What octain rating for me?

Would someone tell me if 94 octain fuel is the best fuel for an early, stock 71 2.2 911?
If not what is the propper O.R.?

Thanks,
david w.

If you are running MFI that may be too high. I beleive on this site Pelican has the "Blue book" posted peruse through that.

My "Porsche 911 Engine History and Development" book states 98 octane. I found that hard to believe, but what do I know?

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Well, it would be helpful to know which version of engine you have!

Per the 'spec book,' the 'S' engine needed 98 Octane, because of its' 9.8:1compression ratio, but with slightly retarded timing, you might be able to get along with 94 octane go juice.

The 'E,' with 9.1:1 compression needed 98 octane, too, per the factory, but that was 'iffy' even 30 years ago, and your 94 juice should suffice.

The 'T' engine, with only 8.6:1 compresion, even though 96 octane was recommended back then ... should be fine these days with 89-91 'pump octane number' these days.

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Warren Hall
1973 911S Targa

I understood from reading articles on this board that as long if your engine doesn't "knock" then the octane rating of your fuel is adequate. I'm running a '70 911E with Weber carbs on regular gas with no problem - I've run it on higher octane fuel and it doesn't seem to make any difference to performance.

The previous owner of my 72 S used a lead additive whenever he filled up. From what I've heard this is unneccessary. Also the 2.4 S had lower compression than the 2.2 so the 93-94 at the pump should be fine. Is this true?

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Greg
72 911S

Thank you for all of your responces. I am running a 2.2 with the Zenith carbs, and it is a T model. I guess the 94 oct. is ok. It is the highest octane I have seen available anyway.


Thanks!
david w.

I use the super-duper unleaded. My pistons are 9.3:1 I think. I've never heard of too-high octane being a problem, just too low.

Higher octane gasoline simply ignites at a higher tmperature and pressure combination. If there is pinging (detonation), then going to a higher octane can stop it.

Usually you can detect pinging, but it's difficult if it happens at higher rpms. I just use the super-duper to be safe.

Can't imagine needing 98 octane gas. Guess you could drive from airport to airport.

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'83 SC

I think the early books were specifying octane in the Euro measurement (RON?) whereas in the States we now use an average RON+MON/2 or something like that. Very fuzzy, but I do seem to recall that comparing today's 92 super to the 98 cited in the early manuals is apples to oranges.

Anybody have the details on this?

BTW -- I agree w/ Warren & just about everyone else that for an early car (single plug, no knock-sensors & computers to bail you out) that 9.5:1 is about as high as you want to go on C/R with today's gas.