Exhaust Valve Opinions ?

[350HP930]

There is a little debate going on where I work about my project so I decided to get the opinion of my fellow pelican members on the subject at hand.

My 930 valves have about 130K miles on them but are still in spec and have reground perfectly. Between worn exhaust valve guides, a couple of eroded seats and the fact that the EGTs were at one time hot enough to have melted off a few of the air injector tips I am planning to buy a new set of exhaust valves.

I have seen what kind of carnage can occur when the head comes off of a valve and don't want to see that occur to my rebuilt motor.

I also still remember the part of my materials engineering classes concerning cyclic stress fatigue and realize that my valves are probably most of the way through their safety factor.

The other guys at the shop understand where I am coming from, but for $350 a couple have said thats a lot of money for peace of mind.

Do any other DIY rebuilders or machinists care to share their opinion or policy concerning the replacement of exhaust valves, even ones that clean up perfectly and are well within spec?

Thanks . . .

[TimT]

but for $350 a couple have said thats a lot of money for peace of mind

I think $350 is cheap insurance. How many time have the valves been ground?

Youll kick youself in the butt if you do have an exhaust valve related issue that costs $10000

[350HP930]

Thats the way I look at it.

I am the first person to regrind these valves, but its the heat and stress fatigue of the stem where it connects to the head that I am worried about.

With the additional spring pressure and the extra severe duty they will have to put up with when the engine is back together, I think the old valves are no longer up to the job.

[strokher racing]

I have a set of intakeand exhaust valves with 400 break in miles on them. Let me know if you might be interested

Eric Hood

[350HP930]

Are you willing to sell just the exhaust? What did you do, go to oversized valves?

[Wayne 962]

In a normally aspirated engine, like a 2.2 T motor, I wouldn't sweat it. But the margin for error is much higher in your Turbo engine. I would replace them.

-Wayne

[afterburn 549]

When in doubt throw them out......and valves I rarely measure...as stated above.......plus "do I feel Lucky?"I think you biggest question to debate on is which kind of valve to use>......I lean on the sodiums

[Wayne 962]

Sodium without a doubt - it's what the factory used...

-Wayne

[strokher racing]

SS valves are fine in the turbo heads....they offer improved flow, lighter weight, smaller stem sizes undercut etc. They are much cheaper as well than the porsche stuff. Yes, I went to larger custom valves that is why I have the extra set. Here is a pic of my valves and combustion chamber for you.

Eric Hood

[afterburn 549]

I dont want to say whats right and wrong....but this is what I do know.
The sodium ones are slightly more hvy..but in a turbo your not going to see 10000 rpm..and there is the heat problem asso with turbos (more heat at lower rpm so it is nice to have a way to flush it out.)
All class 8 big truck eng use sodium.....and these things put out big pwr at 1200 rpm.
Is true you cant hardly burn a SS valve but its the residual heat that might cause some problems........just m.o.

[WERK I]

What about dimensional stability? Which of the two mentioned (SS or Sodium) provide the best wear characteristics when it comes to ensuring long life for the valve guides?

[cnavarro]

Eric, who does your stainless valves? I've heard that Del West makes a damn fine stainless valve. How about inconel? Although not a "shelf" item, they can be custom made, along with custom guides and seats (the seats used with stainless valves, or stock ones for that matter, are too soft. I think I have some research we had done way back for a customer. I'll see if I can dig it up- drop me an email and i'll forward you anything I can find.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

[strokher racing]

We use copper on our exhaust seats. The valve guides are custom made bronze units. As for valves, we either use ferrera or manley lines. We do use the higher temp valves. Inconel is another option that has been used, but never held up any better than the high end stainless stuff we use. My head porter has never had an issue with the stainless stuff, and he is responsible for the head work on several of the fastest Porsches in the world. I have used del west stuff on my mustang engines but never in the Porsche stuff. They make real nice titanium valves, but that will not last on the street. I have never used their stainless valves.

Eric Hood

[afterburn 549]

werk-1......just refer to what the owner of the mother ship said and you cant go wrong........worked for Porsche too.....the inventer of this ans.

[350HP930]

Even though a good modern exhaust valve can survive without sodium, it will run hotter than a sodium valve will.

The last thing a hi-po 911 or 930 needs is a large glowing hot area in the combustion chamber.

Sodium keeping the head of the valve cool has positive benefits beyond extended valve life.