BMW M5 F90 Downpipe Guide — S63 4.4TT Catted vs Catless, Stage 2 Power & Install
The BMW F90 M5 uses the S63B44T4 — a 4.4-litre twin-turbo V8 that produces 591–617 HP from the factory depending on variant. It is one of the most potent sedans ever built, and it has substantial untapped potential locked behind factory exhaust restrictions. The stock catalytic converters downstream of each turbocharger are the primary bottleneck, and replacing them with performance downpipes is the foundation of any serious M5 build.
Why the S63 Needs Downpipes
The S63 positions its two twin-scroll turbochargers outboard of the cylinder banks in a traditional hot-outside-vee layout. Each turbo feeds exhaust through its own catalytic converter before the gases merge into the rest of the exhaust system. The factory cats are dense, emissions-optimised ceramic units that create significant backpressure — measurably restricting turbine efficiency at the boost levels the S63 can safely run. The result is higher exhaust gas temperatures, slower spool at partial throttle, and a ceiling on how much power the ECU can safely deliver.
Performance Downpipe Benefits
Aftermarket downpipes for the F90 M5 replace each factory catalytic converter with either a high-flow 200-cell metallic cat or a catless straight pipe. The improvements are immediate and measurable:
- Reduced backpressure across the entire RPM range
- Lower sustained EGTs under track or spirited driving
- Faster transient spool response
- Unlocked tuning potential — the S63 can safely run significantly higher boost with the exhaust restriction removed
| Engine | S63B44T4 4.4L Twin-Turbo V8 |
| Factory Output | 591–617 HP (M5 / M5 Competition) |
| Downpipe Configuration | Twin downpipes (one per turbo) |
| Common Materials | 304 stainless steel |
| Catted Option | 200-cell high-flow metallic cats |
| Catless Option | Straight-through race pipes |
| Estimated Gain (with tune) | +60–90 HP / +80–120 Nm |
| Recommended Pairing | Stage 2 ECU Calibration |
Catted vs Catless for the F90
For a street-driven M5, high-flow catted downpipes are the practical choice. They deliver the vast majority of the flow improvement over stock, produce no in-cabin exhaust odour, and avoid persistent check-engine lights. For track-only or drag builds where every last fraction of backpressure matters, catless downpipes maximise flow. An ECU tune is essential with either option to extract the full power benefit and manage any O2 sensor fault codes.
The Stage 2 Power Level
The F90 M5 Competition with downpipes and a Stage 2 ECU calibration from YPG Motorsport typically produces 700–750 HP at the crank. The S63 platform has well-documented tuning headroom — the block, rotating assembly, and fuel system can handle Stage 2 power levels on the factory hardware. A TCU calibration is strongly recommended alongside the ECU tune to raise the torque limits in the ZF 8-speed automatic and match the shift strategy to the increased power output.
Installation Overview
The F90 M5’s twin-downpipe layout requires removing heat shields, disconnecting four O2 sensors (two per pipe), and carefully extracting both OEM units from below. Professional installation takes 4–6 hours. The exhaust-side turbo flanges and V-band clamps must be torqued to specification with new gaskets. For GCC-based customers, YPG Motorsport handles the full installation, ECU tune, and TCU calibration in a single visit.
Build It Right — Supporting Mods
- Performance intake — complement the exhaust flow improvement with better intake flow
- Upgraded intercoolers — manage charge air temps in GCC heat
- Spark plugs — colder-heat-range plugs recommended at Stage 2 power levels
- Cat-back exhaust — complete the exhaust path for maximum flow
Frequently Asked Questions
How much HP do downpipes add to the F90 M5?
Downpipes alone add approximately 15–25 HP on the S63. Combined with a Stage 2 ECU calibration, total gains of 60–90 HP over stock are achievable. The S63 responds aggressively to reduced exhaust backpressure.
Are F90 M5 downpipes the same as M8 downpipes?
The F90 M5 and F91/F92/F93 M8 share the S63 engine but have different exhaust routing, mounting points, and subframe clearances due to chassis differences. Downpipes are generally not cross-compatible. Always source downpipes specific to your platform.
Do F90 M5 downpipes affect the all-wheel-drive system?
No. Downpipes modify the exhaust path downstream of the turbochargers and have no interaction with the xDrive all-wheel-drive system, transfer case, or differentials.
What does a Stage 2 F90 M5 produce?
A properly tuned F90 M5 Competition with downpipes, Stage 2 ECU calibration, and supporting intake mods typically produces 700–750 HP at the crank. The S63 platform has well-documented tuning headroom.
Can I fit downpipes with the stock M5 exhaust?
Yes. Downpipes connect between the turbochargers and the OEM mid-section. The stock cat-back exhaust, M Performance exhaust, or any aftermarket cat-back will bolt up to the downpipe outlets.