Editing Openai/6902a8c8-76f4-8001-a86a-93fe7b5e36c6 (section)

=== Potential downsides / caveats ===
* High-RPM peak horsepower tradeoff: Very long runners push the tuned-wave benefits down in RPM. If your original targets were high peak HP at high RPM (e.g., >5–6k RPM peak), this runner length will make it harder to reach that peak. If your targets were low-to-mid RPM torque (street torque, towing, rolling acceleration), you’re well poised to hit them.
* 180° U-bend location & sharpness: a tight 180° bend can create flow separation and turbulence. Make that bend as smooth as practical, with generous radius and well blended transitions into the runner to avoid losses. Sharp edges at the head/plenum interface will hurt VE more than you’d expect.
* Throttle control & idle tuning: a 56 mm TB plus long runners can produce a lopey idle if idle air control (IAC) or ECU fueling/idle map isn’t tuned. If running an idle valve or ISC, make sure it’s functional and the idle stop is set for a predictable position. If carbureted, you may need smaller bores or a good jetting/tuning session.
* Port matching: ensure the runner ID and the head port are matched (or properly tapered). Sudden contraction/expansion at the head undermines the runner tuning benefit.
* Resonance details: I avoided giving a single “tuned-RPM” number because intake wave reflection timing depends on valve timing, effective length (including head trumpets, corrections), and temperature. Qualitatively — this length favors idle→midrange tuning, not a high-RPM quarter-wave tune.