carb question

[mikeyo]

my mechanic told me i will continue to get 6 mpg unless i replace the carb (4 barrel), which is a poor design anyway. he said i'd get way better mileage with a 2 barrel but i'd have to change the intake manifold too. is this right? is it a pain to change the manifold? thanks a million. mike

[Horst]

Not sure I believe your mechanic.
My mileage (on a 360) improved significantly when I went to an Edelbrock 4 barrel as opposed to the stock 2 barrel Carter.
Yes - I did have to replace the intake as well.
But that is becasue the primaries on the Edelbrock are WAY more efficient than the Carter
A well tuned 440 Clipper can get 7.5+ mpg with a four barrel OEM carb - the trick is to drive smart.
Slow down, and stay out of the secondaries.
Just as an example - at 52 mph, on a flat road, I get about 10mpg. At 65 mph I get about 7.5 - ouch!
Back when we took many  Clipper trips - I would travel at night - less wind, cooler air, less traffic, and I could easily cruise at just under 55, and get really good mileage, and not offend all the freeway speed demons.
With gas priced the way it is today - that's the only way to fly in my opinion.

[Conrad]

I would replace the mechanic!

Before taking his advice, get ed-jew-meh-ka-ted.  What kind/brand of carb do you have?  

Horst is absolutely right with his comments on the 4bbl.  Typically 4bbls have smaller diameter bores for the primary (two of the four) barrels.   The secondaries will be utilized when one needs more power as when going up a hill.   Increased load on the engine requires more power to maintain speed.  More power means more gas is consumed.

I have the 2bbl dodge 360 and plan on upgrading when I replace my mufflers.  Gonna do the whole exhaust system.  

Add a vacuum gauge and you will get an idea of engine loading and your driving habits  :wink:   I use it as feedback for my driving habits.

[Andy Illes]

Amen on both Horst and Conrad's comments.  To give an even more dramatic example, my old International Cargostar (semi tractor) with a gasser was getting about 3.4 - 3.8 with its original 2bbl Rochester, which I replaced with some kindda 4bbl (sorry, don't remember which) and manifold.  The mileage rose to between 4.3 to 4.9!   The reason's exactly what's been said... 95% of the time you're just in the 4bbl's smaller primaries.   Add to that the more efficient manifolds around now, and you'll do ok.