MPG beter with or without DUAL CARBS?

[Powerhouse]

I have heard that it is better from some and it is worse from others when it comes to MPG with a dual carb set up.

Can anyone shed some light on this?

[claybill]

interesting to learn how 2 carbs would be more efficient than 1. 2 mouths to feed no matter how you look at it,.

i had a lot to say, but couldnt prove anything so i erased it all..!

bill.

[Powerhouse]

That's what I thought...2 carbs = more gas.

But I heard that 2 carbs makes the engine work less...so less consumption???

[TodFitch]

If I recall correctly, the economy/business versions of the 1930s Plymouths used a carburetor with a smaller bore than the normal one. Sounds like adding carburetors (increased effective bore) would be moving in the wrong direction for economy.

But there are so many variables including the driver and driving conditions that I would be surprised if the number or size of properly calibrated carburetors was the major factor.

[Powerhouse]

"economy"(as in less money spent on gas?) can effect engine performance...so maybe less gas=less power produced...which would make more power needed to get to previous performance which would then equal more money spent on gas to cover the same power production????

[greg g]

most of us who have added carbs have also upped compression. but if you think about the system, half the air and therefor half the gas is flowing through each of the 2 as opposed to the one. Chances are the fuel air mix is better atmized and delivered over a shorter route so less chance for the gas to reform droplets thereby being a more efficient charge.

My experience was from 17 with single carb 218 to 19 with 230 dual carb. But my compression went from 6.7 to 1 to 8.5+ to 1. More squeeze bigger bang.

[Powerhouse]

Thanks Greg...that makes sense the more I read about it. Found this on a VW sight:

Carb throats that feed multiple cylinders (the case in stock engines) have to be adjusted to a compromise setting, and the result is that all the fed cylinders run at a less than optimal air/fuel mixture. This is one reason why dual carbs provide better mileage than centermounted carbs (including stock) assuming they are driven similarly.

[1941Rick]

I put dual carbs on last year and do get better fuel economy....040 off the head and whatever that did to the compression. Car drives so much better at bottom end...

[MarkAubuchon]

Duals on my 49 BC +22 47 Sedan 16,

[roadworthy]

I can only imagine that if I ran dual carbs, my foot would get heavy, thereby negating any economy advantage

[austinsailor]

But you'd have more fun per mile, so you might be ahead.

[Powerhouse]

yes...the same symptom i have...once I put the dual progressives on their...my foot got kinda heavy.

But not all the time...the reserve power is nice to have.

[Al B. Bach]

I know that with the Ford big sixes (240 and 300) dual exhaust and either dual carbs or a 4bbl can take a half ton truck from around 16 to 20 all the way to 25+. The way it was explained to me is that the engine has to work less to produce the same power and therefor less gas and a happier engine. Of course that's only as long as you have the self disipline to keep your foot out of it.

We have a guy locally that has dyno'ed his truck at over 450HP and yet still gets 28mpg on the highway. Just like the flat sixes in our MOPARs, the big Ford sixes are great engines.

[Powerhouse]

I know that with the Ford big sixes (240 and 300) dual exhaust and either dual carbs or a 4bbl can take a half ton truck from around 16 to 20 all the way to 25+. The way it was explained to me is that the engine has to work less to produce the same power and therefor less gas and a happier engine. Of course that's only as long as you have the self disipline to keep your foot out of it.

We have a guy locally that has dyno'ed his truck at over 450HP and yet still gets 28mpg on the highway. Just like the flat sixes in our MOPARs, the big Ford sixes are great engines.

GREAT to know. Thanks man.

[claybill]

the obvious theory, but cant be correct, is that 2 carbs each will run at 1/2 that of a single carb. thereby providing only 1/2 charge to the front 3 and rear 3 cyls. it doesnt sound right.! in a dual set-up...both carbs run the same as a single carb, offering same air and gas flow. only twice as much.! the efficiency of burn due to a better distribution might make a difference.

economy models had smaller carbs....logic.??

2bbl carbs in '57 etc added more hp due to more gas used oin a bigger charge....logic.?

go figure.

bill

Edited April 29, 2011 by claybill

[greg g]

The engine can only pump so much air. So with two entries instead of one, half the air flow will go through one and half throug the other. Not 2x as the pump is moving the same amount of air either way.

[Scruffy49]

Plus you step the jets down a size or three for multi-carb set-ups. Just don't go too lean or you'll blow the engine. Ask me how I know (2300+cc Bug with dual Webers)...