944 Valve guides in a 911?

[YTNUKLR]

Today I was thinking about different ways besides porting to increase head flow; obviously minimizing the valve stem cross-sectional area, valve guide "support" and using a less obtrusive valve guide are ideas that come to mind... I seem to recall something of the use of 944 valve guides on the 911. Does anyone know if that actually does work? I know they are shorter than 911 guides and thus would seem more prone to wearing out. Are there other valve guides (perhaps non Porsche) that can be fitted?

Cheers

[911pcars]

Typically, you'd want all the valve stem support you can get, so I'd suggest not shortening the guide. You should be able to reshape the aluminum valve guide boss to a more aero shape, the valve head as well.

Engines do like more valve lift for better breathing. :-)

Sherwood

[patkeefe]

Shorten them, intakes more than exhausts. They will wear out considerably faster. Also, port the boss as Sherwood says. Life span becomes very short.
Pat

[YTNUKLR]

I was thinking that it would start to wear very quickly without the necessary support. This is for a 3.0L that runs the big valves (49/41) and I just don't think it's the right move, even considering the lengths we're going to to make high-rpm power. Thanks !

Scott

[tctnd]

As an old hot rodder I can remember (funny how that sounds....) when it was common to shorten guides, somtimes flush with the port wall. It had two very negative effects; first the guide and stem wear increased, and second, the valve was not located as well so the seats beat out and deteriorated quickly. For drag racing we didn't care but for distance use (race or street) it just wasn't worth it.
That said, specialty makers like Manley produce valves with stems that are necked down in the port area and these seem to work well. I don't know if they are available in
porsche applications but they might be worth trying. These are only suitable for the intakes as the exhausts need all the cooling help they can get and that nice fat sodium filled heat pipe is barely enough.
regards,
Phil

[YTNUKLR]

Phil, interesting.. I haven't heard Manley mentioned in a while, but now there are many valve manfacturers doing narrow valves that flow really well. For the motors you mention that "barely" cool, are you talking Turbos? Standard valves in N/A engines have been pretty darn good even for high mileage, in my experience. I guess YMMV?

Cheers
Scott