Gasoline - 90 Octane, Ethanol Free (89), or additives, How to reduce valve knock Options

[dcecc1968]

We are having some Spring weather this week in Charlotte, NC (and no rain!) so I've been driving the 914 and noticed that after about 20 minutes of driving, the valves intermittently knock from "normal" to very loud for no apparent rhyme or reason.

Outside of the obvious that it may be time for a valve adjustment, I wondered what Gasoline grade folks are using.

What Petro are you using in your 914?

[porschetub]

Loose valves are a clatter/rattle not a knocking,if you have knocking it is most likely detonation (pinking) which is caused by incorrect timing,a lean condition or even old fuel.
Running an engine with the above condition will cause severe damage in a rather short time,I have personally seen a rebuilt T1 motor that only lasted 700kms with a lean condition and over advanced timing.
Do check your valve clearances as it is important they are correct in any aircooled engine and run the highest octane fuel you can find,good luck.