kellyk

I am running the 16 valve head on my 968 turbo motor and remember that there were ceramic valve liners on the exhaust side of the head. Can anyone tell me what the benifits of this are? Originally I wanted to port and polish the head but couldn't because of the ceramic liners. Does the 951 use the same ceramics?

Danno

Yeah, the 951 has the same ceramic liner in the exhaust ports. The liner's there to keep heat in the exhaust gases. It insulates the head from the heat so less of it goes into the water-jacket. More heat in the exhaust gas makes it to the turbo and more energy is available to drive the turbo (less lag at low-RPM).

However, it does take up some room. I remember Chris Cevelli mentioning that on his 968 TurboRS engine, he uses the head from the 2.7L NA car because the exhaust ports were larger without the liner and he was able to flow more and get more power.

I remember seeing a photo of a semi cross-section of the 951 head and it shows the liner partially exposed. Anyone have a copy of this photo?

Brian Morris

Kelly,

You can have the ceramic lining re-done, I assume Vision had it coated in the first place since the 968 head doesn't come with this lining (this was going to be one of my questions for you). You could have the head ported and then have the ports relined - it's something like $20 a port, I've just been looking into this for my 968 turbo motor.

Here's two places that do it:

<a href="http://www.swaintech.com/price.html" target="_blank">http://www.swaintech.com/price.html</a>

<a href="http://www.performancecoatings.com/prices.html" target="_blank">http://www.performancecoatings.com/prices.html</a>

--Brian Morris
89 951

Danno

I'd be interested in a comparison of those coatings and the ceramic liners in the stock Porsche heads. There's definitely a difference in thickness with the Porsche one being a full 4mm thick porcelain-type insulator. You can probably hold a blow-torch on one surface and it's be cool to touch on the other side for quite a while.

kellyk

thanks for the responses guys!

I'm not sure how or what Vision used when doing the heads. Next time I am at the shop I will remember to ask. My question was more to "why" use ceramic as opposed to "how". Now I know!

Danno

I saw a show with some new materials being tested. One of them was this stuff called 'AeroGel' or something like that. It's basically silicon-foam or some such thing with mostly air; it floats on water. The guy was holding a sample in his hand (about 1/4" thick) and there was a blow-torch blasting down from the top. And the piece was glowing brightly, but nothing got through to burn the skin. Wow... Wonder if we can get some of this stuff to line the exhaust ports and maybe even the entire exhaust pipe, eh?

kellyk

Kind of like the ceramics they use on the space shuttle tiles. They are so heat non-conductive. I saw a show where these tiles were heated in a furnace to cherry red in the center and the corners could still be held in the guys bare fingers. Pretty impressive.

How about a ceramic turbo hot-side?

Danno

I'm going to try a ceramic coating on my turbo hot-side next. And the downpipe too. Hopefully keep some of that heat out of the engine bay and the intake-manifold right above it!

Kelly, what kind of maintenance does that monster car of yours require?