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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.
Why Are There No Compounds for the 7.3L?
Question: I’m looking at building my old ’99 Power Stroke into a do-it-all sort of truck, so I was looking for a set of compound turbochargers for it. After searching high and low—and calling multiple companies—I couldn’t find anyone who makes a bolt-on compound-turbo kit for the 7.3L Power Stroke. Is there a reason for this?
Bob Miller
-Springfield, Massachusetts
| In 2011, Brian Jelich’s ’00 F-250 powered by the venerable 7.3L engine made a killer 689-rwhp dyno pull on an 80mm single turbo. At the dragstrip, and even with compounds, the truck never ran faster than it did with the single S480.
"A strong 7.3L Power Stroke should be able to break 600 rwhp with a single turbocharger."
Answer: Actually, there are a few reasons why there aren’t any bolt-on compound-turbo kits out there for 7.3L-powered Fords. First off, the 7.3L is a fairly large displacement engine for the diesel market, meaning it can spool a pretty large turbo low in the rpm range. Second, the hydraulic, electronic unit injectors (HEUI for short) are somewhat fuel-limited in the form of ultimate power, as compared to other mechanical or common-rail systems. Third, the 7.3L Power Strokes aren’t exactly rpm-limited and can make good power at 3,500 rpm or more, which means a whole lot of airflow and boost. Finally, most larger turbochargers (S300 and S400s) on a 7.3L need a dedicated mount kit. After buying that, and an aftermarket turbo, consumers aren’t usually ready to cough up thousands more for a second turbo and custom piping to make compounds work when a strong, S400 single-turbo truck can break the 600-rwhp mark.
Why Do You Hate VP44 Trucks?
Question: I read your magazine all the time, but I hardly ever see any VP44 trucks in it! I have an ’02 Dodge Ram with a 5.9L Cummins diesel with the VP44 injection pump, and I am looking for information on how to modify it. If there were examples, that would be great, but I can’t find any in your magazine. I was thinking about an add-a-turbo kit and some 200hp injectors, but I don’t know where to start. What gives? Why do you hate VP44 trucks so much?
James Michelson
-via email
| A properly built VP44 truck can make some serious power, and even at the 500hp level, it can maintain streetability and towing capability.
Answer: We actually don’t hate VP44s at all. It’s just that they get a little lost between the competition-dominating 12-valve P-pump engine and the new-age common-rail Cummins engines. We’ve seen some darn strong 24-valve VP44 trucks, so we’ll try and help you out. First of all, it looks like you’re already looking past the simple intake, exhaust, and programmer stage, which is good. Properly built VP44 trucks have no issues making 500 to 600 rwhp, and that’s without an upgraded injection pump. If your injection pump does fail (usually a 150,000- to 200,000-mile occurrence for VP44s), then you can always upgrade at that point.
For guidance, we turned to good buddy Cory Dow, the brother of 2010 Diesel Power Challenge competitor Cole Dow. It turns out that he had just the type of VP44 build you’re looking for: a compound-turbo truck that has run 12.2-second elapsed times at the track (11s on nitrous), made 609 rwhp on fuel, and still tows, hauls wood, and does regular work truck stuff. After some prodding, he gave us his combination of power parts, which consists of 220hp injectors (F1 Diesel Mach 6s), 62mm/75mm compound turbos, and a TST comp box stacked with an Edge EZ. The truck also has upgraded valvesprings, head studs, and an O-ringed head to handle the extra power. Of course, at this level, you’ll need either a serious dual-disc clutch, or a built automatic transmission, as a 600-rwhp VP44 truck is no joke as far as performance goes. Best of all, Cory reported seeing a max of 1,300 degrees on his pyrometer and said the injectors have a pretty light haze at idle. An add-a-turbo kit should also work well if you decide to go that route, or a 64mm-ish single could keep things driveable yet still crack 500 rwhp.
Why Do LBZ Duramax Pistons Crack?
Question: I’m 62 years old and looking to buy a diesel for my retirement years. Someone told me to stay away from the GMs with the LBZ Duramax (’06) engines because their pistons crack. Any truth to why that year engine would crack more pistons than other ones?
Tim Moline
-via email
| If your LBZ Duramax engine has a lot of white smoke and a miss, a cracked piston is probably the result. Unfortunately, the only option is to pull the motor and fix it, which can be as much as a $10,000 hit to the pocketbook.
Answer: There’s a whole lot of conjecture about this subject, so we actually went to a reputable source and talked to a representative from Mahle Motorsports at this year’s Diesel Power Challenge concerning the LBZ piston cracking phenomenon. From his standpoint, there wasn’t any structural reason that LBZ engine pistons seem to crack more than any of the other designs. However, starting with the LBZ pistons (and we’ve heard some ’06 LLYs), GM’s piston castings switched foundries to a facility in Korea. While this facility makes many pistons for a variety of diesel engines, it’s possible that they had early quality control problems in the metallurgy of the piston casting, which would explain why some LBZ pistons crack and others can handle a fair amount of horsepower. It appears that they got it worked out by the LMM (’07 to ’10) stage of the game, as there have been very few reports of cracked ’07½-and-up pistons.
As a side note/disclaimer in case you’re now scared of LBZ engines, we should point out that most of the cracked-piston LBZs we’ve run across have had big-horsepower tuners on them, or have been owned by folks who have towed very heavy, while running a programmer. If you’re a normal guy with a normal truck, chances are you’re probably fine—even with a mild programmer. And it’s not just the LBZ—we’ve seen cracked pistons on LB7s and Power Strokes, and melted pistons on Cummins engines.
The point is, if you abuse your vehicle, you can break anything. Since you’re retiring and probably have a good amount of money to spend on a truck, we’d probably opt for an ’07-and-up LMM model, or even an ’11 LML-powered Duramax, which have very good power and get excellent fuel economy even in stock form.
