Eran Sharon

Thanks, wally and co.

Our (European) fuel type are RON rated. I am filling up with 96 only because it has lead in it. I take it my 1980 928S will not be damaged from unleaded fuel with regular use (and the occasional sprint here and there), correct ?

Thanks Again
Eran

Bill 86.5 928s

To steal the words from my deceased father in law I think this pretty much sums up this thread...

Four Gals for a Dollar...try Ethyl First

Good Thread everyone lots of info here
Regards Bill 84 928s

Jim bailey - 928 International

Anthony no need to "miss " ethyl .....the lead is still here all around us !!

Jim bailey - 928 International

Higher Octane fuel is not better.....just more expensive burns slower ..makes less power . As Wally points out , use only what the manual calls for which means USA 78-84 cars run fine with lower octane "regular" .

Bryan

To further complicate, don't forget the knock sensors on the '87 and up cars. If your knock sensor gets into the act, then low octane DOES mean less power and higher octane means more power. When your knock sensor detects detonation (long before your ear does) it immediately retards the timing until the detonation stops. This reduces the power output of the engine. Increasing the octane of your fuel eliminates the detonation, so the knock sensor leaves your ignition timing fully advanced for maximum power.

Bryan

Jim bailey - 928 International

If for some reason your S-4 is pinging " detonating " on the premium fuel it is designed to run with ....then higher octane might give better performance . BUT I think I would want to know WHY it is pinging and address that issue . The 89 and later LH brains store faults one of which is excessive detonation . The knock sensors which fail tend to fail putting the ignition into the retard mode retard all the time and that does reduce power. The GTS with the higher compression ratio does tend to run right near the point of detonation .

taffelman

Maybe a dumb question, but how can I be sure that my 1990 S4 is running max power?

Does the LH adjust to a "max" setting based on the knock sensors after LH "reset" (disconnected battery) and then compensate for lower octane while running.

OR, does it always try to run at "max power" as a factory preset, and then compensates when needed because of knocking?

Btw: I filled up with "Shell V-power Racing" 99 octane (RON) for the first time on my way to work today. But on the way home the shark felt lazy... got to stop looking at commercials...

edit: oops, just discovered how old this thread was

928autobahndreamer

It took me awhile to notice the age of this thread. When someone was complaining of 93 Oct gas being $1.60/gallon I was wondering where in the hell they lived. I wish gas were still that cheap.

WallyP

By using the knock sensors on the S4 and up engines, Porsche was able to greatly reduce the "safety factor" that they formerly had n the ignition timing maps. The knock sensors, combined with the positional input from the Hall-Effect sensor, allows the ignition system to run the optimum advance all the time.

If, due to low fuel quality, higher-than-normal operating temps, carbon build-up, or any other factor, detonation starts ocurring in a cylinder, the ignition timing will be retarded for that cylinder until the detonation stops. This happens almost instantly, so there is no damage from the incipient detonation.

The system then starts gradually (but very quickly in real time) advancing the timing for that cylinder again until either detonation occurs again, or the timing advance reaches the designed amount.

And yes, the system can and does control the advance on individual cylinders.

Bottom line - your '90 will always be running the optimum ignition timing for the fuel and conditions of the moment.