safulop

Interesting that I couldn't find much on this by searching, but, is there any good reason to use premium gas in my S4? I always have, on the working theory that it would be somehow closer to the "pure" gasoline of the 1980s. I've read that this is not right, but my old 944 just *hated* anything but premium. I remember the first time gas hit $4 back in 2008, I put mid-grade in the old 944 one time and it stalled almost immediately. It was a pretty clear memo from a car that *never* stalled otherwise.

oldfrat

If you have an owners manual see what it recommends. My 1981 calls for 87 unleaded. I put a tank of premium in it when I first got it, but then checked the manual. It has been running great on 87 ever since.

Brad

safulop

Yeah well, gas was different then. My owner's manual says 87 is OK, but it is also very careful to state that I should *never ever* use gasoline with *ethanol* in any proportion. So good luck following the owner's manual.

My 944 owner's manual also said 87 was OK, but the car disagreed for 12 years.

oldfrat

I hear you! My owners manual says my 1981 is designed to run on up to 10% ethanol, but recommends straight gasoline if available and lists symptoms indicating gasoline is needed. Near as I can tell, though, there are no 100% gasoline pumps near me and I rarely see them while traveling.

I'm no expert on this, and hope the experts will chime in, but I don't think that increasing octane is going to improve my performance if it remains 10% ethanol.

Brad

The Forgotten On

87 is okay for the low compression US 80-84 cars. All others should run premium as they run at higher compression ratios and or have more spark advance.

Also, ethanol is the new octane booster. Back in the 80's I think they used methanol instead, which is dragster fuel .

safulop

I know that in Idaho, Premium grade at BP stations is "pure gasoline" with no ethanol. That's the only place I've seen it in my travels. I stuck a tank in my 928 and got 23 mpg! Makes a difference.

linderpat

you have a high compression engine so you should be using premium. From US '85 on, use premium, highest grade. Lower grades will cause knock. On US '84 and earlier, regular is fine, and premium is a waste of money, as it adds nothing to the detonation process.

19psi

No, your Porsche manual does NOT state that in any way, shape or form.

murfthesurf13

We have two Sinclair stations in Southern Utah that has no ethanol gas available, but you will "pay" for it. I use to run it in my hot rod, 1974 Dodge Challenger w/440 magnum engine, and it made quite the difference. In my 928, Premium 91 seems to be fine with ethanol. Haven't tried regular, 87.

WyattsRide

I use 91 + octane or Ethanol Free 89 octane gas in my 85. Not always convenient to get the Ethanol free, even though there are a couple stations very local selling it. My car seems to run the same on either one. "I" feel better when I use the Ethanol Free though.

Here's a link to find the Ethanol Free gas stations in the US.

http://www.pure-gas.org/index.jsp?stateprov=NC

Don Carter

Usually the 10% ethanol is a result of government regulations in different states.

I have had no problems with mid grade in my S4's and my S3 with Ken's chips that were designed for mid grade. I never really buy premium any more. I actually didn't know I could burn regular in the 82 I just bought, that's going to save some money!

Also important to buy name brand gas (Shell, Exxon, Chevron, etc...) since it contains more additives than generic gas and will keep your valves and piston's cleaner.

hwyengr

Ethanol shouldn't have an impact on how your engine runs, just how the fuel lines react. If you've already replaced your fuel lines with something modern, you don't have anything to worry about. You just get the reduced fuel economy. Aren't there posts from guys who run E85 in their 928?

Premium fuel, though, is different. Its more critical for 85-86 owners to run 91+ since there aren't knock sensors, but even with knock sensors it's often false economy to run lower grade since the timing retard can reduce gas mileage to the point where you aren't saving money.

Interestingly, though, my first car (1986 GTI) had 10:1 compression and the manual still specified 87 octane...

dr bob

Less than a year into 928 ownership in the late 1990's, I was driving back to SoCal from a Devek event, hot August day. I stopped for fuel and accidentally put regular into my S4. Even with all the spark-retard and knock-sensing systems intact, it still complained with a few audible pings and continuing poor performance. I drove it gently for the rest of the ride home (maybe 50 miles), and ended up transferring most of the remaining fuel to my other less picky car's tank.

Fast-forward to today. Fuel quality here in Oregon is much better than what is available in southern California. Mileage is much better here, some because of lack of traffic I'm sure, but mostly because the fuel blend is much better. I've only passed a couple tanks of fuel into the 928 since arriving here, still enough to see 22-25 MPG average results. The Honda has done much better too, with mid- to high-twenties mileage here vs. high teens in SoCal. I have an OBD onterface set up on the Honda to datalog to my tablet. One of the available parameters is the sensor that reads the amount of ethanol in the fuel. In California it showed around 12% most of the time, but sometimes showed as high as 20%. Mileage was affected almost directly by this number. Local fuel here shows no ethanol at that sensor, and mileage has improved by some 20-25%. Again, driving patterns have changed too, so I can't attribute it all to the fuel.

On other past "regular gas " cars with knock and exhaust oxygen sensing, premium fuel would often more than pay for itself in improved fuel mileage. I'm pretty religious about tracking miles and costs, and with the increase in gas costs over $3/gal even the "just needs regular" cars would improve enough percentage-wise to justify the extra twenty cents fer gallon for premium. The cars also saw mileage and performance improvements with new oxy sensors, easily enough to justify replacement every 40-50k miles.

Don Carter

Bob,

Interesting observations. Did you notice a difference between winter and summer? The fuel recipes often change between winter and summer.

I know we are getting a bit off topic by talking about ethanol, but it is an oxygenate used to reduce emissions, so if anyone is interested in learning more about it and other oxygenates, like the ill-fated MTBE, there's some good history and info in this PDF.

http://www.arb.ca.gov/fuels/gasoline/pub/oxyrprt.pdf

safulop

Wait, it doesn't? Well if the S4 manual doesn't say it, I *know darn well* my old 944 manual warned against "gasohol" as it used to be called.

-Sean