BMW's S55 engine comes from the factory with excellent power and torque for its small 3.0L design. However, for some, it's simply not enough. Bolt-on mods are a popular option to push the S55 engine to 600+WHP. Upgraded downpipes (DP's) are one of the key bolt-ons to unlock the S55's true potential. In this guide, we will compare catless and catted DP's, run through the pros and cons of each, and list some great options on the market.
BMW S55 Upgraded Downpipe Performance
Catalytic converters (cats) in the OEM S55 DP's were designed to minimize emissions. They do a great job at that. Unfortunately, those cats are also highly restrictive leading to worse power and performance. Pressure drop from pre-turbo to post-turbo plays an important role in a turbochargers ability to spool. As such, reducing back-pressure behind the turbo allows it to spool faster and build more boost. Removing the entire S55 exhaust system from the turbo back would provide the biggest performance benefits. Likely not the best proposal. However, catless and high-flow catted options are an excellent way to reduce back-pressure and free up power.
S55 Catless Downpipes vs High-Flow Catted Downpipes
Catless DP's are less restrictive as compared to high-flow catted downpipes. As such, they will result in better power, torque, and spool. Though, catless downpipes do come with one downside. If your state has inspections and/or emissions testing the S55 will likely fail with catless DP's. Those concerned about potential emissions issues might be best suited to catted DP's.
Otherwise, we highly recommend opting for catless downpipe options. They will definitely offer the best bang for your buck. High-flow catted downpipes are often pricier and offer less performance benefits. Though, catted DP's remain a good option to get some performance gains while also meeting emissions requirements.
S55 Upgraded Downpipe Pros
- 20-25whp (10-15whp w/ catted DP's)
- Comparable torque gains
- Less turbo lag & lower boost thresholds
- Improved top-end performance
- Exhaust sounds
Generous power and torque gains are probably the biggest selling point for upgraded downpipes. Catted and catless DP's will both provide the pros listed above. However, the performance gains are more impressive with the catless downpipes. Expect about 20-25whp on a tuned S55 with catless downpipes. FBO or upgraded twin turbo S55's may even net a bit more than 25whp. On the other hand, catted downpipes will likely only pick up 10-15whp. Both will improve turbo spool and reduce boost threshold but, again, expect better results with catless. Additionally, quicker turbo spool will make it feel as if the S55 gained even more power and torque than it really did. As boost comes on, the upgraded DP's will kick you back into the seat more aggressively.
S55 Catless Downpipe Sound
Exhaust and engine sounds are a bit of a touchy subject when it comes to the S55 engine. Some M3 fans haven't fully come around to the inline-6 twin turbo sounds when compared to the high-revving E9x M3's. We personally like the sounds of the S55, but definitely not as much as the N54 and N55. Regardless, catless downpipes will add a deeper, more aggressive note to the S55 under heavy throttle. Cold starts are also louder and deeper. However, once the engine is warm then catless DP's are hardly noticeable at idle. Likewise, the exhaust sounds mostly stock for normal cruising around town and on the highway. Stock-like sounds when you want them but a more aggressive note when it's time to have fun.
*Continuing the trend, high-flow catted DP's are louder than stock but to less of an extent than catless DP's.
BMW S55 Upgraded Downpipe Options
Let's move on to a few of the popular, quality S55 downpipe options. We'll list a few catless DP options as well as some high-flow catted DP's. It is important to note - this is not an exhaustive list and there are tons of choices out there.
1) VRSF S55 Catless Downpipes
We recommend VRSF bolt-ons parts, when available, for all modern turbo BMW engines. Their balance of price, quality, and performance are nearly unmatched, in our opinion. It's hard to go wrong with S55 catless DP's from VRSF. They're a popular choice for an excellent price. Therefore, they're also highly tested and proven with the quality to match. The only downside - they only offer catless DP's. Those looking for catted options must look elsewhere. As with S55 catless DP's, expect power and torque gains in the ballpark of 20-25 to the wheels.
VRSF S55 Catless DP's Price: $499.99
Buy Here: BMW S55 VRSF Catless Downpipes
2) Masata S55 Catless Downpipes
Masata catless downpipes are the best option for our UK and Europe readers. Their products are a lot less expensive and easier to obtain compared to importing US brands and are just as high quality as our favorite VRSF brand.
Masata's S55 downpipes are unique in that they feature flex sections that prevents cracking and also reduces stress on the turbocharger flanges. Overall, this is a great product. We do recommend these downpipes for US folks as well but the cost of shipping them in reduces the bang-for-the-buck factor so we generally recommend these for European folks and VRSF for US folks.
Buy Here: Masata S55 Catless Downpipes
3) Turner Motorsports S55 High-Flow Catted Downpipes
Turner Motorsports offers well priced high-flow catted DP's for the S55. Coming in just under $650 they are the only catted downpipe we're aware of that is less than $1,000. It's pretty standard for S55 catted downpipes to be considerably more expensive so it's definitely an attractive price point. They appear to be a quality product too, but we're not as familiar with Turner products. Nonetheless, they may be worth a shot for the price if you're only option is a catted DP.
Turner Motorsports S55 DP's Price: $649.95
4) Active Autowerke S55 Catless Downpipes
Active Autowerke (AA) is a well-known name when it comes to BMW performance parts. Initially, the AA S55 prototype DP's did not have the flex joints which they claimed led to vibration within the cabin. As such, these DP's come with the flex joints to allow for some wiggle room over bumps, cornering, etc. Otherwise, they're a similar product to the VRSF downpipes mentioned first. Great quality and performance with a slightly higher price point.
AA S55 DP's Price: ~$750
Buy Here: Active Autowerke BMW S55 Catless DP's
BMW S55 Upgraded Downpipes Summary
Upgraded downpipes are an excellent mod for any turbo engine, especially the BMW S55. Catless downpipes provide power gains in the ballpark of 20-25whp with a tune. Expect about 10-15whp for catted downpipes. Additionally, they will both reduce turbo lag and lower the boost threshold. S55 exhaust sounds can be debated all day but upgraded downpipes will definitely add a deeper, aggressive note under heavy throttle.
For those going the catless DP's route, we highly recommend opting for the S55 VRSF catless DP's. Turner Motorsports makes high-flow catted downpipes for an excellent price. Otherwise, there are dozens of other options on the market for both catted and catless S55 DP's. Regardless of your specific choice it's hard to go wrong with upgraded downpipes.