I've been told that the new exhaust valves on some of the newer 'vettes are filled with sodium and or potassium. Is this true?

I assume this aids in cooling as the heat capacity of these elements in the liquid state is extremely high. I also assume this transfers heat from the hot face of the valve to the relatively keeper end of the valve stem. Is this correct?

What form is the sodium/potassium in when cold? When Hot?

What is the volume of the hollow stem and how many grams of sodium/potassium?

Although I have a low tech 68 vette, I am a high tech guy with a background in chemistry and materials engineering who is always interested in the latest technology.

I posted this on the C5 forum but did not get an adequte reply.

Thanks,

Scott

 

Quote"I've been told that the new exhaust valves on some of the newer 'vettes are filled with sodium and or potassium. Is this true?"

I don't have a clue on the newer Vettes but I do not see why they would.Sodium filled valves came out in the 70's in part because of unleaded gas.They are "were" heavy and the newer stainless steel valves are more than up to the task of taking heat made by the 120 degree exhaust center lines of the newer motors.If in question of the endurance capabuilities of a good stainless steel valve there are Iconel available.
For your motor and the cam it uses or other wise needs this is a non issue
Sorry I could not answer your question as to the property's and the form of it when hot or cold but weight and endurance is what matters most in a high performance situation concerning valve train components

 

The LT4 had sodium filled exhaust valves and hollow stem intake valves. The sodium is to cool the head of the valve for better resistance to detonation as the exhaust valve is often the hottest part in the chamber area. An exhaust valve has a temperature gradient that is lowest at the stem and seat where heat is transferred out of the valve to the valve seat and valve guide. The center of the valve face and the portion of the stem that protrudes from the guide are the hottest. The sodium splashes around and makes a more uniform temperature. Hollow stems reduce the weight of the valves for better high rpm capabilities without going to overly strong valve springs. I'm not sure about the state of the sodium when cold (maybe solid) but under operating conditions it's liquid.

All the aftermarket people I talk to like inconel for the exhaust valve but I think they are looking at race type applications. For racing the advantage of inconel is that it's stronger and tolerates heat much better than other alloys. This doesn't help with detonation but that doesn't matter as much if you're running race gas (you can also use ceramic coatings to help). The strength also allows very radical cams with high spring pressures.

The sodium filled valve is a better compromise for high performance street where you run pump gas but want to run higher cylinder pressure. It allows lower spring pressures so you don't have to rebuild the valve train as often. The factories seem to like them. GM uses the same LT4 valves in their fastburn cylinder heads. Porsche uses sodium filled valves on their turbo motors. Availablity and cost are the biggest problems I see for the sodium filled valves (I don't know any aftermarket companies that sell them).

edit: here's a website that has a very good description of the LT4 engine. It lists the weight of a standard LT1 1.5" exhaust valve = 95 grams and the LT4 1.55" sodium filled exhaust valve = 75 grams. A pretty substantial weight savings. http://home.tir.com/~steveher/lt4.html



[Modified by torquejunky, 11:58 AM 12/27/2001]

 

Yes they are sodium filled and it something thought up prior to 1970 because Porsche was using it in the late 60's in race cars.

Sodium is a metal. With a melting point something not much over 600 degrees F.

I have never seen tech data to the total weight. But it couldn't be very much.

 

I had never heard before of the LT4 having sodium filled valves, but the Z06's LS6 does in deed have them. They are lighter and allow the valvetrain to rev' up a little bit faster.