28 mm (2020+ models): The throttle body and intake manifold are used to control the amount of air flowing to the engine’s combustion chamber, they are important elements of the admission system. Using Koso’s 28 mm throttle body in conjunction with their 23 to 29 mm intake manifold will allow a better air/fuel mixtures for a quicker throttle response. Allows better air/fuel mixtures for a quicker throttle response. 34 mm (2014 - 2020 models): As the throttle body and intake manifold are used to control the amount of air flowing to the engine's combustion chamber, they are important elements of the admission system. Using the Koso 34 mm throttle body in conjunction with their 30.5 to 34 mm intake manifold will allow better air/fuel mixtures for a quicker throttle response.