What are butterfly valves?

[Chappy64]

Hey everyone I'm new on here and it started out my buddy got a 94 gsr bone stock with 88k miles on it. And I loved it and have always loved honda so I'm buying myself one . I am getting a shell and dropping his engine in it. We were talking about the ls/vtec compared to the gsr b18c1 and he was talking about the gsr being different because of the butterfly valves in it and I heard about them but I never really knew what they were or what they actually did. I tried searching it and couldnt find anything so if you could help me out thanks.

 

[mjones73]

Basically the intake on the B18C1 has a set of secondary runners with valves in them that open at 5900RPM to increase the airflow to the motor to go along with the VTEC engagement at 4400RPM.

 

[Chappy64]

Thank you for explaining that to me I was really interested in what they were for some reason lol.

 

[mjones73]

No problem, some people mistake them for opening for the VTEC engagement I think. I can clearly hear the VTEC hit at about 4400 on mine then the intake gets louder at 5900 when the secondary runners open up.

 

[Chappy64]

Yea my buddy's did that a little but you couldn't here it that well with his being completely stock.