denniscasey

Have an interest in acquiring 2005 Carrera S (seem reasonably priced, would pay for LN Engineering IMS bearing upgrade) and have downloaded owner's manual to read about car. On page 268 (Technical Data) it says for optimum performance only use 93 octane (AKI/CLC one of these is USA standard I assume), but car "will operate properly" with "at least" 90 octane.

Difficult to find 93 octane so is sort of a moot question, so I assume 90 octane works fine or do you add some "octane enhancer" product to get to 93 octane?

Use would be daily driver, not track time.

SoCal C2S

Can't get 93 Octane is CA....only 91. Runs just fine.

extanker

you will be fine with pump high test,no need for any boosters

Wayne Smith

The sensors tell the computer how to adjust for the different octane. Down to 90 gives you the range limits that the system can adapt to. 91 octane in Cali works fine.

Side bar ...
I didn't write the code of course, but standard methodology would imply that the computers adjust down quickly but up slowly to protect the motor. High octane would probably give you a small power advantage, but you would have to be consistent for a tank or more (guessing based upon career experience with my own auto adaptive controls, but backed up by what others have also said).

Macster

The word I get -- but I have not studied the code -- is the DME is "programmed" to run the engine close to incipient detonation, that is running the engine with as much ignition advance just short of detonation as is possible. With as much timing advance as possible, but just short of detonation for the sake of engine longevity, is where the engine is most efficient.

The adjustment of the timing, down or up, is pretty quick. In the case of the knock sensors signaling detonation the DME has to retard timing immediately. In advancing the timing this has to be also very quick, but there is probably some kind of delay, debounce, or something present in the code to keep the DME from getting into some kind of state where it is retarding the ignition timing then immediately advancing it only to have to retard it again, then advance it, and so on.

Macster

If 93 is not available where you are run the highest octane you can find/buy. I don't think I have come across 92 octane but there are many places where 91 octane is available. Where I live/drive is one and both of my Porsche engines are ok with 91.

I can tell you I have had a chance to run 93 octane in my Turbo and the engine's response/transformation when fed 93 is rather remarkable. Were 93 available at a competitive price to 91 I'd run 93 all the time.

Oh, there are a few places where just 90 octane is available. These are at higher elevation locations. 90 octane is ok for an engine's octane needs go down as the elevation rises. However, keep in mind the tank has 90 octane in it if you descend to a much lower elevation.

For instance I fill up the car's fuel tank with 90 octane gas in Flagstaff (at around 6900 feet above sea level) and then head west. At Kingman AZ at around 3K feet I fill up the tank with 91 octane then drive on with no real worries even though the elevation drops to 600 feet where I-40 crosses the Colorado River at the AZ/CA state line. It soon goes back up as once proceeds west from there, but stations on further west, at least on the route I drive, carry 91 octane.

If you want you can experiment with different brands of gasoline to see if your engine has a preference. Be aware that in some cases if the engine seems to like a brand of gasoline over another the odds are high the difference arises from the differences in freshness. Thus it is very important to buy gas from a busy station to ensure you get the freshest premium gasoline.

I have found no difference between the various top tier gasolines. I use whichever one is handiest and has the lowest price. Around town where I live Shell is the most convenient station and offers the lowest prices. Because its prices are low this station sells a lot of gas so I am sure of getting fresh gas there.

On the road I use Shell, Chevron, UNOCAL 76, Philips 66, whatever is station is nearby when the tank needs filling.

I avoid using supermarket or discount gasolines.

denniscasey

Thanks to all for informative replies--I thought car would have most of its performance available with 90 or 91 octane vs the recommended 93 octane but just wanted to double check. However, with the Turbo model it did seem to make a noticeable difference to owner when 93 octane (or maybe octane additive) was used vs readily available 90 to 91 octane.

Edgy01

Turbos are particularly sensitive to octane--more so than the NA engines. Knock is more critical to a turbo engine. You can destroy a turbo engine quickly with insufficient octane.

On the other end if you find something like avgas to mix in with your 91 octane stuff, don't go overboard. Too much octane is wasted on these engines.

RobC4sX51

A good quality gas (no ethanol) at or above 91 is just fine. Don't recommend avgas, it has different anti-ice properties that isn't made for our cars. My $.02

dalancroft

^ Second this.

Although we ran 100 race gas at the Sonoma Point Raceway last weekend, which didn't seem to make a difference. (We were at 1/4 tank and my wife, the driving course student, decided to just add 10 gallons of 100o at the track.) I've been told it takes a few tanks for the ECU to notice and adjust. She refilled with four gallons of 100o still in the tank so is probably now running 93-94o right now. I'll ask her tonight if she noticed any improvements.

dalancroft

If you haven't already, clear corners stat! Especially on a silver car. You'll be surprised how much difference this $40-45 mod makes.

sjfehr

Octane retards detonation. Reduced atmospheric pressure at higher altitudes (and thus reduced cylinder pressures) also retards denotation. So most cars can get away with lower octane fuels at higher altitudes without the ECU having to retard timing. Turbos are different because they can compensate for the drop in atmospheric pressure. So, you can top off your C2S anywhere but might want to look a lot harder for stations with 93 octane in for your Turbo.

I wonder if the growing prevalence of high-compression turbocharged 4-cylinders will drive the rest of the nation to the same 93 octane fuels used at sea level? Sure would be nice. I really hate putting 91 octane into my Porsche when I'm driving through fly-over country; just feels so wrong.

denniscasey

Good point about "no ethanol." In mid-west ethanol is in all the "standard" gasoline and we don't even think about it, but were MY 2005 Porsches "ready" for ethanol? I don't think German gasoline had ethanol in 2005 and maybe not even now---one version of BMW high pressure fuel pump problems in 335 series in 2011 or whenever it was blamed ethanol in US gas--something they did not plan on.

dasams

I don't know about anti-ice, but avgas is high octane but contains lead


The US gasoline pool has 10% ethanol so this isn't a midwest thing.

It's not sea level that drives the production of 93, it's the ability of the refiners to meet the gasoline sulfur requirements while preserving octane. Truth is that the nation is moving to Tier 3 gasoline with low sulfur and octane will suffer. When Cali made the move, octane dropped from 93 to 92 and then to 91. It's unclear what will happen nationally but I can tell you with absolute certainty that octane will not go up

Fahrer

Most cars needing premium fuel specify 93 RON ( research octane number). The pump number (listed on the gas station pump is an average of RON and MON ( motor octane number). You will often see RON+MON/2 on the pump. A pump number of 91 is about the same as as 93 RON.