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DSPTurtle's Avatar
 
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8mm valves

Anyone used 8mm stems in a 930 turbo motor? Do they hold up? Was the weight advantage worthwhile? TIA
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Old 12-28-2017, 07:23 PM
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Been doing it for years, yes. It means switching all related valve parts:
valves
keepers
retainers
guides
stem seals

If it's a typical CIS 930 or has stock small 32mm ports, there's no advantage.
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Old 12-29-2017, 11:04 AM
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Well , you just got all the advice you need. As usual.
Thread closed :-) Chris is the man.
Alan
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Old 12-29-2017, 10:51 PM
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Well, the 993 EVO intake valve can be had with a 2.5mm bigger intake diameter (51.5 vs 49) but that is hard to fit in a 97mm bore. It can support a 46mm intake port, the biggest ever on an air cooled 911 motor! So, probably overkill without some port work.

The regular 993 turbo intake valve is 49mm, the same as the 930, with the thinner 8mm stem.

The secret here is that it is sodium filled, unlike the 930, which has only the exhaust sodium filled. The sodium cools the intake valve, which is the hot spot in the whole chamber at WOT. Much more resistant to detonation. I always use them. Definitely worth it IMHO. Slightly pricey though.
Old 12-30-2017, 09:26 AM
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Thanks Chris. This is the turbo motor I am putting the 3.2 (40/38) heads on. Isn't there a Toyota valve that works that's a lot cheaper than the 993 valve? I want to buy a few and weigh them to see if it's worth having the heads redone for the 8mm valves. I imagine it's a lot bigger weight reduction that the Ti retainers.
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Old 12-30-2017, 11:22 AM
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I’m afraid that light and cheap are on opposite sides of the equation. The 993 turbo intake valve has a hollow stem, half-filled with sodium, so it is going to be the lightest. Making such a valve is not cheap though, unfortunately.
Old 12-31-2017, 07:11 AM
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Quote:
Originally Posted by Speedy Squirrel View Post
Iím afraid that light and cheap are on opposite sides of the equation. The 993 turbo intake valve has a hollow stem, half-filled with sodium, so it is going to be the lightest. Making such a valve is not cheap though, unfortunately.
I respectfully disagree. Toyota makes many many many more units than Porsche. The quantities allow for the NRE to be amortized over many more units. So even though it is lighter it could still be the same quality and much much cheaper. I spent many years in aerospace and if we could use a commercial part... exact same specs mind you, it would be 10% of the cost.
Old 12-31-2017, 07:37 AM
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Don't know about Toyota valves. The only time we'll use non-OEM valves in a 911 is in a set of Xtreme's cylinder heads.
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Old 01-03-2018, 01:10 PM
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