For many BMW performance enthusiasts the single stage intake manifold leaves you wanting more. The 3 stage manifold is a fantastic option, but may not fit your budget or may not fit the rules for your specific race class. The N54 is also a common “upgrade” but the torque loss is massive and the power is only better than that of the 3SIM above 6500 rpm, so taking advantage of the possible gains is usually impossible. There wasn’t a good low cost high power alternative commonly used until we realized the similarities between the 3SIM and the stock single stage manifold.
The single stage manifold is basically the 3 stage manifold but without movable DISA valves, with the lower small DISA open and the larger upper DISA closed. This locks it in “mid RPM” mode. “Opening” that upper “valve” would replicate the high RPM mode of the 3SIM. In our case removing the internal baffle can unlock additional performance potential.
As this is becoming a more common modification for track use we have decided to document the process. This guide will highlight the main points of the process used to optimize a factory manifold.
Step 1 – Disassembly and Preparation
Begin by removing all components from the manifold — sensors, throttle body, EVAP equipment, and brackets. Once stripped, thoroughly clean the housing to remove carbon buildup and oil residue.
Step 2 – Removing the Internal Baffle
The stock plenum includes an internal baffle that smooths airflow and limits resonance noise. While useful for emissions, it restricts performance at higher RPMs. To remove it:
Make two vertical cuts through the manifold housing.
Connect those with horizontal cuts along the top and bottom of the plenum.
Carefully free and remove the internal baffle section.
Once removed, clean up the cut edges using a file or rotary tool to remove burrs and plastic shavings.
Step 3 – Final Cleaning
After cutting, plastic and dust debris must be completely removed. Flush and blow out the manifold using compressed air and a mild detergent. Continue cleaning until no residue remains, and allow it to dry fully before assembly.
Step 4 – Block‑Off Plate Installation
With the baffle removed, we fabricate and install a block‑off plate to seal the plenum. This strengthens the component while maintaining smooth airflow. Each plate is 3d printed with the same material as the manifold (PA6-GF) to fit the perimeter and bonded in place. Ensure thia is airtight before proceeding.
Step 5 – Race Prep and Port Blocking
For full race preparation, unnecessary vacuum or emissions ports are sealed. This reduces oil contamination, prevents leaks, and creates a clean, efficient system to keep things easy to manage at the track. We use our crankcase vent plug kit for this.
Step 6 – Engine calibration
This modification changes the airflow characteristics of the intake manifold. For optimum performance we need to match the calibration to the hardware. TRM Tuning offers calibrations for this modified intake manifold as well as any other intake manifold configuration. Available here.
Results and Conclusion
A properly modified manifold improves high‑RPM performance. By removing the internal baffle, cleaning the plenum, and sealing redundant ports, airflow becomes consistent and predictable — ideal for track builds.
Contact TRM Tuning: For manifold modification, ECU tuning, or complete race prep, email info@trmtuning.com.
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