I have a rad valve and spacer on the 97 k5 of mine. Its aluminum and I think Boysen also. My problem is keeping nobbs on the tire!!!!! Hits hard on bottom thru top. I'm basically all stock except for that and pipe(pro circuit platinum) and silencer, and am competitive with everyone. My bike had them on there when I bought it, but the guys on here, who know, say it helps bottom end.