BMW M5 G90 Exhaust Sound: Why a 717-hp Hybrid V8 Wants Titanium (and What It Actually Changes)
The moment it lets you down
You write the cheque for the most powerful M5 BMW has ever built — 717 hp, 738 lb-ft, a 4.4-litre twin-turbo V8 bolted to an electric motor. Then you pull away from the dealer in Efficient mode and… it whispers. Because the G90 is a plug-in hybrid, half your commute is dead silent on battery alone. The first time you stab the throttle expecting a V8 bark and get a hybrid whoosh instead, something feels off. The car makes supercar numbers on paper and sounds like a quiet 5 Series in person.
That gap — between what the spec sheet promises and what comes out the tailpipes — is exactly why this owner ended up with a titanium valved catback for the M5 G90 on our bench.
Why the stock note is muted (the engineering part)
Here's the uncomfortable truth about the G90's S68: it's a twin-turbo V8. Two turbos sitting on the exhaust manifolds do more than make boost — they smooth out the pressure pulses that give a naturally aspirated engine its voice. A 9000-rpm flat-six (think 718 GT4 RS) fires sharp, regular spikes the exhaust can sing along with. A twin-turbo V8 has already been calmed down before the gas even reaches the muffler.
Then BMW layers on the modern stuff: an OPF (gasoline particulate filter) for emissions, and valve timing tuned to keep things civil when the neighbours are asleep. The result is a V8 that's monstrously fast but acoustically polite.
This matters for one specific decision: material. On a high-revving NA engine, titanium genuinely changes the tone — it rings higher and sharper. On a twin-turbo V8 like the S68 (or the M177 in the E63, or the S58 in the M2 and M3, as we wrote about in the M2 G87 SUS304 piece), the turbo has already taken the edge off. So the metal you choose matters less for pitch and more for weight and character.
What we changed in the workshop
Our fix for the G90 is a valved catback. Same logic as every other M car we touch: keep the valves shut for the school run and the car's silent EV mode, crack them open when you actually want the V8. The valving strategy is identical whether the shell is steel or titanium — the shell is the only variable.
We build both versions for the G90. This owner went titanium. Fair call, and here's the honest reasoning.
The customer's own footage (the good and the not-so-good)
The clip below is the owner's own drive-by and rev on the titanium valved system — not a studio render, not a marketing reel.
Two things worth saying plainly about it:
- It's short, about ten seconds, and it peaks at −0.3 dBFS. That means the recording is essentially sitting on the 0 dB line — it was captured straight off the tailpipe, not through a quiet cabin. What you hear is what the exhaust actually does, hiss and all.
- Our band split on the file: 100–800 Hz dominates at −15.9 dB mean (that's the V8 body and thump), the sub-bass under 100 Hz sits at −18.6 dB, and the highs above 2 kHz are way down at −29.5 dB. Translation: this is a deep, mid-bass-heavy note. There is shimmer up top, but it is not a screamer.
Honest downside: if you were hoping titanium would turn the S68 into a 718-style shriek, it won't. The turbo won't let it. What titanium gives this car is a deeper, raspier, lighter note — and a specific lift-off crackle that steel doesn't quite deliver.
Two routes — how to actually choose
Route A — Titanium valved catback (what this owner picked): the titanium G90 system.
- Wins on weight. The G90 tips the scales at 2,435 kg — the heaviest M5 ever, roughly 450 kg more than the old F90. A titanium catback sheds a meaningful chunk off the rear axle (typically 10–15 kg vs steel). On a car this heavy, every kilogram off the back helps.
- Wins on character: titanium's lift-off crackle is more pronounced, and the tips blue under heat if you drive it hard — some love that, some don't.
- Wins on the M5 buyer who already went this route on other BMW Ms — the titanium note is the one people post videos of.
Route B — SUS304 valved catback: the stainless G90 system.
- Wins on cost and on not caring. Steel dents instead of creasing, doesn't discolour, and looks new for years.
- The valving behaviour is identical. On a turbo V8 the tone gap between the two is smaller than the weight gap.
Our straight answer: on the G90, weight is the real reason to go titanium, not sound. If you track it or you're obsessed with mass, titanium. If it's a daily and you want it to look factory-fresh forever, SUS304. Browse the full BMW catalogue here.
The ugly bits we won't hide
- It's a hybrid. In Electric mode the exhaust is silent, full stop. No catback on earth changes that. If you wanted constant noise, this isn't the platform — and as every reviewer notes, on a 2,435 kg car, suspension (coilovers) is job one, exhaust is job two.
- Titanium tips blue. Heat discolouration is normal, not a defect. Some owners treat it as a feature; if you want mirror-finish tips forever, steel is your friend.
- Catback only. The turbos live up front in the downpipes. If you want more than a catback delivers, that's a bigger, emissions-sensitive job — the M340i titanium + 300-cell downpipe write-up shows what the next step looks like on a BMW turbo.
- No free power. A catback on a twin-turbo V8 is about sound and weight, not horsepower. Don't believe anyone selling you 30 hp from a muffler.
A question for the comments
On a 717-hp plug-in hybrid, is weight the actual reason to spec titanium — not the sound? Where do you land: titanium for the grams, or SUS304 for the peace of mind? Tell us below.
FAQ
Will it throw a check-engine light? No. A catback is downstream of every sensor and catalyst — no CEL, no tune required.
Is it still silent in EV mode? Yes. Electric mode stays electric. The catback only speaks when the V8 is running.
Does it fit the G99 Touring? Yes — same 4.4T S68 powertrain, same system, sedan and wagon both covered.
Warranty? It's a bolt-on catback with no engine management changes, but check your local consumer rules before fitting.
Valves — how are they controlled? Same as factory: via the drive-mode and exhaust-button logic. Closed = quiet, open = V8.