Spooling Up While Keeping Cummins EGT Down
Diesel enthusiasts know that aftermarket tuners and electronic modules deliver more fuel to the engine in order to increase performance-up to a point. Dodge Cummins owners, in particular, find their stock Holset turbo is quickly overtaxed when fuel is added. Exhaust gas temperature (EGT) can climb rapidly and almost uncontrollably on modified Cummins trucks. The factory recommends keeping the EGT (measured by a probe installed into the exhaust manifold) in the 1,300-1,450 Fahrenheit range, even in extreme conditions. These limits are easily exceeded by the stock turbo system, especially when towing heavy trailers or adding a lot of fueling for more power.
Aftermarket solutions to this problem have centered on fitting larger turbos from medium-duty Cummins applications, such as semi-trucks or buses, to the 5.9L Ram powerplant. Potential turbo lag is the major compromise to this approach. To keep EGT low at full power, a turbo that is too large is installed, and the truck owner is forced to live with a setup that won't build boost, or spool up, anywhere near as quickly as the stock turbo did. Furthermore, on the computerized Cummins turbodiesel engines, the computer withholds fueling because boost is low, further hurting performance. When an aftermarket fueling box overrides this limitation from the engine's computer, billowing clouds of smoke appear because large amounts of fuel won't be burned properly at low boost levels.
No-Compromise Engineering
Engineers have a difficult time designing a turbocharger that builds boost quickly without exceeding a reasonable boost limit (over-boosting), especially under heavy loads with large fueling increases over stock. Over-boosting is a serious problem that can cause intercooler boots to blow off or leak, the intercooler to split open, or the head gasket to fail. Further, if the accelerator pedal is side-stepped or released quickly while the turbo is being over-boosted, the turbo instantly ceases to build boost and barks when the boost air tries to kick it backward as the compressed air rushes back into the turbo from the discharge side. This barking frequently destroys stock-application turbos.
Edge Products has spent about two years developing a solution. Although the company specializes in fuel-management electronics, the R&D department realized that a hard-part solution was needed, particularly for Dodge Cummins that tow heavy loads. Lessons learned from a still-in-development Wolverine tube-framed drag truck also had a bearing on the new Edge BB turbo for the Cummins.
The Edge ball bearing turbo achieves the difficult balance between increasing airflow for lower EGT while spooling up quickly through its proprietary housing design. The Edge turbo spools almost as quickly as the stock turbocharger, but total boost (even with large fueling increases) isn't much more than stock-around 35-38 psi. The housing's internal size supports much greater airflow than the stock turbo without incurring turbo-lag or over-boosting penalties. Should strong barking occur, the housing's materials are robust enough to resist damage.
Further, standard turbochargers have bronze sleeve bearings. They are adequate for stock applications. At high boost, combined with dirty or contaminated oil, and with the possibility of hot shut-downs, ball bearings show a tremendous advantage. The only trade-off is the higher initial cost. Waiting until the EGT drops to 300 degrees before shutting off the engine isn't always possible or convenient, and shutting down at higher temperatures is hard on the turbocharger because the engine oil tends to coke up inside. Sleeve bearings are much less tolerant of this situation. The premium-quality ceramic ball bearings used in the Edge BB turbo maximize durability under extreme conditions, including heavy towing.
In summary, many turbos were blown up while R&D'ing the Edge BB. However, Edge feels it ultimately came up with an attractive, minimal-compromise system for Cummins-powered Rams that improves performance where owners need it most: in towing and heavy-load situations. Not only does this turbocharger easily support the fueling increases afforded by aftermarket enhancements, it adds 25 hp to the stock fueling levels. While not designed to serve ultra-modified motors making more than 525 hp, the Edge BB is built to tow.