2004 Dodge Cummins HO Budget Hop Up

by Gary Scott

I got my first diesel in the fall of 2003.  I was nearing retirement age and my wife and I decided that a pickup and travel trailer would be he best combination for us as I wanted to keep the pickup bed open to haul my dirt bikes and mountain bike.

We were really looking for a low mileage used diesel because I'm a Scotsman and try to save where I can.  You'll see examples of my frugality as you read on.

I talked to many pickup owners before buying a diesel and the 3/4 ton gas rigs were getting around 15 mpg highway and the diesels around 20 on average.  The diesel guys were also absolutely ecstatic about the torque that made towing effortless, so it looked like a diesel was the way to go if I was willing to make a long term commitment.

I hadn't heard anything bad about any of the new quieter diesel motors at the time, so I was initially just looking for the best deal, not a particular brand although there were some things I liked about some models over others.

My wife and I decided that we wanted a short bed extended cab 4X4.  The reason for the short bed was for turning radius and parking in normal sized spots, and we wanted an extended cab so we could occasionally haul passengers.  We didn't want a crew cab because we'd end up with a longer wheelbase and we didn't haul passengers that often.  We didn't think we would use the 4 wheel drive much, but since we live in northwest Oregon and expected to keep the truck till we got to old to travel, we thought it would be a good idea.

We liked the Dodge passenger arrangement the best because it had normal opening rear doors and a little more back seat room than the competition.  The Chevy/GMC was a close second, but we didn't like the suicide doors as well and the fact that you had to open the front doors first.  Ford was last because of its small rear passenger area.

There were two things we didn't like about the Dodge however.  It was the tallest truck and the hardest to get into, and it had an old tech 4 speed automatic transmission with questionable reliability, so we would have to go with a manual if we got a Dodge.  Both my wife and I have plenty of experience with manual transmissions, so we could make that sacrifice if we had to.

The combination of the lowest step-in height and 5 speed Allison Automatic made the Chevy/GMC our first choice even with the silly suicide back doors.

On Thanksgiving day 2003 a local Dodge dealer advertised a 3/4 ton short bed 4X4 with a Cummins and six speed for about the same price we'd budgeted for a year or two old unit.  We were waiting at the door when they opened the following day.

The first salesman tried to show us some different units, but when we were adamant about seeing the advertised vehicle he passed us off to a rookie as there apparently wasn't going to be much profit or commission involved.

We drove the truck and liked it with the only exception being that darn step in height.

Shortly after we purchased the truck we went shopping for a travel trailer as we knew we could get the best price in the off season.  Within a few weeks we found a 27 foot Jayco owned by a private party.  Just as we were hooking up the trailer it started to snow.  If we hadn't had four wheel drive we couldn't have gotten the trailer home as I hadn't purchased chains yet for the truck.

Oregon winters often have periods of mild weather, so we had the opportunity to try out both the trailer and the truck right away.

The truck towed the trailer effortlessly and on mostly level ground would get 12 to 14 mpg.  We enjoyed the trailer except the hassle of hooking up and unhooking the weight distribution hitch.  I'd done WD hookups a few times before on a car hauler trailer, but in that case it was usually just once a trip.

My wife and I like to explore, so we were moving almost daily and I thought there must be a better way.  Being a design engineer I started working on what would become the Fastway hitch - but that's another story.

During the development of the hitch I drove the truck without the trailer many times from Portland to a metal fabrication shop owned by friends of mine in Idaho.  At higher speeds and over a couple of mountain passes I was getting 17 to 18 mpg.  Not bad, but not the 20 mpg I was expecting.

The truck was geared perfect for towing, but a little low for high speed running.  With 3.73 gears, 265-70-17 tires, and the six speed manual I was turning 2200 rpm at 72-73 mph.  It would get much better mileage if it were cruising nearer the 1500 rpm torque peak, but adding an overdrive unit would cost more than I could recover in fuel savings.

All engines are more efficient if they can inhale and exhale easier, but turbo diesels move so much air that they benefit the most so I decided to see if I could get more mpg that route.

I looked at the multitude of intake and exhaust available in the aftermarket and once again it looked like the investment wouldn't result in a reasonable payback.  I especially didn't like the noise of the straight through mufflers offered, so I decided to see if I could do something on my own.

I pulled the muffler, cut open the side and discovered that there were three tubes inside.  The exhaust first ran down the lower tube, had to turn 180 degrees and run backwards through the center tube, then another 180 before running down the top tube and out the exhaust.

That obviously wasn't a free flowing design, so I cut an opening in the muffler right at the end of the lower tube and ran a piece of tubing at an angle from the bottom of the muffler up to the exhaust pipe.  I put in a flap valve so I could adjust the flow and noise level as needed.

It turned out that I never had to use the flap valve as apparently the rest of the muffler now works as a resonance chamber and the noise level is barely more than stock.

I next turned my attention to the intake where the designers had routed the air around the side of the air cleaner box through a small opening between it and the fender.  I knew it was restricted as it "honked" when full throttle was applied.

The air box was ABS plastic, so I just took a short section of large diameter ABS tube and after cutting a matching hole right in the front of the airbox, glued it in place with common ABS cement.  I covered the end of the tube with screen to keep the large chunks out and for about five bucks had a direct ram air intake, but it cost me another $40 for a gauze air filter to take advantage of the increased airflow.

The combination of intake and exhaust modifications yielded about one more mpg.  Not bad, but being a Scotsman, I was hoping for more.

I consulted my friend and truck expert Kent Sundling - better known as MrTruck, and he recommended an Edge module to take advantage of my breathing improvements.

I got an Edge module that had four stages and settled on stage 2.  Stage 4 yielded the most power and a little more mileage, but the engine didn't seem really happy at this setting.  Stage 2 gave me the best mileage and still yielded an increase in power that you could feel in the seat of your pants.

And finally the bottom line - on the bottom line of course.  Combined with my intake and exhaust mods I'm getting from 2 to 4 mpg more and I'm very happy with both the truck and the results of the changes.  Your results may vary of course.