N20 4-Inch Turbo-to-2.5-Inch Mandrel-Bent SS304 Stainless Steel Downpipe

The ARM Motorsports N20 Catless Downpipe is a performance exhaust upgrade designed to eliminate the restrictive stock catalytic converter, a primary limitation for N20 engines. This upgrade is considered the first essential hardware modification for N20 owners seeking to maximize power output, enhance turbocharger responsiveness, and achieve a more aggressive exhaust tone. Constructed from durable SS304 stainless steel with mandrel bends for optimal flow, the downpipe features a precision CNC-machined 4-inch turbo v-band inlet that smoothly transitions to a 2.5-inch diameter to mate with the stock mid-pipe. It includes two O2 sensor bungs for the reinstallation of OEM sensors. However, a tune or a CEL Delete will be required to prevent a check engine light. By significantly reducing back-pressure on the turbocharger, this downpipe prepares the N20 engine for higher boost levels and advanced tuning. Performance gains are substantial: testing with a Stage 1 tune alone yielded an impressive 17 whp and 25 wtq. When combined with a Stage 2 tune, an additional 13 whp and 12 wtq were observed, totaling a 30 whp and 38 wtq gain over Stage 1. Beyond power, the downpipe also enhances the exhaust note, providing a noticeable increase in volume under acceleration and a moderate improvement at part throttle. It is designed to connect with aftermarket exhausts compatible with the stock N20 downpipe. This product is intended for off-road use only and is illegal for use on public roads in most jurisdictions. The downpipe is backed by the ARM Limited Lifetime Warranty. Fitment is confirmed for various BMW models including the F22 228i, F30 320i/328i, F32/F33/F36 428i, and F10 528i, all equipped with the N20 2.0L engine. While many users report a perfect fit, some have noted potential fitment or rattling issues, suggesting careful installation or potential modifications may be necessary in some cases.