Valve stem seals

Guys, for street only engines, positive valve stem seals or standard umbrella? MANY years ago I ran teflon seals, seems like IIRC, after ~ 10,000 miles the guides were worn out? Wondering if things are different today? If you've already got positive seals can you just remove them and install umbrellas?

TIA

Everything coming off the assembly line today has positive style seals on it....not necessarily Teflon but positive style seals. You also didn't mention what heads/guides/application. Iron, aluminum or ??

Just standard BB iron heads, 915, 906, 346 or 452, I think they're all pretty much alike save for the closed chambers of the 915's? I have access to any of them. My '69 (~ 60,000 miles) has never been apart, I'm sure the original nylon timing gear is beyond brittle and the valve stem seals in little pieces all over the engine.

Street engine is good with stock type umbrella seals. Never had a problem using them.

Viton positive umbrella type work great on the street
Teflon not so much on the street

i use comp cams 504-16 big block chevy umbrellas for 3/8" valve stem, single spring, big block iron heads. inexpensive, easy to find, and work quite well. be sure to monitor your retainer to guide clearance.

That depends on the engine. Running any seals on a flathead is a bad idea.

Don't forget some have hardened valve seats and others don't. You don't want to run them(non hardened) on today's gas with out hardened seats or the valve will wear into the head.

I would go with the silicone material.

Well, this is timely...FF to ~ 4:20

Unless you have the guides tops machined the only thing that is going to work is the umbrella seal , if having the heads redone then machine for positive seal .

'452 heads are the wild card with the larger intake guide boss. they did use a positive seal but i never considered it a good choice. i used to buy some positive seals for a 3/8" stem from Goodson (similar to the edelbrock seal) some years back. guide needs to be trimed to .625" to use them. to be honest i've never found any seal easier or more effective than an old umbrella in a stock or near stock build.

I have had the best luck with a Viton seal with a steel jacket. Everything that touches the valve and guide is Viton, but there is a steel sleeve around it. When I tried some seals that had a Viton seal to the valve but a steel sleeve to the guide(smaller OD) they leaked like it didn't even have valve seals. I have had the scenario with two different cylinder heads. The Viton with steel jacket has worked both times and the other style has failed.

If the guide bosses are unmolested, I’d just use whatever is listed for the application of the year for the heads your using.

As has been said, it will normally just be umbrellas....... except for the 452 intakes.

I'm not sure if a stock big block valve guide has the same diameter a small block? I had a stock 360 and used 3300 series CAT valve seals on it and worked great. They're for a 3/8" valve stem and was a positive lock on a stock 360 valve guide. I know it's out of the norm, and might not be an option for some people. Just throwing out an alternative.