The first message was not what you'd expect
A customer sent us 22 seconds of his E63 on a country road, and the first thing he wrote was not "it sounds amazing." It was: "Why did it take me this long to figure out the stock car was lying to me?"
Why the M177 sounds the way it does
The M177 is a 3,982 cc twin-turbo V8 with a long-stroke layout - 83.0 mm bore, 92.0 mm stroke, 8.6:1 compression. Two turbos sit between the exhaust pulses and the tailpipes, and they do two things to the sound: they flatten the sharp edge of each pulse, and they push the note down into a thick mid-band. That is why a stock E63 with the Performance Exhaust still sounds "produced" rather than mechanical. The pulse detail never reaches the tailpipe. We covered what catless downpipes actually do to a Mercedes biturbo V8 on the E550 W212, and the M177 behaves the same way.
How we built the valved catback
We built the W213 valved catback in SUS304 with one goal: keep the mid-band the turbos already deliver, and open the top end without turning the car into a drone machine. The valves stay shut at low load so the cabin stays livable, and open on demand for the full eight-cylinder noise. It sits in our catback collection alongside the rest of the valved systems.
What the clip actually shows
The clip runs 22 seconds on a narrow country road. We measured the audio: the 100-800 Hz band dominates at -17.7 dB mean - that is the turbo V8 mid-band doing the work. The above-2kHz band sits at -32.9 dB mean but peaks at -6.5 dB, a 26 dB gap. That gap is the crackle and upshift transient: it only appears at full load, and it is the part turbos normally swallow. Honest note: the phone recording clips at 0.0 dB on the hardest blips, so treat peak numbers as a floor, not a ceiling.
SUS304 or titanium on the M177?
Same logic we gave the M2 G87 owner and the Genesis G70 3.3T owner: on a twin-turbo engine, the turbochargers already trim the high-frequency detail titanium preserves best. SUS304 gives you the durability and the tone thickness the M177 wants. Titanium on an E63 is a weight-and-looks purchase, not a sound purchase - and at roughly two tonnes kerb weight, the weight argument is thin.
The ugly parts, said up front
A catless downpipe on this car will smell at cold start, may throw a code without a spacer, and will not pass strict inspection in some regions. The valved catback alone is the sane build; the downpipe is for people who already accepted those trade-offs.
Your call
Valves open all the time, or stock behavior with a remote? Tell us which camp you are in.
Questions we actually get
Does the valved catback need an ECU tune? No - the valve controller is standalone.
Will it drone on the highway? Valves shut at cruise, it stays close to stock comfort.
Is the downpipe required? No. The catback transforms the sound on its own; the downpipe adds the last aggressive layer.
Everything we build for the three-pointed star lives in the Mercedes-Benz collection.
HMD builds the Mercedes-AMG E63 W213 valved catback in SUS304, with a titanium valved version if you want the weight saving anyway.