Floating Doc (Forum Supporter) said:
I'm surprised at the low mileage estimates for the 302. I've always liked the idea of a 302 ranger, but I figured that it would be capable of at least 18 to even the low to mid 20 range MPG with a manual with overdrive.
Now, this wasn't a jaguar, but I'll still relate it to my own experience with some small block fords in my panther platform 79 LTD. It weighed about 3700, I'm assuming that to be more than the Branger.
Overview: I had a couple of different 302 short blocks, with a couple of different holly vacuum secondary 600 carbs (the 650 double pumper we'll ignore for this discussion), a performer 289, ported and decked E7 heads and a flat tappet Competition cams Extreme Energy 260H. Short tube Hedman headers, cats with dual 2 1/4 exhaust and (of course), three chamber flowmasters. So, pretty basic mild build.
I doubt I had enough cam to reach your goal of 275/300, but I would expect at least 250/275, with more weight, fewer gears (wide ratio gear set in the C4), and a 2.26:1 rear end. 2000 RPM at 60 MPH.
Would a presumably lighter, fuel injected, roller cam, more efficient GT40p heads, overdrive manual transmission truck really get 3-5 MPG worse? That would really be a disappointment to me.
I can't even get close to 20 mpg with the 4.0L stripped down to nothing but me and fumes in the tank. The 302 is based on 1960s architecture and limited by Ford's and the aftermarket's lack of availability of evolutionary head designs. They are just old-school. My estimates were based on the current 4.0L numbers. Currently I can hypermile about 17 empty and hope for 11 towing 3500 lbs in the mountains. That is with all brand new maintenance items; plugs, wires, coil, fuel filter, new injectors, cleaned TB, etc. I can't imagine a 302, even with modern chambers and ports doing that well.
Your Panther LTD also had 2.26 gears compared to my 3.73s. It also probably had 235/75-14 all-season whitewalls compared to my 265/75-16 A/T. It also wasn't an aerodynamic brick with a lumber rack like my truck is. Curb weight on my truck is about 3300 if I believe the googles, but weight is more important for stop/start than it is on the highway. Once you're moving and maintaining speed, weight has less of an impact on mpg.
Trucks are really where the mileage difference between gas and diesel really collide. You might have a Jetta that gets 35 mpg with the gas 2.0L or 39 with the TDI 1.9L, but in a (for instance) Silverado you might get 14 mpg with a 6.0L gas and 22 mpg with a 6.6 Dmax. Aero, gearing, weight, tire rolling resistance... they really bring out the fuel consumption disparities.
Dad's hopped-up Dmax puts 938 lb-ft to the wheels and I can get 14 mpg towing 10k. My BIL's same exact truck with the 6.0L gas struggles to make 14 mpg empty and gets 9 mpg with the same 10k behind it.