Exhaust Valves

[t70]

Well folks, I have sent an exhaust valve down to my parts supplier in the states (Atomic Speedware.) Nick Arias (the owner) sent the valve off to SI Valves and they immediately made a full set of 8. I didn't mean to have them made, but they are. The price I'm giving you is my cost! I will not be making any money off of this at all. The price is $296 USD plus shipping for all 8 valves. The Valves are swirl polished stainless valves that will be as good or better than the stock sodium filled valves for heat dissapation... plus they will flow much better. The are also hardened tips.. I've used similar valves in my supra... and my flow numbers were noticeably changed. I think it was somewhere between 5 and 10 cfm... i'll have to look up my old flow sheets to check that though.

Just post here if you want a set, or call (403) 581 6875 and ask for me, Mark... or you can e-mail me at mark@southlandvw.ca

[Vulcan Grey]

Not sure I understand why stainless steel exhaust valves would be better or transfer more heat than sodium filled?

Stainless is a poor conductor of heat, low coefficient of thermal transfer.

Lotus, and many others, see the need to use sodium filled valves and silicon-bronze guides on the exhaust side of most turbo car (well the well designed ones anyways).

for example, a silicon-bronze valve guide conducts heat 2X better than grey cast iron, and berylium conducts 2x better than silicon-bronze.

and of course cost goes up with the better materials.

Last time I bought valves for the Lotus 910 (chargecooled) Stainless Steel intake valves wer $29ea and sodium filled exhaust were $89ea.

What information do you have that these S.S. will conduct more heat?

[t70]

Not sure I understand why stainless steel exhaust valves would be better or transfer more heat than sodium filled?

Stainless is a poor conductor of heat, low coefficient of thermal transfer.

Lotus, and many others, see the need to use sodium filled valves and silicon-bronze guides on the exhaust side of most turbo car (well the well designed ones anyways).

for example, a silicon-bronze valve guide conducts heat 2X better than grey cast iron, and berylium conducts 2x better than silicon-bronze.

and of course cost goes up with the better materials.

Last time I bought valves for the Lotus 910 (chargecooled) Stainless Steel intake valves wer $29ea and sodium filled exhaust were $89ea.

What information do you have that these S.S. will conduct more heat?

Hmmm... I've had this discussion with Nick Arias a few times and he continuously has stated that the heat conduction is the same or better... but I think I will delve deeper into this now, given your current information.

[Vulcan Grey]

Stainless steel (304 for ex.) Thermal Conductivity =16.2 W/m-K

http://www.matweb.com/search/SpecificMater...?bassnum=MQ304A

Sodium Thermal Conductivity =135 W/m-K

http://www.matweb.com/search/SpecificMater...bassnum=AMENa00

So sodium is 8.4x better, faster, at transfering heat.

And the sodium is intended to melt and splash back and forth from the inside of the head to the stem transfering heat with it into the stems and into the highly conductive silicon-bronze guides.

The Sodium filled valves still have a stainless exterior, so to a point they are the same (with the sodium valve probably being weaker). Though thermal conductivity decreases with decreasing cross-setional area, but increases with decreasing thickness. So the heat will transfer faster into the heart of the sodium filled valve through the thinner walls, and the sodium helps it transfer up the length of the stem faster, bypassing the thin and restrictive walls in the lengthwise direction... Best of both worlds.

[Artie]

Travis,

Jeez dude, did you help build the space shuttle or something? That's some intense stuff, I think I pulled a hammy reading your reply!

Artie

[t70]

Wow! That's some pretty intense information man! Now I understand what's going on... and it's gonna be tough to sell these 8 little buggers.. hmmm... what to do now? However, all that being said, the only reason I began this project was the problem of exhaust valve availability... so I guess these are still do-able. I will be e-mailing SI valves tomorrow to see if there's any evidence to support just using stainless or if they can make them sodium filled. The valves might just end up on my dining room table as candle holders... lol

[lotus4s]

Travis,

Jeez dude, did you help build the space shuttle or something? That's some intense stuff, I think I pulled a hammy reading your reply!

Artie

[USAndretti42]

Provided they are the right size, those valves should be more than adequate for a N/A car.

[t70]

agreed there

[t70]

Okay, I talked to SI Valves and they said they use 214n stainless and that it's heat conductivity is basically as good as sodium. The reason they used to use a sodium filled valve is the lack of metalurgical abilities in the past. Porsche used to use sodium filled valves as well and has since stopped. Apparently the 214n is good to 1800 degrees. The guy I talked to at SI runs 28-30 lbs of boost on his buick grand national turbo with this type of valve and has no problems. If you are hitting EGT's of over 1800 degrees, you've got serious AFR problems! So, in the end, these valves ARE just as good in terms of longevity/ability as the previous sodium filled valves... I am going to do more research on the heat dissapation, but my understanding is that its a moot point.

[Vulcan Grey]

Ah 21-4N steel is an austenitic Chromium (21%) & nickel (4%) steel

it is very strong, not quite 2x stronger than a 304 Stainless Steel.

I haven't yet found any thermal data for 21-4N

but this is a good read if you are interested.

http://www.automotiverebuilder.com/ar/ar99946.htm

and

http://www.automotiverebuilder.com/ar/eb120524.htm

[t70]

yeah... i've been trying find some data on the 214n... no luck yet... i'll read your links later tonight.. I'm off to go work on Otis right now.

[wiseraven]

I found this PDF file on the web from G&S Valves. It's an 8Mb download, but contains a lot of interesting stuff about different materials.

According to this 21-4N thermal conductivity is 14.5 W/(mK), but I've no idea how accurate this is.

[t70]

Well... it looks like 214N is actually one of the better all around materials for valves to be made from. The heat transfer rate of sodium is really quite fantastic, but the entire valve is not made of sodium. If it were, it would be molten at engine temp. So, there has to be more information about the sodium filled valve and it's specific heat conductivity. Correct me if I'm wrong, but all the sodium would do (in terms of heat conductivity) is actually just insulate the centre of the valve. The Sodium would actually be very good at reflecting the heat back to the valve stem. This would actually make the thermal conductivity worse than a standard valve due to the surface area of the valve (outside surface and inside surface combined) would be greater than a standard valve. The advantages of the sodium bouncing around "cushioning the blow" would be counter-acted by the additional heat created by the friction of the sodium movement. Then there has to be some sort of static charge being created by the friction of the sodium movement within the valve... This could lead to pre-ignition. I fully realize the fact that I'm not a chemist or a metalurgist, but if you can shed some light on my logic... That would be fabulous and very educational. (I know, I seem to enjoy a good dispute, but it seems to speed up the learning process)

[USAndretti42]

A lot of heat is conducted out of the valve through the stem to the guide. The edge of the valve, near the seat, is relatively thin so does not hold much heat. Also, when the valve is open it's not losing heat to the seat. It's picking heat up from the gas leaving the cylinder.

The middle of the valve is thick and heavy and contains a load of heat well away from any where it can get rid of it. So anything that can whistle the heat up the stem and out to the guide could be a benefit. Sodium, as said, melts when the valve gets hot and then convection comes into play. The hot molten sodium near the head of the valve tends to rise up the stem and cool and then sink again helping the cooling further.

You are right that the valve is not all sodium. About half the cross-section is sodium giving a much better overall thermal conductivity than the base metal alone. The question is how much heat transfer does the engine need to stay reliable?

[t70]

There is a factor that none of us have considered... weight. I've received the valves from SI and they are significantly heavier than the stock sodium filled valves. So, all this heat discussion is actually inconsequential when considering the added issue of valve float due to excess weight in the valve train.