I've seen several times where people have asked about the benifits, if any, of a 4 barrel carburetor over a 2 barrel.
My recient story.
One of the things I needed to do to prepare for getting my new(ish) Conestoga ready for daily driving duties, is to put a 4 barrel carbutetor on the 259 out of my ol 60 Lark. My current 59Lark wagon will have to forgive its Offenhauser manifold and Edelbrock carb. up for the original 2 barrel and manifold that were on it when I bought it. Yes, I still have it from almost 12 years ago..!
The carb. is a 500cfm, "well..." used (up) version of the Edelbrock carb. Its seen many many miles on two different cars. The throttle shaft/base holes are shot. You have to tap the throttle to get the butterflyes to fully close for a proper idle..! I did buy a fresh one for after all the little problems that may crop up during the initial assembly into the Conestoga, (had a flat head 6), I know this one works well, fuel metering wise.
Anyway, I rebuilt the original carburetor, cleaned the spiders out of the original manifold, even did a little (porting) radiusing of the hard corners from the throttle bore holes that lead into the runners..and made the swap about three weeks ago. So despite doing this backward from most of you, all details still directly apply.
Now what many/some want to know -
I'm not going to quote MPG here, just basic differences. Just note, that I took the time to make the Edelbrock carb. and engine happy together. I didn't just bolt it on and go. The the needles/metering rods are different, the springs that help control the rods are different thAn what comes in the stock carb.
To start with, yes, "overall", the 500cfm AFB style carburetor has better driveability and gas milage in all circumstances thAn did the OEM 2 barrel (while on my 259, automatic trans., 59 Lark 2dr. wagon). Your results may vary.
- The 4 barrel, good things -
1. Part throttle sensetivity is much better thAn the 2 barrel.
2. The around town drivability (see #1) is much nicer. Less throttle is used with the 4 barrel thAn the 2 barrel.
3. Around town milage is better by a little over (1-1/2) mpg.
4. The power is somewhat obviously better for getting on the freeways with all four barrels being allowed to open. The initial throttle response is better, just like it is for city driving, but when the secondaries start to open, you feel it.
5. While not a long trip, I went to the Chino Air show yesterday (05.04.13), about a 45 mile one way drive the way I had to go, with about 80% of it freeway, and or faster two lane highway. The "passing" power it had....is now gone, even accelerating to change lanes...is gone. Sure, the engine/car will still accelerate, just not nearly as quickly. The smaller, primary throttle bores in the 4 barrel, again respond better to throttle pressure changes.
6. Freeway milage is also better with the 4 barrel by a notable amount.
- The 4 barrel bad things -
1. Needing to "buy" the manifold, the carb., and an air cleaner.
2. Need to adjust the throttle linkage, and if you have an automatic trans., you NEED to make sure the throttle pressure is correct, or very close. Shift points, etc.
3. Had to make a new fuel line section from the fuel pump to the carb.
- The 2 barrel good things -
1. No money is required to install it....! (sorry).
2. It keeps the engine looking stock.
- The 2 barrel bad things -
1. See 1 thru 6 above.
This has been my experience over the last few weeks. As noted, MANY things can affect this swap, the state of tune of the engine, the transmission, the way the carb. and trans. throttle linkage is adjusted, etc., etc., even the way you drive. There may have been a coupla things I forgot here, but I can assure you, they were positive on the side of the 4 barrel carburetor.