Dartmouth

Is anyone using less than 93 octane in a 997.2 S or 4S? What are you experiences with the performance and knocking using less?

dasams

In CA, our premium is 91 and the car performs just fine with no knocking. Probably down a few ponies but I can't say whether it's noticeable as I don't have easy access to 93 for comparison. Why do you ask?

On a separate note, reduced octane is coming to all 50 states as the refiners will be required to reduce sulfur in the gasoline and a side effect is lower octane. Expect to see 91 and a wider gap in the price differentials as the refiners balance the supply & demand between the various grades.

PJorgen

I'm in CA as well so use 91 as I don't have a choice; never had a problem. When I go to the track I juice it up with some 100 octane because I can, but don't really notice a difference except for some additional lightness in my wallet.

Swoody

Arizona, 91 octane...car adjusts. Not much else you can do about it unless you want to have a can of Torco on hand to blend your Octane rating up.

chris.hanle

Oklahoma and Arkansas 91 is max, no problems (13k miles).

wc11

Most stations here is 91
Costco gas is 92.
Shell is 94

Edgy01

With the California max of 91 there is knocking but it is minimized by the rapid changes within the engine management system. There definitely is knocking.

Porsche recommends 93, and no higher. Any higher and it is simply wasted. If you have to mix your own (for racing, etc.) then take that into account.

Dartmouth

At the Jersey Shore we are getting 87 - 93.. I've put nothing but 93 in my 09 4S - no knocking. So dropping to 89 or 90 I think I'm hearing that I will get knocking, it's ok and it bothers me a little.

RobC4sX51

" On a separate note, reduced octane is coming to all 50 states as the refiners will be required to reduce sulfur in the gasoline and a side effect is lower octane. Expect to see 91 and a wider gap in the price differentials as the refiners balance the supply & demand between the various grades. "

Are you sure about this? Where did you get your info? Link? I just had my car tuned from sharkwerks/EVOMSit and specified 93 octane as it is readily available here in KY. There are some ethanol 10% blends in TN and AL but they still claim 93. Another Obama mandate I presume?

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Jaws1

Huh? We could all hope for zero sulphur. There's no relationship btw sulphur and octane.

mattyf

I bought my car in Washington and drove it down to LA. Definitely did a little pinging when I was forced to switch over to 91. The engine learned quickly and it's extremely rare that get a ping now. But if you can get 93 use it.

Macster

It ought to bother you enough you switch back to using the proper octane grade of gasoline in your high compression Porsche engine. 90 is as low as I think Porshe says you should go down in octane and really 91 is probably as low as you should go though in some areas 90 is acceptable. These areas being located at higher (>5K feet?) elevations. I'm thinking of Flagstaff, Albuquerque and higher locales.

We in CA get nothing higher than 91 (except at track and special gasoline stations) and both my cars run OK. But a trip that had me driving my Turbo up through Wyoming (among other states) and with opportunities to fill the Turbo's fuel tank with 93 octane (at low prices only dreamed of here in CA!) I wish I had 93 to run here. The engine was noticeably more responsive and just seemed more alive.

I never felt any gain in HP which makes sense. The energy content is nearly the same (and premium often has more energy per unit than low octane) between 91 and 93.

The real difference, the real benefit, in running the right grade of octane is the DME can trigger the spark a lot sooner so the fuel starts burning sooner and develops max pressure just the piston is best positioned to turn this in to rotational energy at the crankshaft. Because 93 is more resistant to forming pre-ignitable compounds ahead of the advancing flame front 93 octane doesn't lead to detonation.

Running too low an octane costs you fuel economy. The spark is delayed -- to avoid the higher pressure in the cylinder which leads to detonation -- so the pressure developed is less and peaks at the wrong time. Less energy is derived from the burning of the lower octane fuel. Additionally the retarded spark raises exhaust gas temperature which subjects everything it comes in contact with to higher operating temperature which is life shortening.

Macster

EPA has proposed lower sulphur content in gasoline starting in 2017. It is referred to a Tier 3. Tier 2 lowered sulphur content by 80 or 90%. I did not find by how much more Tier 3 would lower sulphur content compared to Tier 2. Oh, wait it is 10ppm. Tier 2 was at 30ppm, IIRC, with some room to go higher based on some goofy CAFE scheme.

Here's a link:

http://www.epa.gov/otaq/documents/tier3/420f13018a.pdf

The fine print:

http://www.gpo.gov/fdsys/pkg/FR-2013...2013-08500.pdf

Don't go blind reading this last document.

EPA estimates the cost at 1 penny per gallon. And if you like your health insurance you can keep it. Oh wait, wrong forum.

Oh, I don't know how removing sulphur affects octane. In diesel fuel removing the sulphur affected the cetane rating of the fuel, lowered it as the chemical process used to remove the sulphur was rather brutal, chemically speaking.

One possible way -- just a WAG -- is the refineries in order keep the cost of fuel down might cut back on octane as this adds cost to the fuel.

rankoutsider

Brisbane, Australia - 98 Octane - Generally Shell V-Power...

Didn't realise petrol in the US had such a low Octane rating (although the US may use MON, not RON or similar). We have
- 91 (ULP)
- E10 (10% Ethanol)
- 95
- 98

Its worth noting that the Octane rating does not refer to the amount of Octane in the fuel -its a relative measure of the fuel's anti-knock properties (see wikipedia)

Quadcammer

based on your prior posts...are you sure a 911 is for you?