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November 2005 Issue

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Big Block Mileage, Small Block Power

I own a ’96 Ford F-350 4x4 Crewcab longbed with the 460ci EFI engine. It has 112K miles. For the most part it’s a sound truck but it’s sluggish on acceleration. I have tuned it up, changed out the distributor, changed the coil and run numerous cans of injector cleaner through it. No check engine light. I have considered purchasing a new cat. Please help.

I’m assuming your complaint is based on it being faster when you first purchased the truck and that it’s slowed down since. My answer will be based on that assumption. Otherwise, you’re looking at making modifications, not repairs. Your instinct to replace the cat may be right on, but I don’t suggest you replace it willy-nilly without tests. Cats can plug up with age and the backpressure will slow the truck down. The simplest answer is to remove the cat temporarily and see. If it were me, I would find a local stretch of quiet road and time my acceleration from one landmark to another, or check my speed at the end of the run. You don’t need a super high speed run... stay under the speed limit but do the test in a place that you can get up to about 60mph. Do a run with the cat, then remove it and do another run under the same conditions and in the same place. If the rig runs substantially better without the cat, you’ve found your culprit. If not, you can bolt it back up and look elsewhere.

Sergeant Yukon

I have a 2000 Yukon and want to install a lift, larger tires and increase the horsepower. I plan on a 5-inch lift and 35-inch tires. I want to be able to use it for mud and as an everyday driver. First, are there any benefits to dual shocks? Can I mount 35-inch tires on the factory stock rims or should I go to 10-inch rims. As far as increasing the horsepower, I plan on headers with a dual exhaust, a throttle body spacer, a cold air intake and possibly a Hypertech programmer. I am not sure if the truck came with a limited slip, but perhaps you can tell me. I am currently deployed to Iraq in support of OIF and my wife sends me your magazine every time she gets a new copy.

It’s an honor to hear from one of the Builders of Freedom, Top! It sounds like you have a good plan there, except that you left out the gearing changes needed for the 35s. According to my books, your rig could have either 3.42s or 3.73s. If you have 3.42s, you absolutely need to swap gears. You could skate by with 3.73s, but I’d advise a 4.10 axle ratio if you stay on the street most of the time and a 4.56:1 if you want more pep and better off-road performance. Unless you are a fast mover, there is really no need for dual shocks. The main idea behind them is to share the heat and dampening load of lots of fast suspension movement. The average ‘wheeler doesn’t generate that much action and a single, high quality shock is usually more than enough. As to rims, you should upgrade to 10-inch rims but pay attention to what backspacing the lift kit manufacturer may recommend for the particular lift. For some reason, a limited slip doesn’t show up as an option in my 2000 model year Yukon info. Odd that I see it listed the year before and the year after. If it does have one, the RPO options list (usually on the glove box lid) should list “G80” as a code. If you don’t have it, I’d recommend installing an Eaton Posi with the new gears if you want a limited slip. If you have a few extra bucks, go for an ARB Air Locker. I wouldn’t advise a locker or limed slip up front. That 8.25 IFS unit is fragile and a locker usually just kills it faster

One Barrel to TBI

I have a ’76 CJ-5 with a stock 6-258. It has the 1-bbl carb and I want to put Howell TBI fuel injection on it. The Howell system calls for a 2-barrel intake manifold. Will a ’79 intake manifold fit on a ’76 and will the exhaust need to be changed too? Will the cam need to be changed for the TBI?

Barlow Pinole, California — Via e-mail

The first thing I want to warn you about is emissions regulations. I still wake up in a cold sweat every once in a while after a nightmare about the tough and ever-changing emissions regs I experienced during my many years in sunny California. Up to the ’81 Model year, there was a mix of 2-bbl and 1-bbl 258ci engines, both with cast iron intake manifolds. Starting in ’81, an aluminum 2-barrel intake was used along with an improved exhaust manifold. Supposedly both of these manifolds are better than the old ones, but probably not enough better to warrant many small changes you’d have to make bolting them up. Both the one and two-barrel cast iron intakes will bolt up to your existing exhaust manifold, but not the ’81-later aluminum unit. If you have access to a ’79 2-bbl intake, you’re pretty much set. A cam change won’t be necessary, though you might gain a little by upgrading to the 4.0L cam, which is a slight improvement over the older grind. There are also many aftermarket cams, though I caution you to stay on the mild side. My advice is that, unless you plan to rebuild the engine, stick with your original cam. If you rebuild, boost the compression to something close to 9.0:1, and then go with an aftermarket cam appropriate to that compression ratio and your new EFI.

