Originally posted by MadMax
OK, seems like larry got some points there, my main question is, what do I leave stock because cost would simply be too high for the increase in mileage (no use spending a thousand bucks on cam and lifters if that saves 200 bucks gas in a lifetime) and what do I change because I will see real increase?
From what I gather from all the answers put together is:
-get a near new 350. (which I have)
-take it apart and have it blueprinted (what do you mean by that, never had a blueprint done so far?)
-put in forged pistons
-port the heads to match intake manifold or other way round
-port ex runners (headers)
-go for FI rather than carb
- what FI? Holley or Edelbrock? TB or Port?

Is this overall correct?
Why would a 305 be killed in a truck that heavy? I've seen those vans being moved with the small V6s and they run OK (but I want a V8)
OK, this is only one opinion, and its only my opinion, but to try to reply directly to your questions:
What to leave stock - Leave crank and rods stock. The pistons you suggested going to forged, that is most likely overkill, you will be all set if you get a hyper, just dont get the cast junk. I like a file fit ring, but set your ring end gap as per the towing/RV gap. THis will allow your rings to take the heat of lugging around that brick of a van without butting end to end and destroying the piston.

Now, here is where your disposable income comes into play. You can save internal losses due to friction by making all things you can ride on bearings. Go to a hydraulic roller lifter set up, I like Crane Cams. Go to a roller rocker arm set up, once more I like Crane Cams and I really like the gold series with the oil restrictors that spray the oil directly at the fulcrum and then bleed the oil out over the roller tip. If you call Crane call 386-252-1151 and ask for extension 4211, this is Pat, he is my rep and he is a great guy. He can help you choose a cam.

As far as the 305/350/383 your going to get your best economy out of a 383 I would suspect. Just like it was discussed, a engine that is running in the "bog" or "lugging" area is running in a very unefficiant way. Get a nice 383 package and cam it with a cam that makes good grunt down low and your going to have plenty of power where its needed for the engine to run on the least fuel. A 305 will have to work harder to pull the weight, it will lug itself much more. If you drive primarily on flat open roads a 305 will give you better mileage because your not using the start out power much, your in the cruise power and even a 305 is OK there. But, if your in hills and mountain area, or not on open roads a 305 will have to work double hard to do the job. Think about it, plain physics say it takes a given amount of energy to move a given mass, your engine has a hard time making the energy that a 350 or a 383 makes so it requires more fuel, more air, and more RPM's to get the energy to be equal.

Blue printing is a generic term. In the case of what I like to do, I like to have the mains re centered, have the cam re centered, and the mains are done with torque plates on the block to simulate the heads. This is called line boring or align boring, depends on who your talking to...lol. Then when you do the cylinder bores you do the same thing, use tq plates so that the cylinders are actually round once the engine is bolted together. THere is more that can be done if your picky, like have the bore stop at .008 from finished size and bring it in with the hine machine, this is done race engines to get a smoother finish on the bores.

Another thing that you can do based on finances is ceramic coat the tops of the pistons to stop heat absorbtion and you can also do the cumbustion chambers. Do the anti-friction coating on the sides of the pistons to make things more slippery.

The thing is, how much are you willing to spend to gain 2-5 MPG? Assuming you can gain 5, how many years will this old van have to last at your average miles per year to pay for the engine? If you spend and extra grand on the rebuild to gain 5 mpg and you drive 20K a year..... you could make back 1200 the first year, but what if you only gain 2 mpg? than you make back 600 bucks, so you need 2 years to break even.

OK, always gasket match your heads and intake. Take the new gasket and a sharpie marker and hold the gasket in place centered over the bolts and mark the metal that is showing inside tha gasket port holes. Use a dremel or die grinder and make a nice smooth funnel like transition from the original port to the gasket size. Do this on all gasketed surfaces of intake and exhaust, on manifolds (both intake and exhaust) and heads.

A well tuned carb will make as good power as a FI system, only if you travel to extreme conditions of temps or elevations a carb is not going to self adjust. A FI system will keep itself adjusted from pikes peak in winter to death valley in summer.