justin

Right now I am running 87, but I noticed that the motor will "clatter" in higher RPM's. do I need to run 92 or 93 octane fuel? What are all of you guru's running? Mines a stock 80' model.
Thanks

WallyP

The Tech Spec booklet says 91 RON Leadfree. Today's 87 (R+M/2) should be 91 RON, so it "should" be OK. Sounds like it isn't OK.

If I were getting noticeable pinging at any speed, I would want to check the ignition timing. If it is per spec, and you are running normal engine temps, I would run some Techron thru and see if that helped. I would also be running mid-level fuel with the Techron to prevent any possible damage. After a couple of tanks of mid-level with added Techron, I would then try the regular again...

justin

Wally. How should I check timing?

Mark

I've run regular, mid-grade, and hi-test...never seen/felt/heard any difference.

justin

I just filled up with 93 octane, we will see.

IcemanG17

I heard the 4.5-4.7L 16V cars were all designed to run on normal 87 octane gas? The 32V cars were designed for 91+ octane...Also there is a switch/loop that you can enable to run lower octane in the newer 32V cars? Again I remember hearing this but don't know where the switch is?
Brian

Jack '84 928s

I put 87 in mine and i cant tell a diffrence in it when i put 91 in it...

WallyP

The proper fuel is the lowest octane that you can run without getting detonation or excessive pinging, at least on the pre-S4 cars. The S4 and up have knock sensors, so lower-octane fuel might work, but will give lower performance and mileage if the knock sensors continually retard the ignition timing.

Octane has nothing to do with fuel quality or engery content. It is a measure of knock resistance, nothing else.

The best fuel for your car will NORMALLY be the Porsche-recommended fuel.

If you get detonation or excessive pinging with the recommended fuel, there is something different (usually wrong) with your car.

On earlier cars, the ignition timing is adjustabe, and may be set incorrectly. On later cars, the timing is not adjustable. An inductive-pickup timing light will show you what you have.

Only the '84-'86 cars have the "octane adjustment loop". This is a set of connectors on the ECU wire harness that, when connected, allow you to temporarily run lower octane fuel when the proper grade is not available. These loops should NOT normally be connected, as there is a loss of performance and mileage when they are connected.

hacker-pschorr

I just finished a track event with my stock US 81 - just over 2 hours of track time in two days running 87 pump gas from Citgo - no issues. I know my cam timing and ignition timing are dead on.

Mongo

using a grade higher than 91 octane will not produce any noticeable gains in power on an NA car. HOWEVER, the fuel will burn a lot cleaner in the cylinders and even produce better gas mileage. I have run the test of 89 and 91 octanes on my car and noticed that my car runs cleaner and more efficiently on 91...but at the price of $2.75 a gallon now