I have found my self at a delima. Being laid off at the end of the month and going back to school. I have a couple months in between and I have a mass of parts, so I will be assembling my car. How ever when in school money will be tight. I am looking to squeez the most mpg in reason so I won't be building to strong 300hp motor untill I can get back to work. I have a stock 225 bottom end new bearings, pistons and rings. The head has stock valves 340 springs, will be 9.5-1 compression. Ignition will be HEI conversion. The car has a t5 and ford 8.8 in the rear 3.73 gears, 245-45-17tires. My question is should I use the stock cam or the comp cam 264s that I allready have degreed in to the block? And I was planing to run offy 4bbl manifold with a holly 390 parts I already have. Would I be better off with a two bbl setup say a progressive 2bbl like the weber 32/36 over the holley 390? I also have a stock super 6 set up. I am hoping for 20-25mpg. Am I being unreasonable?

Not unreasonable, depending on the length of the trips. Short trips might not realize 20 mpg without careful driving techniques, and the four barrel would be hard pressed to do this in stop and go.

Out on the freeway, I doubt there would be much difference between the Weber and Holley. For combined and city driving, the Weber progressive should deliver better mileage, though I can't speak to what those numbers might be. I ran DGEV's on much smaller displacement engines. They did tend to do very well for economy, and at least on 2L class engines, respectable power.
A single Weber 32/36 would like the OEM grind. The Holley could run well on either cam. With your compression, freeway mileage could be pretty good with the 264S. The Late OEM grind would likely be better yet. The 244 mechanical is a well designed profile.

For either, the timing curve will need to be explored. Recurve will be necessary to realize the greatest potential.

CJ

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Part of Tyrde-Browne Racing

I ran a 625 AFB on an Offy manifold years ago, the vehicle was a 79 D150 and 3.55 gears. Commute type driving (a few miles, cold starts twice a day, etc) got me a whopping 14 - 15 mpg, in the winter that fell to 11 to 13. In the summer, however, on a long highway trip where you stayed out of the secondaries and didn't go over 60, you could expect 20 to 22.

Yes, I know, the 625 was too big. But that's what I had. It ran well, but had a bog if you tried to get into the secondaries below about 2500 to 3000. Above that... It flat out ripped. I also ran a lumpy Iskendarian cam.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

The trick with the big AFB's to slow down the secondary was to drill and tap a hole in the air valve weight, then screw more weight to it, a little bit at a time. Something like a thin piece of steel.
That way, more air flow was required to open the valve, and it hits later.
You just have to make sure the weight will still move freely.

CJ

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Part of Tyrde-Browne Racing

It was stumbling with the air valves CLOSED. Still enough air going through them to make it miss on the back cylinder or two ( fed by the secondaries when open when sitting on the offy manifold).

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.