Eh....It's pretty snappy as it is. You may notice some up top, but that may not be worth all the money that goes in to it, if that is all you plan to do.
The size of the 2 bbl? If it's an Autolite/Motorcraft 2 bbl then the throat size is cast into the left side of the fuel bowl, behind the accellerator pump rod. Usually .98, 1.08, 1.12, 1.23, up to 1.33. the largest was a 456 cfm. the 1.21 is a 356 cfm.
What is the list # on the choke horn ? If it's 4412, then you've got a 500 cfm 2 bbl already, swapping to a 4 bbl won't make much difference ( that you could feel) in performance with a stock motor. If not then it's a 350 cfm, I don't recall the list # for the 350.
20 % is a bit optimistic. If you have 200 hp, you'd be looking at a 40 hp gain from intake and carb. But if you have a holley already on there, chance are you wouldn't see a difference.
It would be a start, but with the stock heads and cam, the change will be mostly cosmetic. Oh, and stock exhaust manifolds are not too good for power either. I don't think I would bother w/o at least a cam and headers.
Swap to a 4 bbl and you'll see about a 20 hp gain EVEN with stock cams, intakes, etc. Changing jet sizes will only richen the fuel mixture, this MAY net you some gain, but will hurt your mileage. Another choice is to swap on a Holley list #4412 500 cfm 2 bbl on your intake, that will definately net you 20 hp without swapping intakes.
i say swap it, ive asked all around and everyone says do it. I had an A code 289 in my 65 FB and it would dead kill this 67 302 2bbl easy. I could roast the tires on that one, this one I cant get anything out of, sometimes, if im lucky, i can powerbrake it, other times when i try the tranny bogs down from no power.
also, stock 2bbl 289 is rated at 200hp, 4bbl stock 289 is rated at 225hp, PLUS aftermarket manifold and carb, youd end up easyily getting the 40hp over the stock 2bbl. if you wanna go cheap just get an aluminum manifold off a ford truck
how do i know if the manifold off of the truck is non emisions or whatever? or should it matter? so your sayin that changin it would give me about 40 horses and whata buot tq?
I wouldn't bother swapping to a factory 4 bbl intake, unless one fell into your lap. Go for a good used aftermarket intake. Lots of them listed in the classifieds here and on ebaymotors. Look for a Ford A321, Edelbrock F4B, Performer RPM, Weiand Stealth, or even an older Ford C9OX or Shelby "Cobra" high rise. All these will work with what you have and any other mods you may do in the future, like cam, heads, headers, etc.
ya, listen to hearme. 2bbl intakes are very restrictive, like alot of stock 4bbl manifolds are. If your engine is stock Id pick up something like a performer intake. Whatever you do dont waste your money on those knock off manifolds, most dont line up for crap and will actually hurt performance. I'm actually suprised SN sells that crap.