Rennen

I haven't seen a post about the best octane gasoline to run in the car. I always fill my cars with premium and have been doing so in the 964. However, there is nothing that recommends this in the 964 unlike my other cars. Since Octane really just involves predetonation related to higher compression engines, I'm wondering if I'm putting the right gas in or not. What do you fuel up with?

investlt

I use Premium - 93 Octane. I could be wrong, but I thought there was a recommendation that you use a minimum of 91.

springer3

I also recall the owner's manual stipulates a minimum octane. The knock control system retards the ignition timing at the onset of pre-ignition. This means for most conditions, your performance and fuel economy will be better with higher octane fuel. I run (R+M)/2 93 octane, and I still get high counts on the knock sensor system when accelerating. This means that the engine takes full advantage of the 93 octane.

Johnny G Pipe

I run 95, like most UK owners. Can get 98 in UK, 100 in Europe. I read someone did some pretty exhaustive tests (Adrian?) with the higher rating stuff with no discernible difference. I resisted the temptation lately, the car runs so sweet at the moment..

91 Octane not available over here afaik.

R6XTERRA

I use 91 oct. and 94 whenever possible. 94 is the most you can get at our pumps here in Canada. I am sure you can get higher octane at specialty places...however, never concerned me.

My P-car runs like a top.

Jeff

Cupcar

You are all so lucky to have better gas than the 91 octane R+M/2 we have in California.

At least the 964 is tuned at the factory for R+M/2=90, so you don't really need more than that. The Euro 964 RS was tuned for R+M/2=93 though and my USA Cup car, which came with the Euro RS chip, pings on Caifornia's 91 octane so I have to mix with 100 R=M/2 unleading racing gas

Kahdmus

This must be a real PITA!!!

Cupcar

I don't drive my car much except at autocross and fortunately the *only* 100 unleaded at a pump in town is about a mile from the stadium where we hold our events.

Randall G.

Hey Springer...this is very interesting. How are you measuring knock sensor activity? I seem to recall you bought yourself a "hammer."

Unfortunately, there are lots of 964/993 owners on the West Coast that are experiencing pinging, with the crap 91 octane fuel--knock-sensors checked out okay, unmodified DME. In most cases, the pinging goes away when higher octane gas is mixed in. You would think the knock-sensors would prevent audible pinging, but this isn't the case (I still don't understand it...).

Rennen

Thanks everyone. Looks like I'll be sticking with premium.

Phil Raby

It's worth knowing that US octane ratings are different to the rest of us. Don't have the info to hand - anyone?

Christer

I only use 97/98 RON now, which I think is equivalent to 94/95 Yank style.

investlt

Hope this helps on Ratings:

The RON method of octane measurement is not used in the United States. In the US, a different method entirely is used, called the CLC method. The number that results from this method is the average of the RON octane number and the MON octane number, so (RON + MON)/2 = CLC octane number. This is the number that you will find printed on a yellow label on gas pumps in the United States.

Example, 91 RON octane is equivalent to 87 CLC octane.

springer3

You are correct, I am using the Hammer to count the knocks. I can't hear them above the normal engine noise, unless I deliberately drop the hammer suddenly in a higher gear while at low RPM (not recommended, BTY). It is clear the DME is acting quickly enough, at least for the local 93 Octane. I recall Adrian recently responded on a thread related to knock problems that the California fuel is too low to prevent knocking even with the DME functioning properly.

Octane number is the "anti-knock" rating for the fuel. I don't recall for certain the compression ratio for the 3.6 liter, but I think it is 9.8:1. It may be that the default ignition retard is not sufficient for your fuel at such a high ratio, or possibly it is not possible to retard the spark enough to prevent knocking.

Can you get "octane booster", or perhaps mix in some 100 octane avgas?

Randall G.

>I recall Adrian recently responded on a thread related to knock problems that the California fuel is too low to prevent knocking even with the DME functioning properly.

Yup, he sure did.

>I don't recall for certain the compression ratio for the 3.6 liter, but I think it is 9.8:1.

Actually, it's 11.3:1.

>Can you get "octane booster", or perhaps mix in some 100 octane avgas?

Yes, many of us have access to stations selling 100 octane unleaded racing gasoline. There's a 76 station selling 100 octane about 7 miles from my house. The way the cost of "premium" (91) has gone up lately, it doesn't cost all that much more to add 5 gallons (or so) of 100 octane (~$4.50/gal.) with a fill up.