O.S. Speed B21 AD4 Adam Drake 4 Competition 3.5cc (.21) Off-Road Nitro Engine Combo w/EFRA2089 TB02 Tuned Pipe

Reliable Nitro Engine Performance

The O.S. Speed B21 AD4 Adam Drake 4 Competition Off-Road Nitro Engine is the latest evolution in high-performance .21-class racing engines, developed in collaboration with world-renowned driver Adam Drake. Built for serious 1/8 scale off-road competition, this engine focuses on delivering improved balance, stronger torque, and smoother overall power delivery. With refined internal components and updated external design, it offers racers a competitive edge on demanding tracks.

About the O.S. B21 AD4 Engine

Redesigned Internal Engine Components

The AD4 features a highly developed 3-port cylinder liner and a revised crankshaft design, both tailored to Adam Drake’s specifications. The updated exhaust port timing enhances low-end torque while maintaining strong top-end power. Additionally, the crankshaft’s modified inner diameter improves throttle response, especially in the low to mid RPM range. These upgrades work together to deliver a smoother and more controllable powerband for improved drivability.

Enhanced Combustion Efficiency

A redesigned inner head combustion chamber increases overall efficiency, allowing the engine to produce more usable power with better fuel burn. This results in stronger torque output and more consistent performance across the RPM range. The improved combustion characteristics also contribute to better throttle feel and tuning stability, making it easier to dial in for varying track conditions.

Lightweight Cooling Head Design

The outer cooling head has been reworked with a double anodized black and blue finish and a fresh laser-etched design. Not only does it provide a striking appearance, but it is also lighter than the previous generation, improving overall engine balance. The optimized cooling design helps maintain stable operating temperatures during intense racing conditions, ensuring consistent performance run after run.

Features:

• Adam Drake Collaboration Design
• 3-Port Cylinder Liner Configuration
• Revised Exhaust Port Timing
• Improved Low To Mid-Range Throttle Response
• Redesigned Combustion Chamber
• Increased Torque Output
• Lightweight Dual-Anodized Cooling Head
• Improved Engine Balance
• High RPM Capability Up To 42,000 RPM
• Includes EFRA2089 TB02 Tuned Pipe