Brian
Straight stem valves or undercut??
Moderator: Team
Straight stem valves or undercut??
I've used the undercut stem valves for years, but recently have noticed that in some heads there tends to be less turbulence with straight stem valves. I tried 2 same size valves from same manufacturer with identical cuts and even though flow was about the same, the undercut stem valve seemed to produce more rough air sound. According to the pitot tube and superflow flow com the airspeed was about the same...the straight stem was pulling 360fps and the undercut stem was pulling 352. Anyone ever do a comparison of valves on a running engine? Probably not, but was wondering if any of you guys have run into this? Or maybe a well kept secret...that I just let out
Brian
Brian
Test them as exhaust ports and see what happens too.
The undercut stem isn't the hottest idea because as the valve opens the larger diameter of the non-undercut area enters the port and decreases the area over the short side turn while the choke (throat) area right before the seat remains the larger size afforded by the undercut portion of the stem.
Personally I'm not a big fan of them. If you want a smaller sized stem, go with a smaller sized stem and forget the undercut idea. It's a band-aid in my opinion.
SWB
The undercut stem isn't the hottest idea because as the valve opens the larger diameter of the non-undercut area enters the port and decreases the area over the short side turn while the choke (throat) area right before the seat remains the larger size afforded by the undercut portion of the stem.
Personally I'm not a big fan of them. If you want a smaller sized stem, go with a smaller sized stem and forget the undercut idea. It's a band-aid in my opinion.
SWB