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?

Check your timing

A well-tuned stock engine (with stock compression and fuel injection) should run 87 octane just fine. That's what I run. No issues.

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.

I agree. Last thing to worry about. Check your fuel filter and gas tank first.

You also might have water in your fuel so maybe an additive for that. You can get it at any FLAPS.

If it really is valve noise, the probable causes range from valves sticking in the guides, to wiped lifters and/or cam lobes. Even dropping valve seats...

Is the motor stock or modified?

If it is pinging, there are other things to check. How's your ignition timing? Air/fuel mixture?

--DD

Thanks for your suggestions. I will definitely check the timing on the engine. Little is known about the engine historically other than I've been driving it for 4 years. Was told it was a 1.8L when purchased, but the stamped engine code says it should be a 1.7L.

The engine knock sometimes is more like a rattle/clatter.

I'm running dual weber carbs IDF40's with the air mixture screws @ 1.5 turns out. I didn't think of the engine running lean... that may be part of the problem.

If it's a 1.7 I would use 92 or 93 octane....it's a higher compression ratio engine.

At what compression should you start thinking about higher octane? More specifically, 8.0:1 compression?

Side question: Anyone know why they raised the octane of regular gas in high elevation states? Until a couple years ago, regular gas in Montana and surrounding states was 85, then a couple years ago, they suddenly raised it to 87. Emissions standards? I always thought it was better to run a little lower octane at altitude to compensate for lower atmospheric oxygen content.

Check around at Pure Gas.com and see if there is any close gas stations that have no ethanol.

I only run ethanol free and additive for lubrication (as we are lead free now).

These engines were designed with leaded gas on mind.

I'm betting it's cost. If they don't have to deal with making a separate grade of fuel for high-altitude states, it probably costs them less.



NOTE: These engines were not designed for leaded fuel. They have hardened valve seats from the factory, and the guides are a material that does not require lead for lubrication. If there are any Porsches that require leaded fuel, they would be fairly early 356 models. All others should be fine on unleaded fuel.

Heck, some of the 75-76 914s required unleaded gas because they ran catalytic converters.

--DD

VW/Porsche only used steel seats, it's cast iron that needs lead.
Some shoddy rebuilders used cast iron seats and guides, a no-no for rebuilding our heads.

this thread is close to my question so I'll continue it

just got off the phone with Richard Parr of PMO. Very knowledgeable. He emphasized the desirability of using ethanol free gas. (And I am hearing this more and more from small engine repair guys.) There is a place here that sells it (ironically, the agricultural coop place) but the octane isn't that great. I forget, but maybe 90. I am running 10.8:1 and want higher octane, say 93.

Has anyone done the research on off-the-shelf octane enhancers. Do any of the many fuel additives help with what we need for our engines in terms of octane and lubrication?

@mikey914 - what additive do you use?
this car is new to me so it's all new to me....I can get ethanol-free...