What is the difference between a 2 barrel intake and a 4 barrel intake manifolds? I have a 302 with a 2 barrel carb and want to have a 4 barrel carb now.

 

I'm tempted to say "2 holes". But, that wouldn't be nice so I'll not do that.

But, that really is the main difference in the stock 2 bbl and 4 bbl manifolds. Well, there are a few more, such as the two bbl manifolds I've seen, both 1982 351W manifolds, were aluminum. And, I believe the only Ford 4 bbl manifolds were cast iron.

The Ford 4 bbl manifold didn't have a place for the EGR valve behind the carb, but did have passages for an EGR valve under the carb.

Other than that and the ability to mount a 4 bbl carb, and the necessary passages to support it, that's about all I'm aware of.

 

I have a cast manifold and has a 2 barrel carb on it with a EGR valve so the first comment would have been not polite. I work at a Ford Dealership and work on the newer vehicles. I am 35 so this carb stuff is almost before my time. :-)

 

I missed that yours is a 302 when I posted. Obviously those manifolds are different than the 351W manifolds, so essentially all of my comments were wrong.

At 64 I grew up with carbs, and am more at home with working on them than EFI. But, if I were picking a vehicle to be a DD and gas mileage counted it would be injected. On the other hand, if I were to pick a vehicle to maintain forever I think I'd keep it simple - a carb.

Ok, now let's talk about the real diff. A 2 bbl factory carb was almost without exception too small to give good horsepower since that requires RPM, and that requires deep breathing. And, if the factory wanted to give decent performance w/a 2 bbl the carb had to be large enough that it actually was too large at low RPM.

Enter the 4 bbl. By having 4 throttle bores but only 2 being used at part throttle, it provided good low RPM metering awa high RPM volume. IOW, it did everything better than a 2 bbl - IMHO. Yes, it is more complex, but not too complex.

So, the factory needed manifolds for both. I've heard, but don't really believe, that they spent far more time on the 4 bbl version since it needed to flow the most. In any event, since 2 bbl carbs are rated at a different level of vacuum than 4 bbl carbs, there is no easy way to compare 2 bbl carbs or manifolds to the 4 bbl versions. The only thing that can be done is to compare the results, and everything I've read or seen says a 4 bbl carb on a 4 bbl manifold will win. Now, that's assuming you compare like for like, because there are several kinds of 4 bbl manifolds, although I don't think that's true of 2 bbl manifolds. by that I mean there are manifolds for low RPM power, there are those for high RPM power, and some in between. That's done by changing the size and length of the runners, with long narrow runners giving better low end power.

Is that what you wanted to know?

 

X2 on what gary said.
Just to show the difference in flow ratings.:
A 500 CFM holley 2BBL (List # 4412) is exactly the front half of a
A 750 CFM Holley 4bbl (List # 3310) as far as air flow.
So you can see if they were rated the same a 500 2 bbl is really a 350 CFM if they were rated at the vac level of 4bbls carbs.