What would be a more effective boost for my situation? The motor is a 318, .477/.480 lift cam, stock compression pistons, headers, 904, stock converter, 3.21 non sure grip 8 1/4. I want to get the tires to break free a bit easier and pull a bit harder in second gear. Should I go with a 2000-2200 stall tc, or just up the ratio in the 8 1/4 to a 3.55 or 3.73 with a sure grip? I pull 16-18 mpg at 65 on the hwy now and would like to retain as much as possible, as well as getting my ets down to the solidly in the mid to high 14s. So far, my best is 15.02.

The tire is a 235/70/15 and it currently turns 2750 at 65 and 3000 at 75.

Sounds like a little more convertor would be give the most benefit. Call Turbo Action, Dynamic, etc...They can recommend something just right for your combination and still maintain your highway fuel economy.

Check out the convertors from Mopar Performance too. They don't cost a fortune, and are perhaps the best milder performance convertors for the money. I have a 904 behind my mild 360 and I'd have to look up the number, but the one that I have is the highest stall they offer (around 2200-2500), and very streetable. Also, I agree on going with the convertor instead of gears to retain better mileage.

I agree it needs a looser convertor but I'd go with a set of 3.91 or 4.30's and you have all the tire spin you want.

With that short of a tire you change gears the freeway will really buzz the motor. I have cars with 410's, 430's, 391's and the freeway is not something I do unless I have to, now light to light is great.

convertor,definitely. i dont think a 2000-2200 would be much, if any, improvement over a stock 318 convertor.something on the order of 3500 or so would make your 318 come alive. night and day difference for sure. as already mentioned above, contact a few of the reputable convertor companies and listen to their suggestions.

A stock 904 converter behind a 318 should stall in the range the OP desires.

Changing to as higher stall converter with low numeric gear ratios can result in the converter slipping at medium road speeds.

IMHO, the 3.55/3.73 gear change would be wiser than a converter change.