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March 2005 4x4 Tech Questions - Tech Line

Posted in How To: Tech Qa on March 1, 2005
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Four Wheeler
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Los Angeles, CA 90048-5515.

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Question: I have a Ford F-250 with the 6.0L Power Stroke diesel. I am disappointed in the fuel mileage of the truck. Someone told me that I can purchase a chip that would not only raise the mileage, but would give it an extra boost of power. I looked into these but I can find little information concerning them. I am concerned about how they work. Nothing added can be completely good, because then Ford would already have it on the truck. What are the drawbacks of these chips? Second, I cannot find information leading to a good one. Everyone who has one is so biased towards their own that they give little help in leading me to a worthwhile product. Do you have any suggestions?
Scott Duncan
via e-mail

Answer: Yes, I have heard that from several people about the lower-than-expected fuel mileage on the new 6.0L motor. Edge Products (888/360-EDGE, has just recently released a new Juice module that when used in conjunction with its Attitude controller allows power increases at five different levels with just a touch of a button. Power increases from 40 hp and 80 lb-ft of torque all the way up to 115 hp and 290 lb-ft are available. The first or lowest power setting is claimed to actually increase fuel mileage.

The nice thing about turbocharged diesels is that they are very fuel-dependent when it comes to making horsepower. Basically what this means is that the more fuel you put into them (up to a point with the proper fuel map), the more horsepower they produce. What this amounts to is that you're not working the engine any harder under normal operation, but the added performance is available when needed. However, I always like to keep in the back of my mind that there are only so many horsepower-hours available from an engine.

Question: My cousin and I are building a Jeep for my first car. We have a postal Jeep frame, a '72 CJ-5 body, and an old military CJ-5 tub, in which we are going to put a Chevy 4.3L V-6 hooked up to a Chevy TH350 tranny and a Dana 18 transfer case. Is there any way I can get near or have a 100:1 crawl ratio, and also be able to go 80 on the highway (or at least around there)?

We are going to rebuild the tranny soon, so if I have to switch out the First gear for a lower gear to achieve this ratio, I can do that. I don't have a very long driveshaft, so I really can't run any underdrives until I stretch the wheelbase. If there is no way I can get this ratio, what is the lowest ratio I can get? I'm going to run 33s or 35s. What crawl ratios do you like for small Jeeps with a good-sized motor?
Brian Huntziker
via e-mail

Answer: Eighty mph in an 81-inch-wheelbase Jeep is pretty scary. If you plan on driving that fast, I suggest you extend the wheelbase by at least a few inches. You can easily move the front axle forward a couple of inches by extending the frame and remounting the springs. (Yes, the steering box will have to move forward also, but most likely you will be putting in a GM power box so you can build the mount wherever you like.) You can also trim the rear section of the body and move the axle rearward also.

I really don't think that there is a need for a 100:1 crawl ratio for most situations, and you can't do it with a TH350 and still maintain the highway speeds you want without screaming the engine. If you want to go with the lowest ratio possible, use a GM 420 transmission (found on '47-'67 1/2- to 2 1/2-ton trucks) as it has a 7:1 first gear. You convert the Dana 18 over to a 4:1 low-range, but I would really suggest starting out with a Dana 20 and converting it into an 18-style as it's a stronger case. This now gives you 28:1.

If you use a 4.10 axle ratio, that makes for 112:1. With a 35-inch tire, which most likely has a rolling height of less than 34 inches, you would be turning about 3,300 rpm at 80 mph, or a more reasonable 2,700 at 65 mph.

To save money you could keep the 2.47:1 low-range gear in the Spicer 18 case. This would give you (2.5x7x4.56) which comes out to about 80:1. The 4.56 gears are going to kill your speed unless you like to hear the motor run at 3,700 rpm.

While the 420 is a very strong transmission and is quite short, it has a few shortcomings. First, it shifts like a 50-year-old truck transmission. Second, it is a 50-year-old truck transmission, and third, there's a big gap between the gear ratios. What works out very well is to add to the back of the transfer case an old Warn or new overdrive unit from Advance Adapters. This is cool because you can use the unit even in four-wheel drive and split each gear. Then you could leave the transfer case alone, go with the 4.56s and the overdrive would bring the engine speed down by about 1,000 rpm.

Question: I have am '01 Dodge Ram 1500 with a 4-inch dual-shock Rancho lift and 35-inch BFG K/O Mudders and a factory limited slip. It does pretty well in the swamps where I hunt and the beaches I run on the Cape Cod seashore fishing for stripers and blues.

I want to know if I can put an electric locker in the front axle with the stock locking axle setup, or do I need to put on locking hubs to be able to install it? I like the stock limited-slip rear in the truck now, and for my driving it works fine, but I would really like a locker in the front. I have also looked at ARB Air Lockers but don't want to deal with air lines.
Gary Wrisley

Answer: I was pretty sure I knew the answer to your question, but to make sure, I contacted Scott Frary, the Aftermarket Sales Manager at Tractech, for a correct answer. This is what Scott had to say:

"We don't have an Electrac for that application. The front axle disconnect requires a C-clip. Our Detroit Locker or Truetrac could be used without the C-clip because the axle can't slide out and the internals of those two units won't allow the axle to go in too far. The Electrac has nothing inside to prevent the axle from going in too far and possibly engaging the side gear of the opposite side. If the disconnect axle could be changed to a solid one-piece axle, the Electrac could then be used with or without locking hubs.

"The Truetrac should be more than enough for the application in question. Unless the driver is frequently lifting tires, the Truetrac will provide excellent traction in sand and dirt. Additionally, steering effort is changed very little, if any."

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