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> Diesel Exhaust Systems Research Guide

Diesel Exhaust Systems Research Guide

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Performance Diesel Exhaust versus Factory Diesel Exhaust

The factory exhaust on your diesel truck is functional, but then again so was the Pontiac Aztek. To gain the maximum performance, efficiency, and sound from that Powerstroke, Cummins, or Duramax, getting rid of the OE exhaust is a great place to start.

The major advantage that a performance diesel exhaust system, such as a Magnaflow exhaust system, has over a factory system is the ability to move exhaust flow more easily, creating less strain on the engine to push the exhaust through the system. Increased flow is achieved by two primary methods. First, using mandrel bent tubing creates a consistent diameter for full-flow of exhaust, where pinched tubing has points of high-pressure, reducing flow. Second, large diameter tubing allows for greater volume to travel through the system with less back-pressure, which in turn helps reduce turbo-lag.

Also, a larger diameter tubing is going to create that awesome, deep growl that every diesel truck owner is after. A good rule of thumb is that a larger exhaust will create a deeper tone, while a split-dual system will create more of a throaty tone closer to a gasser.

Aluminized Steel versus Stainless Steel

Another area in which performance exhaust systems outpace the systems used by the factory are the materials used. A vast majority of performance diesel exhausts are constructed using T-409 or T-304 stainless steel. Stainless steel is very durable, corrosion-resistant, and looks much better than the aluminized steel. Due to lower production cost, aluminized steel is commonly used by automotive manufacturers and what you’re most likely to find at the local parts store. While sound and performance are not affected by using aluminized tubing, a stainless steel exhaust system is going to outlive the truck – even in northern climates where rust is common.

What’s the difference between aluminized and stainless steel? Aluminized steel very similar to galvanized steel. Instead of being coated with zinc, the steel is coated in an aluminum-silicon alloy which makes it more resistant to corrosion than steel alone would be. Stainless steel is an alloy created by combining steel with chromium, nickel, and other elements. The combination and ratio of these other elements is what determines the grade.

T-304 versus T-409 Stainless Steel

Stainless steel owes its superiority thanks to the addition of chromium and nickel. T-409 is the most common type used for performance exhaust systems due to its balance of corrosion resistance and reasonable cost. T-304 stainless steel is a higher grade that carries with it a higher cost. While this is a fine material for cookware, it isn’t necessary for exhaust systems.

The main difference between T-409 and T-304 stainless steel is the chromium and nickel content. While T-409 contains approximately 11% chromium and 0.5% nickel, T-304 contains approximately 18% chromium and 8% nickel. Either way, your oil-burner’s sweet exhaust system will outlive your truck.

If your exhaust system includes a polished stainless steel tip, keep it looking great by washing it when you wash your truck. Over time they may take on a bronze hue or lose some luster. While regularly washing them helps prevent this, 3M chrome and metal polish does a great job of restoring them.

DPF-Back, Cat-Back, Downpipe-back, and Turbo-Back explained

Here we will review the different types of diesel exhaust systems

DPF-Back and Cat-Back

DPF-back exhaust systems are the most common for newer diesel trucks. In this setup, the exhaust system replaces everything behind the diesel particulate filter to the tailpipe. A cat-back exhaust system is the same setup. The only difference being 2007 and newer trucks use a diesel particulate filter while some pre-2007 trucks use a catalytic converter. So for a cat-back system, everything behind the catalytic converter is replaced.

Downpipe-Back and Turbo-Back

A downpipe-back exhaust system replaces everything behind the downpipe. Since many pre-2007 trucks don’t have a catalytic converter, this is a very common style. Keep in mind that if your truck has a DPF or catalytic converter, removing them is not legal for registered vehicles.

The only difference between turbo-back and downpipe-back exhaust system is the inclusion of the downpipe itself. Both will create similar gains in power and efficiency, with a turbo-back system getting a slight advantage because of a wider-diameter, performance downpipe.

Turbo-back systems are going to win in a performance competition with a cat-back or DPF-back. For trucks with a DPF or catalytic converter, the only drawback of a turbo-back or downpipe systems is that they are not legal. If a truck or SUV was originally equipped with a catalytic converter or DPF, then installing a turbo-back or downpipe-back system will make the truck only suitable for off-road use.

What is a DPF?

Starting in 2007, diesel trucks used for on-highway applications are required to have exhaust treatment system that reduces emissions by screening out large particulate matter. A diesel particulate filter (DPF) is designed to physically filter soot from the exhaust flow, and then a regeneration process removes the accumulated soot. It’s during this process that exhaust temperatures are need to be at 932°F or higher.

Diesel particulate filters were required starting for model year 2007 trucks, while some pre-2007 models used catalytic converters. This doesn’t mean that the catalytic converter don’t exist in a post-2007 diesel truck, they’ve just been transformed a little bit. The purpose of a catalytic converter is to convert gases such as CO and NOx (carbon monoxide and nitrogen oxides) into less harmful CO² and H²0 (carbon dioxide and water) - basically removing some of the soot (unburnt fuel) by burning it before hitting the tailpipe. A DPF actually filters the soot like an air filter. Which is self-cleaning with a catalyst and/or a PCM-induced cleaning cycle to heat up the filter and burn away what it has collected.

Intercooled Exhaust Tips

Intercooled exhaust tips are often associated with diesel exhaust systems, and there is a very good reason to why this is so common. Diesel exhaust is hot; much hotter than exhaust created in a gasoline engine. In 2007, with the implementation of diesel particulate filters (DPF) to reduce emissions, temperatures skyrocketed. For the regeneration process to work within a DPF, the internal temperature must hit at least 932°F. Well, driving around blasting out 1,100°F exhaust is going to cause some issues, like burning people shins and starting forest fires. This is where the intercooled exhaust tips come into action. Louvers at the base of the exhaust tip pull in outside air, which mixes with exhaust, and in turn dramatically lowers the exhaust temperature exiting at the tip.

Diesel Exhaust Muffler – Need it or Not?

In terms of exhaust, diesel engines are just naturally quieter engines than a gas truck, and that’s why you can get away with running without a muffler. Chances are you’ve run a gas-powered car or truck without a muffler in the past and while it probably sounded pretty cool, the sound can be quite annoying in the cab (and your neighbor’s house). With a diesel engine, you’ll actually have an aggressive, yet pleasing tone with a low risk of droning. While most opt to use a muffler to ensure there is no droning, it’s a matter of personal preference. But at least you have the option.