If you're looking for the single best way to wake up that S63 engine, swapping out those restrictive stock units for some high-flow f90 downpipes is probably the first thing you should do. The BMW M5 is a masterpiece right off the showroom floor, but let's be honest—BMW had to play by the rules. They had to meet noise regulations, emission standards, and keep the car refined enough for someone who just wants a fast daily driver. But if you're the type of person who wants to hear the turbos whistle and feel the full weight of that twin-turbo V8, those factory catalytic converters have to go.
Taking the Muzzle Off the S63
The S63 engine is a beast, but it's a beast wearing a muzzle. Stock f90 downpipes are packed with dense honeycomb material designed to scrub emissions. While that's great for the environment, it's a nightmare for exhaust flow. When you're pushing a car that makes 600+ horsepower, backpressure is your worst enemy. It builds up heat right at the turbochargers and slows down the spool time.
By switching to aftermarket f90 downpipes, you're basically opening up the throat of the engine. The turbos can spin up much faster because there's nothing standing in the way of the exhaust gas leaving the housing. You'll notice the difference almost immediately in how the car responds when you tip into the throttle. It feels less like a heavy executive sedan and more like the supercar killer it was meant to be.
The Sound You Actually Wanted
Let's talk about the sound, because that's why most of us start looking at f90 downpipes in the first place. The stock M5 sounds good, sure, but it's a bit muted. Even with the sport exhaust option, it doesn't quite have that "get out of my way" growl that a V8 should have.
When you install a set of catless or even high-flow catted downpipes, the transformation is pretty wild. You get a deeper, more mechanical tone. You start to hear the turbos spooling up and down, which is a sound that's almost entirely hidden by the factory setup. And when you let off the gas? The pops and burbles are significantly more pronounced. It doesn't just sound louder; it sounds more expensive, like a GT3 race car rather than a luxury cruiser.
Catted vs. Catless: The Big Decision
This is usually where people get stuck. You have two main choices when picking out your f90 downpipes: catted or catless.
Going Catless
Catless pipes are exactly what they sound like—just a hollow tube from the turbo to the rest of the exhaust. These offer the maximum performance gains and the loudest sound. However, there are a couple of trade-offs. First, you're going to get a "Check Engine Light" (CEL) almost immediately because the car's computer thinks the catalytic converters have failed. You'll need a tune to code that out. Second, there's the smell. Without cats, the exhaust will smell like raw gasoline. Some people love that "race car" smell, but if you're taking your spouse out to dinner in your M5, they might not be as thrilled about it.
High-Flow Catted Options
If you want to keep the car a bit more "civilized," high-flow catted f90 downpipes are the way to go. These use a much less restrictive metal core compared to the stock ceramic ones. You get about 80-90% of the performance and sound gains of a catless setup without the heavy smell. Some high-end catted pipes even claim to not trigger a CEL, though that can be hit or miss depending on how sensitive your car's sensors are. It's the "best of both worlds" choice for a daily driver.
Heat Management and Turbo Longevity
We often talk about power, but we don't talk enough about heat. The stock catalytic converters sit right up against the turbos. They get incredibly hot because they're designed to "light off" and burn fuel vapors. That heat soaks into the turbochargers and the engine bay.
By installing f90 downpipes, you're moving that heat away from the engine much faster. Lower EGTs (Exhaust Gas Temperatures) are always a good thing for engine longevity. When the turbos stay cooler, the air going into the engine stays cooler, and the car is less likely to pull timing during hard driving. It's one of those rare mods where you get more power and, in some ways, a healthier environment for your turbos.
Do You Need a Tune?
Technically, you can bolt on a set of f90 downpipes and drive the car. It'll run, and it'll sound better. But you really aren't getting your money's worth without a tune. The factory ECU is programmed to work within the parameters of the restrictive stock pipes. When you remove that restriction, the car can handle a lot more boost and more aggressive timing.
A "Stage 2" tune is specifically designed for cars with upgraded downpipes. This is where the magic happens. On an F90, a tune plus downpipes can easily push the car into the 700+ horsepower range on pump gas. Without the tune, you're leaving a massive amount of power on the table, and you'll be staring at a yellow engine icon on your dashboard every time you drive.
The Reality of Installation
I'll be honest with you: installing f90 downpipes isn't exactly a "quick Saturday morning job" if you've never done it before. The F90 engine bay is packed tight. Everything is layered, and the downpipes are tucked in there behind heat shields and various lines.
If you're a seasoned DIYer with a lift and a good set of tools, you can definitely tackle it. But for most people, this is a job for a professional shop. You have to be careful with the oxygen sensors—they're easy to damage and expensive to replace. Plus, getting the v-band clamps to sit perfectly can be a bit of a headache. If there's even a tiny leak, you'll hear a ticking sound that will drive you crazy until you fix it.
Is It Worth It?
If you're serious about modding your car, f90 downpipes are probably the best bang-for-your-buck modification you can buy. They unlock the personality of the S63 engine in a way that an intake or a cat-back exhaust just can't.
Yes, there are things to consider, like emissions testing and the potential for a louder cold start (your neighbors might not love you at 7:00 AM). But the first time you hit an on-ramp and hear that V8 scream without any restriction, you'll realize it was worth every penny. The car feels lighter on its feet, the throttle response is crisp, and the soundtrack finally matches the performance.
At the end of the day, the M5 is a legendary platform. It deserves to be heard. Whether you go with a high-flow catted set for a refined growl or a full catless setup for maximum aggression, upgrading those downpipes is the key to unlocking what the F90 is truly capable of. Just make sure you're ready for the extra attention, because once those pipes are on, people are definitely going to notice when you arrive.