The aFe Silver Bullet Throttle Body Spacer (part 46-37001) sits in the joint where the throttle body meets the intake manifold on the 2.4-liter four-cylinder. The manufacturer machines it from 6061-T6 billet aluminum and pairs a serrated entry with a helix design to swirl incoming air. That serrated entry is aFe's answer to the whistle helix-only spacers often produce at idle and cruise, which makes it a practical choice for a Honda Civic Si 2.4L billet throttle body spacer upgrade.
Buyers weighing this against a cheaper spacer should know what the premium buys. The manufacturer publishes a dyno-proven figure of up to +10 HP and +8 lb-ft and credits the longer intake tract with better air speed and throttle response. Owners on user forums remain skeptical that a spacer like this adds meaningful power on modern direct-injected engines, so treat the gain as modest. What you pay for is precision billet construction and a whistle-reducing entry design, not a guaranteed power jump.
Per the manufacturer, this spacer is listed for the 2008–2012 Honda Accord, 2012–2015 Civic Si, 2013–2015 Acura ILX, and 2009–2014 Acura TSX, all with the 2.4-liter engine, so verify your exact model year before ordering. It uses the factory mounting points, and the manufacturer notes a slight intake tube modification is needed when pairing it with its Takeda intake (TM-1018P-X). For an Acura TSX 2.4L throttle body spacer install, owners on user forums describe a short swap with the airflow arrow pointing downstream and the kit's longer bolts reattaching the throttle body.
The manufacturer lists the Honda Accord 2008–2012, Honda Civic Si 2012–2015, Acura ILX 2013–2015, and Acura TSX 2009–2014, all with the 2.4-liter four-cylinder. Confirm your exact year against the manufacturer's fitment information before ordering.
The manufacturer claims up to +10 HP and +8 lb-ft on a dyno. Owners on user forums are skeptical, especially on direct-injected engines, so expect a modest change rather than a large power gain.
The manufacturer says a slight modification to the intake tube is needed when using its Takeda intake system (PN TM-1018P-X). Other intake setups were not addressed in the manufacturer information reviewed.
The manufacturer's product information references a CARB Executive Order for this spacer, but it also lists exclusions for certain engine test groups. Confirm coverage for your specific engine with the manufacturer before purchase.
Owners on user forums rate this job as straightforward, roughly a 1.5 to 2 on a 10-point scale, and one describes it as about 20 minutes. The sequence is to lift off the engine cover, detach the intake elbow from the throttle body, remove the four throttle body bolts, and lift the throttle body off the manifold. Set the spacer and supplied gasket between the manifold and throttle body with the airflow arrow pointing in the direction of air flow, reattach the throttle body with the extended bolts from the kit, and then reconnect the intake elbow. Because that write-up came from a different truck application, check the sequence against the manufacturer's installation instructions for 46-37001. If you run the Takeda intake, plan for the intake tube modification the manufacturer describes before you start.
