Hello!

I'm the beginner here, so let me briefly introduce myself. My name is Łukasz (wookash) and I live in Poland so please take it easy with my language mistakes
I’m the owner of the W107 450 slc ’77.

Since the manual for my car specifies that 98 octane fuel is allowed for M117986, I’ve decided to feed my car with the BP Ultimate unleaded 98 + the Millenium (from Shell).
I have two questions:

1. Won’t that be “too much” for the engine?
2. Are there any necessary or potentially beneficial changes in the ignition system (ignition timing, sparks, etc.) I should consider?

Thank You in advance, wookee

You should be fine so long as the octane rating of the fuel meets the recommended minimum value. No other changes would be necessary.

230/8

Thank You

It would be really hard for me to get the worse fuel than recommended

Hello and welcome to the forum, Lukasz. I understand that Polish is such a difficult language that anybody from Poland can easily learn other languages, but the opposite is not true...... so you have no disadvantage here.

There are adjustments to allow lower octane fuel, if you ever get stuck with it.

1960's 220Sb 'fine-tuning' ignition adjustment on the distributor collar tells us that slightly advanced/retarded timing accomodates different fuel octane levels. That's what the W111 fine-tuning ignition adjustment was made to do.

Therefore, if fuel octane is low you can slightly advance or retard the ignition timing to allow for it.

And spark plugs with slightly hotter heat ranges can help with lower octane fuel too.

Octane too low causes "pinging," rough idle and loss of power.

There is no maximum octane that can harm your engine.

I have a 1977 450sl 107. I use regular gasoline and have had no problems or knocking. Suggest go with lower octane of 87 and see if engine runs OK or knocks. This is the requirement for US 450sl 1977. Timing adjustments are made only when needed to meet gasoline availability. Good luck, Abe G

Abe: You probably have an 8.0:1 compression engine with calmer cams. He probably has an 8.8:1 engine with hot cams.

You might get away with 87, but even mine pings on 87 and 89. I can run 92 but prefer 93.

Łukasz: Use whatever you want as long as it meets the manual requirements. In fact, if you run higher octane, you can set timing 3-5° more advanced (further BTDC) to get more power as long as you don't get pinging (pre-ignition, also called "knocking").

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But one needs to use language to know it and I’ve only watched some movies for the last few years

That's fine. Few months ago I was wondering about using the V-Power Racing - just for checking if any difference occurs, but I had been informed that this kind of fuel would have been too "dry" for the older engine.

Exactly. I’ve got M117986 with 8.8:1 compression ratio.
"cams" - do You mean camshaft?

That's something I’ll check during my next visit at engine diagnostics service. Thanks.

Taken from an article in the Star magazine Sep/Oct 2003 the old ratings were RON number. Today it is RON + MON divided by 2. This calculation makes 91 RON regular gas today. I used to run premium until I read this. If you have a low compression engine its fine. RTegular gas is more volatile and can cause vapor lock easier. A mid grade works better for this problem. Be sure timing is correct. Hope this helps.
450SLC