Poor economy–318 Mopar
filed in Misc Car Questions
Question: At any rate, the engine is a 1983 with 80,k mi, and a Holly Economaster >>Lean Burn Carb. The ignition system has been converted back to >>breaker points after the computer started acting up. >You ARE joking, right? When the motor was swapped, the 4bbl intake, >carb, and ignition should have been put on the “new” motor. >So now you have a computer carb with a P&C ignition. Jeeeez, who did >this motor swap, Sears? >At least if the computer was acting up, you should have replaced >the computer distributor with a vacuum advance electronic.
>Strangely, most 318’s seem to do shitty on gas.
Answer: 1–4bbl carb in a 2bbl motor: The Direct Connection and Moper Performance manuals, written by the Chrysler development engineeres, strongly suggest that you not run a 4bbl on a base 318 because the valves are not sized for the increased flow required to take advantage of the second half of the carb. A stock 318 runs a Carter 350CFM 2bbl with no electronic mixture adjustment. According to the dealer, the police 4bbl is an 850CFM, produced by GM and with electronic feedback for mixture adjustment. Additionally, the 318 4bbl had a different cam than standard 2bbl motors, making the swap from 2bbl to 4bbl even less effective. To produce an effective 4bbl swap, MP recommends a new cam as well as new heads, and once you’re in that deep you might as well rebuild the motor from the bottom up.
2–breaker points: I put the points in after the car was already out of the shop. Sunday evenings 1200 miles away from home often don’t leave you with too many options. At least I had the distributor with me to get the car home. A stock elctronic ignition system offers little above points except for its dependability. The spark is marginally hotter than with new points. The downside of converting is the parts involved and the need to cut into the stock wiring harness, as well as mounting the module, which requires drilling holes in the firewall.
I have owned 9 318 powered mid sized Mopars. My 1970 Coronet 500 with points got the best milage at 24mpg from Boston to Phily and back, but I had fabricated a hood scoop, and it 2.71 gears behind a 4-speed, so maybe that is a bad example. My 1971 Sebring got 18-20 consistantly with an auto trans and 3:23 gears. Even now, running bad gas and with points, my 67 Charger 383 4bbl 4-spd will turn 14-15 with the cruise on. The 318 in my 4×4 will turn 13mpg with the cruise on. In general I have found most people will get at least in the high teens for milage, which isn’t bad for a 4,k+ car with no overdrive.
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