Upgraded Carburetor

[haulnazz15]

Well, while I'm upgrading everything on the 20' runabout, I thought of another item. I currently have the 351W with a 2bbl rochester carb, there were 4bbl versions made according to Seloc. Is there any real efficiency increase in moving from what I think is about a 300cfm carb to perhaps something like a 450 or 600?

The 300cfm seems pretty small for a 5.8L engine, but I could be mistaken with my volume numbers. I'm not looking for a major HP increase or anything, just something as simple as a carb swap, or at the most swapping the carb and the intake, although there isn't any room for a high rise intake.

Any suggestions?

 

[Bondo]

Re: Upgraded Carburetor

Ayuh,.... It's doable,... You'll see a 20/ 30hp Increase....

 

[rdj59]

Re: Upgraded Carburetor

From what i've read is that the 4brl version had 255hp and was mated to a trs drive. I've done some internal mods to my 351w (pistons, cam, and ported heads) but am still running the factory 2brl. My low end is awesome but my top end is lacking. At wot i'm still pulling a vacuum which means that the carb is to small. You only need a 600cfm vac secondary. Anything bigger is a waste of money and fuel. When figuring out cfm using 100% ve i remember it being less than 600cfm required. Get yourself a nice 600cfm marine carb and an aluminum dual plane intake if you can use it. Otherwise go to the JY and get yourself a 4brl iron intake and be done with it. I think that's about the max you can do to gain noticeable power.

Jeramie

 

[haulnazz15]

Re: Upgraded Carburetor

Well that's kinda what I figured. Like I said, I'm not looking to gain 10mph or anything. Just want to let the engine breathe a little better and get everything out of it that I can. I'm sure this 30+ yr old engine isn't putting out the 233HP it had when new anyway, so I think adding the intake and 600cfm 4bbl carb and an intake would help get it back a bit.

Anyone know where you'd even find an intake that would be close to the factory height? The flame arestor on this engine sits about 1/2" from the top of the engine housing, so I don't want to modify it if I don't have to.

 

[lostriver]

Re: Upgraded Carburetor

I just got my carburetor back from http://www.kineticperformance.net/ . These guys got their reputation from modifying carburetors for the racing industry. They are extremely knowledgable. They will modify your existing carb increasing the air flow and the fuel. You will need to tell them what engine you are putting it on. They charged me about $200 including shipping. I would recommend checking them out.

 

[rdj59]

Re: Upgraded Carburetor

Go to the JY and buy a factory 4v intake. I think fords used a plate for the egr so just don't use that. It should be very very close to the factory height. I actually might be a little lower because you don't have the adapter plate for the 2brl.

Jeramie

 

[haulnazz15]

Re: Upgraded Carburetor

Alright, well does anyone think it needs to be the factory intake? I almost wonder if the factory intake I have is a 4bbl with the carb using a 2bbl block off plate. That way I could just swap to a 600cfm carb and not even have to take off the manifold. Otherwise, I saw some Edelbrock Performer intakes that seem to be low-profile and optimized for torque from the bottom-end up to a max RPM of 5500 or so. (I know that I won't be going past 4,600 or whatever the recommended rpm limit is).

On a side note, if I go to a 4bbl carb, is there a preferred brand for marine use (aside from making sure it's a marine carb)? I have the Rochester, and I know they make Rochester 4bbl carbs but I don't necessarily need to go with the same brand. I know Holly and Edelbrock are both well-known carb makers. I would like to keep the electric choke and use vacuum secondaries as opposed to a double-pumper setup. My current carb uses a front mounted female fuel inlet, but I can always change out the hard line for a ss-braided fuel line if the fuel inlet is in a different location.

 

[Howard Sterndrive]

Re: Upgraded Carburetor

If running in salt water with RWC, you would probably want to stay away from an aluminum intake, other wise, the Edelbrock or similar is fine.

 

[haulnazz15]

Re: Upgraded Carburetor

If running in salt water with RWC, you would probably want to stay away from an aluminum intake, other wise, the Edelbrock or similar is fine.

Boat is freshwater-only, so no worries about that.