To Smoke A Muscle Car…LB7 Duramax Edition
We’ve shown you how easy the 6.4L and 6.7L Ford diesels are breaking into 12-second range at the drag strip, but now it’s time to shed some light on the GM camp. With little more than ECM programming, an LB7 Duramax-equipped ’01-’04 Silverado or Sierra can tear through the quarter-mile in low-13 to mid-12-second intervals. This means late-model Camaros, Mustangs and Chargers are all in the kill zone for a tuned Duramax. And even though the LB7-powered GM’s don’t quite match the high-powered Fords pound-for-pound on the dyno, they have a hidden trick for equaling them at the track. Hint: the truck the LB7 came in is much lighter, and any hot-rodder knows that dropping weight is like adding horsepower.
To bring your LB7 up to speed, the mods list is surprisingly short. Below, we’ll fill you in on how you double the power of GM’s first 6.6L diesel V-8, along with how you can go about enjoying that additional power for the long-term.
High-pressure common-rail fuel injection is the key to the Duramax’s hidden performance potential. Thanks to the Bosch system’s CP3 high-pressure fuel pump and quick-firing solenoid valve injectors, in-cylinder injection pressure crests 23,000 psi. With the ECM infiltrated and the keyboard in the right hands, the factory injection system on your ’01-’04 GM HD can support a 510 to 550rwhp effort. That’s twice what an LB7-powered truck makes in stock form.
Custom Tuning Files
EFI Live software has been the leading method for tuning Duramax-powered Chevy’s (and the LS crowd even before that) for more than a decade, and the industry’s top calibration experts have tuning down to a science at this point. To double the horsepower and torque output of the LB7, added timing, injector duration and rail pressure are all part of the deal. There’s more to it than that, obviously, but those are some of the fundamental ways to a diesel power plant’s heart.
Some consider it an obligatory mod, but aftermarket exhaust systems do help engines breathe better. The LB7 Duramax is no different. With double the horsepower in the mix, exhaust gas temperature (EGT) gets toasty after prolonged, wide-open throttle runs. With a free-flowing 4 or 5-inch diameter exhaust system you can drop EGT and uncork the LB7’s one-of-a-kind (fixed geometry turbo-induced) exhaust note at the same time. At $300 or less, bolt-on aluminized 4-inch systems for the LB7 are very affordable, too.
Lift Pump: The Mandatory/Not Mandatory Mod
With tune-only power-adding, fuel is the primary ingredient. And when additional injector on-time is commanded via tuning, it’s a fine-balance to keep rail pressure from dropping. But before the CP3 can supply the rail with 23,000-plus psi of pressure for the injectors to use, the CP3’s suction valve on the low-pressure side of the pump is taxed to its very limit. For the record, the suction valve is not a lift pump, hence the reason aftermarket electric lift pumps are common additions to ’01-’16 Duramax engines. While a lift pump isn’t 100-percent necessary to get to 500rwhp, there is a noticeable seat-of-the-pants feel at higher rpm on an engine equipped with one…and all the GM’s we’ve seen making 530rwhp had a FASS, Fuelab or AirDog system hanging along the frame rail.
Your 330-LB Stumbling Block (The Allison)
Ready for your first roadblock? Look no further than the Allison transmission. Although we’ve seen mint condition, stock Allison’s live at 500rwhp for a while (and versions graced with a TransGo shift kit last a little longer), none of them lasted forever. Simply put, there is no way around an eventual performance rebuild of any Allison automatic if you intend to run your race file. However, one way to ease the Allison’s workload is to start with the lightest overall package possible: a regular cab truck.
The Classic Body GM’s Biggest Secret: It’s Light!
Trust us, Duramax-powered trucks aren’t Fords, or even Rams. They are much lighter, especially prior to ’11 models, which were beefed up quite a bit in the frame and suspension department. We’re talking about a 6,600-pound proposition in a world where most diesel trucks weigh more than 7,500 pounds. As a bonus, a lighter curb weight is always easier on the transmission. So if you’re in a regular cab Duramax you’re in business. You can go faster than the extended cabs and crew cabs and your Allison will be happier while you do it!
Supporting The (530rwhp) Effort
Surprisingly, the fixed geometry factory IHI turbocharger—the smallest turbo to ever grace a Duramax—can live at power levels beyond 500rwhp. The key is to make sure boost never exceeds 30-31 psi, so don’t disable the wastegate. To be sure, the stock IHI is moving a lot of hot air at 500-plus horsepower, but heat isn’t what kills it. Overspeeding due to a small turbine wheel is the biggest concern with the IHI charger.
Because launching in four-wheel drive is a requirement for a tuned Duramax to hook at the track, make certain you add a set of tie-rod sleeves. Under big load and while working to provide maximum traction, GM’s independent front suspension has a tendency to toe in the front tires. This causes the tie rods to flex and can even lead to snapped tie-rod ends. Aftermarket tie-rod sleeves strengthen the factory tie rods considerably, eliminate toe-in and can be had on the cheap ($75 to $90).
Here, a pair of well-matched, Duramax-powered regular cab Silverado 2500’s storm through the quarter-mile in the mid 12’s. In addition to being aggressively tuned, both trucks were equipped with a lift pump, a 4-inch exhaust and a built Allison. Each truck was also sporting the stock turbo, CP3, fuel injectors and an internally-untouched engine. With both trucks also cutting high 1.7-second 60-foots on this pass, the race was won on the tree.
Looking to take your LB7 past a simple tune? Check out the Budget Mods list we put together for the O.G. Duramax here.