Well, "miracles" seemed to exist for the then-new 1974 Chryslers. That was back in the days of the 55mph national speed limit. With those concerns, Fenner Tubbs C-P in Lubbock, TX did a mileage check of their own. They took one each of the Formal C-bodies from their demo fleet. A '74 NY 440, a '74 Newport 400 2bbl, and a Fury 360 2bbl. Being on the southern part of town, on the main highway south out of town, plus across the street from a Shell station, they took those three cars over there and filled them up. Then headed south with the factory cruises set at 55mph once they gotr to that speed limit area. Drove south to the edge of the Caprock, turned around, and drove the same route back to the Shell station. Cars were filled up again for a mileage check.
They printed some pages of teh results for each car, notorized, and put them on a table on the showroom floor. The results were higher than I suspected. Basically a 100 mile trip.
'74 NY 440 20.66mpg '74 Newport 400 2bbl 20.33 mpg '74 "big" Fury 360-2bbl 19.66mpg Being West Texas, NO hills, just rises and such, which means the fuel mixture was always in the "cruise" orientation.
As a point of reference, I was driving our '66 Newport 383 2bbl, which at that time had the Holley 2210 (1970 version, OEM replacement from Holley). I had gotten a bit nerdy on the mpg numbers, documenting my trips home by how many miles on the highway, how many through towns and city streets, throttle amount (in per cent), etc., etc., etc. For the highway segments, me and my K+E slide rule concluded the highway segments were right at 20mpg. Phillips 66 FliteFuel, which was 95.5 pump octane back then. 15* BTDC with stock advance curve. B ias-belted tires inflated to 30f/28rr, cold. 2.76 and H78x14 tires.
In normal driving back then, average mpg was usually in the low 15s, except when the vac advance stopped working and the way I knew it wasn't working was that the normal mpg went to the 12mpg range. Same when the airhorn on the old Stromberg WWC3 warped and the power valve mixture was operative all the time, city and highway.
Of course, the mpg numbers mentioned above were for "real" gasoline. When ethanol was minimally used for an octane enhancer rather than a oxygenate. So the above figures can be reduced by 6% for ethanol'd fuels.
When I upgraded my '67 Newport CE23 to a 9801 TQuad and an Edelbrock Torker 383, from the OEM AFB the car came with, the mpg did NOT increase enough to worry about, if at all. In spite of teh more efficient primaries on the TQ and the more equal A/F mixture distribution o fhe Torker intake. Never saw anything over 15mpg on trips. 3.23 and P225/75R-14 radials on it. Kind soured my on the alleged efficiency of the triple-boost primaries on the TQ! AND that it was allegedly "matched" to that intake on an existing OEM 4bbl motor. The car ran well and I could afford the fuel, so I just dealt with it. Adding the MP electronic ignition made it start a bit easier, but no mpg improvement either.
Just my experiences. I got tired of messing with it. Whatever works for y'all.
Fenner Tubbs used those mileage statements to sell lots of NYs that model year. If an Oldsmobile of Buick customer came in "laughed" at their results, they got offered the keys to a NY for the weekend. The vast majority bought a NY on Monday.
The cotton crop had been good that year, so money was available for vehicle purchases. None of the test drivers complained that their mpg did not match what the statements claimed. So the mpg was definitely better than what their existing cars did and maybe the better access to the rear seat (as they might take another couple with them to go out dancing on the weekends) played a role, too
CBODY67