What year and what is your current set up? There are lots of guys here running mild 318's with more close to 100 HP over stock that are getting MPG's of 20 or more. If you want to keep your car all original keep the slant if you want power in a mostly stock package then go with the 318. You can certanly build the slant to V8 power levels but what is your budget, and your MPG will suffer too. I had a 78 Aspen with a super six set up slightly modified, same gear as my 73 Dart had and MPG was higher on the 73 and 1/4 mile times of 15 vs 18 seconds. That being said slants can be great turbocharged motors, what kind of fabrication do you feel your capible of? My current set up is 73 Dart 318 .030 over, 340 cam and valve springs, old streetmaster intake with 600 holley, recurved dist, MSD ignition, running stock manifolds, 904 with Transgo TF-2 kit. I run either 2.76 or 3.23 gears. High 15's 22 MPG hwy(65 mph) with 2.76's, Low 15's with the 3.23's and can still make 20 MPG if you can stand to drive 50-55on the hwy. While my combo is fairly well set up others here are even better. If it was me I would go with the 318 and someday maybe add a stroker motor of some kind.
