Q: I’d like to install a larger throttle body on my Dodge Challenger with an automatic transmission.
The car currently has a Summit Racing exhaust system and a Trick Flow cold air intake, and future plans include headers, a camshaft, an intake manifold, an SRT differential, and lower rear-end gears. Should I wait until I do more extensive modifications before I replace the throttle body?
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A: Aftermarket throttle bodies are available in various internal bore dimensions (usually listed in millimeters) that have been designed and tested to work best with different levels of upgrades. Increasing your throttle body size is generally considered an accompaniment to modifications that improve airflow through the engine, or raise its effective operating rpm range.
BBK recommends its 85mm BBK-1781 throttle body for mildly modified 2003-12 5.7/6.1/6.4L Hemi engines, and the 90mm BBK-1782 for heavily modified or supercharged engines. Based on your planned upgrades, you
could likely get away with the larger throttle body if you first change your
axle ratio. A lower (numerically greater) ratio would allow the engine to reach its powerband more quickly—taking advantage of the increased airflow—and would be an excellent complement to your future upgrades.
Because of the NAG1 5-speed automatic’s very low 3.59:1 first gear, be judicious in your gear ratio choice. Also, you may need to perform a re-learn procedure with a scan tool or programmer due to the change in airflow.
When planning your engine or driveline modifications, it’s critical to properly match components to achieve the best possible outcome.
The wrong combination of upgrades could actually end up reducing performance, limiting the engine’s power output to a small, high-rpm window, softening initial acceleration, or hurting throttle response at cruising rpm.
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