Great site you have here. Maybe this topic has been discussed before, but I can't seem to locate it. I have a 71 Skylark that needs a new carb. Instead of rebuilding the old one I was thinking about upgrading to a 4bbl carb instead. What parts do I need to make this work and does anyone have any recommendations on the carb and intake manifold?

Thanks.

your 71 2v is the 350, yes? what is your intended priority, street or strip and expected rpm limit?

It is a 350. The intended priority is strictly a cruiser. I want to have a little fun with the car, but not going to drag strips or anything.

as i understand it, there aren't any aftermarket intakes for the sbb. you're pretty much restricted to finding a used 4v manifold at a junk yard or making something from scratch.

but then, i don't know that you're going to see much of an improvement with a big carb anyways.

from the horses mouth; Holley.com
http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/FMSC.html

Engine size (CID) x maximum RPM / 3456 = CFM
CFM @ 100% volumetric efficiency
However, most Street engines are capable of achieving only about 80% VE

using your stock engine you'd have to turn 7500rpm to need something larger than 600cfm which is a very large two barrel.
350ci * 7500rpm / 3456 * .8 = 608cfm
even if we assume 100% volumetric efficiency you'll still be able to get up to 6000 rpm before the carb starts to choke you.

do you really think you're going to ever be turning this engine up that high? i hope you have it rebuilt before you start doing things like that.

even if you do, you say that most of your use is going to be cruising ... well, an oversized carb is going to kill your throttle response.

why don't you look into rebuilding your existing carb or getting a large 2v and then putting a ~1 1/2" spacer under it? it'll be less money and i think you'll be more pleased with the results. jim burek of PAE says that's the sweet spot thickness for the 350.

you might also consider having your carb race prepped by someone with a flow bench.

question? i have a 350 4 barrel carc, what would happen if i put a spacer under the carb?

you can use a phenolic spacer to isolate the carb from a marginal amount of engine heat. supposedly, it will give you a bit more low end torque, but nothing you are ever going to feel.

found the thread dealing with the buick 350.

"We have tried various spacer combinations, the 2 inch open is by far the best"
"The divider has been cut down aprox 3/4 of an inch. Jim Burek"
"The limiting factor at this point is definately the intake manifold, by changing from a 1 inch 4 hole spacer last night to a 1 inch open spacer this evening, we picked the horsepower up to around 410. I then decided to toss on a 2 inch open spacer, holy cow batman, 435 horsepower. The other really interesting thing is that with the 4 hole spacer , we were making peak horsepower at 5100 rpm, now, we are at 5600, and actually it was still climbing.
It's still making right at 400 ft'lbs at 3000 rpm .
This little 350 is gonna rock. Jim Burek"

before trying any spacers this engine pulled 400hp and then made 35hp more by doing nothing but adding/changing spacers. it makes a difference and it's not just due to the insulation factor. of course, with a stock engine you're not likely to see as large of a jump and you won't know for sure what you're doing w/o putting this on a dyno.

this engine wound up making 551 hp/ 506 ft.lb tq, but that was after extensive head work.

oh, and it seems that there are no SINGLE plane intakes, TA has a dual plane 4v you might be interested in if you really want to do this.
http://www.taperformance.com/350stage.htm

Thanks for the great advice. I'm going to stick with the 2bbl carb for now. Thanks again.