Chubbybunny

• Anyone using race fuel? I'm curious to know if there is an actual benefit to utilizing 100 octane with the GT3. I found a couple of old posts dating a few years back, however, nothing recent as of late model year (991). Since taking ownership, I always filled the tank with Chevron 91 octane, nothing else. Everything is great, but ready to try something new!

• Living in the SF Bay Area, we have a couple of stations that dispense this stuff at reasonable price given the cost of oil these days. So I'd like to consider running a few gallons as a comparison over the weekend before heading over to the Willows.

• Should I deplete the tank and refuel at Thunderhill? Or move along.

Charles@dundonmotorsports

i tested it on the dyno earlier this year but saw no gains. Im sure it was ECU based limiting the power increase though.

Oh, this was WITH my exhaust setup, so stock may have some gains.

Either way 100 octane is better than 91-93 when its really hot out

SmokinGTS

My car loves the octane my pocketbook doesn't.....

WonderWagon

My buddy will fill his tank with 3/4 91 and 1/4 100. He swears his car runs better when he does this. Octane boost.

mooty

ur cats will die

Mike in CA

According to Porsche, max horsepower is delivered with 93 octane fuel so under normal conditions using higher octane than that is a waste of money.

For street use, I'm OK with the 91 octane stuff we get here in CA. For autocross, on the assumption that 93 octane might give a small performance advantage, I blend 100 octane unleaded with 91 to get something just a bit over 93. I fill several 5 gallon containers at the track a couple of times a season as 100 isn't available at any stations near me.

If you have a convenient source you might consider blending a few gallons of 100 with your normal fill up. But a full tank of 100 would just be throwing money away for a stock engine.

BTW, assuming you have the extended range tank, you have to mix about 7 gallons of 100 octane with 16 gallons of 91 to get a blend of just over 93....

anjum

Surely you need an ECU remap to deal with the higher rated octane fuel?

I tried the 100 Octane around Silverstone - 5 times more expensive than regular 97 (in UK) - and saw no power difference.

I used to have a TVR Cerbera with switchable maps for 95, 97 and 100 Octane (Part of the Red Rose Pack Option) - now this did make a difference!

RealityGT

^This

CDinSing

We have a supply of no ethanol 93 provided by a club member which we use at the track. Not sure if it gives much or any boost but it is safe for the cats.

NateOZ

As Charles mentioned, the big benefit of 100 Oct is that it combusts at lower temperatures which helps with cooling. I use it in my Cayman as a typical day is 4 to 5 hours of seat time and the 9a1 runs pretty hot.

A418t81

Simply not true. 100 octane is not leaded like the higher 110 and 116 levels. It will not harm the catalysts in any way.

DrJupeman

+1

I think there is little point in running >93 in these cars, but you'd be safe to do so. I've done back to back comparisons of 93 vs 100 in other cars and without the car being set up for it, it is a waste of money.

The one I debate all the time is the lore of running 100 in the GT3 Cups. It has been what folks have been doing forever, and the confusion, I think is that the car is rated at 98 RON gas (not the same as U.S. octane rating, but generally believed to be about 93 octane). The answer for using it when I challenge "experts" is always "it is cheap insurance". I fall for it and run 100 in my Cup, but I'm convinced I don't have to and may even be losing something for doing so.

RealityGT

Ah yes! thank you for the correction.. I somehow read 110 octane.

Cheers,

Mike in CA

I'd love to find a solid technical analysis of that theory other than the opinions I've been able to locate by Google-ing the subject. If someone has a link to something definitive, I'd be interested to see it.

My understanding has always been that high octane fuel has the same energy content as a low octane blend therefore they will burn at the same temperature, all else being equal with regard to the fuel formulation. The difference is that higher octane helps prevent the fuel/air mixture from igniting prematurely. Premature ignition could cause higher cylinder temperatures but in cars with knock sensing this is prevented from happening so I wouldn't have thought that there would be a significant temperature difference.

Even if one assumes that pre-ignition and higher burn temperature on a hot day is an issue, the question is; how much octane do you need to keep that from happening? In an engine like the GT3/RS that has knock sensing and gives peak power with 93 octane fuel it seems possible that only a small octane headroom is required. Filling up exclusively with $9+ a gallon 100 octane may be overkill, even for the track.

Just musing. Like I said, would love to see a good engineering analysis of the question....

Alan C.

I ran a 944 turbo in the old GT3 class in Club Racing. For engine management I used an Electromotive Tec 3. I had maps for 93 and 100. If I had 100 octane in the tank and loaded the 93 map I didn't see any gains on the dyno. Downloading the data at the track with 93 octane on the 93 map I didn't see any signs of knock.

Certainly not the same engine but I would think if the car is mapped for 93 it's only going to allow X amount of ignition advance and fuel. My simplistic view.