I'd like to use some positive valve seals for my stock 1986 350. I've got the guide boss machined, so I'm ready to go.

I have three choices: rubber, teflon, teflon/rubber type. Which ones are best?

Second, do I need to watch out for overheating the seals on the exhaust valve? Are there special seals that are made to withstand the higher temps?

I haven't had a problem with the teflon valve stem seals, such as the Perfect Circle design.

I have had a bit of trouble with the solid PC style only once. I was spinning the engine up quite a bit and the retainers hit the top of the seal for one reason or another graemlins/clonk.gif -He -He
That broke them all and oil consumption went up a bit. I found out about the broken seals at dissasembly. Some were not even attached to the guide boss anymore and just rode up and down on the valvestem.

The rubber with teflon insert style are a pain as the teflon seems to pop out and it is difficult to get it back in there.

All things considered, I like the full rubber type. No fuss, no muss and my head machinist likes them for all the track heads he does so I run them.

-Mark.

I've run the teflon type on big block and small block engines without any troubles. The most recent big block I only took to 6300, but the small block was seeing 8500 a lot without any problems. Consider edge orifice lifters also if you are running a solid lifter cam. This will reduce your oil supplied to the top by about 15 to 20% and could help.

check this artical on Viton Positive Seals:
http://www.aera.org/Members/EngineTech/edge797/valve.htm

This is all good info.

Has anybody had any experience with the positive seals that don't require machining of the guides?