N54 Catless vs. Catted Downpipes
Why Upgrade my N54 Downpipes?
One of the biggest restrictions on the N54 powered 135i, 335i and 535i is the factory catted downpipes. Downpipes bolt directly to the turbochargers and the factory catalytic converters create significant back-pressure which results in slower turbo spool. Modifying your N54 with catless or high-flow catted downpipes results in faster spool, tremendous power gains, and an aggressive exhaust note. Upgraded downpipes are a great modification especially for N54’s that have dual cone intakes. Dual cone intakes bring more air into the engine, and the more that flows in, the more that has to flow out.
As with any turbocharged car, exhaust backpressure post-turbine, leads to a significant loss in turbo spool and power. I don’t want to delve too deep into the boring details of backpressure pre/post turbo, but it is an important relationship that affects turbo spool. The drop of pressure from the exhaust gas pre-turbo to post-turbo plays a key role in why a turbo is able to spool. A larger pressure drop causes the exhaust gas to accelerate quicker leading to an increase in turbo spool. In a perfect world, the best post-turbo exhaust would be no exhaust at all. Of course, for those of us daily driving our n54’s on public roads, having no exhaust is likely not a viable option.
Catless downpipes help mitigate the downside of having an exhaust system post-turbo; they lead to a considerable decrease in backpressure and allow the turbocharger to spool faster. Additionally, as air is accelerated faster towards the turbine, boost pressure increases thereby causing an increase in power. OK fine, I will move on to why I believe catless downpipes are one of the best mods for the n54 powered 135i 335i and 535i:
- +15-25 Horsepower and Torque
- Incredible turbo spool
- Intoxicating Sound
I run VRSF catless downpipes on my 335i, of which I am very impressed with; the quality and welds looked excellent. Combine that with a lifetime warranty for fitment and defects and a price of only $305 it’s hard to pass up on them. I bought the downpipes with the goals of spool, power, and torque in mind and boy did these deliver. The turbo spool is immediate and the instant low-end torque is unbelievable. A loud car is never something I have been interested in – I love that the 335i appears to be a sleeper on the surface. Once again, the VRSF catless downpipes delivered. While idling or cruising at any speed it is hard to notice a significant difference between stock downpipes and catless. However, at WOT or on a cold start the catless downpipes are intoxicating; the exhaust note is very aggressive without being overly intrusive.
High-Flow Catted Downpipes
Similar to cattless downpipes, high-flow catted downpipes will allow your turbos to spool faster and deliver more power. However, as you likely assumed, these downpipes have catalytic converters and are more restrictive than catless downpipes. They still provide relatively solid gains for turbo spool, power, and sound. Although, the biggest benefit of opting for high-flow catted downpipes is that your car will still pass emissions testing.
Overall, if you are looking for the best power and spool catless downpipes are the way to go. High flow catted downpipes are typically more expensive than their catless counterparts and do not offer as much of a benefit. However, if you are worried about having an exhaust system that won’t pass inspection then high flow catted downpipes are the right choice for you.
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