911 Valves - OEM v Stainless Steel

[NevenM]

Hi All

(esp Wayne just finished reading your book!) I'm doing the heads now and strongly suspect that the valve stems will be worn ('73 911E) but am wondering if anyone has any opinion on the advantages of using stainless steel valves (esp Exhaust) v OEM

The guy thats doing the machining has made relevant points about technology changing in the last 30 years and that sodium cooled exhaust valves are not the 'trick' item they once were

Before you write him off as an idiot, I like to tell you that he gets more power out of a normally aspirated Type 4 VW engine than
you could out of the same size 911 6!

Look forward to your replies

Neven

[Wayne 962]

Hmm, thinking back to recent experience, I can't recall if I've seen 911 valves rust. Perhaps it's because they are coated in oil all the time, but also perhaps they are already made of a stainless alloy - I'm not sure on this one.

The Porsche airplane heads I have up on eBay:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&category=33617&item=2427480510

(subtle plug) have some surface rust on the seats, but none on the valves, if that is any indicator.

I'm all for newer technology, but I haven't seen any specific studies that say any of the newer valves are better than sodium-filled ones - especially for air-cooled engines...

-Wayne

[NevenM]

Wayne

Nor do they get subjected to acid though titanium has great acid resistance qualities!. Seriously this may not apply to 911's, some sodium cooled valves are prone to snapping (Ferrari Dino's spring to mind) and a lot of engine builders now use SS as a matter of course

Hans's experiance is in building 300hp Type 4 offroader engines and
he no longer uses sodium for exhause as austentitic SS wears better

Neven

Neven

[Bill Verburg]

Stock valves are stainless steel. Some are hollow for weight some are hollow and sodium filled for cooling.

There are trick valves which are also stainless and have features such as undercut, polish, coating etc.

The lighter the valve(and rest of the valve train) the better the engine will rev.

I am not at all familier w/ the smaller engines but for 3 liter thru 964 3.6 the hollow 49mm 3.2 cubsport and sodium cooled 41.5 mm 930 valves are pretty trick

If you need larger valves then you go to the aftermarket for their version of ss/Ti or whatever valve.

[350HP930]

I would like to see some additional input on this subject since I too have been concidering replacing my overly expensive sodium filled valves with more practical solid stainless valves.

I figure my engine will never see periods of WOT long enough to justify the heat conducting capabilities of the sodium valves.

[Tim Walsh]

Some of my valves rusted but that's only because my engine sat unused for about 18 months or more. The other contributing factor was the water that was sitting in my cylinders. If I remember right the only valves that rusted were the exhaust valves. Just a data point for everyone. I'm having them replaced with stock valves

[snowman]

Stainless valves do not retain or conduct heat like any other valve. I suspect that they are better for any practical use of a 911 engine and certainly are a whole lot cheeper than the sodium filled valves. I have no data on this but the hot rod world is using them big time, with much success.

PS they will not rust.

[Bill Verburg]

The undercut, coated valves are available in 52mm(and larger sizes) and are well thought of by some engine builders.

I think that w/ an air cooled engine anything that removes heat from the combustion areas is an asset, Na filled valves do that and are light as well. If the cost a C note a pop, so be it.

The turbos use some pretty exotic alloys to help their cause.

[beepbeep]

Hmm...SAAB (very very high EGT) used sodium-filled valves in late 70's and replaced them with some other SS alloy that was "Stelite"-coated whatever it means...

My understanding is that you don't need sodium-cooled valves anymore

[Bill Verburg]

one data point
993 uses Na cooled intakes and solid ss exhausts.
993RS used Na cooled intakes and exhausts.

Stellite is a hard coating used on valve tips to prevent mushrooming and wear.

By all mean if you feel that the Porsche engineers don't know what they are doing do as you feel is best.

Here is a short list of some alloys used in making valves and they're applications

Steel Alloy (Chromium/Silicon)
Intake Valves

Steel Alloy (Chromium/Silicon)
Heavy Duty Intake Valves

Stainless Steel (Chromium/Nickel)
Racing Intake & Exhaust Valves

Stainless Steel (Chromium/Nickel) + Tungsten
Racing Intake & Exhaust Valves

Stainless Steel Hi-Temp
Turbo Intake & Exhaust Valves

Stainless Steel Hi-Temp
Racing Exhaust Valves

(Nickel Base + Niobium + Tungsten)
Racing Exhaust Valves

Inconel Alloy 1.800 ºF
Turbo Intake & Exhaust Valves

NICKELVAC N80A
Super Alloy (Nickel Base) 1.850 ºF
Racing Exhaust Valves

NIMONIC 90
Super Alloy (Nickel Base) 2.000 ºF
Turbo Exhaust Valves

NICKELVAC 600
Super Alloy (Nickel/Chromium) 2.200 ºF
Racing Exhaust Valves

NICKELVAC 800
Super Alloy (Nickel/Chromium) 2.400 ºF
Racing Exhaust Valves

(Funny Car/Top Fuel)

ASTELLOY 75
Super Alloy (Nickel Base)
Turbo Exhaust Valves

PYROMET
Super Alloy (Nickel Base)
Turbo Exhaust Valves

STELLITE
(Chromium/Tungsten)
Seat & Tips Applications

[Bill Verburg]

One additional point
none of the regular production 3 or 3.2 or 3.3 motors used Na in the intakes, only the 3.2 clubsport used hollow intakes

All of the tubo 911/930 used Na in the exhausts.

As w/ the 993 the 964 uses Na in the intakes but not the exhausts. The ceramic shield in the exhaust port is used to deal w/ the heat.

they are all ss with an inconel alloy used on the turbo exhaust valves

[NevenM]

I'm in no way feel that Porsche Engineers don't know what they are doing but what was 'de riguer' in 1973 possibly has moved on since,
They don't use MFI pumps anymore either :-) I'll probably use OEM Valves (as I am restoring the car to Orig Specs) but It was an interesting point for discussion

[NevenM]

Bill

Are Na filled Valves any lighter or is is simply a heat disapation issue?

Also I pulled one of the heads apart and mic'd the stems, its a pain 'cause they we both slightly less than 0.01 mm undersize, still
within spec...just

What to do?

Neven

[Bill Verburg]

The laws of physics haven't changed since '72 and air cooled engines have heat related problems that water cooled do not.

As I stated in my first post
"I am not at all familier w/ the smaller engines but for 3 liter thru 964 3.6 the hollow 49mm 3.2 clubsport and sodium cooled 41.5 mm 930 valves are pretty trick"

You could also use the 964, Na cooled, 49mm intake w/ the turbo valve. It all depends on the hp(read heat, the engine is expected to handle) and durability that you desire.

use w/ phosphor broze or the newer mandgenese bronze guides and some good performance spring retainer kits like JWEW or AASCo sells and you valve train will be as near bullit proof as you can make.

[snowman]

I am a bit puzzled by the use of Na cooled valves on the intake but not the exhaust. Are you all certain that it isn't the other way around, ie Na cooled exhaust and solid intakes? The reason I say this is that the intakes are cooled by the intake charge, while the exhaust are heated by the combustion.

[Bill Verburg]

Are you all certain that it isn't the other way around, ie Na cooled exhaust and solid intakes?

I only post facts.

My theory is weight. The factory engineers have shown great concern for reducing the mass of all of the rotating and recipricating components. Why, not hollow? either $ or there was an undisclosed issue w/ the hollow stems(strength? durability?)