Carb Questions

Red Green Jr · Jun 1, 2009

I am wanting to swap out my stock motorcraft 2bbl with a new Holley 4bbl. My truck is mostly used as a daily driver/mild off roader, and I was wondering if there would be any consequences of the 4bbl upgrade. Also what CFM should I get? I was looking at a 570 CFM or a 770 CFM.

Justshootme84 · Jun 1, 2009

A 550-600cfm 4bbl carb would be fine. I'm running the Edelbrock 1400 series carbs on the 78 and 79 351M engines. You'll also need the kit for the C6 linkage, JSM84

bvteachey · Jun 2, 2009

Im pretty sure you need to change intakes right??? I switched my 351M over to a Holley 600cfm 4 bbl using a Weiand Performer Plus Intake, used Flowtech Headers... Its a beast!

Broncobill78 · Jun 3, 2009

Swapping to a 4bbl intake is the best way to go. There *are* 2bbl-to-4bbl adapters out there but without the proper intake you're kinda ******' in the wind. I wouldn't bother with it.

As far as size goes I'd stick with 500-550cfm for a small block. I ran a 750 on a reasonably well built 460 and had to jet it down 3 times before I got it running well. Even a 500 is a lot for a 351M/400 unless it's running a decent size cam & has modified heads.

If it's a basically stock engine then I'd either stick with a *new* 2bbl or a very small 4bbl. Bolting a larger carb on really doesn't do anything other than drop your mileage & **** performance. Combined with other upgrades it can help but all on it's own I'd say it's a bad idea.

rednck7736 · Jun 15, 2009

I have gone from a 2bbl to a 4bbl on my 351M.I bought eldabrock alum intake and a 600 carb.A 600 cfm carb is plenty on a stock 351M.You will have a noticable power difference in that alone.Tried a 750 double pump with a big cam in it once.Pulled both them out cause I could not afford the gas to feed it.

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Red Green Jr

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