With nearly 15 years of production, the 6.6L Duramax V-8 found in GM trucks has proven itself to be a durable and dependable diesel. Throughout its lifespan, the Duramax has gone through several revisions to improve performance and drivability as well as reduce emissions. Internal changes to the latest Duramax, the 2011-2015 LML, include new connecting rods, pistons, additional emissions equipment and a variable-geometry turbocharger, all of which have raised output to nearly 400 hp. One piece that has remained virtually unchanged, however, is the Alternate Firing Camshaft, which can fail prematurely when subjected to undue stress, especially in a high-performance or competition application.
The aftermarket has done some incredible things with the 6.6L Duramax, pushing it to performance levels that were never imaginable. It’s not uncommon to see all-out drag racing and sled pulling trucks with engines producing 1,500 hp or more. Getting that kind of power is no easy task: Shops specializing in Duramax performance have had to get quite technical and come up with some rather ingenious products to make a motor live at those levels. One such company is Empire Diesel of Dubuque, Iowa. Empire Diesel quickly gained popularity on the competitive sled pull scene in the Midwest thanks to their custom-built engines and overall knowledge of the Duramax platform. With their sled trucks pushing 1,000 horsepower, they too ran into the limitations of the stock crankshaft.
Empire determined that the factory firing order of the Duramax engine could be causing major stress along the crankshaft plane. By creating a new camshaft profile that changes the firing order, they thought it would be possible to distribute the stress of combustion more evenly across the crank. We interviewed Chad Remakel, CEO of Empire Diesel, to learn more about the Alternate Firing Order camshaft, and our conversation revealed some very interesting technical knowledge about the inner workings of the Duramax diesel and what it takes to really push these things to the limit.
DIESEL WORLD: What’s the reasoning behind the Alternate Firing Camshaft order for the 6.6L Duramax?
CHAD REMAKEL: The main reason for modifying the Duramax firing order with the camshaft is to relieve stress on the front portion of the crankshaft in higher performance applications. The factory firing is 1-2-7-8-4-5-6-3, but this new camshaft design changes that to 1-5-6-3-4-2-7-8. Changing an engine’s firing order isn’t a new science, as GM gas guys have been doing it for years in with the LS engine 4-7 swap. It’s just something we wanted to try and help reduce part breakage in the Duramax application. Every engine platform within the Duramax family—including the LB7, LLY, LBZ, LMM and LML—suffers from these issues with the crankshaft breaking just behind the snout back to the #3 rod journal. We’ve seen these failures on everything from mildly modified daily drivers to full-blown competition engines with internally balanced aftermarket billet cranks. There is just something to do with the Duramax engines harmonics at higher rpm and bigger power levels that causes a lot of stress on the crank due to the factory firing order.
DW: When did Empire Diesel start to notice these problems and try to resolve them with this new camshaft design?
CR: In 2009 we continued to see Duramax crankshaft failures at around the 1000-horsepower mark. It seemed to be a roadblock we had to get around to push performance any further. We all sat down together to brainstorm, trying to come up with a simple and cost-effective way to make broken crankshafts a thing of the past. Looking at similar engine failures in our early performance gas engine background, these issues were more than likely related to harmonics and stress within the engine. There are only two legitimate ways to overcome that. One is to back down the power output, and the other is try to more evenly disperse that current stress across the crankshaft.
DW: When it came time to actually change the firing order, how did you determine the order for the injection events?
CR: Looking at our options for firing order really just took a pencil, paper and some pretty terrible drawing skills. We basically just had to connect the dots to see which pattern would distribute the stresses of each cylinder’s combustion event on the crankshaft most efficiently.
DW: Once the firing order was determined, was it just as simple as making a new camshaft and replacing the stock cam?
CR: In theory, yes, but it wasn’t quite that easy. Back then the major performance camshaft manufacturers were only up to speed with gasoline engines and wanted nothing to do with diesels. It was a pretty long, drawn-out struggle getting somebody to produce exactly what we were needing for what they referred to as a ‘limited market’ at a reasonable price. After months of calling and tons of legwork we finally had the first alternate fire order Duramax camshaft in our hands. This wasn’t the end, however, as we still needed to figure out how to get the ECM [engine control module] to recognize the change in camshaft profile. After some investigation we discovered all the ECM needed to initiate the firing order of the injectors was to see the trigger on the tone wheel. This trigger tells the ECM when it needs to fire the #1 cylinder injector, after that, the ECM doesn’t care in what order the remaining seven injectors fire. So if an injector signal was moved from its original intended firing location, as long as the moved injector signal matched the opening or closing strokes of valves in that particular cylinder the engine would run like factory.
DW: So what electronic changes are required to adjust the injector firing order when making this camshaft change?
CR: There are two ways to go about the electronics for this. One would be moving and extending your factory injector wiring harnesses and the other would be moving pin locations on the injection harness itself. We’ve heard that EFILive is currently working on new tables that will allow firing order changes to be done within their custom tuning software. However, even if this does become an option, while it would be easier, we’d still suggest making the change by doing the pin swap as there would be less risk of causing engine problems from the possibility of loading the wrong tune.
DW: After running this Alternate Fire Camshaft and selling to so many customers through the years since its inception, has your initial camshaft profile stayed the same or do you continue to try new things to improve performance and reliability?
CR: Over the past five years we have had great success with this process and helping to keep the Duramax crankshafts and engines alive. Some customers think this alternate firing order also better distributes air through the intake manifold for better combustion, but we haven’t been able to verify this. Since that early testing our camshaft profiles have become more aggressive and we now offer a Street or Competition version, along with being able to build a custom profile to fit a customer’s specific requirements. This past 2014 sled pulling season was very successful for us and our customers running our camshaft designs. While we would love to give specific examples of each of our customer’s accomplishments, many are competing against each other and we need to keep some of that information to ourselves. We have recently teamed up with Wagler Competition Products and have seen extremely impressive results when our cam profiles are paired with Jeremy Wagler’s Duramax cylinder head program.
DW: What kind of performance gains can be expected from making this camshaft change?
CR: In our early engine dyno testing in 2009-2010 we immediately noticed a much smoother idle along with a noticeable difference in engine tone at higher rpm. To date, the biggest horsepower we’ve seen from this camshaft over a stock cam is about 28 hp on the engine dyno. But this wasn’t developed with more horsepower in mind. We were really looking to improve durability at higher horsepower levels, which this technology has done. While this Alternate Fire technology has made major improvements when it comes to durability and pushing the horsepower limits of the Duramax platform, nothing is ever a sure thing. This camshaft design is not the “golden ticket” to guarantee your engine won’t fail, as your choice of other parts, assembly and tuning is just as vital. There are a few other little tricks we do to the engines we build in-house, but we can’t give away all our secrets.
DW: Are the alternate fire camshafts only required in full competition builds?
CR: We actually recommend making this conversion in any engine build from a mild towing and street application to our all-out 1,500-hp+ competition builds. We’ve seen completely bone-stock trucks come through our shop with broken crank snouts so we offer our Alternate Fire Camshaft in multiple profiles to suit each application. Our mild Street grind works in an otherwise stock motor with stock pistons, no valve reliefs required. These can help with the power and torque curve making the truck better to daily drive and tow with. Our more performance-oriented grinds get much more aggressive and require other engine modifications to work properly. We also offer the camshaft as a “blank” so it can be purchased and sent to your preferred engine builder or machine shop to accept the profile they prefer. DW