Sodium Valves? Options

[stugray]

I was once told by one of the resident "experts" on this forum (who has not been around lately) that I should replace my sodium filled valves with stainless. However after visiting the local RSR racing mechaninc (who is machining my case and inspecting my heads), HE said that he goes out of his way to FIND sodium filled valves for race engines. He said that on Air-cooled engines, the sodium helps pull the heat from the heads.

Any comments or suggestions regarding sodium vs. stainless?

I also heard that a simple change from two-angle to three-angle valve seats can increase flow by more than 20% with no other changes to the heads.

Good news is that I should be re-assembling the engine without the deck height problems over thanksgiving weekend. Hope to have it running by Xmas. (IMG:style_emoticons/default/piratenanner.gif)

Stu

[HAM Inc]

The Sodium in the valves transfer heat away from the valve head by reciprocating up into the valve stem allowing more than the typical amount of heat (around 20%) to be transferred through the stem to the guide.

I think they serve a purpose and are beneficial where the amount of heat generated can't be handled and transferred away adequately by a solid valve. I have seen no evidence of this issue when S.S. valves were coupled with the appropriate seat and guide materials, even on high compression race engines running high egt's and long cams that hold the valve off the seat much longer than a street engine cam.

Over the years I have seen countless examples of failed sodium valves. Were they old? Yeah.
Were the engines abused? Probably.

New replacements are available and relatively expensive compared to S.S., though I might be hesitant to use them with the O.E. valve seats, but that is moot point with me as I never build T4 heads with the O.E. seats.

My attitude about sodium filled is this; If a customer wants to use new ones in a pair of stock heads that I'm building I'll install them. But if they plan to up the spring pressure for higher revs, I won't.

I know, there are plenty of examples of folks using sodium filled exhaust with dual springs, so obviously they don't all fail in that application. But enough have that I can't see the value in taking the risk when S.S. coupled with the proper valve seat material and modern guide materials do a fine job of handling the heat.

I would imagine that aircraft engines utilizing sodium filled valves have a regular replacement interval that is waaaaay less than 35+ years.