Variable-length runner systems are an ingenious technology used in intake manifolds to provide a significant boost in engine performance. First popularized by the high-performance segment, variable-length runners are increasingly common in everyday cars. Auto manufacturers use a variety of names for these systems, but they all use the same basic principles in operation.

Variable-length runner systems alter the intake’s path through the manifold to optimize flow and volume for different engine speeds based on sensor readings and careful tuning. When the engine is running at low speeds, the manifold’s flaps select a longer runner length for improved low-end torque. Those flaps move to open a shorter path for the intake flow as revs climb, maintaining power across a broader spectrum of engine speeds. Pressure waves, or pulses, within the manifold are also manipulated by the runner length to extract the most from each combustion cycle.

Variable-length runner systems are often paired with other systems, like forced induction and variable valve timing (VVT), to further improve engine performance and efficiency. For example, a variable-length runner system can smooth out a turbocharged engine’s power delivery by serving up additional intake volume and reduced runner length to match the spooling turbo’s needs. And for engines with VVT, valve timing can be linked to runner length control to enhance the value of both systems.

Our IMRC replacements are designed to save you money and keep perfectly good manifolds out of landfills.

However, a malfunctioning variable-length runner system will cause a car to run poorly at most engine speeds. Performance and efficiency take a dive when the manifold’s flaps can no longer do their job.

If you’ve worked on Chevy Cruzes and Sonics with a 1.8L engine, you may be aware that they use variable-length intake runners. GM uses a flap system that closes and opens different sections of the runners, changing the length. That high-tech manifold relies on a simple actuator and mechanical linkage to function. Those pieces make up the intake manifold runner control (IMRC). The problem is that the IMRC arm has a weak plastic ball that can wear to a nub, creating excess freeplay, and can cause the IMRC motor to burn out.

Adding insult to injury, the OE only sells the entire intake manifold including the gaskets, purge valve, fuel rail, and all four injectors for a staggering amount of money. On top of that, the new OE intake manifold they sell you still includes the same failure-prone plastic ball that will likely just wear down again.

Problem OE FIX

Durable brass ball stud replaces failure-prone plastic factory design for a more reliable connection to the motor.

Our OE FIX solution for this problem features two approaches. First, we upgraded that plastic ball to a rugged brass ball stud that is designed for a more secure, longer-lasting connection to the motor assembly. Second, instead of the entire intake manifold, we sell the individual IMRC arm (911-929A) or the IMRC motor/arm combination (911-929), so you only have to install (and pay for) the part or parts that failed rather than the entire assembly.

Our parts are a fraction of the cost of the entire OE intake manifold and are designed to save you up to approximately 90 minutes of repair time. In addition, installation of both is easy; in fact, they’re much simpler than the factory solution of replacing the complete manifold. If you can do that, this will be a cakewalk.

OE runner arm can only be purchased with the intake manifold, gaskets, purge valve, fuel rail, IMRC motor, and all four injectors.

If you are replacing either piece, you’ll pop the ball stud from the butterfly shaft. For motor replacement, simply remove and replace the actuator, and reinstallation involves merely snapping the new arm into place. Once installed, the improved tuning arm design will solidly capture the existing linkage, provide increased service life, and reduce future related repair costs.

Intake Manifold Tuning Valve Runner Arm

911-929A

911-929A: Chevrolet Cruze 2015-11, Chevrolet Cruze Limited 2016, Chevrolet Sonic 2018-12

Intake Manifold Runner Control Motor And Arm

911-929

911-929: Chevrolet Cruze 2015-11, Chevrolet Cruze Limited 2016, Chevrolet Sonic 2018-12

Our IMRC replacements will save you money and keep perfectly good manifolds out of landfills. By sticking beefy arms like this one on motors, perhaps our old Motormite logo is as relevant as ever.