I'm sure this is in a FAQ somewhere, but I can't seem to find one associated with our forum.

I'm running 91 right now, which certainly won't damage the engine, but I'd rather find a higher octane. We used to go to Sun for 100 octane in the good old days, but I'm sure that's impossible now, and I haven't seen a Sun station in years anyway.

Where do we go?

 

Some select Union 76 have racing fuel 100 octane.

http://www.davebarton.com/Unleaded_Racing_Fuel_in_SoCal

 

You need to blend 4 gallons of 100 octane to 12 gallons of 91 to get you just over 93 octane..here's a chart for you.



A website that has different locations for racing unleaded. I was getting F&L 105 unleaded and I only had to blend 2.5 gallon to 14 gallons to get right at 93 octane. Can't find it now...back to 100 unleaded.


http://www.davebarton.com/Unleaded_Racing_Fuel_in_SoCal

If you are in S. Cali there are a lot of places.





Dave

 

Do you guys really notice a difference between 91 and 93? What about beyond 93, any extra gains to be had?

 

Its not night and day but there is a difference. I feel its like the car is chomping at the bit more. The point of diminishing return is 94.5-95 octane. Unless the DME is remapped to take full advantage of higher octane fuel its just going out the exhaust.

Dave

 

No need to get 93. 91 is fine as long as it is Chevron or Shell.

 

Thanks, Tony. As it happens, all I ever use is those two. Mostly Shell because the Chevron dealers I've used around here are a little flaky about their equipment.

From the chart Dave Barton posted and the prices on his list of suppliers in SoCal, it would only add twenty dollars to each tankful, but it does not sound like the higher octane is worth that much. Not to speak of the annoyance of driving out to Willow Springs for the first four gallons everytime I need fuel. In fact, without breaking out Google Earth, I'd say that my new 911S -- delightful though it is -- will be using up two gallons of mix to go buy those four gallons of race fuel. I'm definitely not going to put gas stored in cans in an engine like this one.

But Dave, I will keep in mind your list of purveyors in case I decide to try a DE day. Thanks for all the work putting up that page.

 

Shell and Chevron are what I use but my preference is Chevron. Techron is good and they may use less ethanol (hopefully).

 

Someone wrote that the 997s were designed for 93. Is that incorrect? I found a calculator that is easier for me than the chart to mix the octanes. http://www.bazellracefuels.com/Calcs/OC1.htm

I found a 76 near me with 100, so I mix the 91 and 100 to get to 93.

 

The 3.8L is rated at 355hp with 93 octane..you want to run 91 octane and you will lose approximately 8hp. Keep in mind that fuel in California regardless of brands comes from a few refineries here in Cali. When it gets shipped to dealers is when the additives (of that particular brand) are added. I can tell you right now I have seen 8rwhp from 91 octane to 93 octane. Like I said in a previous post is it night and day...no. However, the car does feel more responsive and it feels like its just chomping on the bit a tad more...more eager to romp. My car only sees about 400 miles a month..so it isn't that much more per month to operate.

Dave

 

A quality Octane Booster such as NOS or Outlaw brand should boost 91 octane unleaded about 1.5-2 octane points at the proper gas to booster ratio. I know there are plenty of junk brands on the shelf at the local auto parts store, but the better known brands tend to do what they advertise. Although it is probably not something you would want to do with every single fill-up, adding a bottle to a tank of gas for events such as an autocross or a weekend at the track should get the results desired.

 

when I was on the road once and local station where i had to stop was out of 93 so I did put 89 in and it felt quite different not in a good way. but I have softronic tune to 93 octane maps plus 89 is not exactly 91 but, still, it did feel like night and day.

 

I did that intentionally with a Corvette C6 when gas was over $4 a gallon. "Night and Day" doesn't begin to describe the difference. It was like riding around with the parking brake on!! The difference between a fill-up with midgrade and high test was all of about $1.50 (.10c/gallon) so the degraded performance didn't justify the economics. Trust me, I only did it once.

 

I did a test when my wife bought her BMW 330xi. Filled up 93, the car got 21.6 mpg. Then filled with 89, that yeilded 21.4. Put in a tank of 87, dropped all the way to 19.6. This told me that the car pulled a lot of timing with 87 and was pulling little or none with 89. She's been running 89 ever since.