If you're looking to really let your truck breathe, installing a 5 downpipe back exhaust 6.7 powerstroke kit is probably one of the most satisfying mods you can do. There is something about that deep, hollow rumble that just makes a diesel feel like a diesel. But beyond just the sound, there's a whole lot of physics going on under the truck that actually helps your engine live a longer, happier life.
Let's be real for a second: the factory exhaust on these trucks is built to be quiet and comply with a million different regulations. While it does its job, it's basically like trying to run a marathon while breathing through a straw. Opening things up with a 5-inch diameter pipe changes the game entirely.
Why Go Big with a 5-Inch System?
You might hear guys debating between 4-inch and 5-inch systems all day long. For most moderately tuned trucks, a 4-inch system is technically "enough" for the airflow. But we aren't just looking for "enough," are we? The main reason people flock to the 5 downpipe back exhaust 6.7 powerstroke is the resonance.
A 5-inch pipe has a much deeper, throatier tone compared to the 4-inch, which can sometimes sound a bit raspy at higher RPMs. If you want that classic "big rig" sound, 5-inch is the way to go. It gives the exhaust gases more room to expand and cool down, which brings us to the most important technical benefit: lower EGTs.
Keeping Your Cool with Lower EGTs
If you're towing heavy or running a spicy tune, heat is your biggest enemy. High Exhaust Gas Temperatures (EGTs) can wreck a turbo or hurt your engine over time. By swapping to a larger diameter pipe right from the downpipe back, you're reducing backpressure significantly.
The turbo can spool up faster because there isn't a wall of hot air pushing back against it. When that air can escape quickly, your engine doesn't have to work as hard to push out the spent gases. Most guys notice a drop of 100 to 200 degrees in their peak EGTs just by switching to a more efficient exhaust setup. That's a massive safety margin when you're pulling a 15,000-pound trailer up a steep grade in the middle of summer.
The Reality of the Installation
I'll tell you right now, fitting a 5-inch pipe under a 6.7 Powerstroke isn't always a "walk in the park." It's a beefy piece of metal, and things are tight under there. Most kits are designed to bolt right up to the factory hangers, but because the pipe is so wide, you have to be careful about clearance around the transmission crossmember and the spare tire heat shield.
One tip I always give: don't tighten everything down until the whole system is hanging in place. If you tighten the clamps as you go, you'll almost certainly find that the tailpipe is hitting the body or the leaf springs once you get to the end. Keep it all loose, get your clearances right, and then crank those clamps down.
Also, if you're doing this in your driveway, get the truck as high as you safely can. Maneuvering that long mid-pipe section is a lot easier when you aren't constantly hitting your elbows on the pavement.
Stainless Steel vs. Aluminized
When you're shopping for your 5 downpipe back exhaust 6.7 powerstroke, you'll usually have to choose between aluminized steel and stainless steel (usually 409 or 304 grade).
- Aluminized is the budget-friendly choice. It's great if you live in a dry climate like Arizona or West Texas. It'll last a good while, but once that aluminum coating gets scratched or chipped, it's going to rust.
- 409 Stainless is the middle ground. It'll get a brownish surface oxidation over time, but it won't rust through. It's perfect for most people who deal with a bit of rain or light winter weather.
- 304 Stainless is the top-tier stuff. It stays shiny (mostly) and won't rust even in the salt-heavy regions. If you plan on keeping the truck forever and you live in the "rust belt," just bite the bullet and go 304.
The "Drone" Factor
We have to talk about the drone. Some guys love hearing their truck all the time; others want to be able to have a conversation in the cab without shouting. A straight-piped 5-inch system is going to be loud. It's going to hum at highway speeds.
If you do a lot of long-distance driving, you might want to look for a kit that includes a high-flow muffler. A 5-inch muffler won't restrict your flow much, but it'll take that "ear-stabbing" edge off the sound and help eliminate the highway drone. You still get the deep growl when you step on it, but your ears won't be ringing after a four-hour road trip.
Performance Gains and Fuel Economy
Don't expect the exhaust alone to turn your truck into a dragster. While you might see a slight bump in horsepower and torque—mostly due to the turbo spooling quicker—the real gains come when you pair the exhaust with a proper tune.
As for fuel economy, it's a bit of a mixed bag. In theory, reducing backpressure makes the engine more efficient, which should lead to better MPG. In reality, most guys (myself included) can't stop stepping on the pedal just to hear the new exhaust note. If you can keep your foot out of it, you might see a 1-2 MPG improvement, but don't count on it as your primary reason for the upgrade.
What About the Downpipe?
The "downpipe back" part of the name means the kit starts right after the factory downpipe. On the 6.7 Powerstroke, the stock downpipe is actually pretty decent, but some people choose to replace that too. If you're already under there getting dirty, it's worth checking if you want a full "turbo-back" system. However, for 90% of owners, the 5 downpipe back exhaust 6.7 powerstroke provides the best balance of performance gains versus installation headache.
Making the Final Call
At the end of the day, putting a 5-inch exhaust on your 6.7 is about making the truck yours. It gives the Ford a much more aggressive presence. When you start it up in the morning, people are going to know there's a real engine under that hood.
Before you buy, just make sure you check your local regulations. Every state and even some counties have different rules about what you can and can't do to your exhaust system. It's always better to know the rules before you spend your hard-earned money and spend a Saturday afternoon under the truck.
If you're looking for that perfect mix of lower engine temps, a killer sound, and better throttle response, you really can't go wrong here. It's one of those mods where you'll finish the job, start the truck, and immediately realize it was worth every penny. Just make sure you get some high-quality clamps—nothing ruins a nice exhaust setup like a leaky joint that soot-stains the underside of your beautiful truck.
Happy wrenching, and enjoy that new sound! It's going to make every drive a lot more fun, whether you're just heading to the grocery store or hauling a heavy load across the state line. There's just something about a 6.7 with a 5-inch pipe that sounds "right."