Porsche Enthusiasts Club Forum

My '81 s will be back on the road for 1st April and will be taking her for a run up to York for a 'romantic' weekend to keep the lady happy:roll: the drive there and back's got me excited!
Question is,which grade of unleaded do you use?Reason i ask is that on the inside of the fuel flap it has '98RON',so i assume it has to be super unleaded,is that the law with these engines or can you use normal 95RON unleaded?
It's an early 928 so no knock sensors but were they run on 4star back in '81 and what is best now?
kind regards,GN

Hi

I use Shell V-Power as thats closest to 98 Ron... there is a electrical link wire near the fuse board that when connected will allow you to use normal unleaded BUT connecting it retards the timing by 6 degrees which is a LOSS of around 10hp

I did try it once but the engine "felt" flat if you see what I mean....

All the best Brett

What about my 1989 S4.....should I be using Super Unleaded in that? The handbook says 95 RON but is that a minimum, so I am going to get better response with Super?

No better response because the higher octane fuel has no more energy density, but simply resists knocking better.

But you can't take advantage of this, because the ignition advance curve is fixed in the EZK map, and is very conservative anyway so knock events would be very rare with 95RON fuel (the default ignition curve is fixed but your 928 will alter the timing on a per cylinder basis if it detects knocking - it's a pretty sophisticated ignition system considering its age).

You can take advantage of 98 Octane by Sharktuning. The knock control system will prevent any occasional detonation if you have to use inferior fuel.