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January 2014 Top Diesel Tech Questions

You’ve got questions? We’ve got answers!

Jason Sands
Dec 24, 2013
Photographers: Jason Sands
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.comand we’ll do our best to answer it.
Must-Have Maintenance
Question: My name is Dan Pavlock, and I am an avid reader of Diesel Power magazine. I own an ’04 Chevy Silverado with the LB7 motor. I’ve had the truck from 45,000 miles to 132,000 miles. Besides routine maintenance, I haven’t touched a thing on the motor. I have always changed oil and fuel filters frequently and run Diesel Kleen. I was wondering if I should do any maintenance on it other than what I’m currently doing? Also, I’d like to install a few add-ons to gain some horsepower, something in the 400 to 450 hp range.
Dan Pavlock
Sinclairville, New York
Photo 2/4   |   A leaking injector cup is another common repair needed for medium-mileage Duramax engines. Unfortunately, it requires a lot of labor. On a positive note, various fixes are available to ensure that once put back together, the injectors will never leak again.
Answer: Hi, Dan. We’re glad you asked about Duramax maintenance, because there is a secret to it. Much like the 6.0L Fords, the coolant needs to be changed at least every 50,000 miles—especially if the vehicle still has the factory red coolant. If it is not changed, it loses its corrosion defense properties, and the head gasket (and even the aluminum on the head) will start to corrode. Best-case scenario on a truck with used-up coolant is a blown head gasket; worst-case is having to buy a set of new cylinder heads.
As for the horsepower part of the equation, we’d get the balance rates on the injectors tested (this can be done with a GM scan tool) to make sure they are within specification. If an injector is going south, adding a bunch more fuel and timing is just about the last thing you’d want to do to your engine. If the injectors read OK, then we’d step up to an 80 to 100 hp tune—or about 350 hp at the wheels.
If that’s not enough for you, we’d suggest going straight for a built transmission and 500 rwhp. Making 400 to 450 rwhp is sort of a middle ground—where your transmission might be fine, and it might not. If you do decide to build the transmission, many different performance levels are available from companies like ATS, Pacific Performance Engineering, and Sun Coast Converters.
Mechanical vs. Common-Rail, Auto vs. Manual Part Two…
Question: In your debate section (Taking Sides, June ’13), I was very interested in the mechanical vs. common-rail debate and the manual vs. automatics. It seems like many of the faster drag racers are common-rail automatics, while the sled pullers are manual and mechanically injected. I was wondering if you could give me some insight on percentages of manual and automatic trucks, and also common-rail vs. mechanical injection in top-tier sled pulling and drag racing classes.
SFC Smithers, Darren R.
Platoon Sergeant
2nd PLT, A Btry, 3-6 FA
1st BCT, 10th MTN DIV
Photo 3/4   |   The ZF-6 manual transmission that’s available in ’99 to ’09 Fords and ’01 to ’06 Chevys can be shifted fairly fast without breaking. With a good driver, it’s one of the few manuals we’ve seen keep up with an automatic at the dragstrip.
Answer: We’ve been watching the mechanical vs. common-rail, automatic vs. manual transmission debate grow bigger and bigger as time has marched on. When it comes to pulling, the vast majority of trucks at large events are mechanical, and manual-transmissioned—somewhere along the lines of 80 percent. However, that doesn’t mean common-rail-injected trucks, or automatics, can’t compete. Case in point, in the 2.6-inch- inducer Class at this year’s Scheid Diesel Extravaganza, the winner on Friday was a common-rail GM with an Allison automatic. On Saturday, the winner was a manual transmission, mechanically injected Dodge.
This year’s TS Performance Outlaw Drag Race and Sled Pull saw some of the fastest trucks go down the dragstrip, with many competitors in the low 9-second and high 8-second range in trucks that weighed more than 4,500 pounds. The final two? A two-wheel-drive, common-rail Dodge vs. a four-wheel-drive, mechanically injected Dodge. The 4x4, driven by Seth Sullivan, also had the odd combination of a large, multi-disc clutch hooked to a Dodge transmission, making it a hybrid of sorts, while the two-wheel drive was a straight-up automatic.
The exception to the rule in this debate is Super Stock Diesel sled pullers, which are currently at about 2,000 to 2,500 hp. At that level, no light-duty automatic can handle the torque these engines produce, while no common-rail system has made much more than about 1,500 hp—the injectors simply aren’t designed for it. At most levels, though, there’s no clear-cut winner in the mechanical vs. common-rail, auto vs. manual debate, which makes sled pulling and drag racing so fun!
Rebuild Questions
Question: I have an ’06 Dodge Mega Cab with a 5.9L Cummins that I got a deal on because an injector stuck and washed out a cylinder. The engine needs a rebuild, but I am unsure of which parts I should replace while the engine is apart. Do I need a stud girdle? Should I coat the pistons? Valvetrain? Camshaft? My questions are endless. I’m not looking for anything crazy, probably a reliable 600 rwhp (nozzles, turbo size, need help here, too). The truck already has a tuner, dual-disc clutch, and a few other bolt-ons. I just want to make sure all my parts match up before I purchase them.
Nathan Scott
Wilmot, South Dakota
Photo 4/4   |   While a cam swap in-truck isn’t easy, if the engine is already apart, it’s a good idea. With larger turbos, more rpm, and more fuel, the engine itself is starved for air, and a cam with higher lift and more duration will help match the engine to its other performance modifications.
Answer: It does indeed sound like you have many questions, Nathan. So, we’ll try and help. For your engine build, working with a reputable machine shop is key. Provided that is taken care of, you’re really not going to need too much to have a reliable 600-rwhp engine. We’d double-check to make sure the head is flat and install a new gasket with ARP head studs. Since the engine is already apart, we’d also install a camshaft. You might not see hundreds of horsepower like in gas applications, but in diesel engines a camshaft can help a lot of things. You’ll see a reduction in EGT, an increase in fuel economy, a slight power increase, and better spooling. While swapping a cam is a pain if the engine is in the truck, for your scenario, the extra labor will be minimal.
As for your horsepower goals, a set of injectors with 100-percent-larger nozzles should help top end power, while a 64mm turbocharger should be able to move the air for 600 rwhp, keep EGT low, and also be quite snappy on spooling when combined with the camshaft. Aside from the turbo and nozzles, a good fuel supply system (if you don’t already have one) should be added to ensure the CP3 is moving all the fuel it can.
The final step we’d take is tuning the truck via EFILive. With EFILive, the low-end smoke can be minimized with the larger injector, while up top, a narrow pulse width with a larger injector will maximize horsepower when using the factory CP3 pump. If more power is desired, a modified CP3 (or twin pumps) should be your next upgrade.

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