Stephen,
Thanks for your reply.
Guy's,
I guess it has its pros and cons. Some say its good and some say you dont really need it. To each is its own.

 

When done properly, the sealing between the Head and Cylinder will always net better results. The problem is that the old cast iron ring and its application was copied but never understood. It was originally done to stop the burning blow torch effect that happened when on the overrun/part throttle, the fuel was limited going into the chamber but the Turbo still produced alot of air. The engine would instancely go lean. A way to stop the blow tourch effect was to fit the cast ring and stop the head or Cylinder material from been burned. It was never really meant as a true sealing ring. That is why in most copied cases, the ring floats in the receiver grooves.

If you call Performance Developments, 949 646 7461, they have their own sealing system that uses a Compression ring and a Head Gasket. They used this sytem on my engine and there is no sign of any leakage on the bottom split line. I believe they use a Copper berylium material for both rings and each is under some controlled crush. I know they have done this sort of modification for many other Porsche engine builders with great success. I'd call them.

 

Sameer:

I'd concurr with Stephen,.......they have their places on certain engines under extreme conditions.

Don't forget that 935 engines used a special kind of nirist ring and very special head studs. The metallurgy of that time was every bit as good, or better, than today in this respect. These things ran at 1.2 to 1.6 bar and their "Achille's Heel" was the sealing between cylinders and heads.

High boost pressures simply lift the heads off the cylinders as the heads bend between the studs.

Nowadays, there are better materials to use instead of the factory rings.

 

Steve,
This is what I gather from this other tuner:

"they have their places on certain engines under extreme conditions.

Don't forget that 935 engines used a special kind of nirist ring and very special head studs. The metallurgy of that time was every bit as good, or better, than today in this respect. These things ran at 1.2 to 1.6 bar and their "Achille's Heel" was the sealing between cylinders and heads.

High boost pressures simply lift the heads off the cylinders as the heads bend between the studs.

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Tuner B:
"Yes this is true to an point. The writer is correct in what he wrote in relation to the setup of that time frame. They had special studs and slightly different rings than today. But to be considered better quality than that of today is pretty thin. Metallurgy is quite advanced over the last 30 years. I have no problem stating today's hardware is every bit as good if not better than the 935's factory hardware.

It isn't really high boost pressures that lifts the heads. It is a combination of too much timing causing detonation AND high boost.

Every motor has a thresehold. Meaning there is a point that you just can't fix it with retarding the timing or adding more fuel. So it is the quest to try to improve the efficiency to extend the performance threshold. On the contrary it is not the thresohold of the engine that is reached on CIS cars the engine is capable of more power just not with the CIS once you have reached the 450HP mark the CIS is the limiting thesehold.

Also on 935's the ignition timing was locked at a fixed timing curve much like a CIS ignition so it is also a timing issue to compound on top of the fuel issue. All this with too much timing and detonation causes the heads to lift. This is why EFI helps so much as WHEN the engine is properly tuned the maximun threshold can be reached IF all the components are matched and right for the application.

As far as the Nirosist rings they are a insurance when ultra high HP is trying to be reached or you decide to stay CIS at 450+. But if you are trying to push more than that out of the CIS it is a matter of time for failure.

With EFI and fresh machined surfaces and high quality studs I feel 650 at the wheels is safe with a good tune. If you go higher than that the niro rings are good insurance due the fact that fuel consistancy changes constantly from week to week. Temperature changes many different variables can be added to change a fixed condition. It is a good practice to tune a turbo car at about 12.5 A/F to have a safety margin to counteract these inconsistant factors.

Bottom line is if you are CIS and the 450 mark is reached then the upgrade to EFI shoulkd be the next step and not Nirosist rings. I know the most people are wondering what do I get with EFI. You can't imagine the drivability improvement over CIS. Reguardless of power increase just the low end response rapid boost completely changes the characteristics of the car, all for the better. I am not trying to sell anything at all here. I can only say driving a EFI converted car with a good state of tune with less than what you have will make you pissed, cry and happy at the same time. Pissed because you don't have it in your car. Cry because you spent so much to improve that outdated makeshift injection system called CIS, and happy due to the acceleration and all around performance enhancement of the EFI conversion."

So from what I gather from reading above, going Nirisist is added insurance for really big big horsepower, 650 and above. Below that, a well surfaced head and good fasterners shld be more than adequate.

 

Stephen - do I have Nirisist rings in my car? I am beyond the magic 450 HP and still using the CIS.

 

Nope, you are certainly above the 450mark, however the power band is a safe one on the back end. The sustained long haul pressure as not as brutal as it could be with say a T66 and 964 or bigger cams.