McLaren 720S Downpipe Guide — M840T Catted vs Catless, 800 HP Stage 2 & Sound
The McLaren 720S is powered by the M840T — a 4.0-litre twin-turbo flat-plane-crank V8 that produces 710 HP from the factory. It is one of the most technologically advanced engines in any production car, and it has significant untapped performance potential. The factory catalytic converters, positioned downstream of each turbocharger, are the single biggest restriction in the exhaust system. Replacing them with performance downpipes is the foundation of serious 720S power builds.
The M840T Exhaust Architecture
McLaren’s M840T is a bespoke unit — not shared with any other manufacturer. The flat-plane crankshaft delivers an even firing order that naturally produces excellent exhaust scavenging, and the twin turbochargers are sized to maximise response across the RPM range. The factory exhaust system routes exhaust from each turbo through a close-coupled catalytic converter, then through a secondary cat, before reaching the mid-pipe and tailpipes. The primary cats — dense, emissions-focused ceramic units — are the major restriction. They create measurable backpressure that limits turbine efficiency at higher boost levels and force the ECU to run conservative timing maps to manage exhaust gas temperatures.
What Downpipes Change
Aftermarket downpipes for the 720S replace the primary catalytic converters with either high-flow 200-cell metallic cats or catless straight pipes. On a flat-plane-crank engine, the effect of reduced backpressure is particularly dramatic:
- The even firing order means both turbos benefit equally from improved exhaust flow
- The flat-plane crank’s natural high-RPM character is unleashed — the M840T pulls harder above 6,000 RPM with the restriction removed
- Turbo spool is measurably faster, reducing the minimal turbo lag the 720S already exhibits
- The ECU can be calibrated for higher boost targets and more aggressive timing with lower EGTs
| Engine | M840T 4.0L Twin-Turbo Flat-Plane V8 |
| Factory Output | 710 HP / 770 Nm |
| Downpipe Configuration | Twin downpipes (one per turbo) |
| Common Materials | 304 stainless steel / Inconel |
| Catted Option | 200-cell high-flow metallic cats |
| Catless Option | Straight-through race pipes |
| Estimated Gain (with tune) | +60–100 HP / +70–110 Nm |
| Recommended Pairing | Stage 2 ECU Calibration |
The Sound Factor
The 720S with the factory sport exhaust is already one of the best-sounding modern supercars. Downpipes take the experience to another level. The flat-plane-crank V8 with reduced exhaust restriction produces a higher-pitched, more intense exhaust note — closer to a naturally aspirated Ferrari than a typical turbo V8. Turbo whistle becomes prominent during spool, the overrun crackle is sharper and more frequent, and the top-end scream from 7,000–8,000 RPM is exhilarating. Paired with an aftermarket exhaust system, the 720S with downpipes sounds genuinely exotic.
ECU Calibration Is Non-Negotiable
The M840T’s factory ECU calibration is sophisticated — McLaren’s engineers calibrated boost control, ignition timing, and fuelling specifically around the backpressure profile of the OEM exhaust. Changing that profile without recalibrating the ECU means the engine runs with incorrect assumptions about exhaust flow. A Stage 2 ECU calibration from YPG Motorsport recalibrates all relevant parameters to safely extract 60–100 HP beyond the factory 710 HP. This is not optional — it is essential for both performance and engine protection.
Catted vs Catless for the 720S
For road-driven 720S cars, high-flow catted downpipes are the recommended choice. They deliver exceptional flow improvement over stock while maintaining a degree of refinement appropriate for a supercar that may sit in traffic, idle in underground parking, or carry passengers. Catless downpipes are for dedicated track builds, drag cars, and owners who prioritise maximum performance and sound above all else. The exhaust odour and volume with catless pipes are significant.
Installation Considerations
The 720S’s carbon-fibre monocoque and mid-engine layout mean downpipe access is from below the vehicle. The installation does not require engine removal but does require careful navigation around the carbon structure and various heat shields. Use an experienced McLaren technician — the tolerances and fastener specifications on this platform leave no room for error. Installation typically takes 4–6 hours. For GCC customers, YPG Motorsport handles the complete downpipe installation and ECU calibration.
The Stage 2 720S
A 720S with downpipes, Stage 2 ECU calibration, and supporting intake modifications produces 780–810+ HP at the crank. That is hypercar territory from a platform that already handles like a scalpel and weighs 1,283 kg dry. Supporting modifications to consider:
- Performance intake — improve airflow to the turbo compressor inlets
- Sport exhaust or race mid-pipe — complete the exhaust flow path
- Intercooler upgrade — manage charge temps during sustained track sessions
Frequently Asked Questions
How much power do 720S downpipes add?
Downpipes alone on the M840T add approximately 15–25 HP. Combined with a Stage 2 ECU calibration, total gains of 60–100 HP over the factory 710 HP are achievable. The M840T’s flat-plane V8 responds exceptionally well to exhaust flow improvements.
Do McLaren 720S downpipes affect reliability?
Quality stainless steel downpipes from reputable manufacturers do not inherently affect reliability. The critical factor is pairing them with a proper ECU calibration that maintains safe air-fuel ratios, EGTs, and boost levels. Running downpipes without a tune can cause lean conditions that risk engine damage.
Are 720S downpipes compatible with aftermarket exhaust systems?
Yes. Downpipes connect between the turbochargers and the mid-section of the exhaust. They pair with the factory exhaust, OEM sport exhaust, or any aftermarket cat-back or mid-pipe system designed for the 720S.
What does a catless 720S sound like?
The 720S with catless downpipes and a sport exhaust is one of the most dramatic-sounding modern supercars. The flat-plane-crank V8 produces a high-revving, Ferrari-esque scream with pronounced turbo whistle and sharp crackle on overrun. It is loud — significantly louder than the factory sport exhaust.
Can I install 720S downpipes without removing the engine?
On the 720S, downpipe access is from below the car and does not require engine removal. The carbon-fibre tub and mid-engine layout make access tighter than front-engine cars, but an experienced McLaren technician can complete the installation in 4–6 hours.