Engeljizzle

I'm moving to colorado on Tuesday. Car transport just picked her up today and it will be there on Thursday. Super excited!

One issue, they only have 91 octane here and I am a little concerned. I've heard the altitude is the reason but I'm still worried. Porsche said I'll be fine but they haven't really impressed me much lately lol..

Any thoughts? Will my car be okay?

LexVan

You're fine. Just ask the Calli guys.

ToyGuyAZ

We have 87 89 and 91 at the pump here in AZ. You'll be fine

PC Valkyrie

So here is another question: if both 91 and 93 octane are available, it is worth it to put in 93 octane?

And does the answer depend on the type of usage?.......ie whether the car is mostly driven on the street with occasional track use, or if the car is primarily used on the track?

Jimmy-D

If you have 93 you should use it. The car will adjust to the octane level any way but I always opt foy the highest octane avail. here in Chicago 93 is every where so I use that. The difference between 91 and 93 will only be a couple dollars per tank. Your buying ~$150,000 car so I would not sweat the few extra dollars

frayed

ECU will adjust timing based on octane levels. You effectively have a lower hp car with low octane (or high altitude or high temperature).

Terrence

Get the 93 if you have a choice. I get 100 and mix it to get 93 here.

Mike in CA

Agree. Mixing not worth it for the street, IMO, but for timed events I do the same.

Cyrek

Travelled across country this summer only saw 93 once which is ridiculous because it's everywhere in the Midwest under $4. Colorado has more 87 than I saw anywhere.

GrantG

Here in Colorado the air density is so low, that it effiectively lowers your static compression by a large amount making high octane unecessary to produce the maximum potential hp (which is down over 15% in Denver and almost 50% if you drive up Mount Evans). 91 is fine, but if you like, I can direct you to several stations that have 100 or more. The biggest benefit is finding Ethanol-free fuel (like Brad's Conoco in Lakewood).

PC Valkyrie

It's not really about the money or cost, but convenience. Not every station in the greater Toronto area has 93 octane, but all have 91 octane.

I'm just curious to know if people actually notice the decline in performance if 91 was used, on the street, or on the track.......(do people actually notice a difference in laptimes because of 91 vs 93 octane fuel??)

Macster

No lap times to go by but I can tell you based on my seat of the pants dyno running 93 vs. 91 makes a difference. While HP is unaffected -- both grades have the same BTU content -- my 03 Turbo's engine felt noticeably better on 93 and this was in Wyoming at some altitude, up to a bit over 8K feet.

Now an important difference has to be noted and that is the engine in my car was of course turbo-charged. Thus cylinder filling was not as much affected by altitude as would be the case with a NA engine.

In your case where elevation is not a factor I'd use 93 instead of 91 unless 93 was inconvenient or way more money. I'm not sure how much more money would be too much more money. I'd have to do a mileage test -- over several tankfuls of each octane grade of fuel -- to see what the mileage hit was with 91 vs. 93 then work the numbers.

I would only go to the trouble of blending 91 and 100 octane gasolines for track days. I would not bother doing this for just street driving.

You have 93 and 91 octane gasolines available to you. Try a couple of tankfuls of both and report back. I think you'll find with 93 in the tank the engine is more responsive and the car markedly a better drive because of it. Unless there is a severe price premium on 93 the cost will be about the same. With 91 the engine derives less energy from burning this grade of fuel thus requires more of it. So gas mileage with 91 is less than it would by with 93. Thus while you pay less for the 91 you buy more of it.

Macster

The engine will be ok. Just buy a top tier gasoline and buy from a busy station.

Even at sea level here in CA 91 is ok. Not ideal, as 93 would be more fuel efficient, and drivability would improve some, but 91 is all we can get with few exceptions.

But with a diet of 91, both my Boxster and my Turbo run just fine.

reidry

I'd like to expand this discussion.

Octane
93 octane is not available in several locations within the United States, Porsche must be comfortable (and it's probably in the owner's manual supplement) with 91 octane fuel. It would be unreasonable for Porsche to require mixing 100 and 91 to maintain an average 93 octane.

The 991 GT3 uses a modern Engine Control Unit (ECU) capable of adjusting engine parameters to account for the lower octane. A good question is whether the 991 GT3 makes full power at sea level (notice I did not say specified power) with 91 octane fuel or if it makes slightly more power with 93 octane fuel.

Ethanol
Most fuels in the US are now mixed with a percentage of Ethanol. I don't want to discuss the politics of Ethanol, but it's important to understand the impacts Ethanol has on our vehicles.

Ethanol contains less energy per unit volume than pure gasoline (E10 has 96.7% of the energy of pure gasoline for like volumes). So that's less energy by volume so a closed loop fuel injection engine will use more to produce the same amount of power at lower fuel economy (lower mpg). Ethanol also burns cooler than pure gasoline, it would be interesting to know the peak hp comparison vs pure gasoline at sea level.

The other side affect of Ethanol is material compatibility. Materials compatible with pure gasoline are not necessarily compatible with fuel containing Ethanol. It appears that E10 is now widely available in Germany so I doubt there is a concern about compatibility in the modern fuel system in the GT3.

I'm interested in any discussion about what folks are going to use in their GT3, especially if there are facts or rationale behind it.

If someone is aware of a hp (dyno) comparison with a fuel injected engine on various octanes and ethanol blends I'd love a link to read up.

Thx,

Ryan

Mike in CA

Ryan, Porsche does feel comfortable with 91 octane. While the owner's manual states that the engine will "operate properly" on 91, it also states that "optimum performance" is achieved by using 93 octane fuel. The only time I blend to achieve 93 octane is for timed events where tenths and hundredths may matter although the practical benefits may be more in my head than in meaningful results.