hi
I am old school mpg makes me feel better. I think if I remember rightly about 18 to 20 mpg on trip work which is what most of my traveling is.My 360 charger that I had done porting and cam etc and 4b used to do 18 mpg on a trip.
But I also used to get down to 5mpg a set of disc per tank, collapsed torsion bars and crack in the roof line after a wild night or 2.
Oh to be young and stupid again, but many of my mates did not make it. Could not blow up that old girl.
Better behave when I get the Hemi on the road.
Don't forget the US figures are not relevant if mpg as their gallon is shorter.
The motorcraft late 2barrel was very economical as it had a 2 stage power valve very hard to get. A couple Mustangs used it also. Other parts like jets are holley as they also made a licensed carby in the sixties. Great 4 barrels if you can get one , somebody stole mine. I had swapped it from a carby builder as he was getting 27 mpg on a stinking hot 302 with it.
The secondary venturi is the go have a look in one sometime.
My 4.7 averages about 20mpg but on a trip getting a draft up to 24 and I have not put the 5sp computer in to upgrade the overdrive which would give it a couple extra mpg as it drops the revs about 200 to 300 revs. The wj is gutless though, as soon as you tow halve the fuel consumption.
The sj uses a heavy duty thermo fan coupling, and I replaced it with a Holden one, this is also a saving in fuel.
Tyres make a big difference and even pressures on some vehicles. I always run higher pressures but the SJ just did not like it, my Dad said 34 psi and he was right.
Sorry this is the best I can do, but you will not get late model economy out of one, as new engines can be very eco. But I had a 4cyl Mazda ute and it was on Gas and it was no better then the SJ and i tuned and set up both. My mate had a customers 626 mazda and he had the same problem on gas it drank like a horse.
My mum sad the Sj was as good on fuel as her Fairlane, same gas kit.
Old V8s only on lpg unless your racing
Bugger petrol unless avgas.
Try v12 jags for a shock, again lpg but most can't convert properly as they don't understand the way the petrol system works.
Cheers
peter
jagonev12