Tuning the length of the runners (attached to the head) is what alters high end vs. low end strength. Longer means lower frequency, which helps the low end. Narrow runners increase velocity, which can cause a slight ram effect at low RPM, but hurts airflow at high RPM. That's different from what goes on before the throttle. Getting less turbulence through the airflow sensor is what helps there. That's a different matter.