Left, 911 95mm Right Type 4 104.9

The 911 cylinder is sealed with a wire sandwiched by I believe aluminum, when torqued the wire crushes in the aluminum against the head and against the cylinder, making a well known seal.
The type 4 cylinder has been groved for a wire O ring. The wire is .033 dia, the grove is machined .033 wide and .029 deep, allowing .004 to protrude above the cyl sealing area. A copper head gasket will be used. When torqued the the wire will be crushed into the copper head gasket, making for a better seal.
I've even thought about taking this further, by having another grove machined in the head, .033 wide, .029 deep, thus further sealing both sides of the copper gasket.
And I thnk that, this would be as close as one could get to 911 sealing with cast iron cylinders.

This is only my opinion, and skeptics need not apply.


Richard

I would think that machining the top surface with a .0015"-.003" runout (taper) per the specifications for a 3.2 Carrera would provide a better seal, but would be hell on the heads unless a copper gasket was used. I'd be concerned with the physical lack of surface area when machining in the sealing groove. But what you suggest isn't too far off of what I have seen on the Pelican boards offered by a few machine shops, although they use a thicker piece of aluminum. I can't remember where I saw it (it might have been these forums of shoptalk), but someone machined a physical step precision matched on the head, to simulate the indexing created when flame ringing, but again, that solution leave you with two smaller sealing areas and I would think would be equally hard to seal up.

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

Interesting idea. If I were going to do a mod, it would probably be more on the lines of the later 964 engines. You know they first had no seal ring, had some leaking problems, and then had a seal. Being one of the last of the aircooled engines, I'd think they may have gotten it right by them.

The other consideration is that there is a boatload of aircooled engines out there, six and four that don't have anything between the head and cylinder, and don't leak.