4″ vs 5″ Exhaust: How to Choose the Right Exhaust Size for Your Diesel

If you’re thinking about upgrading your diesel truck, you might want to take another look at your exhaust pipe. The tailpipe controls the flow of exhaust coming out of your vehicle.

The faster the exhaust flow, the more power your truck will produce, but lots of trucks aren’t designed to be fitted with a larger exhaust.

The size of the exhaust pipe will also affect how much sound your truck makes on the road. Most drivers will purchase an exhaust kit when upgrading the tailpipe. You may need to purchase additional diesel parts to accommodate the upgrade.

4” vs 5” Exhaust

Learn more about this important decision and whether or not it’s a good choice for your vehicle.

4” Exhaust

Most vehicles come with a 4” exhaust, which is considered the standard in the diesel industry. But you can still upgrade your 4” exhaust depending on what you want your truck to do. Aftermarket 4” exhaust kits can improve performance or change the way the exhaust flows out of your truck.

5” Exhaust

The 5” exhaust is an aftermarket addition that increases the flow of exhaust coming from the engine. It is generally much louder and more powerful than the 4” exhaust, but not all trucks can be equipped with such a wide exhaust.

Performance

The truth is upgrading your exhaust may not have any impact on performance or power at all. That’s because most diesel trucks come with either 3” or 4” downpipes that limit how much exhaust is flowing from the tailpipe. If you upgrade to a 5” tailpipe but your downpipe is only 3” wide, you’re basically carrying around a larger exhaust system for no reason.

The exception is Duramax. These trucks don’t have a lot of space in between the engine and cab, so the downpipe is essentially flattened to a 3” full bore downpipe, which limits how much exhaust flows out of your truck.

Upgrading the exhaust on a Duramax can have a major impact on performance. Increasing the diameter of the pipe will let more exhaust flow out of the tailpipe at one time. It also reduces the temperature of the exhaust gas, which reduces wear and tear.

This will do wonders for your exhaust gas recirculation (EGR) cooling system, which is designed to reduce exhaust gas temperatures to limit NOx emissions. You won’t have to replace your EGR coolers as often with a larger exhaust.

For example, the EGR cooler tends to be particularly problematic on the 6.7L Powerstroke. Ford trucks can’t fit anything larger than a 4” exhaust but upgrading the system can help you preserve your EGR cooler.

The same is true of the Cummins 6.7. Exhaust flow and EGR cooling often go hand in hand. Find replacement 6.7 Cummins EGR coolers online to improve flow in your new exhaust system.

Enhanced Performance

A typical aftermarket exhaust can improve power by anywhere from 2% to 5% as long as you are using the right make and model. The 4” exhaust tends to be the preferred choice for 450-500 HP applications.

They also produce more bottom-end torque compared to the 5” exhaust. But you may need to use the 5” if you are running above 500 hp.

If you’re using a heavy-duty turbocharger, you might want to invest in a turbo-back exhaust system to improve performance. The turbo increases the amount of air going into the combustion chamber, which means the engine needs to send more air out of the engine.

The turbo-back essentially replaces your existing exhaust system and downpipe. It links directly to the turbo to increase the volume of gases leaving the exhaust.

Some turbo backs need to be wrapped in special materials that can withstand the heat coming from the turbo. Installing a turbo back can be expensive, considering all the parts that need to be replaced.

Fuel Efficiency

Upgrading to a 4” or 5” tailpipe can also help improve fuel efficiency. Aftermarket pipes come with smooth, mandrel bends and a high-flowing muffler or muffler replacement pipe to create a “straight pipe” system that reduces fuel consumption and improves engine performance.

Straight pipe systems reduce backpressure coming from the engine to let the exhaust gas flow freely out the tailpipe.

An aftermarket exhaust can improve fuel economy by as much as 3%. That may not sound like a lot, but you can save several thousand dollars a year by optimizing the way your vehicle releases and dispenses exhaust.

Sound

Nothing changes the sound of your truck like adding a new exhaust. The 4” exhaust is much quieter and produces little to no drone, and your neighbors will likely thank you for keeping the sound to a minimum.

It produces a higher-pitched sound compared to the 5” exhaust. The latter is much louder with more drone that is bound to turn heads pretty much wherever you go.

Upgrade Considerations

Upgrading your exhaust can help you make the most of your truck, but larger isn’t always better. You may not need to go as large as a 5” tailpipe unless you have a serious turbo with the horsepower to prove it.

Consider talking to a professional that will inspect your existing exhaust system before making any changes. They will help you choose the right upgrade for your vehicle based on your priorities.

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