3 replies to this topic

[unburntfuelinthemorning]

Does anyone know why the 998 head gasket has egg shape sealing rings around the cylinders?  Surely round ones would have made more sense?! 

 

It seems to create an inefficient pocket with a high surface area between the head and block faces which would be largely untouched by air/fuel mixture turbulence.

[DeadSquare]

It will be interesting to see which reply gets bestowed with "Answered".

 

It seemed like a good idea at the time.

[Spider]

I'm not certain, but it appears that they were trying to get the firing rings of the gasket away from the heat of the exhaust valves. I'd say, if this is the case, it goes back to the very early days of these engines, when they had fairly low compression ratios and only poor grade fuels were available.

 

As years progressed and better fuels became available, it's likely this was something that was overlooked. The gasket shape is unchanged since the engine's introduction in 1951.

 

I have (years ago) made copper gaskets for the engines with circular firing rings and without issue.

[unburntfuelinthemorning]

Hmm.  Interesting.

 

Does this extra area get forgotten about when calculating compression ratios?

 

I've heard that the 998 gasket volume is around 2.7cc (I think) per cylinder but is that just for the circular area and without the strange bit?