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The Scooter Parts Registry

EPA engine family

Engine family RHSNX.546USV

If this code is printed on your emission label, this is your machine's federal record: sold under Hisun Motors Corp., U.S.A., with an engine built by Chongqing Huansong, certified as ATVs and UTVs and side-by-sides.

Displacement
—
Model years
2024
Models certified
23
Certificates
1

What this record says

Sold in the US by
Hisun Motors Corp., U.S.A.
Engine built by
Chongqing Huansong
Vehicle category
ATVB & UTV - EPA only
Certificate numbers
RHSNX.546USV-014

What the number itself says

Reading RHSNX.546USV left to right: R is the model-year letter for 2024, HSN is the three-character code the EPA assigned to Hisun Motors Corp., U.S.A. as certificate holder, X marks an off-road certification, .546 is the displacement in litres, so 546cc and USV is Hisun Motors Corp., U.S.A.'s own sequence for that year. Nothing in the number names the factory — that comes from the certificate itself.

The engine, as described on the certificate

The test vehicle Hisun Motors Corp., U.S.A. submitted for this family (model HS550UTV-2) carried engine code HS191MR. In the Chinese engine-model convention that reads as one cylinder with a nominal 91 mm bore, MR series.

The certificate describes a four-stroke, single-cylinder engine with 2 valves per cylinder fed by sequential multi-port fuel injection, with an oxygen sensor for closed-loop fuelling, run by an engine control module (ECM). There is a catalytic converter in the exhaust, recorded as "Three Way Catalyst (TWC), single-bed, closed-loop warm up".

Rated power on the record is 20.2 kW (about 27 hp) at 5,500 rpm, driving through a CVT (belt and variator).

Engine code on test vehicle
HS191MR
Nominal bore (from the code)
91 mm
Cylinders / valves
1 · 2 per cylinder
Cycle
four-stroke
Fuel delivery
sequential multi-port fuel injection
Oxygen sensor
yes (closed loop)
Engine control
ECM
Catalytic converter
Three Way Catalyst (TWC), single-bed, closed-loop warm up
Rated power
20.2 kW (≈27 hp)
Rated speed
5,500 rpm
Transmission
CVT (belt and variator)
Sales area
50S+49S
Vehicle built by
Chongqing Huansong Science and Technology Industrial Co., Ltd.; Vietnam New Century Industrial Company Limited
Test vehicle model
HS550UTV-2

Filing history and where it was sold

Hisun Motors Corp., U.S.A. filed one certificate under this family, for model year 2024, sold as both a 50-state and a 49-state version.

The vehicle itself is recorded as built by Chongqing Huansong Science and Technology Industrial Co., Ltd. and Vietnam New Century Industrial Company Limited in China and Vietnam, while the engine came from Chongqing Huansong. Chassis parts and engine parts therefore have different origins.

Certified emission levels: CO 3.2, HC+NOx 0.6 g/km.

Other records carrying the same engine code

Hisun Motors Corp., U.S.A. certified an engine with this code under 21 other family numbers — the same engine filed again in another year, or in an off-road and a street version:

A shared code from the same factory is a strong search lead. From a different factory it is as often a naming coincidence. Either way it narrows the search; it does not settle it — measure before you buy.

Models certified under RHSNX.546USV

Every model designation the importer listed on this certificate. If your machine's model name appears here, this is the right record — even if the name on the bodywork is slightly different.

Axis 500 · Axis 550 · Bad Boy 550 · Big Dirty 500 · Big Dirty 550 · Challenger 500 · Challenger 550 · Challenger M550 · Challenger MX 550 · HS500UTV-3 · HS500UTV-4 · HS500UTV-5 · HS500UTV-6 · HS550UTV · HS550UTV-2 · HS550UTV-3 · HS550UTV-4 · RK Performance 550 · Sector 550 · Strike 550 · Strike 550R · Vector 500 · Vector 550

Other American badges on engines from the same factory

Related in the registry

Source. US EPA annual certification data — EPA Certified Highway Motorcycle Test Results, MY2006-present; EPA Certified Off-Road Motorcycle / ATV / UTV / Rec Vehicle, MY2006-present. Retrieved 2026-09-07. Full provenance and method.