Sodium fill exhaust valves

[Al 96 Ram Air T/A]

So, what is the verdict on these things? I know the LT4 used them, and that they were used in 60's era heads, (I believe in the Corvette 427) but do they work? I thought they were superior to standard valves in weight and heat dissapation. So then why do alot of head companies replace the LT4 valve with same sized stainless steel valves? If they are not "increasing" the valve diameter, why not use them?

[wolfdogs]

So, what is the verdict on these things? I know the LT4 used them, and that they were used in 60's era heads, (I believe in the Corvette 427) but do they work? I thought they were superior to standard valves in weight and heat dissapation. So then why do alot of head companies replace the LT4 valve with same sized stainless steel valves? If they are not "increasing" the valve diameter, why not use them?

i ditched em in my 396 ....68 chevelle. bent two of them after installation of the isky rpm 300 high lift cam i installed... i made a mistake of keeping the stock rockers though, after i went to roller rocks..things got better. i went to solid valves and never had a prob though.

[Al 96 Ram Air T/A]

So, does the sodium-filled hollow stem inherently make them weaker at higher rpm? If so, why did GM spec. them for the LT4 motor? Also, doesn't the LS6 motor use them? Or maybe it was the new LS2...I read it somewhere recently...

[Injuneer]

The sodium is intended to cool the valves. But, it doesn't necesarily make for a "streamlined" design. Although the LT4 exhausts are already 1.55", it is typical to remove them and replace them with a valve that produces better flow, typically 1.56" diameter, with a tulip head design. If you are worried about high temperature problems with the exhaust valves - e.g. a 300-shot of nitrous - there are non-sodium filled valves that will flow a lot better while standing up to the heat. The Manley Severe Duty would be a good example.

[Al 96 Ram Air T/A]

So, in summary, does the added benefit of "cooler" valves negate the poor flow characteristics? Apples to apples, will the same size (e.g. 1.55") valve with a tulip shaped head outperform a sodium filled valve? I'm confused as to why GM uses them over a traditional valve with better head design. Perhaps the high compression of the LT4 was a concern?

[SteveH95Formula]

There seem to be two schools of thought on this. The hollow sodium filed valves are lighter that solid ones. If you go with solid valves you will need heavier springs to keep them closed at higher RPMs where as the hollow you you don't need as heavy of spring and there will be a bit less friction in the valvetrain.