On a rare occasion, the cool factor can set the bar for function. This is definitely the case with Rolling Big Power's (RBP) new Turbo Back exhaust system. The exhaust on our Duramax provided excellent power, but it was hard on everything behind it. The side-exit exhaust would coat not only the paint in front of the rear tire but the rim, the tire, the spring pack, and the shock on the passenger side in soot. This took some of the fun out of the exhaust, because cleanup was always a rag-wasting bummer.
RBP has been developing exhaust systems and other diesel performance goods for the past five years. Recently, the company has come out with an after-turbo exhaust system that exits in the center of the truck, just behind the rear differential. A 4-inch stainless steel downpipe is flanged to couple directly to the turbo. It uses mostly stock exhaust hangers up till the free-flowing muffler, and then the exhaust bends into the center of the truck and exits above the center of the diff.
Most stock trucks splay the left and right shocks to help manage wheelhop as well as standard suspension action, with one leaned forward and mounted to the front of the diff tube, and one laid back, mounted to the back of the diff tube. Many aftermarket suspension setups relocate the shocks symmetrically on the rear of the differential tube. RBP's center-exit exhaust is perfect for lifted trucks that relocate the shocks like this, because it reroutes the exhaust away from the shock mounting locations. Another great fact of RBP's new exhaust is it looks sick on a lifted truck, and it exhales the diesel exhaust away from the suspension, body, and rims.
So, how does this exhaust raise the bar on performance exhaust? It works, that's how. The center-exit exhaust has unnecessary bends that add to the backpressure-reducing exhaust speeds and increasing turbo lag, right? That's almost true. Some backpressure is needed to prevent the combined cylinder combustions from creating an exhaust pulse. The pulsing wouldn't apply a steady pressure to the turbine wheel, reducing the turbo's efficiency. RBP's exhaust increases the tubing size all the way from the turbo downpipe and outward, providing more volume. The two bends it takes to place the exhaust in the center of the differential, along with the muffler, supply an excellent balance between low-speed spooling and high-speed huffing.
Turbo wastegates are electronically operated on all new passenger turbodiesels, so the system didn't make more boost over our short side-exit exhaust. The most notable changes are the turbo came up on pressure a bit faster and the average exhaust temperature was about 175 degrees cooler. This was largely due to the replacement of the stock downpipe and the increase in overall exhaust flow. This increases low-speed power, because most stock engine management programs force the fuel system to defuel on low boost. An increase in the flow spools the turbo faster, reducing defuel time and increasing midrange power.
We didn't dyno this scenario for comparison, because we didn't expect to see a gain in power. It was more about relocating the exhaust for suspension work, and controlling the soot mess from our truck was the original focus. One thing's for sure, the RBP Turbo Back exhaust system does those two things, plus it provides turbo response, enhances power, and looks sick with the 18x5-inch mirror-polished stainless RBP tip.
1. The side-exit exhaust...
1. The side-exit exhaust on the truck was configured to exhale the diesel exhaust gases right in front of the rear wheel. Even though this exhaust made good power, it made cleanup significantly less desirable and kept our garage rag reserve in a constant state of despair.
2. You never know what to...
2. You never know what to expect when you get work done to your truck. Two exhaust hangers were added to fit this high-flow, shorty exhaust to our Duramax. The last hanger was welded right to the bottom of the framerail in plain view. This not only looked bad, but the welds looked like ABC gum-not to mention they welded to the frame, instead of a crossmember. You want to weld as little to the frame as possible, especially for something as trivial as an exhaust hanger.
3. The wide band clamps...
3. The wide band clamps used to hold the tubing together were tacked in place, but the bolts had started to back off, allowing our killer exhaust to leak at every coupling.