A chassis dyno measures a vehicle's torque production at the rear wheels. The numbers are always lower than what the manufacturer rates the engine at because engine power is lost spinning the transmission, transfer case, driveshaft, axles, and wheels before it ever makes it to the dyno. In our most recent test of 2006 model-year trucks, the Dodge Cummins rated at 325 hp and 610 lb-ft of torque (at the crankshaft) actually made 289.9 hp and 530 lb-ft of torque at the rear wheels. The 6.0L Power Stroke that's rated at 325 hp and 570 lb-ft (at the crankshaft) managed 274.8 hp and 443.6 lb-ft of torque at the rear wheels in our testing. And the Duramax diesel that is rated at 360 hp and 650 lb-ft (at the crankshaft) proved to be capable of 315.7 hp and 569.5 lb-ft of torque at the rear wheels.
The rear wheel horsepower and torque numbers are very informative, but they only tell part of the story. When combined with multi- speed transmissions, the three trucks' performance gap widens even more. Again, based on our testing, the General Motors Duramax has a clear advantage over the other two engines. But the torque wars still rage on!
ATF as a Diesel Fuel Additive?
Q: I have a 2000 Ford F-250 7.3L diesel. Is it a good thing to run automatic transmission fluid in the fuel tank to clean out the fuel system? My grandpa has a 2003 F-350 with the 6.0L and he is an old-school diesel mechanic. He uses ATF in all his diesel cars and trucks. He has also had many problems with his 6.0L engine, injectors being one of them. Basically, does it hurt the new motors because they are so electronic? If it does hurt them, could you please explain why?
A: Pouring automatic transmission fluid into the fuel tank with diesel fuel is a practice that's over 50 years old. The ATF burns just fine in the engine and seems to loosen and lubricate everything in the fuel system-in a positive way. We've been known to mix a bottle of ATF in with 30 gallons of diesel fuel at each fill-up to smooth out rough injectors and add a level of protection to the injection pump internals. Why does it help? We're going to have to find a chemist who's willing to go on the record to say exactly why, but we can tell you it works on mechanical injection diesels.
The one caution we have to share is that those of you with high-pressure (common rail and 6.0L Power Stroke) injection engines should avoid using ATF as an additive. It seems that at pressures near 26,000 psi the ATF can harm the injectors and pump. Again, more research is needed in this area, but we'll only recommend using ATF in 7.3L Power Strokes, '02-and-earlier Cummins engines, and 6.2 and 6.5L GM diesel engines.
Power And Fuel Economy
Q: I currently own a 2002 Excursion 4x4 with a 7.3L Power Stroke and plan on buying a 2007 Ford F-350 crew cab 4x4 with the 6.0L Power Stroke. I am not a mechanic and have limited knowledge with diesel engines. I have owned a diesel truck for the past 11 years and am a huge fan of diesel engines. I would like to upgrade both vehicles to get optimum mileage. I was looking at installing a new air filter system, exhaust, and some type of performance chip. As I said, my goal is to improve my mileage to the ultimate I can. The problem is, there is an overwhelming amount of advertisements for upgrades (just look at your magazine) and I do not know where to start.
I would like to upgrade the suspension as well-about 2-3 inches on the truck to improve ride. I will carry a pop-up camper on occasion, weighing about 2,000 to 2,800 lbs. I would really appreciate any suggestions and input you may have in regards to these matters.
A: If you're looking for mild power gains in addition to the best fuel economy you can get, start with the basics. A free-flowing 4-inch turbo back exhaust system will alleviate your engine from having to push the exhaust out of the motor. A free-flowing cold-air intake kit will also free up some power that would otherwise be wasted trying to suck air in.
Beyond that, you want to play a conservative game and go with a mild towing calibration upgrade that is designed to maximize fuel economy and performance and not harm driveability. We also recommend installing an exhaust gas temperature gauge (EGT). A high EGT means lots of fuel is being burned. A low EGT means you're maximizing fuel consumption.
Lately, we've heard claims of power and fuel economy improvements that come with a set of Extrude Honed injectors. Basically, the power and fuel economy come from better flowing injectors that don't rob as much power from the injection pump as it tries to force fuel into the combustion chamber. Stay tuned for the results of our testing.
Cummins B-Series Dimensions
Q: I am considering a couple of swaps for the Cummins 5.9L. Do you know where I can get external dimensions for this engine?
A: Length: approximately 40 inchesWidth: approximately 24.9 inchesHeight: approximately 35.5 inchesWeight: approximately 1,185 lbs
Cummins 4BT 3.9L Power Output
Q: I would like to know what the torque rating is on a Cummins 4BT 3.9L diesel engine. I have been watching a few auctions on eBay, both looking for a diesel Suburban or Yukon, and possibly getting one of these four-cylinder engines for my old FJ-40. These ads on eBay only tell the horsepower, not torque. Can you help me out?
A: We've seen the naturally aspirated version rated up to 76 hp and 136 lb-ft of torque. At the high end, the turbocharged versions are capable of 150 hp and 221 lb-ft of torque.
Ideal Cummins Swap Candidate
Q: First off, I want to say your magazine rocks! But I have a problem. I want to put a newer Cummins engine in my 1991 Dodge Ramcharger. I am currently looking for an '04-'06 Dodge truck that has been wrecked. Any tips on the install or any other parts of this process would be really helpful.
A: If you plan to run your current transmission, you'll want to get a Cummins engine from a manual transmission application so that the computer isn't looking for feedback from an automatic transmission that isn't there. You'll want a lot of parts from a '93 Dodge Ram diesel truck. Pieces like the intercooler, radiator, plumbing, and radiator core support. And you'll need to upgrade your front suspension to handle the extra weight. You'll also quickly find out the stock axles you have won't handle the torque, so plan on swapping in a '77-'93 Dodge Dana 60 front and Dana 70 rear axle.
Low Buck 6.2L Upgrades
Q: I've been following along with the new diesel trend and like most 16-year-old kids, I can't afford a new diesel pickup, so I purchased a 1984 Chevy K20 with the 6.2L diesel engine and 4-speed manual transmission. Right now, the only performance it has is dual 3-inch exhaust pipes (without mufflers) and I love it. But I want a little more performance from it. I am looking for something small, like a cold-air intake or propane injection, just to make it run a little hotter. Can you please help me with this power problem?
A: Propane is always an option, though we know of no commercially available kits for the 6.2L. Basically, you'll be stuck retrofitting a system designed for a Power Stroke or Cummins engine. There is a new dual-snorkel cold-air system from Ram Air Box (www.ramairbox.com, (905) 549-6135). We'd add both and install an EGT gauge so you can tune-in the fueling rate without exceeding 1,200 degrees under load.
Lift Pump Upgrade
Q: I have a '97 F-350 with the 7.3L Power Stroke diesel and I will be purchasing an Edge Evolution here in the very near future. I have installed a K&N intake and a 4-inch turbo-back exhaust. I have heard that if you program or put a chip in your truck that you should also upgrade fuel pumps. Is this true?
A: Even at these power levels (in the 350 hp range) your factory lift pump will be enough. When you start adding larger injectors, it'll be a different story.