Finding the right honda 400ex exhaust systems can feel like a bit of a rabbit hole once you start looking at all the different pipes, headers, and canisters available online. Let's be honest, the stock exhaust on a 400EX isn't exactly a masterpiece of engineering. It's heavy, it's quiet—maybe a little too quiet for some—and it definitely holds back the engine from breathing like it actually wants to. If you've spent any time on the trails or at the dunes, you know that a "corked up" engine just doesn't have that snap you need when you're trying to loft the front wheels over a log or blast up a steep face.
Upgrading your exhaust is basically the "Day 1" mod for most owners. It's the easiest way to wake up that reliable old air-cooled thumper and give it some personality. But before you go out and drop a few hundred bucks on a shiny new pipe, there are a few things you should probably think about so you don't end up with a quad that's too loud for your neighbors or a setup that actually kills your bottom-end torque.
Why Even Swap the Stock Pipe?
The main reason people look into honda 400ex exhaust systems is performance, obviously. The stock system is designed to meet strict noise and emission standards, which usually means it's pretty restrictive. When you swap it out for an aftermarket setup, you're essentially letting the engine exhale more efficiently. This usually results in a noticeable bump in horsepower and, more importantly for a quad like the 400EX, a lot more throttle response.
Weight is another big factor. The OEM muffler on a 400EX feels like it's made of lead. Most high-quality aftermarket slip-ons or full systems are made from aluminum or stainless steel, which can shave off several pounds. It might not sound like much, but when you're tossing the quad around in tight corners, every bit of weight reduction helps. Plus, let's face it, the stock pea-shooter look isn't doing anyone any favors. A nice brushed aluminum or carbon fiber canister just looks better.
Slip-On vs. Full System
This is the big debate most riders have when they start shopping. Do you just buy the muffler (the slip-on) or the whole kit and kaboodle (the full system)?
Going with a Slip-On
If you're on a budget or just doing casual trail riding, a slip-on is usually plenty. It replaces the heavy stock muffler but keeps the factory header pipe. You'll get the improved sound and a bit of a power bump in the mid-to-high RPM range. For a lot of people, this is the sweet spot because it's cheaper and way easier to install. You just unbolt the old can, slide the new one on, and you're mostly good to go.
Stepping Up to a Full System
A full system includes a new, larger-diameter header pipe along with the muffler. This is where you really see the power gains, especially if you've done other mods like an intake or a high-flow air filter. The factory header on the 400EX is actually decent, but it has its limits. If you're planning on doing a big bore kit or aggressive cams later on, don't waste your time with a slip-on—just go for the full system now. It ensures that the entire "breathing" process of the engine is optimized from the cylinder head all the way to the back.
The Big Names in the Game
When you start browsing for honda 400ex exhaust systems, a few brands are going to pop up over and over again. Everyone has their favorite, and it usually comes down to what kind of sound and power delivery you're after.
FMF Racing is probably the most common. Their Powercore 4 is a staple in the ATV world. It's loud, it's punchy, and it's usually pretty affordable. If you want that classic "thumper" bark, FMF is a safe bet. They also make the Q4 series if you need to keep the noise levels down for state parks or sensitive riding areas.
HMF Engineering is another huge player. Their Performance Series is famous for having a deep, growly tone that sounds absolutely mean on a 400EX. One cool thing about HMF is they offer a ton of different color options for the canisters and end caps, so you can actually match the pipe to your quad's plastics or frame.
Curtis Sparks is the "old school racer" choice. Many 400EX purists swear by the Sparks X-6. It's widely considered one of the best-performing pipes for this specific machine, especially if you're looking for top-end speed. It's loud though, so don't say I didn't warn you.
Yoshimura is known for incredible build quality. Their systems fit perfectly and the finish is usually top-tier. They tend to be a bit more expensive, but you really get what you pay for in terms of durability and a refined exhaust note.
Don't Forget About Jetting
Here is the part where people usually mess up. If you change your exhaust, you must check your carb jetting. You're letting more air out, which means the engine is going to run "lean" (too much air, not enough fuel) if you leave the stock jets in the carburetor.
A lean engine runs hot, pops on deceleration, and can eventually cause some serious damage to your valves or piston. Usually, when you buy one of the popular honda 400ex exhaust systems, the manufacturer will give you a baseline recommendation for jetting. You'll probably need to go up a size or two on the main jet and maybe adjust the needle clip position. It's a bit of a pain to pull the carb, but trust me, the quad will run a thousand times better once it's dialed in correctly.
Noise Levels and Spark Arrestors
We've all been there—that one guy at the ride spot with a pipe so loud it makes your ears bleed from fifty yards away. Don't be that guy. While we all love a good-sounding machine, many public riding areas have strict decibel limits.
When picking out your exhaust, check if it comes with a removable spark arrestor. Not only does this help keep the noise at a reasonable level, but it's actually a legal requirement in most National Forests and state-managed trails. If a ranger catches you without one, they can hit you with a hefty fine. Most systems from FMF or HMF allow you to swap inserts in and out, which is great because you can run it "open" at the MX track and "quiet" on the trails.
A Few Installation Tips
Installing most honda 400ex exhaust systems is pretty straightforward, but since these quads are getting a bit older, you might run into some crusty hardware. Here are a couple of things that might save you a headache:
- PB Blaster is your friend: Those header bolts have been heat-cycling for years. Spray them down with a penetrating oil the night before you plan to do the swap. The last thing you want is to snap a stud off in the cylinder head.
- Get a new gasket: Don't try to reuse the old crushed copper gasket at the head. They're cheap, and using a new one ensures you won't have a pesky exhaust leak that makes your quad sound like a lawnmower.
- Spring pullers: If your new system uses springs to hold the sections together, get a cheap spring puller tool. Using pliers is a great way to slip and gouge your brand-new shiny pipe (and your knuckles).
Making the Final Call
At the end of the day, the "best" exhaust for your 400EX depends on your budget and where you ride. If you just want a bit more "umpf" and a better sound for weekend trail rides, a slip-on from a brand like FMF or Big Gun will do the trick perfectly. If you're building a dedicated sand or track machine and want every ounce of power, go for a full system from Sparks or Yoshimura and spend the extra time getting the jetting perfect.
Whatever you choose, it's going to make your 400EX feel like a brand-new machine. There's nothing quite like that first ride after a pipe swap where the quad finally feels alive. Just remember to keep an ear out for how the engine is running and maybe keep a few extra spark plugs handy while you're tuning the carb. Happy riding!