924Board.org

[Peter]

Hi All,
I have a 1980 924 Turbo engine that I am rebuilding for track use and wondering what is everyone’s thoughts about having the block O-ringed with a copper head gasket. The head has been milled down, but within specs, ported and polished. I am using gapless rings and plan on adding an intercooler, aux fuel pressure switch to add fuel upon boost, and running 1 bar of boost. I know in the future that I will switch heads, so a reusable copper head gasket is a good investment. Other than the cost of having it done, any down sides to O-ringing a block? Any comments welcome.
-Peter A. Holiat

[Patrick]

Hi Peter!

First I would like to say that you don't need to o-ring the block for boost as low as 1 bar. If you are getting above 1.3 bars of boost then it will be necessary.

Of course this also depends on what turbo you are using. A Turbonetics T72 will blow the engine apart at 0.4 bars of boost...


"what is everyone’s thoughts about having the block O-ringed with a copper head gasket.

It is a well known problem that the oem gasket can't handle high cylinder pressure. On the other hand the head gasket works as a kind of fuse - better to blow the gasket than a piston.


"Other than the cost of having it done, any down sides to O-ringing a block?"

If you run too lean, or if any other factor causes detonation, the gasket will not function as a fuse and you might melt a piston or a valve. But if you have your air/fuel ratio under control and a good ignition system then there should not be too much to worry about.

With my new turbo (anyone has a 26/27 hybrid for sale? Trade for "new" 26-6?) I will be running at 1.6 bars of boost, 12:1 a/f under full boost and an MSD ignition should keep me safe.

L8ta
Patrick

[Peter]

Hi Patrick,
The "fuse" issue is very important; rather replace the gasket than replace a piston.
Are you running a copper gasket? If so, I hear a lot about sealing problems for copper gaskets even when O-ringed. I was informed by a Porsche after market tuner (951s primarily) that it is better to O-ring the head because its easier to reseal the copper gasket on the head than on the block, which must be removed. Also that all copper gaskets will leak but since they are used for high compression engines that are rebuilt regularly, the issue of leakage is not that important.
Anyone hear similar or different?
-Peter A. Holiat

[Peter]

After talking to a few VERY knowledgeable Porsche tuners I discovered that to use a copper head gasket properly, both the head and block have to be machined (one has a groove cut into it the other a receiver ring installed into it) and that sealant is used to prevent leakage. As to the issue of leakage, no they don't leak because after every race season you are rebuild the block anyway so you then put new sealant on the copper gasket. That is, copper gaskets require periodic resealing. This is something that I don't want to do so I am sticking with the stock gasket.
-Peter A. Holiat

[Rick MacLaren]

Excuse me if I sounds like a dufus, but what is 'O ringing'?

[Peter]

Hey Rick,
Basically, when you use a copper head gasket you must have groves and receiver rings (o-rings for short) cut into the head and block to allow for proper mating of the head and block to the copper gasket. Regular gaskets compress after they are torqued to spec. This compression compensates for any distortion in the head and block and allows for a tight seal (although the head and block are milled, there is always some distortion and the compression of the gasket material compensates for this). Copper gaskets do not compress and will not seal properly without these o-rings, which act almost like male to female connectors. However, copper gaskets require liquid sealer to be applied upon installation and periodically re-applied on the gasket to keep coolant form seeping into the cylinders. High maintenance.
-Peter A. Holiat