1976 Jeep FSJ Cherokee daily driver
 

Just bought it and and gas mileage is abysmal, yet I still love driving the thing. I'd like to get some opinions from guys that have made some sizable gains without extensive aero mods. Here's where I am right now:

I can't top it off yet to do a mileage test due to deteriorated fuel hoses, but I'll have that fixed next week. So far it's looking to be 10-12mpg with it's original 360 2bbl, turbo 400, full time 4wd quadra trac, etc.

Engine: I ordered an Edelbrock airgap performer rpm, a new Holley demon 625 carb (1 3/8 primaries versus the 1 9/16 primaries on the original motorcraft 2100). I chopped off the ancient factory muffler and went with a 2.250 i.d. straight through muffler on the original 2.500 o.d. exhaust. I checked the factory advance curve and it's conservative for a jeep that doesn't tow very often. I've got a new HEI for it and I'll correct the curve. We'll chassis dyno it with the center diff locked and prop shaft disconnected to get some additional data.

The next thing is going to tee-off some purists, but I'm putting the original 4wd system on the shelf for now. I ordered up an .78 o.d. 5 speed AX15 trans from a 2wd 4.0 Cherokee. Conversion parts are about $1000 plus a centered differential rear axle (3.54 to 3.08 gears) and drive shaft. Removing the front stub axles so the internals aren't moving. I'll build a fuel cell behind the rear axle that cleans up the aero coming off the axle. I can block off part of the grill opening and do some panels underneath to clean up the aero further. Cruise rpm in the mid 60mph range drops from 2800 to 2000 rpm. Net weight reduction is 175 lbs and acceleration should be much better when it's required. Zero toe alignment and LRR tires when the BFG's are shot.

I don't know that I can achieve 25mpg without EFI, but I'm at least hoping for 20. Even at that with the mileage I drive, my $2600 investment only takes a year to pay itself off.

Any thoughts (other than buying a diesel rabbit)?

You will probably need EFI and aero mods and slow down to 55 MPH and tire pressure and LRR tires and get good with both DWL and DWG to get to 25 MPG. That's a lot of AND's, but this is Ecomodder.com.

Fuel log. Please start a fuel log. I want to see how this all works out.

Yeah, 25 is a stretch as there's a lot of modern vehicles that can't achieve that. Is there a standard fuel log format that people use?

EFI is a good improvement, specially if it's OBD2-compliant, allowing you to use a ScanGauge or a MPGuino to check your real-time mileage.

Seems odd to buy a classic truck and then put LRR tires on it and stuff. Anyway, I got good results from a lawn edging air dam on my 352ci F100, if only for the highway trip, after which I removed it for aesthetics. It was surely a lot less work than underbody panels. Larger OD tires will help on the highway, though if you're doing much city driving that might cancel itself out.

Pull the passenger mirror off, and the driver's side if you're comfortable with that legally and safety-wise. You could also simply swap out for smaller mirrors. If there's a way to remove the wheel arch extensions and get flush-fitting wheels/tires, I'd do that too. Get some Moon-style wheel covers, or make some. Ultimately you might want to swap in a smaller engine if you really want low 20's MPG. A 4cyl diesel would be perfect.

For the fuel log, go up to the top of the page, click on "Garage" and add your vehicle. There will be a self-explanatory fuel log entry area there. You can see the results underneath your avatar on the left.
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