Hey guys,
i've been reading this forum for a while and theres lots of great info on it.
What i was wondering is about (i know its not exactly the same on each engine)how much MPG would a stock 225 /6 get out of a 1973 dodge dart swinger.

Also i was wondering if i were to change all this stuff listed below how much this would improve my HP and how much less MPG would i get after adding this stuff:
1. Manifold for 4 barrel carb
2. 390 4 barrel carb
3. New headers
4. New exaust
5. New cam
and
6. New rear gears( which ever would be the best ones for a everyday street car)

Also the engine is in a 1973 dodge dart swinger.

Thanks,
Mike.

Take it for what its worth:

My slant is roughly what you have lined out above with a few exceptions:

1) I have 10:1 compression and a big valve head
2) I run an MSD ignition
3) I currently have 2.76 rear gears
4) My slant is in a truck, that weights ~3800 lbs

I get 14-15 mpg no matter how it is driven.

-S/6

with a holley 390 4 barrel, clifford headers and manifold, stock everything else, and a 3speed in my 74 duster I got 24 mpg

-dave

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what part of "illegal" is so confusing???

It has been my experience that even a really built motor, if the right combo, can get very good mileage. It depends almost entirely on the combo you have put together, and how carefully it is tuned. I've gotten 12mpg on low power buildups, and 26mpg on high power buildups.

Getting higher than 25mpg is pretty hard. 20mpg is not too hard. This assumes an A-body car.

Man trans is worth a lot, as are a carefully done timing curve and properly jetted/tuned carb.

Lou

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Home of Slant6-powered fun machines since 1988

Those items you list will not get you the best performance/fuel mileage balance.

Cam and compression and headwork followed by exhaust and ignition curve will net the best combination. I would follow these things with your 4 barrel and headers if money permits.

MY Valaint has gears , Comp 264. 9.25CR, 2 1/4" exhaust, big valves and headwork with stock Super6 manifolding and BBD. It gets better mileage than stock and will probably beat a car with 4 barrel, headers , cam and no headwork. I figure about 200hp. It is as fast as my GFs Eagle Talon TSI (200hp , 3000lbs). It is also extremely easy to drive with a very broad torque band.

Something I noticed in Las Vegas was that the cars without headwork were all in the 18-20 second range regardless of other modifications. The head is the bottleneck!

Headwork alone (bigger valves, higher compression) will get you further. Add gears and ignition curve with a cam and you are in the 15-16 range.

Then add the headers and 4 barrel for 14 sec ETs

Dennis can tell you what comes next.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks for the imput guys it all gives me a good idea on MPG.

sandy in BC, I am very intrested in what you said. Can you tell me what would invole doing all this such as would i need to pull the engine and mabey a little more detail on what brands or parts to use and what to tell the machine shop. also mabey about how much would cost me?

sorry if i sound a little stupid but im not really familiar with this type of work as im young and havent been around engine rebuilds and performence builds or any major car work.

Thanks,
mike

Read everything here: http://www.slantsix.org/articles/articles.htm

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Yeah....Im the one who destroyed this rare, vintage automobile.....