Ive been reading through a few threads and I can't seem to find a difinitive answer when it comes to the super six and mileage. I have two things I can do. Either take my Holley 1920 to a good carb man and pay to have it rebuilt the right way to get the best mileage out of it. Or I can find a super six setup and then take the 2bbl to a carb man to get the best mileage out of it. In the end, will I get better mileage out of the super six or the holley 1920? Im not as interested in the added HP as I am mileage.

Definitely get the super six. I put one on my 68 D100 a few years back and the milage improved. It went from about 15 mpg to about 22. The added power was also nice! Remember to get a bigger exhaust, if you dont already. There is a thread on here, "beyond the supersix", by one of the members, Duster Idiot, that explains how he put a larger two barrel holley on the supersix intake. I am looking forward to finishing that in the near future. He said it offered more oomph than the regular two barrel. Good luck and let us know how it turns out.

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Excuse me, does this smell like chloroform to you?

I would go for a Carter BBS, but if I would have to chose of Holley or Super Six, I would go for the Holley.
Now I am talking about mileage nothing else.

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Lasse

Signet -66 225
Holley 600 Offy-5270 Dutra Dual,regrind. cam 272 0,420 110, head shaved 0.100 slight.ported
MSD6A
A904
7 1/4 3.23

I used to get 12-14mpg around town with my 1920 and 16-18mpg around town with a bbd. I never got better than 17 pmghighway with the 1920 and got a best of 21.1 with the bbd. Get the super six.

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I got 18-21 with the stock single barrel setup and I get 18-21 with a rebuilt Super Six.

lurker here with a interest in this thread...

now i am really confused...

is it car specific or jetting or all the components together???

for me the mileage is a number one thing....i don't care if i go fast, just wanna make it as cheap as possible....i have seen a couple super six set ups on here for like 150-200(*with manifolds i think???)...some gaskets and you're set ....true??(*although a rebuild could be involved i would imagine...)

have a 1920, dunno when it was rebuilt or if it was??? kinda don't wanna fix anything that's not broken....still got broken stuff to fix as it is...

so the question is....is there a defined BEST gas mileage for the slant? or is it somewhat power to mileage ratio people shoot for?

blind curious :shrug:

Many different factors impact MPG so you may want to search the message board for some of those threads, lot's of good info. is already posted about improving MPG with a SL6 vehicle.

In the end, carb. choice has less impact on MPG then people think.
Yes, the carb must be in good working order and jetted correctly. The only small advantages the BBD will have over the 1920 is the two smaller ventures (barrels) which can help atomize the mixture a bit better. The only other "nice thing" about the later "tin lid" BBDs is the ease of mixture adjustment. Pop-off the lid, loosen the clamp and reset the step-up rods for a leaner / richer mixture.

The engine is an "air pump", it will use a set amount of Air/Fuel mix at an RPM. The A/F mix will be in the 12 - 16 to 1 range, 14 to 1 is ideal.
All this leads to the fact that a 225 ci engine running at 2800 RPM with a 14 to 1 A/F ratio will use a set amount of fuel, no matter which carb. (or EFI system) is on it.

We all know that other factors come into play, such as good fuel mixing, good fuel distribution, correct spark advance, vehicle weight, wind resistance, mechanical drag, vehicle gearing, etc. We all know that the "other peddle" (braking) takes a bit out of MPG. (city vs highway driving)

I look in a lot of other places for MPG improvements, the carb is only one of them and if you consider the cost of the parts, the intake system is an expensive area to make changes.
DD

if you really want mileage my quess would be to go for fuel injection

With respect to carburetion, fuel economy is primarily a function of fuel mixture and fuel distribution. There is an ideal fuel mixture for best fuel economy. If the fuel distribution is uneven, the overall fuel mixture must be enriched to provide a combustible mixture to the leanest cylinder. For operation at a constant highway speed, if the intake manifold is capable of evenly distributing a best-economy fuel mixture, the type of carburetor does not matter as long the carburetor is capable of supplying properly atomized fuel. It's just easier for 1bbl carbs to do this because of the higher air velocities through their venturis.

Where the size of carburetor (1bbl, 2bbl, 4bbl) does matter is in city driving because the accelerator pump becomes an important factor. However, when the accelerator pump is rarely used (as in steady speed highway driving), ability of the carburetor to provide a well-atomized fuel mixture is important.

Having said that, typical slant six-equipped a-bodies can easily achieve 23-25 mpg (US) or 28-30 mpg (imperial) at a steady 60 mph.

THANKS DOC!!!!

that really helped "how" things happen...and i appreciate the input.

makes more sense now!

blind, maybe less now....

I would have to disagree on this, to a point. I have a BBD from a 318, and the bores are much smaller than the venturi on my 1920. So the atomozation and fuel/air velocity will be great per given throttle bore; on the BBD. Power=Economy in this case.

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225 Cubic Inches of Iron-Head American Muscle

225 bored .040 /.100 off block, Schneider Cam 224@.050~ .480 lift - Stock valves, blended bowls, Offenhauser intake with 500 Edelbrock carb

The air velocity through the single venturi of a 1bbl carb should be higher than the velocity through either of the venturis of a 2bbl carb or of the primary venturis of a 4bbl. The only point I was trying to make was that the higher air velocity should do a better job of atomizing the fuel.

However, there is more to fuel atomization than the air velocity through a venturi. There is also more to good fuel economy than good atomization. At low loads (high manifold vacuum), the cylinders see very little atomized fuel because it is mostly vaporized in the intake manifold (once the intake manifold reaches operating temperature).

At higher air flows, a bigger carburetor allows an engine to produce more power because it is a smaller flow restriction. In other words, a bigger carburetor allows more oxgen molecules to be packed into each cylinder at full throttle. Because manifold vacuum is very low at full throttle, mostly atomized fuel actually reaches the cylinders. In this case, the atomization capability of the carburetor is important as well as the intake manifold's capability to evenly distribute the fuel.

The good news... the SL6 has a nice intake design and good intake manifold heating.
The only easy improvements are to be sure the heat riser valve is working and you can add a spacer under the carb, to help promote even distribution.
Here is the next step,... think about the liquid fuel the forms and runs down the maninifold walls & floor. Find a way to get it off the walls, vaporized and back into suspension. (Hint, a "dry" manifold does not have this problem)
DD

I might be stupid but isint the only way to get a dry manifold to convert to direct port fuel injection

Will the exhaust manifold on a 71 Duster 225 bolt up to the super six intake?