gas milage question

[quentin hill]

I have a 72 with a 350 automatic it currently has a 4 barrel 600cfm Holley and I was thinking of switching to a 2 barrel.

My question is how much fuel would I really save by doing this? would it be worth it?

[cdowns]

driving habits are more important than the carb// if you are only running on the 2primarys in normol driving you probally wont see an increase in mileage and might see a decrease with the 2barrel carb

[hugger6933]

best thing you can do is tune that thing to the hilt . Set the carb ,timing valves check and make sure that everything is working, I mean pump shooters mech advance as well as the vac. After that the common sense stuff front end alginment air pressure in the tiresand at the extreme end switch to syn, oils front to back

[70cst]

with the above ...

[MrSchaeferPants]

Originally Posted by cdowns

driving habits are more important than the carb// if you are only running on the 2primarys in normol driving you probally wont see an increase in mileage and might see a decrease with the 2barrel carb

Yeah that's what I'm thinking. Don't know anything about the 600 holleys, but if it's a spreadbore, it'll be beneficial since the primaries would be smaller, and your around town/cruising fuel consumption should be less.

Don't think about 2bbl vs 4bbl as using more or less gas. All depends on how much the carb will shoot out of the jets. My 2bbl Stromberg likes to think life's an open bar

[sir_talk_alot]

Spreadbore is pretty good just because of the primarys and secondaries size. Even though everyone calls them quadrajunks, qjets will flow 700 cfm easy, but give you the ability to be modest on fuel usage by keeping your foot off it.
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[CC69Rat]

Rear end gear? Could be too high / too low too ? Does it just putt around like a tractor or high RPM on the freeway?

[stsalvage]

a 2 bb carb has bigger jets then the primary jets on a 4 bb carb you won't win any wars there.Now you can De-jet a 4bb carb down to smaller jets and it will help Most guys i talk to and seen use the 500 CFM carbs cus they have really small jets.But the 2bb no help there.

Here is a big reason Just think about this i have a old man that has tri power on his 1969 1/2 inline 6 it has over 1100 cfm's in all 3 carbs and they have big jets in them

[edhtrd71]

I agree putting a 2bbl wont benefit much, and your time and money would be better spent tuning the holley and ignition, or install a quadrajet which owes its economy to primarys that are only about 225 cfm.

[MrSchaeferPants]

Originally Posted by sir_talk_alot

Even though everyone calls them quadrajunks, qjets will flow 700 cfm easy, but give you the ability to be modest on fuel usage by keeping your foot off it.
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Yup, IMO they're the best carbs ever made. You can take one off a 305, put it on a 350, 400, and they're still big enough. Change jets and off you go. I used to get 21mpg (hwy) in my old Cutlass Supreme.