I've been reading these topics on this forum for about 3 years and I'm always impressed with the wealth of knowledge from it's members and Doug Dutra.
I've professionally built Off-Road racing motors, vw's, Scat v-4's to Nascar and Grand National. I'm a Mopar fanatic and absolutely love these cars. I currently own a 69 Dart GT with a 225, 3 speed auto. I've always owned 318-340-360 Darts, Demons and Dusters always set up for street/strip performance. My new Goal is to build this motor for EXTREME MPG's so we can have a daily driver Mopar instead of buying an econo box. With experience, I know I will spend less time asking people who are more experienced than me with these engines, rather than trying to R&D with my own formulas. My goal is to reach 35 MPG's....Right now some of you are probably lying on the floor laughing at me and wondering where I've been getting my drugs from. But, I know it can be done with a lot of creative measures and the right combination.
Right now I saw an old post of a member getting 39 MPG's and said it was 2-3 more than stock, so I'm assuming this was a mistake. I've seen some combinations that made really good power and still got 22-25 MPG's So I make this as a challenge to see what real MPG's this motor can get even if it's a little underpowered. I rather drive a fully restored underpowered Dart with 35 MPG's than a toyota corolla that gets around 38-40. Nothing against these cars, without the technology from these auto manufactures building this motor would not be possible. And it is truly amazing what kind of power a 1 liter Yamaha R1 motorcycle can make. I'm also a motorcycle junkie!!!
My plans so far are to blueprint the block to make sure all the cylinders are square with the crank, make sure crank is square with the block. Balance and shot peen crank and rods. Pistons, compression and cams I need advice. I would rather have a hydraulic than a solid cam. Seems milling head to get compression is a common procedure, but since I'm changing pistons maybe this is not necessity. I'm really disappointed in the cylinder head design on these motors. The squish area is an old technology and these motors would seem to benefit from a small squash "Wedge type" combustion area greatly. Does anybody make a head with newer "Closed combustion design" similar to a v-8 head. I've read Dutra's article on these heads and it seems only pistons and re-shaping the chamber are the only way to get this effect. This is to bad. Someone should experiment with welding up these combustion chambers and re-shaping into a "Wedge style" chamber. Unfortunately I do not have the resources that I once did nor the time to machine it but it would be a fun project. Also a clean up port from valve to carb would be needed and a Dutra dual exhaust. As many of you guys seem to have a problem with the small collecting area in the stock exhaust manifold. I've replaced the points with a Pertronix but many of you seem to like the factory electronic unit from Australia so I will need one of those. As for fuel the 1920 seems to be an excellent carb but I'm a little skeptical of a 30 year old design. It seems to only have a main jet and the only way to adjust the pilot is to modify the "Pilot chamber" As with all components you can make everything work, but is it really worth it with this carb? I'm planning on restricting flow to the motor by a restricter plate or even possibly a smaller carb like a Solex pict 34. I'm just used to being able to swap out pilots, mains and accelerator pump nozzles to dial it in.
The design of this intake doesn't seem to help with any type of turbulence to help atomize the fuel droplets so machining a defector plate under the carb also might help for more complete combustion. Also adding a GV overdrive system is a must. This car gets to 75 and it sounds as if were going to explode!! And to finish it of.......for the guys still laughing on the ground you are going to have to change your pants after this I'm going to install a HYDROGEN ON DEMAND device to help with the combustion. I know many people are skeptical on these devices but I feel once these HHO Generators are perfected more people will be using them on there cars in the future. It is a great technology, many patents are free to download and build. Many people are using them on YouTube right now with excellent results.
I'm most sure it would be beneficial for all slant/6 owners any type of technology that could come out of this. I hope I'll inspire Dutra to use his gifts to build a motor for MPG's has he seems to have the most resources available. Also, can members post engine/car set-up and MPG's to see where we are all at. This would be extremely cool to see what setups get what MPG's as this would be a good starting point.
I know that this is an extreme challenge, I would rather be building a 225 with the Aussie blower intake and an Kysler 6 speed, but with the sign of the times I think this will motivate people to take a second look at these cars if we can get a true 30 MPG's out of them.
I apologize for the long post!!
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I would love to get 25 driving "normal". For what it's worth......I only get about 16-17 at 75 mph. Beside the fact that I'm turning 3100 rpm....I can start to feel the "wind-cutting" limitations of my old Dart. 
