Marine Blue

So I'm embarrassed to admit that when I filled my 911 up last week I put 89 octane in it since I wasn't sure what octane it needed. I thought I would be safe with 89 (modern engine mentality ). I spent the last week trying to work through idle and cold start issues and had resigned myself to bring the car to the mechanic this Friday for an adjustment.

Well today I decided to fill the tank with 93 octane after reading recommendations from others on here and Pelican. I couldn't find ethanol free unfortunately, the stations that were listed online have 10% so I went for the highest octane.

Well I have to say that my idle issues have gone away, she runs like a freight train now and pulls much harder than before. The engine is incredibly different with this gas. I can't believe it would make that much of a difference.

So my recommendation to all of you who use less than 91, upgrade to the best available!

upier

Do you have a chip in your car? May be set so that you need the higher octane.

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Marine Blue

Mechanical fuel injection so definitely no chip. The Spyder is stock and I always use high octane in that.

911Dave

We should all be using premium, whatever is the highest available. In Colorado, that's 91, which is adequate. The higher you go up in altitude, the lower the octane requirement. Those near sea level should be using 93 at least, which sucks for Californians as I don't believe 93 is available there. In those cases, some guys mix some race gas with 100 octane or better with the normal pump gas to yield a high octane mixture.

race911

With insufficient octane you should have heard audible knock under load, given the piston/cumbustion chamber shape of those 2.0L engines. Not sure what octane/anti-knock has to do with an engine at idle. (Now if we want to talk composition of what passes as gasoline v. what the MFI/carb engines were designed to run on.....different discussion.)

mpiffaretti

I know this is an old Thread, but I was at the Homestead track yesterday doing a DE and I had the option of getting Sunoco 98 non leaded or 110 or 115 leaded (can't remember the exact octane). I have a 2.7 without Cats, so I decided to play it safe and get the 98 octane. My question is, would the 100+ octane leaded gas be safe for my car? and the next question is, would it really make a difference performance wise?

theiceman

personally i find this octane discussion somewhat misguided, but that is just my opinion. This is also a completely separate issue from Ethanol in gas .

all Octane does really is provide stability to gasoline. Gasoline has a propensity to become unstable under higher compression and will detonate before optimal time (knocking ) . This can be detrimental to valves obviously that can burn while open and not have the heat sync properties they require while seated, as well as other effects of combustion directly through the intake or exhaust.

As manufacturers started to make higher compression ratio motors to extract more power and also burn contaminants more completely a need for higher octane " more stable gasoline" was required.

I think going beyond an octane required by the manufacturer will not bring you more power but only flush your hard earned dollars out of the exhaust. I would say if you ran in a substantially higher temperature than normal , say Arizona or Texas, i may want to run an octane level higher .

For example my 78SC has an 8.5 - 1 compression ratio and regular gas is recommended by Porsche ( 87 ) . Thats all I run and i currently have the the engine apart after 250,000km due to the head stud broken issue.
The machine shop gave my heads , pistons and cylinders back to me and said these things are perfect, it would be unjust to do work on parts that absolutely dont need it, everything was well within spec.. He cleaned it all and put new seals in for me , and said i didnt even really need those.

Just one data point.

Amber Gramps

We had a VP Racing gas station locally that sold 100 octane. I would run 2/3 Chevron 91 and 1/3 VP 100. Car ran stronger and smother than ever. Yes, had a chip. Station is gone and I swapped in a stock chip. Always run the best gas you can get.

Steve Weiner-Rennsport Systems

Gasolines are a very big & complex subject and I can assure you there is FAR more to this discussion than simply octane.

Its important to remember that these older cars were designed at a time when fuel formulations were completely different to the swill sold at the pumps now. This applies to any 911 without knock-sensing: '65-'89.

Matt Lane

Hi Steve - here's a question for you on an 86 Euro with the higher compression:

Shell 91 V with no ethanol?

Or 94 with ethanol, plus an ethanol treatment like Stabil blue?

I assume the latter, but the car is new to me.

On the 993 I run Shell 91 on the street when I can, and 94 at the track.

Cheers

Matt

theiceman

Important to point out Matt for our US friends that in Canada Shell V-91 is sold without ethanol, in the US that might not be the case.

Personally I would go without the Ethanol on your car before going for 93 With Ethanol ( if its stock ) . But that's just my opinion.

Steve Weiner-Rennsport Systems

Hi Matt,

94 with ethanol, hands-down!

Just use liberal amounts of that Marine Stabil for effect and you'll be fine.

Matt Lane

Thanks Steve. Appreciate it.

Cheers

Matt

DerkPerk

Not to hi-jack, but on the fuel discussion, I'm new to the air cooled world and have only filled my '87 up once with premium, 91. Should I be using non-oxy/ ethanol free? It is readily available near me.

Edward

Hey Steve,

On my 82SC, stock CIS motor with 964-grind cams (IIRC, who knows at my age ) and SSIs, I've been using stabil as a supplement for several years now (in SoCal). Is this still the wise thing to do? Has gas changed any? What is it that ethanol does that stabil helps counteract? As always, much Thanks sir!!

Edward