D

Could someone define a Ni Resist Ring. Is there modification to the cylinder and the head or is it just a ring in the cylinder similar to the CE head gasket which squishes against the flat head surface. Are they made of something different than a gas filled gasket?

Garibaldi

A ni resist ring, or flame ring, is a ring that will fit in grooves that are machined into the head itself and top of the cylinder barrel where they meet. The ring is made from a high temperature alloy that has a high nickel content. I like to use inconel stainless.

The niresist ring is a band- aid for a Porsche's shortcomings in terms of the engines ability to stay together. The turbocharged race cars that ran high boost and severe loads would use them since the combustion pressures would stretch the engines apart and the seal up at the top of the head would open up and the gasses would escape. SO, as a quick fix, they cut matching grooves into the cylinder barrel and head, dropped a ring in between that could take the heat, and hoped for the best.

Garibaldi

The 962s went a step further and welded the head onto the cylinder . Depending on the year and configuration of engine, some of the 962s had water cooling in some combination and if the heads lifted there, then the cooling passages would be pressurized and then there would be real trouble. The air cooled 911 motors are forgiving in this area since there is no cooling jacket surrounding the head to cylinder sealing surface that will cause an issue if the heads lift off. Don't get me wrong, it will cause damage if it happens, and it still does not solve the problem. Like I said, its a band aid and there are better ways to prevent that issue, but it has been being done since Porsche has been racing turbocharged cars.

D

thanks for the info and a great picture too!

Geoffrey

What better ways?

Tito 911

I too will like to know "of better way"

PCar SBA

My 91 without head gasket leaked on all six barrels. A step was machined into the cylinder only and the heads were resurfaced. There was no modification for the fire ring done to the heads. As the pictures show the top part of the cylinder was left rough on purpose. It cuts into the sealing surface of the head to give some extra protection.

PCar SBA

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PCar SBA

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Sameer

Are there any disadvantages to doing this Nirisist or flame rings?

PCar SBA

I couldn't think of any other than all the time and all the $$$ I had to spend to get this done. Porsche should have done that in the first place. They were simply trying to get away without gasekts like the did on the earlier cars. The 3.6 is what pushed them over the limit......

Ingo

Natchamp

Have you guys considered the fact of heat transfer? A good flat matting surface with out the rings will provide better heat transfer because of the larger surface area. That's one of the reasons to lap the heads to the specific cylinders. Also, once the rings get compressed and have gone through the high heat cycles they are not going to have any spring tension anymore. They will just be crunched rings without any added sealing capabilities.

Garibaldi

That is a pretty rough looking surface finish on those cylinder walls, did you have them honed or did you get them like that. Maybe its just the picture, but they look very rough.

PCar SBA

A special Nikasil hone from what Walt told me. It does not really take much material off but scratches the Nikasil surface insead to help seat the rings.

Garibaldi

That is a whole lot of friable material to break in a modern piston ring.

Explanation- see SAE manual Sealed Power by Donald P Hessling

Friable materail is defined as the amount of microinch finish necessary to bring piston wall and cylinder ring to a homogeniuos state without leaving the cylinder bore with deep microscatches that promote blow by and heavy oil consumption. One might say we are speaking about microdrops which have deposited themselves in the valleys between each peak of the scratch. When you calculate the number of times a piston travels up and down the bore, you can begin to see how oil consumption can reach the level of quarts due to this. This is not the only factor though.

The top of your cylinder looks a bit rough as well, in the area where it meets the head.