Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power?
Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
’03 Cummins with 480 hp?
Question: I was looking on the Cummins website and noticed that its marine 5.9L inboard engine ranges from 225 to 472 hp, with a peak torque of close to 1,000 lb-ft. Can a third-generation engine (like my ’03 H.O.) handle this kind of power and rpm for a significant amount of time (say, one hour) without problems as long as the EGT and water temperatures are kept in check?
Patrick Simard
Ottawa, Canada
| We’ve seen both Cummins and Duramax marine engines, and in some cases, they make upward of 700 hp. While your truck engine can make similar power numbers, in most cases, you’ll have to do numerous upgrades for the sake of reliability.
Answer: The answer here is a definite yes! When looking at power ratings, you have to keep in mind that Cummins rates its engines at the flywheel, while much of the diesel aftermarket uses rear-wheel horsepower numbers, which are about 20 percent lower. That means the 480hp marine engine would make about 385 rwhpa number that is very achievable in the diesel aftermarket.
If you’re wondering why Cummins didn’t just offer a 480hp option for the Dodge Ram, the engine itself isn’t usually what you have to worry about, rather it’s everything around it. Both the engine and transmission cooling systems would have needed to be addressed, as the extra horsepower would create a lot of extra heat. It would also be hard on the transmission itself, rearend, and most likely be non-compliant as far as emissions levels go.
Medium-Duty Transmission Questions
Question: I’ve been searching high and low for performance parts for the Allison 545 and 1545 transmissions. All I can find so far is a converter from Sun Coast Converters, which appears to be about the same stall speed as stock. This is a great transmission for what I want, except for the mushy converter. With the lockup model, I am not sure it can take much more than the factory-rated 230 hp. My plan is to swap a Ford 6.6L from an F600, the Allison trans, and 3.08 axles all into a ’67 Ford F100. I’m just having trouble with the transmission part of the equation.
Dale Kaufmann
Modesto, California
| Wayne Talkington’s big rig drag racer has run a best of 10.69 seconds at 119 mph and has had the same transmission in it for more than 7 years. While the Allison 740 would be extreme overkill for any pickup (and probably wouldn’t fit), we think the MT643 might be a good option.
Answer: With all the talk about billet big-shaft transmissions lately, we’ve been thinking about invading the medium-duty transmission market to create an indestructible transmission to put in a pickup. We talked to a few reputable shops and learned that although the Allison 545 might look good on paper, its input shaft and converter aren’t much larger than current offerings. The design is also some 40 years old!
A shop that builds a variety of medium-duty transmissions for school buses turned us on to the Allison MT643, which has a much larger converter and enormous shafts and clutches throughout the unit. It can also be built to shift manually at high pressures and has a take-apart converter with a lockup clutch. It can also withstand 4,000-rpm engine speeds, which would be perfect for a hot street diesel. Most of these units can also be rebuilt for about $2,000, which would be a substantial savings over most GM, Ford, and Dodge transmissions that would be capable of handling a similar amount of torque.
Ready for the bad part? These things are huge. At 510 pounds dry, you’d most likely need to cut out the floorboards or put a body lift on your vehicle to get the transmission to fit. They also have a 1:1 ratio Fourth gear, which means numerically lower front and rear axle gears (like the 3.08s you mentioned) would be needed, as well as a divorced transfer case to match it all up.
If you could find an MT643 and adapt it to the engine, and if you could find a shop that could rework the converter for a lower stall and run the transmission at a higher pressure, then you would be left with an unbelievably strong unit. We’ve seen a modified Allison 740 (at 800-plus pounds!) handle more than 3,000 lb-ft of torque in a 10,000-pound big rig for years without needing to be rebuilt. Whether or not these types of transmissions will make it into pickup trucks remains to be seen, although we’re sure a few brave souls are willing to try the swap.
Poor Fuel Economy Or Not? Question: I recently purchased an ’06 Dodge Ram 2500 four-wheel drive with a 5.9L Cummins and 60K on the clock. I love the truck, it has lots of power, and as far as I can tell, it’s factory stock. All my friends say my fuel mileage is poor for the truck, but to me it is so much better than the old gas burner that I’m still impressed. On the highway, going 65 to 68 mph and empty, the highest fuel mileage I have seen is 17 mpg. My friends suggest freewheeling front hubs, an airbox, turbo-back exhaust, tuner, and so on. So the big question is: Is the truck down on fuel mileage, and if so, where does one start trying to make cost-effective improvements?
Thomas Weatherston Racine, Wisconsin
| Back in 2008, we did a fuel economy test on various types of vehicles. With fuel prices on the rise again, it might be time to revisit this concept. If you have a diesel vehicle that sips fuel instead of gulps it (especially if it’s a truck), drop us a line at Jason.sands@sorc.com.
Answer: In your case, we’d say you’re doing pretty well if you can hit 17 mpg consistently at the speeds you are driving. We actually had a project a year or so ago in which we looked to add performance and economy (mostly economy) to an ’07 Dodge 2500. We took the truck from 15.5 mpg (stock) to 18.5 mpg with the addition of a cold-air intake, camper shell, free-spin hub kit, and a Fitch Fuel Catalyst. Check out http://dieselpower.automotive.com/tech/02/dodge/ ram-2500/index.html to view most of the old articles. Click on anything that says 6.7L Upgrades That Won’t Void Your Warranty. Even though the truck had a 6.7L Cummins, everything in those articles should still work on your truck.
Other than what’s been mentioned, we’ve also seen a big jump in fuel economy with a set of Flex-a-lite electric fans on a 12-valve Dodge. Although we didn’t get to tow with them, just blasting down the freeway gave us a 2-mpg jump as compared to a factory clutch fan. A programmer or box that adds timing is also a good way to increase your fuel economy, and if you had a smaller, lighter, two-wheel-drive truck, we might suggest re-gearing, but for your application you’re probably fine where you are now. In the end, we’d advise these modifications for added power and reliabilitynot just for fuel economy.
