I just recently bought a 75 duster with a slant six for a daily driver. The thing drives like a top, but I would like to see what I can do to improve the mileage and get some extra power at the same time. Right now the engine is stock so I have a lot of questions of what I need to do. Im thinking of changing to a 2bbl carb putting in a comp cam and running headers. My first question would be what do I need to do to switch to a 2bbl carb? Can I just take the single off and bolt the 2bbl on or, do I need to get some adapter or new intake?

Welcome aboard!

You could use a two-barrel adapter, but that leaves you with a restrictive manifold. The factory two-barrel ("Super Six")setup is better.

Over in the Articles, you'll find some good information including THIS SUPER SIX ARTICLE

_________________
"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Hi there. Welcome to the board. The first thing you'll want to do is to pick up the factory(!) service manual for your car, see this post. The '75s are pretty slow in stock form, but there's a lot you can do to pep them up without spending a lot of money, so you may want to try some of those techniques before you spend significant money and time changing parts. Details upon request, but for now the first thing you should do is follow the distributor's vacuum advance hose up from the distributor. If it goes directly to the carburetor, fine. If it goes to a widget on the side of the air cleaner housing, and then from that widget to the carburetor, go ahead and bypass the widget, connecting the vacuum advance hose directly to the carburetor, and you'll find your driveability and around-town performance will increase significantly.

Is your '75 a Federal, California, or Canada-spec car? Check the emission information label under the hood, or at least check the dash and quarter panel for "UNLEADED GASOLINE ONLY" labels. If you'll post the exact contents of the fender tag — a 2" x 3" metal data plate on the driver's side inner fender, facing the sky and visible when you open the hood — we'll be able to give you detailed information on the equipment your car was built with.

The 2bbl setup is a very good swap. It improves performance, driveability, and in some cases even fuel economy. You will not want to use one of those silly adaptors; they cancel the benefit of the 2bbl swap and create hassles with hood clearance and linkage hookup. Headers? Mmmm...not so much. I'd use Dutra Duals instead.

Be careful with Comp cams; they have a track record of difficulty supplying cams that are what they say they are. Better to get in on the Erson cam buy, if you are interested in buying a performance cam. But again, you'll want to think this through before spending money. Depending on how you intend to use the car, and your budget, it's probably more cost-effective to install a new timing chain and gears with careful degreeing-in of the cam than to pull the engine apart (head's got to come off) to swap the camshaft.

There's a lot of power and driveability to be found with a careful recurve of the distributor, and possibly an see HEI upgrade. You may also want to do the fuel line mod and install one of the electric choke kits (which one depends on whether you're staying with the 1bbl or going to the 2bbl).

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thats some killer info you guys got here. Thanks a ton. Question 2 would be how much of the emission restriction stuff can I disconnect and toss. I have so many freaking hoses running all over the place its unholy. Im just having a hard time figuring out what I really need and what can go.

Seethis post for emissions equipment info.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I would like to add that I have a friend who used to have a 73 Duster (It's my brother's now), but when it was my friend's, he had a slant 6. He put a Mallory ignition on it, and that gave it a significant mileage increase. Next was a 390 carb and an intake. More gas mileage. He was going to put headers on it, but then it threw a rod.

On a side note, the car is now my brother's and has a 440 in it.

_________________
1963 Dodge Dart -225 Slant 6, 904, 2.76's, 18.84 @ 73
1970 Nova 12.53@108
1970 Bug 15.38@87