Oversized valves can help get more flow but go too large on the diameter and they can hurt flow.

Here is a picture of oversized valves done right (on the left) and done wrong (on the right) The faint grey line you see is the contact point for the valve to seat in the head.

At best you want a valve diameter no larger than the seat insert diameter. The one on the right was maxed out for the available seat diameter, and the extra valve diameter just becomes a limiter/shroud. You would need to cut the diameter of the valve on the right down to where it looked like the valve on the left for it to flow properly. Until then this oversized valve will flow less in the head than a stock diameter valve.

BTW - this is an aftermarket valve sold for modular heads, this particular part number does not work at all!

Copyright © 2008-2009 Modular Head Shop All Rights Reserved