The warmed up 261 in my 37 has seen a number of manifold and carb set ups in the past 6 years,a 250 engine certainly has better breathing, but ya can draw a few conclusions from my actual experience.
I started with two Rochester B's on a heated Offy 2 carb manifold.The B's were the larger mid 50's models,stock except the power valve jet was reduced in size by .008 of an inch.The B's ran excellent, but leaked fuel out of the accelerator pump linkage passage in the carb on hard acceleration.Then I got 2 rebuilt Holley Webers with adapters from Stovebolt Engine Co.The Holley Webers carbureted very nicely,smooth power no bogging even when flooring the pedal at relatively low speeds.But the H/W carbs suffered from quality control problems,erratic idle,intermitent hot start flooding problems. Seems the carbs were bead blasted by the rebuilder,constant tiny pieces of grit clogged passages despite repeated disassembly and cleanings.
I then got a Clifford 4 bbl heated intake, borrowed a new 500 cfm Edelbrock from a friend. The carb was too rich during light throttle right out of the box, a change of jets and rods got it running nicely.Very responsive on the primaries but always bogged when opening the secondaries.The Edelbrock has a weight controlled secondary air valve like a Carter AFB,I got the heaviest weight ,messed with secondary jetting, but never cleared the bog.My friend needed his carb back, I then found a nice 500 cfm Carter AFB, same story as the Edelbrock.Next was a 400 CFM Cater AFB, unfortunately this particular model didn't have a secondary air flap,the same bog situation when using wide open throttle at lower speeds.I looked for a 9400 series Carter,$400 bucks, too much for me.
From then on I ran a variety Of Holleys,including a 500 cfm 2 barrel(which is actually 370 cfm when rated like a 4 bbl.Despite everyone telling me the 2 large throttles would kill response, I got the carb to function excellent by swapping out the metering block for one with smaller idle restrictions and reduced power valve channel restrictions.I could floor the pedal at 2000 rpm in high gear without a hesitation and it delivered the same fuel mileage as the other carbs.At one point I even tried a Holley 600 cfm 4 bbl for kicks.It worked quite well once a heavy spring was used to limit the opening of the vacuum controlled secondaries.
I was gonna try a Q-jet, but good ones are too darn expensive for my tastes, but it will probably work ok on a 250-292 engine. The 261 doesn't need more than 350-400 cfm for street use.I have a Holley 390 cfm 4 bbl on it now,runs great.
One time I took a ride in a car. when the guy floored the pedal, the engine bogged, then cleared and took off.The driver was impressed with the power,"feel that pull" he said.His car would have been faster with a smooth opening secondaries but the normal acceleration after the hesitation made it seem faster to him.
Tony
