Well, a friend of mine doesnt think that buick 350's and 455's need more carb than any other 350 or big block of comparable size. So, could someone explain it to me? I know i used to know why, i just cant remember, so if you guys could help itd be awesome!
This is also a personal opinion but most Chevy guys are brain dead morons that could never comprehend how or why Buick's work.
I resemble that remark! Seriously, CFM should be directly related to cubic inches, volumetric efficiency and rpm. I also believe that it is related to what you are doing with the car. on the street, smaller carbs are more throttle responsive. For wide open racing bigger carbs can give more top end HP. What I really wonder is, if using a restrictive air cleaner should be a consideration when picking carb size.
i thought i remember reading something about how the smaller ports on buicks mean that the air needs to move faster though the engine, and a carb that flows more enables that.
Higher velocity intake charge due to port shape and size is the explanation I have been given. All those "CFM requirement charts" usually list the minimum recommended CFM, not the optimum requirement, which throws people, I think Going by CID is a very simplifed approach in my opinion. No engine has the same combustion chambers, runner length and shape, intake design, exhaust design, bore and stroke, etc, etc, as another unrelated engine, so it is logical to me that going by CID is a good guide, but not a hard and fast rule OH- also, those charts don't take into account the aircleaner and filter, in any case I've seen. So your 800 cfm Q-jet is probably really pulling 750 cfm or thereabouts, as a guess
high port velocity and small plenum volume add up to a lot of pulsing at the carb. The result is a carb that has to deliver more air over a shorter duration of time. That is also why a plenum spacer almost always delivers more power on a 455. The larger plenum volume smoothes out the pulses. The price you pay for the extra plenum volume is less low rpm throttle response. What to do all depends on what your goal is for performance. high, low RPM, drag racing, mileage, big car, light car, etc.
so what would ya use for a 350. What cfm carb would ya say would work? i got a 2 barrel now and moving up to a 4 barrel.
Years ago I had to replace the Q-jet, and a guy at a parts store told me a 600 Holley is just right, and bigger would be too much. He was wrong (but I didn't know better at the time). I got it, and it doesn't pull as well as the old 750 Q-jet with only the primaries working. This is a stock engine too. I'll eventually get a 750 q-jet again. I'd suggest you put on a 750, (and 4 barrel manifold, not an adapter).
A standard carb for a 71-73 455 is supposed to work very well on the 350. I'm quoting what I have read elsewhere, so those with personal experience feel free to contradict me.
Unless you've got a real healthy 350 w/ headers, etc, I think the 750cfm Q-jet would be the one to use. I used an 800-cfm one on my mild 350, it worked ok, but the mileage was WAY more sensitive to what my right foot was doing. And I'm sure the secondaries were never opening all the way, or needed to be. I've now got an Osborn-built 750cfm Q-jet, and LOVE it! Unless you're wanting a numbers matching carb, any of the early Q-jets should work. It'd be worth a call to somebody like John Osborn Quadrajet Performance Mod and Rebuild Specialist, 270-737-4467, JOP455@AOL.COM
I've experienced exactly the same thing, when building my 71 455 ( TA Cam, 9,5:1 comp. and a valve job) I was told that a 600 Holley would be perfect, No Way!!! right now I'm rebuilding my good ol' Q-jet with a new set of secondary needles
