4 Barrel for a 305 V6 ?

[boomy3555]

I have a 1960 GMC 4000 15" flat bed dump. Some one over the years has replaced the original carb with an Aftermarket Holley 4412C 2 barrel. I'm looking to replace it. Would it do any good to go up to a 4 barrel or is that just too many CFM's ? The 305 calculates out at around 525 CFM @ 6K redline.

I know that this truck's power comes from the gears, but would a 4 barrel help anyway. The prices are pretty close between a 2 barrel and 4. and would I have to change the intake manifold adapter?

[Warrens69GMC]

IMO the answer is no, The 4 barrel option is moot. The 2 barrel option of 500cfm is max IMO for this engine.

Actually a 390 or 450 is better for the potential for this engine..

[boomy3555]

Thanks for your quick response. It just seems like such a big engine. I thought I could " Up it's game".

[Warrens69GMC]

Its designed for low rpm with 150 hp (112 kW) gross at 3600 rpm and 260 lb⋅ft (353 N⋅m) gross at 1600 rpm . the 600cfm of 6k will never be realized ...

[boomy3555]

Thanks Again.

[mattfranklin]

There's a site dedicated to these cool and novel engines:
https://6066gmcclub.com/forumdisplay.php?f=9

And here's a guy talking about the details of carb swaps:
https://6066gmcclub.com/showthread.php?t=50616

[Tom]

I'd put a 500cfm 4bbl on it before a 500cfm 2 barrel. The 4 barrel will have smaller bores and primary flow so it should work better.

['68OrangeSunshine]

I run a 500 CFM Edelbrock 1404 four barrel on my 292 [bored @ .030-over = 296 CI].
A 305 is within 9 CI of that. Simple design, basically bombproof and parts are still supported.
It's really a modern clone of the classic Carter AFB.

[geezer#99]

Yup!
A 500 cfm 4 bbl would be nice if they made a 4bbl intake for a v6.
But alas only a 1 bbl and 2 bbl were made.

['68OrangeSunshine]

You could write a book or two about what I don't know about GMC V6s.

[Tom]

Originally Posted by '68OrangeSunshine

I run a 500 CFM Edelbrock 1404 four barrel on my 292 [bored @ .030-over = 296 CI].
A 305 is within 9 CI of that. Simple design, basically bombproof and parts are still supported.
It's really a modern clone of the classic Carter AFB.

No it literally is. They bought the rights to the design and changed the name. Added some new versions over the years but the original 1404/1405/1406's are all carter's.

['68OrangeSunshine]

Are there 4 Bbl/2 Bbl adapters? I know there's a one Bbl/2Bbl carb adapter. It raises the throttle plate level up about 2 or 3 inches which might give some people hood clearance issues.
I'm guessing that the market segment inclined to upgrade vintage GMC V6s is too tiny to support R&D, let alone production, so there's no solution, unless someone has the talent and facilities to wildcat a one-off 4V V6 manifold.

With regard to the Edelbrock/Carter carburetors -- Federal Mogul bought out Carter's carburetor patents in the mid-'80s, when Carter saw the Big Three going to Fuel Injection on production mainlines. Edelbrock had been marketing the Performer Series as a premium aftermarket upgrade. Federal Mogul was also selling Carter Performance Series AFB carbs up thru the Late '90s. I bought a 600 CFM 9625S AFB for the 350 in my '71 GMC, when I got a fresh crate motor in 1999. [Still running good. I treat it as a 1405, when tuning.]
When I got my 292 L6 rebuilt in 2005 for my '68 C/10, I could not find a 500 CFM Fed Mog Carter. Only the Edelbrock 1404 was available. [Still running well on my 292.]
The main difference is that the Eddies are shinier and have a big red decal on the front airhorn, instead of a black Federal Mogul plate. Also The FM's may have been set up leaner out-of-the-box than the Eddies. Not sure. Maybe it was the other way around.
The most striking difference was the price. Edelbrocks cost more.

[geezer#99]

Some 2 bbl to 4 bbl adaptors can be flipped over if needed.
https://www.speedwaymotors.com/Speed...-Plate,67.html

There have been a few guys who have milled a 2 bbl intake and grafted on a 4 bbl base for the v6.

A lot of work for not much gain on a low rpm grunt motor.