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ARM Motorsports

ARM Motorsports B58 Downpipe (M240I, 340I, 440I, 540I, 640I, 740I)

ARM Motorsports B58 Downpipe (M240I, 340I, 440I, 540I, 640I, 740I)

Regular price $298.99 USD
Regular price Sale price $298.99 USD
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• Increase Power and Torque
• Faster Turbo Spool
• Improved Exhaust Sound
• Safely Flash Stage 2+ Tunes
• SS304 Stainless Steel


The ARM B58 Downpipe is one of the foundational upgrades for giving your B58-powered BMW more power, torque, and sound.  The stock B58 downpipe comes from the factory with a catalyst that severely restricts exhaust flow, causing excessive backpressure with increased boost.  Upgrading your downpipe unlocks power, improves turbo spool, allows you to safely run stage 2+ tuning, all while increasing the sound of your B58-powered BMW.   


The ARM B58 Downpipe will increase the overall volume of your BMW, open up the exhaust burbles even on OEM programming, and make the turbo spool significantly more audible.  The M240i in the video below is only equipped with the ARM B58 Downpipe, it is otherwise on a 100% stock exhaust. The car has never been flashed, it is on the original DME programming from BMW.  

ARM B58 Downpipe on M240i


The ARM B58 Downpipe is built with SS304 stainless steel and backed by the ARM Motorsports Lifetime Warranty.  The ARM B58 Downpipe starts with a 4.5" diameter precision CNC machined turbo v-band flange

B58 Downpipe

The ARM B58 Downpipe then gradually reduces to a 3.1" diameter before the flex section.  The flex section is incorporated into the ARM B58 Downpipe to relieve stress on the turbo during aggressive driving.

B58 Downpipe

The ARM B58 Downpipe is further secured by the 2-bolt bracket which utilizes the OEM downpipe mounting points.

B58 Downpipe

The 3.1" diameter continues after the flex section to allow for an easy installation to the OEM midpipe, or any midpipe that connects to the OEM B58 downpipe.    

The ARM B58 Downpipe features two O2 sensor bungs to allow for reinstallation of the OEM oxygen sensors.  The O2 sensor bungs are located closer to the turbo on the ARM downpipe to avoid stretching the O2 sensor wires during installation.  A tune or CEL Delete will be required to avoid a check engine light from displaying on instrument panel.

B58 Downpipe


 By improving the exhaust flow on your B58 BMW with the ARM B58 Downpipe, you're prepared for the higher boost tunes.  If you already have a software program for your B58 chances are these tune files are already pre-loaded into your software waiting for you to flash after your downpipe is installed.  Most tunes require an upgraded downpipe to run properly.


• ARM B58 Downpipe


Make Model Submodel Engine
BMW F22 M240i B58 3.0L
BMW F22 M240i xDrive B58 3.0L
BMW F23 M240i B58 3.0L
BMW F23 M240i xDrive B58 3.0L
BMW F30 340i B58 3.0L
BMW F30 340i xDrive B58 3.0L
BMW F32 440i B58 3.0L
BMW F32 440i xDrive B58 3.0L
BMW F33 440i B58 3.0L
BMW F33 440i xDrive B58 3.0L
BMW F34 340i xDrive B58 3.0L
BMW F36 440i B58 3.0L
BMW F36 440i xDrive B58 3.0L


Every ARM Motorsports product is backed by a lifetime warranty which is automatically issued at the time of purchase. Your warranty protects you against any defects in craftsmanship or fitment. The warranty entitles you to a replacement unit.

This product is for Off-Road Use Only. Items sold for off-road use only are illegal to use on public roads in most states and provinces. This product is intended for racing vehicles which may never be used on a public road.
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Customer Reviews

Based on 1 review
Anas Hasic

Garbage downpipe and sound, and service

Thanks for the false review Anas.

Full Story: Customer bought a catless downpipe then emailed us saying 'downpipe sounds like a broken civic with a chainsaw' and they wanted to return it. I asked them what vehicle they installed on, as well as the exhaust setup, it is a 440i with the M Performance (MPPSK) exhaust. The MPPSK is a factory exhaust upgrade that comes with a bigger midpipe with no resonator, and upgraded axleback. When the valves are open, this is a fully straight piped exhaust, no mufflers, no resonator. The MPPSK as well as other straight piped exhaust setups, are known for being raspy when the catalytic converter is removed, which is pretty much the case for any car. The fix is easy and relatively cheap, just add a resonator to the midpipe. Any local exhaust shop can install one in less than 30 minutes, for $100-$300 depending on where you go to and what type of resonator you want.

I told him our return policy states that we don't allow returns on used items. Customer told us that we shouldn't sell a product that sounds like 'shit' and that I was running a shady business. He then threatened to leave 'slanderous reviews' on our website if we didn't refund him. I refused and he told me I run a 'bullshit business'.

I'm sorry you weren't happy with the downpipe, but it is not our fault that it didn't sound good on your particular exhaust setup. After a product is installed, we cannot resell it, therefor we don't offer returns on used items. If you would have emailed us beforehand and asked for advice, I could have told you up front that ANY catless downpipe (VRSF, CTS, ARM, MRM, etc) will sound raspy on MPPSK, and that you should go with a MRM Performance or DAW 5' downpipe (5' Downpipes are much less raspy on upgraded exhausts), or get a resonator installed. We have zero way of knowing what your particular setup is when you purchase. I never lied or mislead you in anyway, so no, I am not running a shady business.

I am going to leave your review there as I never take down reviews, good or bad. But thought anyone reading this should know the full story behind this.

Michael Rich
Owner of MRM

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