gonz911

I currently live in Texas but may move to California. The inside of my fuel door states octane requirement of 93. If I'm not mistaken that's hard to come by in California, LA in particular. What do you do - does it become a tuning issue? Does it effect performance, knocking, etc.?

CarlJ

These cars have knock sensors and will appropriately adjust the timing to avoid detonation with lower octane fuels, however, with the decrease in advance, you'll lose a little power. Nothing drastic, but possibly noticeable in the seat of the pants if you drive aggressively and are well in tune with your car.

Mike in CA

It's not just LA; it's everywhere in California. The good news is that you would have to have an very well tuned butt dyno to tell the difference; your car will run fine. Since autox's can be won by hundreths of a second, for my psychological well being if nothing else, I blend to get 93 octane, but in normal street driving I don't notice a difference.

Aerokitted

You won't be able to tell the difference. Move on and enjoy.

gonz911

Thank you all very much!

Macster

Don't sweat it. Just buy a top tier gas and buy from a busy station. 91 octane while not ideal is all there is.

It sucks really, but I don't know who is to blame.

High compression is one of the best things a car engine can have.

The energy to compress the charge in the cylinder is almost all gotten back from the initial spring back.

High compression improves drivability (torque) at low speeds. We all shop horsepower but we drive torque.

I note my 02 Boxster with its 11.3:1 compression ratio is one of the most tractable engines around. Idle, and even in higher gears just off idle the engine will pull very cleanly and smoothly.

Much better than say my 03 Turbo, with its lower 9.4:1 compression ratio (necessitated of course by the turbo-charging). I have to keep the rpms a bit higher with the Turbo to avoid it complaining by making a noise that indicates it is not happy operating at low engine rpms in the higher gears.

What you will experience though you'll probably not ever notice it -- unless you have the chance to drive the car with 93 octane under the same conditions over a span of time -- is a decrease in gas mileage.

Under part throttle the DME will probably have to retard spark advance to avoid detonation. This affects part throttle gas mileage.

Additionally, with a slightly retarded timing the exhaust gas temp is raised. But as I have found out, it may be raised but the engine, sensors, converters appear to have been unaffected.

Under high torque demands (near to full throttle) the DME can enrichen the mixture -- and chances are detonation will not be an issue -- and the car will make its rated HP or very very close to it.

Sincerely,

Macster.

gonz911

I asked because my prior supercharged M3 (ESS ASA blower) was tuned to 93 and it would've made a big difference in HP to drop down. But my concern was any issues with the 997. All is good now though. Thanks again for the information.

utkinpol

I made a mistake once to put 91 into tank instead of 93 on AX day - difference was very noticable but my car has softronic flash with 93 octane maps.

SToronto

Awesome thread...because I just filled my tank for the first time today.

I did see the 93 in the fuel filler door, but didn't realize I was pumping 91 and that there is indeed a 93 available here. In my previous car 91 was required.

Oops, I'll stick to 93 next time.

VGM911

I've read about the non-availability of 93 octane gas in California, but I don't think I've ever seen an explanation for it. Do any of you know why 91 octane is the highest level available?

Mike in CA

I don't think there's a simple answer to that. It's obviously not due just to the CA requirement for cleaner burning oxygenated fuels because the higher octane unleaded fuels are still legal and available; I can buy them at my local track and a few stations do carry them. I suspect issues around availabilty, refining capability, and cost are at least as, if not more important.

Palmbeacher

My gut and years of living tell me at the root of it is $$$$ which buys political favor. Someone powerful stands to gain financially for some reason. Here in FL 10% ethanol is mandated, and there's talk of upping it to 15%. It cuts gas mileage, which offsets any argument for reducing foreign oil dependency. But ethanol can be derived from from, among other things, sugarcane, which is a huge industry in the state, with a powerful lobbying presence.

RollingArt

+1

It's a money driven political issue.

Has nothing to do with being smart or good for us or the environment. Only thing it's good for is big business.




Phil

Da Hapa

There is no simple answer to what is really a simple question.

The truth is that it has to do with the California Air Resource Board (CARB) and their regulations/requirements. Gas blends here in CA change several times a year to supposedly minimize the impact on the environment. As a result the 91 octane gas you buy at Shell in December is not the exact same chemical blend as the 91 octane gas you buy at Shell in July.

To the original poster...
1) I will respectfully disagree with what some of others have said here. I could absolutely feel the difference in my 2008 997S when I either put 93 octane (the times I was in AZ) or blended 100 octane race gas (auto X).
2) Do a search here and on the "other board" and you will see that there were/are several other 997.1 owners like myself (I'm not sure whether the DFI cars cured this) that would experience occassional knocking in our cars here in S. CA. My dealer and the regional rep both told me point blank it was nothing to worry about and due to the 91 octane in CA but I never liked the sound of hearing my $100,000 car knock... To my knowledge, there's no scientific proof of the knocking being tied definitively to 91 octane gas but I think that sometimes where there's smoke there is fire.
3) The best thing you can do if you move to the great state of California is to stick with top tier gas and perhaps once in a while bite the $9.00/gallon bullet and mix in some 100 octane race gas.

utkinpol

nothing of what happens in CA lately can be explained.