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.
Stu
I'll give you a little hint. Aircraft engines use sodium valves.
I know Chevrolet used sodium filled exhaust valves on their Corvair Turbo engines.
Can't see they would bother if it didn't help dissipate heat..
Sodium valves = good Old school tech , they withstand heat better then stock valves ,
Stick with S.S. valves , they are better & cheaper , Bill D.
As long as the engine is well maintained and not abused you should be fine. The sodium valves installed by the factory in the past had a bad reputation of dropping the 'valve head' into the combustion chamber. However I am not sure if there was any abuse or neglect involved in those cases. But if you keep track of your valve adjustments regularly, you will get a fair warning if the stems are stretching before they would actually fail.
But as mentioned above ........ newer SS valves are inexpensive, plentiful and reliable.
I, also, will give you a little hint. STAY WITH THE SODIUM FILLED VALVES!!!! Rsearch it and I believe you will find the sodium provides much better heat transfer than stainless steel. If you have not had any trouble with the sodium ones and they are in good shape, stay with them. Never had any problems with seats or dropped valves on either my 914s or Alfa Romeos. Always rebuilt with sodium ones.
The sodium allows heat to be transferred from the valve edges up the stem via internal stored sodium and out the valve train, or something like that. Itis also used in some solar energy systems as a storehouse of heat until it is needed to generate electricity during the night time.
Steve Hurt
In theory. The sodium does keep the heat out but I would answer the question this way; 40 year old sodium valves - bad. New - good. Finding them? Not so easy. So there you have it. SS is probably a close second.
Also, is yours a race engine? VW purposely made the later engines run hot with the cam they used. You can probably change cams and take more heat out of the equation than the sodium filled valve stems.
What could go wrong? Drop a 40 year old valve in your new heads, destroy a head and piston and more than likely a cylinder.
I call on that thinking.
Rob sounds like your drinking the Raby Kool aid.
If you tortured over heated & neglected your motor, sure after a few DECADES
your chances of a seat or stem failure are bound to increase.
But if you provide appropriate maintenance, Oil, valve adjustments cooling and dont spin that motor beyond its realistic operating range
(continuously )
I believe you are better off with a technology that was designed for the engine than one that was not (Im pretty sure SS was around in the early 70's?).
As for new valves being hard to come by, IDK I havent had to source any recently.
But they will ALWAYS be more expensive than SS.
False economy.
I thought a bit of raby's thinking was to do with the keeper design which was better on newer as valves
BTW this was beat to death here a few yrs ago.
http://www.914world.com/bbs2/index.php?s=&showtopic=49234&view=findpost&p=649822
Sodium valves transfer heat to the valve guides. They are hollow and filled with sodium. Sodium of course is corrosive to metal and as mentioned sodium valves probably have a limited life (20 yrs?). Many Ferrari's came with sodium valves.
As far as 3 angle valve guides. The three angles are fairly normal in production cars now. Valve guide machines cut the three angles with a single pass using multiple angled blades. A 20% increase in flow is probably a far stretch. Many racers now go for a 5 angle cut or an infinite flow cut (think 1/2 of a bell curve).
The multi angle cuts allow air to flow around the seat/valve with less turbulence resulting in higher flow at lower valve lift.
In addition to having a multiple angle valve seat you can also have the valve seat face back cut. Looking at a valve you have the normal 45 degree cut on the valve face which seals on the valve seat. A back cut is added to the top of the face so air flowing out of the intake port flows easier over the valve.
It is widely accepted that valve seat cuts should not exceed 15 degrees between cuts. When atomized fuel tries to go around an angle greater, the fuel tends to drop out of suspension. Most three angle jobs coming out of the port are 60/45/30.
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.
The stock heads already have a three-angle job on them. Check your manual, and you'll see.
--DD
Just to continue on the thread hijack, I attached a link to an article from my website about a Miata head that picked up 26% ex flow from just a seat cut. The page has a link to the flow data.
http://www.hamincgroup.com/blog/services/valve-seat-cutting
What does the inside of a sodium valve look like?
hollow with sodium in it
another thing I don't see mentioned in this thread....
finding used stock valves won't work if bigger valves are intended.
most race motors go with stainless and also bigger valves
as mentioned, stainless are available and affordable (in a large variety of sizes)
I've run (used up) 3 different race 2.0/4's with stainless and bigger valves.
never dropped a valve or seat in those 3 motors.
(of course I had a great head builder for them also)
A lot of the sodum is better crowd info is coming from the 911, it has bigger 9mm sodium valves that work good. I suspect they are a higher quality valve to start with. They do use lower pressure springs because they don't have to push the extra weight of the pushrods and lifters.
Type 4 I'd use new soduim if you can find them, but often I convert the 9mm exhaust valve to a 8mm quality SS unit. Never seen any issues in doing this.
The worst failures I've ever seen have come from Sodium filled, hollow stem valves.
Not for me... And we've had one stainless valve failure in the last 15 years.
Sodium corrodes steel. Only a matter of time.
I don't think you're going to get a more eloquent and convincing argument against sodium filled valves than this:
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