I have one complaint about my '87 Jeep Grand Wagoneer: the gas mileage. Equipped with the stock 360 V-8 with a two-barrel carb and the Chrysler automatic, the Jeep won't get out of the 10-12 mpg range. It has plenty of power, but I'm thinking of swapping in an overdrive automatic or maybe fuel injection to up the mileage. I'm not sure what to do.
Las Vegas, NV
One of the reasons Jeep quit producing the big Wagoneers was the gas mileage figures the 360 produced, which hurt its Corporate Average Fuel Economy (CAFE) standard. The government demanded better figures for cleaner air, and it just wasn't economical to do that with a carburetor and old technology. So now you have late-model 4x4s with higher figures and smaller engines that get 12-20 mpg if you're lucky, and cost three times as much to buy and maintain. Swapping on a four-barrel carb and a better intake manifold, along with a better ignition system and headers or free-flowing exhaust, will improve your mileage figures if you keep your foot off the throttle. So will swapping in an overdrive transmission if most of your driving is on the highway where the overdrive can be engaged. The tips and tricks on improving fuel economy are endless, and the standard joke is if you used all the gimmicks, you'd be making more gas than you used.
The biggest problem, though, is the cost-to-benefit ratio. By the time you sink all that time, trouble, and money into your older vehicle, you'll be lucky to get a 10 percent increase in fuel economy. That's not bad, but it's only about 1 mpg better. Have you ever figured out how much driving it would take to recoup your investment of the aforementioned modifications? It's something like driving twice around the moon and back, or halfway to Mars. In other words, it just isn't worth it. Be happy you have a great example of good, old American iron for fun, and buy an econobox for commuting to save the environment.
My '87 Chevy K10 has 31-inch tires on it now, and I want to run 33s. Will an add-a-leaf kit lift it enough to run that size or will it need more? Should I change the gear ratio to match the tires? I have a TH700-R4 tranny in it so I was thinking of lower gears anyway.
Most charts for tire size versus lift indicate a 2 1/2-inch lift to clear 33-inch tires, but it depends on the true diameter of the tires and the condition of your old springs. You might be able to get away with a 1 1/2-inch add-a-leaf and maybe just trimming your fenders a bit. The replacement springs of a true suspension lift will clear the tires easily and give you a better ride, but will also be more expensive.
As far as the gear change goes, the fact that you have an overdrive transmission means you can go low on a gear swap and retain the highway cruisability and mileage. Depending on the engine you have and what rpm you want to turn on the road, 3.73 gears will be somewhat close to stock for your increased tire size, but dropping to 4.11 or 4.56 will give your truck better off-road performance.
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