Which fuel for my US 1980 911SC?

[Harvs11]

Can anyone tell me which is the best fuel for my US spec. 1980 911SC 9.5:1 comp.

Here in Australia we have a choice of fuels to fill up on, 91,95 or 98 octane unleaded. 91 is available all over the country, while the higher octane fuels are more readily available in the larger metro. areas.

I've been using 98 for a while which seems to be OK, although acceleration is a bit jerky under very light throttle between 2000-2300rpm (usually stuck in traffic trying to maintain a constant speed) Is this the result of incorrect ignition timing?

Also, what would be the best ignition timing setting for these fuels?

[Oh Haha]

91 octane is fine for your 911. The jerky acceleration is most likely NOT from the fuel but it could be from the fuel/air mixture. The CIS fuel injection is highly susceptible to changes in temperature. Meaning, in the summer time the humidity is higher and the air "thicker".

If the car is running a bit lean, it can cause the symptoms you described.

Changing the mixture is not something to mess around with willynilly. I would suggest researching some threads here to gain some insight on what it entails.

As far as the timing specs, a service manual such as Haynes or the excellent Bentley is a must have for the DIY'er for an SC. You could also do a search here for what specs others are running. We have several AUS members who could help you out with specifics for your climate.

[psalt]

vandha,

Your US 1980 SC (9.3:1) was detuned to run on 87 CLC octane fuel. Your local octane numbers are probably RON and differ by around 5 numbers. What's best ? For performance, 25 BTDC is far from ideal for a wide VIA hemi. Output will increase up into the mid 30's BTDC, but the engine is very sensitive to pinging at high temps. No one can tell what is best over the internet, I use the highest octane available and tune accordingly.

Paul