power. The secondary vacuum pots can have the same springs or slightly different to stage their opening.
With a single large carb driving on the street, airflow through large primary bores is slow so atomization and fuel economy suffer. On a race track the single is fine and may actually put out more power even if the airflow capability is the same.
So application and personal preference dictate the choice.
Many Dodge trucks had 354 Hemis with 2V carburation. Simplicity, low RPM and fuel economy under high loads. Lots were farm trucks with dump boxes.
