Assuming your talking about physically longer valves,,,and not just a taller spring installed height...
Longer valves (either intake or exhaust) are typically used mostly just to allow one to use a taller installed height valve spring,that is done to gain more retainer to guide/seal clearance when employing higher lifts @ the valve.
Now does that help flow,maybe yes,maybe no,depends on how you look @ this,if the head flows well at such higher lifts,then yeah it'll help flow some to do such (open the valve further),if the head(s) are pretty much already well past their peak flow,then no it really wont help flow much @ all.
You'd need to post flow numbers for the given head,and cam specs to get a good idea if that was close to optimum or not.
HTH
Bret P.
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