Vintage Jeep Tech Question

We have a 1948 CJ-3A, restored and mostly stock. It has a replacement Solex carburetor. Is the original carburetor available?

Bob Castro — Via e-mail

I’m assuming this is a typo and that you have either a 1949 CJ-3A or a 1948 CJ-2A. The changeover from 2A to 3A came in 1949, but there was some overlap in the two models that year. The original carb was a Carter WO (probably a 636S), and they’re no longer available new, unless you’re lucky to find a new/old-stock piece on somebody’s shelf. Rebuilts are available, but unless you’re planning to show the Jeep and need a correct period carb, there’s nothing wrong with the Solex in terms of functionality. Some people actually prefer them.

Durango Dreamin’ in Venezuela

I’m planning on purchasing a ’98 Dodge Durango soon. I was wondering if the stock axles will hold up to 35s. If not, what can I do the beef them up, or should I just replace them?

If the rig you want has the normal axle combo, a Mopar 9.25-inch rear and a front D35, the rear can handle 35s, but not the front. A lot depends on how you use it. You’d be fairly safe with 33s, better with 31s. You will need about 6 inches of lift to fit 33s on a Durango. If I were you, I’d stay there or smaller. If you have to go with 35s, find a good fabber and swap in a solid Dana 44. I’m sure it’s been done, but I’ve never seen one.

Four Banger Blues: Gearing

For rigs with four-cylinder engines, do you have different recommendations for gearing and tire sizes? For instance, in my Ranger with a 2.3L, 5-speed and 4.10 gears the truck got way more sluggish off the line and can’t pull the same hills when I went up two tires sizes from P215s to LT235 mud-terrains. Should four-banger owners only go up one size? Should we gear down one more gear size than recommended?

Mac Houston — Via e-mail

You’re right. The standard formulas work to get you back in the same RPM ballpark, but the increased rolling resistance of the bigger tires and loss of aerodynamics that come from lifts and taller tires are also a factor. The other element is that tires and a lift are usually just the first thing on the modification list. The rig usually picks up some weight as well. For all of those reasons, the low power rig needs lower-than-normal gearing. That makes for a rough compromise sometimes. You can get to the point of needing gears so low that your highway cruising is severely compromised. You can deal with the low gears needed for trail work by going to splitters (underdrives) or super low t-case gears, but street performance remains compromised. Bottom line... you four banger guys need to think hard about how big a tire you use and, after mods, make a determined effort to keep your rig as lean and mean as possible. How big a tire is too big? It depends on the rig. Lighter rigs or the more torquey fours can get by with more tire and vice versa. I’d call a 31x10.50 the biggest tire for four-banger people that want minimal mods to compensate for all the problems and a 35x12.50 the maximum that’s practical for a daily driver. Don’t bombard me with exceptions here, people! My recommendations are based on an average of the downsides most people will want to put up with. You may be willing put up with more headaches or spend more money, others less of both.

Towing Grandly

Looking for advice on how to maximize towing and handling with my ’95 Grand Cherokee with the Up-Country Package, 30-inch BFG A/Ts and the tow package. The book says my tow rating is 6,500 pounds. I have replaced the shocks with Rancho RSXs. Are new coils in order? Are air springs better? I’m trying to see about pulling a 30-foot ultra-lite camper, weight 5,400 to 6,900 pounds. Are there better hitches to look for?

To start, Sig, if you stay under Jeep’s towing recommendations, you may not need much of anything. I would start by focusing on the trailer first. One very positive thing to do is make sure to install an equalizer hitch on whatever trailer you use. These really help drivability by transferring some of the tongue weight to the front axle. A sway control device should be included as well. These things may be all you need for happy towing. As to a hitch, a Class-3 unit should be fine, just buy it from a name brand manufacturer. Even with the V8 and 3.73 gears, don’t expect your Grand to tow like a Cummins powered one-ton Dodge. Lock out overdrive when towing and keep to the posted trailer speed limits or about 60-mph. Run max air pressure in your tires and spend some time fiddling with the trailer brake controller to get it adjusted so that the trailer is stopping itself and not overloading your Jeep’s brakes. Gear down for hills and read the road ahead. Stopping distance will be like a freight train’s. Finally, don’t overload the trailer. Don’t do what I did the first time and drive around with a water tank full of about 800 pounds of water!