⟲ 360° — drag meThe facts.
| Brand | Akrapovic |
|---|---|
| Part number | S-K4MET9-FDHLTA |
| Fitment | Kawasaki KX450 and KX450X (2024–2026) |
| Line | Evolution Line (Titanium) — complete system |
| Weight | 3.15 kg (stock 4.49 kg, saving 1.34 kg / 29.8 %) |
| Power | 55.5 PS (stock 54.1 PS, gain 1.4 PS at 9,950 rpm) |
| Torque | 45.7 Nm (stock 43.9 Nm) |
| Headers | Integrated resonance chamber, debossed Akrapovic logo |
| Road approval | None — closed course competition use only |
DescriptionThe whole story▼
Nearly a kilo and a third off a motocross bike is not a detail. At 3.15 kg against the standard 4.49 kg, this Evolution Line takes 29.8 per cent out of the exhaust — and on a 450 that weight sits high and to one side, which is exactly where a rider feels it in the air and in a rut.
Key Features
- Full titanium system, 3.15 kg instead of 4.49 kg
- 55.5 PS instead of 54.1 at 9,950 rpm, torque up from 43.9 to 45.7 Nm
- Headers with an integrated resonance chamber
- Debossed Akrapovic logo on the header, developed with the Racing Department
- Fits the KX450 and the KX450X, 2024 to 2026
Where the weight comes off
1.34 kilograms. On a machine that weighs around 110 kg ready to ride, that is more than one per cent of the whole motorcycle removed from a single component — and from the worst possible place, high on the right-hand side above the rear wheel.
What it changes is not lap time on a dyno sheet but how quickly the bike will change direction and how it lands. Riders describe it as the bike feeling shorter. That is the mass moment of inertia, not marketing.
The resonance chamber in the header
Akrapovic integrates a resonance chamber into the header pipe rather than bolting one on. It tunes the pressure wave that comes back down the pipe towards the exhaust port, and on a single-cylinder four-stroke that reflected wave is a large part of how the engine fills at low and mid revs.
The dyno figures show it: 1.4 PS more at peak, but 1.8 Nm more torque — the gain sits in the middle of the range where a motocross engine actually works.
Not for the road
Akrapovic marks this system for closed course competition only. There is no EC or ECE approval, no type approval number and no homologation document. It is for a track, a closed circuit or private land — not for a public road, and not for a bike that has to pass a technical inspection.
Titanium, and what it costs to work with
Titanium is roughly half the density of stainless steel at comparable strength, which is where the 1.34 kg comes from. It is also the reason a system like this costs what it does: the material is expensive, it work-hardens as it is formed, and welding it needs an inert gas shield on both sides of the seam or the weld turns brittle.
What the rider gets in return is a pipe that dents rather than splits when a boot or a berm finds it, and one that does not rust from the inside out after a winter of pressure washing.
The logo is pressed, not printed
Akrapovic developed a technique from its racing programme for imprinting the logo into the muffler outer sleeve rather than applying it to the surface. On a motocross bike that difference shows within a season: printed graphics come off with the first pressure wash aimed at the silencer, and a pressed mark cannot.
The header carries a debossed logo by the same method. It is a small thing, and it is the kind of small thing that separates a system that still looks like something after two years from one that does not.
Article number
Akrapovic lists this system as S-K4MET9-FDHLTA. The matching optional noise damper for circuits with a 109 dB/A limit is V-TUV385.
FitmentWhich bikes this fits▼
- Kawasaki KX450 (2024–2026)
- Kawasaki KX450X (2024–2026)
- Closed course competition use only
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