Why Diesel Trucks Have Huge Exhausts

The coffee can exhaust pipe is a trademark of our era. From boosted sport compacts to coal-rolling diesel trucks, big exhausts make a visual and auditory statement. Modern diesel trucks utilize turbo-chargers to produce tremendous torque and horsepower. This also results in exhaust gas temperatures exceeding 1,000 degrees when pulling heavy loads. Stock exhausts on diesel trucks have grown from 3 inches to 5 inches to allow the turbos to breathe and expel scorching hot gases. Aftermarket exhaust kits can take pipe diameters to 7 or 8 inches. Does a monster pipe deliver real performance, or is it just for show? Here are the facts.

What’s With the Wings?

Image via Flickr by truckhardware

Image via Flickr by truckhardware

Modern turbo-diesel trucks often have exhaust tips with vents. Why? The gases coming out of a turbo-charged diesel engine can be hot enough to melt a bumper, damage a trailer, or start a forest fire. By allowing cool air to enter the exhaust before the end of the pipe, the Exhaust Gas Temperature (EGT) can drop by 50 degrees or more. That’s why trucks from the Big Three have extra large vented exhaust tips. The exhaust itself is not oversized until the end, where the extra volume helps cool escaping gasses.

Are Stove Pipes Better?

Image via Flickr by Aaron Rome

Image via Flickr by Aaron Rome

You could remove the factory pipes and replace them with something Abraham Lincoln would wear. Monster vertical 7-inch stacks can’t be ignored, but do they improve performance? A curious thing happens when a diesel turbocharger gets rolling. The exhaust removes gases so the turbo can continue to breathe. The faster the gases chug through the engine, the faster they continue to move with no extra effort from the vehicle. A big exhaust makes it easy for air to pump through the system, leading to increases in both power and efficiency. Sound and style are both factors, however. Your ride is an extension of yourself. Your truck should shout: “Hey, this is me.” If a 4-inch exhaust gives you sufficient power but the song of an 8-inch pipe makes you smile, then smile.

What’s the Perfect Size?

Image via Flickr by truckhardware

Image via Flickr by truckhardware

Millions of dollars and numerous engineers designed the powertrain of your truck. If a huge exhaust makes the truck better, why didn’t they make it stock? Truck manufacturers can’t craft a machine just for you. They must satisfy the EPA, the critics, and conservative drivers. Not everyone wants a snorting torque-beast; most truck buyers prefer a vehicle that won’t wake the neighbors. They need to pass emissions, and they’d rather drive a mellow 200,000 miles than race like there’s no tomorrow. That’s why the factory builds the truck with a modest exhaust and tunes it to perform politely. Do you need a bigger exhaust? A slight increase from OEM will give a boost in power and economy, but you don’t need to build a cannon under your bumper. With more power comes higher temperatures and a greater need for the truck to breathe. Jumbo exhaust tips are here to stay.