I run a 9.35:1 compression in my 356. But it is a carb motor (32 Zeniths), 2v/cyls, stock sizes/B heads. All that by way of saying 91 Octane gas is just fine. I tried blending up some years ago but didn't notice anything significantly different in the behavior. Of course, I didn't advance the timing (much), it was too much trouble to set it back after I ran out the "good juice". I wasn't going to romp on it in low-rev 4th anyway, so knocking wasn't going to be an issue. Oh, and it's a '59 so there's no DME to adjust timing or fuel flow In short, "meh."

So then comes to my driveway this summer a fine 997. I drive it on CA 91 non-oxygenated (Summer blend) gas. It seems fine. Why? Because its 355HP, which is 2X more than my previous DD, my 1.8T Audi. Though 355 is less than my truck, it's a diesel, so that's something different. The point being that Of Course the 997 felt DAMN fast--because it is! Right?

Well, kinda. After a few weeks, I recall there's a 100 Oct 76 station on my way (mostly) to the office. I blend in a few gallons to bring it (calculated, measured) to 94 Oct, which is one over what it says is the Minimum(!) on the inside of my fuel filler cap.

HOLY SHMOLEY! What have I learned? I've learned that the panther **** that we usually run around here as "premium" shouldn't be even be used to light a BBQ!

At 94 (RON+MON)/2 or however they caclulate it here in the the Golden Sate, my 997 S feels like a Completely. Different. Car. I mean, wow. It is smoother at all rev ranges, especially at lower RPMs, between 2k-3k. It doesn't burble as much on cold start and I've actually run into the rev limiter a couple of times now--probably because its even more fun to try. Throttle response is better, acceleration happens right Now even in 4th and 5th gears (tip.).

Okay, so maybe I'm paying more attention or trying harder. I studied psychology, I know all about The Hawthorne Effect. I didn't do instrumented measurement. But my well calibrated **** tells me there is a Significant Change. The sound, the feel are unmistakable. This is how the car was designed to operate. It is that obvious.

Which just makes me super sad for all the 911 drivers out there in CA who have never experienced how their Porsche is Supposed To Operate because of the crap that we get at the pump. All I can say to them is to find the stickies that tell you where to get 100 octane gas in your area and blend some in. It costs next to nothing; I figure +$3/gal for +6 gal per tank is round $18 for 300 miles at a significant more amount of fun. More fun than you could get from six Starbuck's Cappuccinos, that's for sure.

Thanks for letting me state the obvious, but it sure was new to me!

 

The issue is that the high octane stuff may actually be E85 and that is bad in many other ways...

 

Not a Porsche owner (yet), but here in Kansas the retailers can put ethanol in the fuel and are not obligated to tell you. Some of the pumps are labled: "may contain up to 10% ethanol"...but you really don't know. 93 Octane is a rarity....91 seems to be the norm. 100 is the Holy Grail. You have to drive to Heartland Park out in Topeka to find high-grade fuel. Even in my old Benz, it makes a difference. I don't know what the Porsche guys in my area do to overcome the lousy fuel situation.

 

Here's a silly question... remember I'm not a mechanic...

Is there any benefit to adding "Octane Booster" from the local auto store?

From what little I know about octane, the higher octane prevents pre-detonation for higher compression engines. So my SUV wouldn't benefit from it... but what about a Porsche engine?

 

Octane rating only relates to what temp the gas will ignite at..........it has NOTHING to do with performance of said engines.

Thats why with higher compression engines you need higher octane, you want a controlled burn and no preignition\pinging. If you are getting a controlled burn with a lower octane, a higher octane will not give you any power increase.

 

adding a bottle of octane booster will only raise the octane from like 91, to 91.1 -- no difference

as for ethanol blend, the only downside i've experienced so far is worse fuel economy.. since the fuel injectors run a higher duty cycle with it.

 

+1: right you are; I've been waiting for someone other than me to post this.

 

ethanol burns hotter than gasoline. it could lead to additional stress to the engine if the mixture is high. there is a movement to raise ethanol to 15% for newer cars.

my lambo manual specifically calls out avoiding ethanol.

 

Not entirely, because the above presumes that the engine has no control over the pressure/temperature within the combustion chamber at ignition. Our modern engines have lots of tools at their disposal: metering the air/fuel mixture, changing timing and even the valve speed and distance.

So your engine may well modify its behavior to work without pinging/detonation using lower octane gas, but that doesn't mean it can't use the benefits of higher octane gas. To a point, of course. Thankfully, the Porsche Engineers have put a sticker on my gas flap telling me exactly what octane number the engine can take advantage of, and it is described as a minimum, not a maximum.

 

I have similar experience in all my cars that specify 93 octane. I have a 100 octane station locally so I mix my tank occasionally. I feel the difference every time, especially on turbo-charged cars.

 

There's quite a spread of Fear, Uncertainty and Doubt in that statement. I'm not going to argue with if/how/why E85 is bad. What I can say without controversy is that it isn't designed to be run in vehicles which are not "Flex Fuel" vehicles. Which our 997s are certainly not. So "bad" for our Porsches? Yeah, I'd say so. Most simply, it will violate your warranty.

But I wasn't proscribing anything with 100 Octane to blend with gasoline. I should have been more specific. 100 Octane gasoline, blended with 91 octane gasoline yields a pretty heady brew at a reasonable cost--when its available. And I don't believe that 100 Octane gasoline "may actually be E85"--legally--if it isn't labeled as-such. There may be shady folk out there, but it wouldn't take but once to know you're not getting the BTUs out of your "gasoline" if it were actually 85% alcohol. You have to go looking for E85 pumps in CA.

Now as to whether any gas might be E10, the American Coalition for Ethanol would rather that gas not be forced to be labeled as-such if it has 10% or less of the grain juice.

I'm blending 100 Octane Gasoline, bought from a single vendor, with whom I've had a conversation about this very topic. So no mystery nor surprises. Even if it were to be E10, and if I ended up with 40% of a tank having 10% alcohol, then I'm okay with 0.6/gal per tank (4.1%) if it raises my Octane from 91 to 96 even if it drops the total available potential energy by 2%. Because its all about how efficiently you can release as many of those BTUs as possible against your pistons.

 

It is already approved for MY 2007 and newer cars. The study is still underway for a waiver for MY 2001-2005 cars. The EPA says they're going to try to come up with new labeling requirements. We went through the same thing a while ago with the introduction ultra-low-sulphur diesel for our truck. We and it survived.

 

No FUD. Legitimate high octane gas sold in CA is oxygenated with ethanol. Check Sunoco race gas - the only CA-legal (and safe) high octane offering is 260 Gold 97 octane.

Re E15... Approved by whom? The EPA? Yeah, right.

Will you run E15 on your 356?

 

Pssst... A little off topic but just a heads up, theres a station over in Mission on Johnson Drive just down a little from the Hobby Lobby that sells Hund-o. You don't have to drive an hour to Topeka for it!

 

They haven't sold 100 over there for quite some time now. Also BP's are 92 and quite a few of them are 93.