what cfm does a carburetor need to have on a 351m. im trying to switch back to a 2 barrel. (4 barrel wastes too much gas )

 

I can get better fuel economy out of a Square bore 4v than I can out of a 2v.

The primary holes are a lot smaller than the 2v holes.

Most 2v 2150 carbs are in the 425-550 range.

My guess with your 351M it is about 450cfm
I need the info off your carb to verify it.

This question actually belongs in the fuel delivery or 335 engine series forum

 

While were on the subject. I wanna do the opposite what CFM carb should i run on my stock 400. As well as what intake? I have an extra 650 DP from my Chevelle But i didnt know if that was to much.

 

Edelbrock Performer Intake with a 650 D-P V/S

 

Holley 650 DP V/S on 351m has worked very well. As far as gas mileage, keep your foot out of it and you wont burn so much

 

I put a brand new 500 CFM Holley street avenger on my 351m a couple years ago, it worked good, but it was a touch too much carb for the motor....if i where to do it again id hold out and find a 380cfm 2bbl.....i can see the reasoning for having a 4v with smaller venturies to get better mileage, but ive never had a use for 4 barrels on trails..now in a mud drag or a long mud pit i could see needing the extra 2 barrels because you actually run wide open, but for a DD that sees mild wheeling i would definitely go back to a 2v...all that said, your either gonna need a 380CFM or 500CFM, it all depends on your motor and preferences, like i said though, i wish i would have went with a 380 in the end....