FX R900 .21 9-Port On-Road Competition Nitro Engine – FX660201

The FX R900 is a premium 3.5cc (.21) competition nitro engine developed specifically for 1/8 scale on-road racing. Designed for the extreme RPM and performance demands of top-level on-road competition, the R900 combines a 9-port design, DLC-coated crankshaft, ceramic rear bearing and precision-balanced rotating assembly. FX lists the R900 as the recommended engine for the current XRAY RX8 platform.

FX660201 is the engine-only version, making it ideal for racers who already have a suitable EFRA exhaust and manifold or want to choose their exhaust system separately.

9-Port Competition Design

The R900 uses a sophisticated 9-port sleeve design developed specifically for high-performance on-road racing.

Unlike an off-road engine where low-speed torque and progressive power delivery are especially important, the R900 is optimised for the high RPM, acceleration and top-end performance required by 1/8 on-road cars.

The genuine FX parts documentation confirms the R900's 9-port piston and sleeve matched set.

DLC-Coated Crankshaft

The R900 features a highly developed DLC-coated crankshaft.

FX specifies a crankshaft with silicone filling and three tungsten balancing weights, helping optimise crankshaft balance and high-RPM performance. The Diamond-Like Carbon coating provides a hard, low-friction surface designed to reduce wear and friction under demanding racing conditions.

Ceramic Rear Bearing

A premium German-made ceramic rear bearing is fitted as standard.

Reducing friction within the rotating assembly is particularly important in a competition on-road engine operating at extremely high RPM, helping contribute to smooth operation and efficiency.

Precision Balanced

The R900 is specified by FX as balanced, complementing its DLC crankshaft and ceramic bearing.

Careful balancing helps minimise unwanted vibration and allows the engine to operate smoothly throughout its extensive RPM range.

Dedicated .21 On-Road Carburettor

FX equips the R900 with its dedicated .21 on-road carburettor.

The engine is supplied with an 8.5mm composite carburettor venturi, while an optional 8.0mm venturi is also available for racers wanting to alter the engine's characteristics.

Sealed Combustion Chamber

The R900 uses a 7-rib aluminium cooling head together with a sealed 16.1mm combustion chamber.

A selection of head shims allows the combustion chamber setup to be adjusted to suit engine condition, fuel and altitude. FX's technical documentation recommends a combined shim thickness of approximately 0.25–0.35mm, with final setup dependent on operating conditions.

Designed for 1/8 On-Road Racing

The R900 was developed specifically for serious 1/8 nitro on-road competition.

It is particularly well suited to the XRAY RX8, with XRAY specifying the FX R900 as the recommended engine in its current RX8 documentation.

The R900 has also proven itself in competition, with XRAY reporting race wins using the current RX8 and FX R900 combination during the 2026 season.

Key Features

• FX Engines R900
• Part Number: FX660201
• Engine-only version
• 3.5cc / .21 class nitro engine
• Designed for 1/8 on-road competition
• 9-port sleeve design
• DLC / Diamond-coated crankshaft
• Silicone-filled crankshaft
• Three tungsten crankshaft balancing weights
• Precision-balanced rotating assembly
• German-made ceramic rear bearing
• Dedicated .21 on-road carburettor
• 8.5mm composite venturi included
• 7-rib aluminium cooling head
• Sealed combustion chamber
• SG-style crankshaft configuration
• Designed for extremely high-RPM competition use
• Suitable for XRAY RX8 and other competition 1/8 on-road cars
• Exhaust and manifold sold separately

Specifications

Brand: FX Engines
Part Number: FX660201
Model: R900
Engine Type: Nitro / Glow
Engine Class: .21
Displacement: Approx. 3.5cc
Application: 1/8 On-Road Competition
Ports: 9
Crankshaft: DLC Coated / Balanced
Crankshaft Weights: 3 x Tungsten
Rear Bearing: Ceramic – Germany
Carburettor: FX .21 On-Road
Standard Venturi: 8.5mm
Cooling Head: 7-Rib Aluminium
Combustion Chamber: Sealed 16.1mm
Exhaust: Not Included
Manifold: Not Included
Completion: Engine Only

Recommended Exhaust System

For a complete FX package, the R900 can be paired with:

FX 669500 – EFRA 2168 3.5cc On-Road Muffler
FX 669700 – Short On-Road Manifold

FX also offers 669550, which combines the EFRA 2168 muffler and Short manifold as a set.

Engine Only – Build Your Own Combination

The FX660201 is the right choice for racers who already have an exhaust system or prefer to select their pipe and manifold separately.

This makes it different from the complete R900 combo, which includes the engine together with the matched EFRA 2168 exhaust and Short on-road manifold.

With its 9-port design, DLC crankshaft, tungsten balancing weights, ceramic bearing and dedicated on-road carburettor, the R900 provides a serious powerplant for high-level 1/8 nitro racing.