Kawasaki Ninja 400cc/500cc Bored Throttle Bodies 2018/Current

Description

Kawasaki Ninja 400/500 Bored Throttle Bodies

Give your Kawasaki Ninja 400 or 500 a stronger, freer-breathing character with Spears Racing’s professionally bored throttle bodies. We start with genuine OEM units and precisely enlarge the bore diameter, allowing significantly more air into the engine. This upgrade improves power and torque across the entire rev range, with the most noticeable gains appearing in the upper mid-range and at wide-open throttle.

Our preparation is a careful multi-step process performed on each set of throttle bodies. Using CAD-designed tooling, we bore the bodies and fit custom throttle blades sized specifically to the new bore diameter rather than simply matching the original plate. Where beneficial, we reduce the shaft profile to minimize restriction, install low-profile button-head screws, mill the topside for proper clearance, and finish with tumble polishing. These refinements can increase airflow by up to 15%.

Horsepower gains depend on the rest of your modifications, but most riders see roughly a 7–15% increase in rear-wheel horsepower when the bored throttle bodies are combined with complementary upgrades. The modification is a direct bolt-on, so you can keep your stock airbox or switch to individual velocity stacks or pods as preferred.

After installation, proper setup is required for optimal performance and smooth running. Synchronize the throttle bodies and recalibrate the Throttle Position Sensor (TPS) so the ECU and any fuel controller receive accurate readings. Confirm that your fuel controller is zeroed and registers 100% at full throttle before riding.

Whether you’re building a sharper street bike or a more competitive track machine, Spears Racing’s bored throttle bodies for the Ninja 400 and 500 deliver measurable airflow and power improvements while remaining a straightforward, reversible upgrade.