Well can we really buy anything here in the USA thats really made here and not just stating that. For that matter most all Titanium valves are made in China then machined here so I don't understand why the country of orgin has anything to do with this.
As for the open pressures I have run more than this also and I have also ran 180 on the seat with stock valves with well over 400 open.
As for the valves creating turbulence the undercut on the valve stem which the manufactures state that they flow more air, well maybe they do but in a GM as the head castings and the shape of the port complement the style or shape of valve used. If you look in most any mag. all you see is SBC and the undercut valves. What the mags. don't tell you is what works best with a mopar. A few years ago when I was talking to Larry Shepard at a national event I was listening to what he had to say to a fellow racer and why the engine wasn't making the power that it was suppose to. When Larry asked him if he had followed the performance build ups in the mopar performance book, he said that he did to the letter. But come to find out that the difference was in the style of valves that he had used. He told Larry that he used the Milodon valves and that they had a undercut on the stems.
Larry told him to take those valves out and put in the mopar performance ones and that the engine would pick up. The difference was that even though the stock valves are nail heads, the aftermarket ones are undercut but still nail heads.
After my friend left I asked Larry why the difference, he then explained to me that the undercut stem made the air change direction and run into the back side of the valve instead of directing it to the cylinder. I looked at him dumb founded and really didn't believe him either. But then the proof was when I put both the stock style and the undercut style valves to the test. Using a head that I already had ported I first tried the stock valve and it flowed like I expected it to and then replaced it with a new undercut valve from Manley. Both margins were similar and both had the same work done to them.
Low and behold Larry was right, the undercut stem had turblence at just over .500 lift and never cleared up even up through .800 lift. Where as the MP valve stayed steady through out the flow range. What I had found was that the undercut valve made just enough change in the air that when the air passed by the valve that instead of making a smooth curve or transition past the edge of the of the valve that it the air started to spin under the head in the chamber. When this happend the air flow is disrupted and the fresh air charge was backing up on it's self. Showing a flow loss on the bench and wild fluctuations on the monometer.
The best that I could figure that was happening was that the air was making a sharp turn instead of a more gentle turn when entering the chamber, creating a high pressure point under the head of the valve. Then when this area fills up the air starts to backup on it's self and disrupts the incomming air flow or charge. Where as the straight stem valve moves the air flow pattern more towards the edge of the valve and makes a smoother transition into the chamber, eliminating the high pressure spot under the head of the valve. The best thing that I found was how thick the margin is determines how smooth the air will pass. Adding .020-.030 more margin to a valve makes the air flow in more of a cone shape or funnel shape. And stops the under head turblence, because the air has to flow further past the head of the valve before it enters the cylinder. When I did this the air flow of the head picked up about 15-20 more cfm's.
The same thing happened to Mikel Beck's heads when using the stock valves. When I replaced them with the MP ones the head flowed nearly 25 more cfm's and this made the low lift flows flow even more. Nearly 10% more at .200 and .300 lifts.
Sorry for being so long winded but Crusher asked. lol
