There are a lot of ways that having two of something is better than one. And with the testing we've been doing in the past year or so, turbos on a diesel truck fit that characterization.
We've done a few compound turbo tests, such as the LBMC project Dodge and a gen-2 24-valve Cummins in the recent past. Now we're focusing on what dual chargers on a brand-new Chevy LMM Duramax are capable of.
A little background: this '08 Chevy is owned by Dan Duffy. He pulls a 40-foot triple slide-out fifth-wheel travel trailer around various areas of the Pacific Northwest. While the stock '08 Duramax would pull the trailer just fine, just fine isn't good enough for Duffy. In fact, it's no where near enough.
Duffy took the crew cab dually to Powerlabs Diesel in Idaho Falls, Idaho. Powerlabs specializes in putting together custom power packages that match what the truck is used for and what the driver wants out of it. Powerlabs works with a few supplier companies to build turbo systems and custom transmissions, which it matches with its own custom tuning.
For Duffy, he wanted a lot of rear wheel horsepower, but usable power that could be put to work when towing big loads like his travel trailer. Duffy is not necessarily easy on his trucks, but can you blame him? It's a work truck, not a show truck.
For this application, Powerlabs installed an MPI (Maximized Performance, Inc.) compound turbo system. This particular system flows air at 105 pounds per minute, and broadens out the power and toque curve in a way that no single charger could match. In fact, we've included two dyno charts to show the difference between Duffy's MPI twin setup and a 520-horsepower Duramax on a single charger. Notice the differences in the power curves, and how the single charger peaks out and falls off sooner, especially on the torque line. The compound turbos make gobs of torque (the stuff you tow with) down low and holds it over a wide range on the chart. It's this torque curve that has admittedly gotten Duffy into a couple interstate drag races against a few muscle cars-with his 40-foot trailer in tow.
That's a lot of power to put through the drive train, especially with a load pulling back on the truck. To handle those issues, Powerlabs works with Adrenaline Performance to offer a custom Allison (Ford and Dodge applications also available) transmission that is built to hold over 700 rear-wheel horsepower. What's unique is that Powerlabs offers a one-year unlimited mileage warranty on this transmission. Sled pull with it, drag race with it, tow the snot out of it. If any issues arise with the transmission, Powerlabs will repair it no questions asked. How can they be so confident? First, this transmission package has been tested on heavily-abused trucks that have put out numbers in excess of 700rwhp in competition and driving applications. Cam Hulse of Adrenaline Performance builds these transmissions using triple-disc billet torque converters, clutch packs and valve body work, not to mention a few guarded secrets that give these Allisons a little more durability than most.
For fueling, this LMM Duramax has a completely stock fuel system. Stock single CP3, no lift pump, just the way it came from the dealership. That's the big difference between the first two generations of the Duramax and the LBZ and LMM-the latter has much better stock fueling capabilities.
Powerlabs did its own custom EFI Live tuning; building a map to maximize the twin turbos while keeping smoke output to a minimum (this also required a new exhaust system). The big dually can tow the 40-foot trailer at interstate speeds without cracking 1,100 degrees F on the pyrometer-something that can't be said of many stock Duramax trucks. The EFI Live tuning by Powerlabs is customized for each truck that comes through the shop. So whether you're running a big single, compounds, dual fuelers or whatever, you will leave with an optimized tuning program.
All of this exposure to compounds lately has us rethinking a few of the trucks we've built. Broad, linear power curves, quick spool-up and throttle response and low EGTs. next time around, we're going to double the fun.