The B48 is a stout motor from the factory. However, many look to bolt-on parts to take the B48 to the next level. Towards the top of the list lies an upgraded B48 downpipe. Remove the restrictive particulate filter from the downpipe to unleash the B48's true potential. In this guide, we will compare high flow catted downpipes to catless downpipes, discuss the benefits of each, and list the top options.
BMW B46/B48 Upgraded Downpipe Performance
A downpipe is among our favorite mods on turbo cars. Modern catalytic converters and particulate filters are highly restrictive from the factory, espcially the B46 and B48. They're great for emissions purposes, but horrible for performance. A large factor in a turbos ability to spool and build boost is the drop in pressure pre-turbo to post-turbo. As the hot exhaust gases try to escape they are attracted towards less dense air. Therefore, reducing back-pressure after the turbo is important. The best exhaust on the B46 and B48 is actually no exhaust. However, that is not realistic for most of us daily driving our cars. As such, a catless or high-flow catted DP are the next best options.
B46/B48 Catless vs High-Flow Catted Downpipe
Catless downpipes are the least restrictive option, and will therefore provide the best power gains. More on the specific gains of each in the next section. However, fully catless downpipes do come with their own downsides. State inspections and/or emissions testing will be an issue. A shop will notice the lack of a cat or particulate filter with a quick peek. Additionally, their systems will pick up on the increased emissions. As such, a catless DP may scare some away due to headaches come emission testing time.
If emissions are not a concern, then we highly recommend opting for the catless downpipe options. Especially since catted DP's can be 50%+ more expensive than their catless counterparts. However, a high-flow catted downpipe is a great option for some performance benefits while remaining within emission requirements.
B46/B48 Upgraded Downpipe Pros
- +15-25whp with catless DP (5-10whp with high-flow catted DP)
- Similar torque gains
- Quicker turbo spool
- Better top-end performance
- Intoxicating sounds
Of course, the biggest upsides to an upgraded downpipe are the power and torque gains. Expect to gain roughly 15-25whp and 20-25wtq with catless downpipes on a tuned B46 and B48. A bit less power should be expected with high-flow catted downpipes. Another huge benefit to upgraded B46 & B48 downpipes is the quicker turbo spool. As mentioned briefly, the drop in pressure from pre to post turbo is important for turbo spool. As such, the turbo will spool faster and build more boost when the cat or particulate filter is removed. Similar to power gains, the results are more impressive for catless downpipes. The butt-dyno will definitely approve of this mod. Quick turbo spool will instantly kick you back into the seat and is sure to impress. Additionally, the turbo will hold more boost on the top-end and result in a phenomenal power band.
It doesn't end there either. In our opinion, a catless downpipe produces intoxicating sounds. Some may wonder, "Are catless downpipes too loud for daily driving?" We think not. Catless downpipes will add a bit of noise on cold starts. Additionally, dig into the B48's throttle and a catless downpipe will provide a deeper, aggressive note. However, cruise around town modestly or on the highway and the DP is hardly noticeable. Stock-like sounds when you want them and a more aggressive note when it's time to have fun.
B46 Upgraded Downpipe Options
In this section we will discuss a few of the popular, quality downpipe options for both the B46 and B48 engines. This is not an exhaustive list, however the current B46 downpipe offerings are minimal. The market will surely continue expanding as the B46 & B48 age.
*The B46 and B48 require different downpipes. Section for B48 below
1) VRSF B46 Catless Downpipe
VRSF, our favorite downpipe manufacturer, offers a catless downpipe option for the B46 engine. VRSF offers the best bang-for-the-buck and value for the price. Fitment and quality are exceptional and can't be matched for anything within a similar price point.
Buy Here: VRSF B46 Downpipe
Other B46 Upgraded Downpipes
There are a few offerings around other than VRSF. However, we're not familiar with many of the other companies making B46 downpipes. There are of course the Aliexpress and Ebay options. Although, we do not recommend going that route. Some have good experiences while others have fitment and quality issues. There are a few options, like Evolution Raceworks in the $500 price range but we just can't justify that price when VRSF has a $279 option.
B48 Upgraded Downpipe Options
Fortunately, the B48 engine has quite a few additional options compared to the B46 engine. Again, this is not an exhaustive list. More companies will likely develop upgraded downpipes in the near future.
1) VRSF B48 Catless Downpipe
VRSF is among our favorite companies for any downpipe, intercooler, intake, and chargepipe mods. In our opinion, their balance of price and quality is unmatched. You can't go wrong with a B48 catless downpipe from VRSF. Tested, proven, high quality and a great price.
VRSF B48 Downpipe Price: $269.99
Buy Here: B48 Catless Downpipe VRSF
2) Evolution Racewerks Competition Series 4" B48 Downpipe
This is essentially the same downpipe we discussed above for the B46. The main difference is that this downpipe is designed to fit the B48, obviously. Again, it's a high quality DP for a reasonable price. We ultimately recommend the B48 VRSF option if you are looking for a catless downpipe. The ER downpipe is excellent too, but we would save a bit of money and opt for the VRSF downpipe. However, if you're looking for a high-flow catted downpipe then look no further than Evolution Racewerks.
Price: $445+ catless ($780+ catted)
Buy Here: B48 Evolution RaceWerks Downpipe
B48 Upgraded Downpipe Summary
We believe catless downpipes are the second best bolt-on performance mod for the B46 and B48 engines, following only tunes. Performance benefits include 15-20+ wheel horsepower gains, along with quicker spool, better top-end power, and awesome sounds. However, catless downpipes do have their own issues, especially come emissions testing time. You may opt for a high-flow catted downpipe which provides about 5-10 horsepower over stock. Though, high-flow catted downpipes are typically close to twice the cost of their catless counterparts.
We recommend Evolution Racewerks downpipes for B46 owners looking for either catted or catless options. For the B48, we believe VRSF provides the best balance of price and quality. Though, they only make the catless downpipe for the B48. Look to Evolution Racewerks for a great catless or catted option. All in all, you can't go wrong with an upgraded B46/B48 downpipe.