why use seals on the exhaust stems ??

[Roslin]

Why use seals on the exhaust stems ?? When the 911 engine have wear problems. Maybe better lubricating of the guide would prevent that..

Roslin

[Walt Fricke]

Good question. On my race motor I don't. Certainly causes no problem.

Little or no vacuum in the exhaust, and gravity is against oil movement into the exhaust port via that route. I think that seldom does the case fill with oil to the point that it (and the cam carrier) have oil above the level of the top of the guide. But when you jack the car up high from the side I suppose that could happen, leading to a belch of smoke on start-up.

However, Porsche uses them on street engines. They must have some reason.

Walt Fricke

[john walker's workshop]

the exhaust flowing through the port creates vacuum in the guide, much like a glass bead machine sucks up the glass bead as air passes a side port. the exhaust guide is real close to oil at the bottom of the cam tower, as well as all the oil that is sprayed around in there.

[MBruns]

We use them on all 911 engines, it keeps the chambers much drier, less prone to preignition,very low oil consumpion, I know alot of builders dont use them but we have found no issues.

Mike Bruns JBRacing.com