HI from MI-Offroad Bronco/MPG project.
 

Hi all. I'm looking forward to some ideas to really squeeze out the most MPG I can from a Full size Ford Bronco, while still maintaining offroad capabilities.

Obviously I will need to make major compromises to MPG, but still want to optimize it's ability to sip fuel. The difference between 10mpg and 20mpg can make a big difference in how much it actually get's used. This is also the vehicle I will tow our travel trailer with.

First things....MPGuino, vac gauge. Then a new exhaust Y-pipe, and a tune up/timing advance.

Things I'm thinking about. Full belly pan that doubles as a skid plate for offroading, extended front air dam that is easily removable, and a partial grill block.
I also want to fab a new hood. Similar to the domestic muscle car cowl induction hoods but covers the entire hood...My thinking is that less windshield will be pushing air this way.

You should know that offroading and high mpg are very much at odds. An offroad vehicle needs lots of ground clearance, knobby tires, four wheel drive, extremely low gearing, and a large displacement engine for low-end torque. A high mpg car needs to have none of those things. Therefore, my advice is to put swampers on the Bronco, and get an old Civic which will use one third the fuel of a stock Bronco.

However, if you wish to improve what you have, you certianly can. I think you've pointed out the lowest-hanging fruit: aeromods and instrumentation. I like the idea of a removable airdam, though some cars with a 100% smooth underbelly show no benefit from an airdam. I would definitely spring for two sets of wheels and tires, as well.

There's also weight reduction, which can help you squeeze out the next half of an mpg. Reduce weight far enough, and you may be able to swap in a smaller, more efficient engine.

What kind of tranny do you have in that Bronco?

I know what you mean. They don't go hand in hand. I'm shooting for 20mpg and very offroad capable.

It currently has a 5L V8, and E40D 4sp auto.

It needs to get decent gas mileage or I can't use it, with many offroad parks being several hours away

I've done a fan delete and grille block, along with engine blanket, and my 5.0 will occasionally hit 20. I think using P- series tires instead of LT- helps. On mine I've found going oversize kills fe. Stock is 235/75R15; it wears 245/75s now; it's had bigger in the past but I won't do that again. The E4OD doesn't like that and upshifts outta OD too much. Forget that hood thing unless you like the idea of the styling change. The airdam idea might have merit. These things are gonna push lots of air no matter what unless you get radical, so the big thing is to keep it under 60 mph.

It already has bigger tires. The rear axle is being re-geared to closely match the stock tire/gear configuration.

The ride height is approximately (or will be when the springs arrive) 5" taller in front and 3" taller in back.
Most all of that is because of the tire change (35"). The only suspension lift is with 2" front coils.

Many folks on FullsizeBronco.com have gotten 20mpg on stock (235's) size tires, or close to it (31" tires)

My goal is 20 mpg with 35" tires.....If I'll be close to achieving 20+mpg with those tire sizes I'll stick to a built for MPG 5L, or possibly a re-built 4.9L I6.

If the best I can push is 16 or 17, I'll start looking into a diesel swap.


I may apply some tricks on the wife's van. It already gets good mileage IMO, but seems like it could be improved.

With the above said, It seems like most of the aerodynamic work will have to come in the way of underbody panels.

Things will either need to be very strong or easily removable. I simply won't be able to prevent air from going UNDER the truck.

Good luck, you will need it.

Sounds to me like you have gotten a very ambitious project on your hands! Good luck and keep us up to date.

Also, welcome to the forum!

Not sure if the exhaust Y-pipe on the trucks is the same as on the Bronco but virtually everyone notes a 3mpg gain from a Y-pipe change. The stock Y-pipe is very restrictive so that is something on my list.

The other thing I would look to doing is high quality ignition components, (including "performance" wires), gap standard copper Autolite plugs to .055, and advance the timing 3.5 degrees from stock....Again virtually everyone who has done so notes a very measurable gain in MPG, and in HP/TQ