89AZ944

Manual says to use a minimum of 90 octane, flap over gas cap says fill with 91.
Premium here in Phoenix at most sites is 91, some have 92 or 93. I went to fill up the other day and the site was out of 91....luckily, I found some at the next station...but it started me thinking....

Is there any harm in running a lower octane in an emergency? I know lower performance/knocking/pinging will be an issue, but does it actually hurt the engine?

I have access to 100 octane racing fuel......Will I burn up the engine if I run a tank of 100 octane through it? Is there any benefit running a higher octane than 91?

Just curious,

89AZ944

Serge944

For a naturally aspirated stock car, running higher octane wont do a thing. There will be no direct harm running lower grade fuel, however; your car wont run very well.

Of course...theres the trickle down affect: your engine starts to vibrate, wearing your motor mounts quicker...

Ok, thats really stupid. Either way, running lower octane for short periods of time wont do anything to your car.

M758

In my 84 I run 87 octane and it works just fine.

HOWEVER you have an 89 motor. I am pretty sure they upped the compression ratio so best to use 91. I run 91 in my 944-spec car straight from the pump has worked fine. I did try 110 leaded race fuel once. Just made my wallet lighter. Never again. I also run standard 91 in my 944 Turbo S. No problems.

The 944 turbo has knock sensor for those "emergencies". Performance was not so good however. Worst case is you can detonate and blow a head gasket. I am not sure if the 89 NA has a knock sensor. It really should not be hard to find 91 around town. If in an emergency throw in the best you have and be gentle. Don't accel hard or she high or low RPM with any sort of load. Put in 91 as soon as you can. I would think that short of the gas issue we had last year it would be easy to get 91.

FRporscheman

From what I remember, octane is just a measure of flamability, higher octane meaning less flamable. High compression engines need higher octane, so the gas can resist igniting early. Lower compression engines can use lower octane. That's why accords are OK with 87 and benzes need 91 - the compression ratios. That's what I remember, anyway. So it's just based on your current compression ratio. If you use too low of an octane, you'll get detonation. Not sure about too high of an octane - might make it run rough due to lack of ignition or something, I guess.

Matt H

Check to see if it says 91 RON or 91 MON, there is a difference.
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bearone

the po recommended reg/87 in the new cruiser and it starts and runs fine.

Porsche-O-Phile

Read the "Gasoline FAQ" on the Racer-X website. Lots of good information there. FWIW higher octane WILL help an n/a car - just ask any hot rodder that's running 13:1 compression!

For our US-spec n/a cars (that have considerably lower c/r's of 9.5-ish:1 versus the Euro 10.5-ish:1 - the exact c/r's vary a bit by year) there will be no serious problem in running 87 or probably even a bit lower octane ratings. In other words the engine will RUN on lower octane, it just runs with more and more stress on components - eventually you'd get to a point where the engine just wouldn't run on the fuel, but that would be a point far lower than 87 octane.

However, since higher ratings do give you more efficient operation, smoother burn, lower CHTs, etc. I recommend it whenever possible. Running higher will probably not dyno you any more horsepower (this is one thing I intend to check at the dyno day next week on the n/a car), but it will be "nicer" to your engine in the long run, put less stress on components and probably show benefits over very many cycles of use.

88BlueTSiQuest

But it's based solely on compression. The higher the compression of the car, the higher the combustion chamber temps are, the higher the chances of detonation are. That's why running race gas in an N/A car with 13:1 compression is so important. It keeps the pistons from developing holes in them.

Running 91 octane in a low compression N/A engine only has one effect, a lighter wallet.

Mongo

The 944 NA can run on gas above 87 w/out any pinging issues. I ran 87 in my 84 one time and it pinged; 89 octane ran with no problems. Today I use 91 because I feel I get the best economy out of this gas.

iloveporsches

Huh? How do you get the best economy out of paying more for something you don't need?

I run 87 octane in my car. Never has given me any problems. The 89 motor will be different. US octane ratings are also different than European ratings. Check what the manual says (RON or MON) and what the pump says. The ones around here, IIRC, are (RON+MON)/2, and the manual/ gas door is in RON.

Mongo

For some reason the 84 gave me problems....I didn't do any internal work on it but maybe it could have had a higher lift camshaft on it. With this 86 I refuse to run 87 and am satisfied with 91 so I'm keeping with it, it's just my preference to run a high grade gas in my car, kinda like how people want to use Zaino or Meguiar's Gold to wax their car, some people just feel they don't need it while others do.

Chris_924s

88 924S, higher compression- I will always run premium. I get midgrade if I'm light on cash and need gas.
I have noticed much less ZOOM when I put regular unleaded in during my "I'll see if there is a difference" phase.

I do not notice any knock, but degredation in performance and mileage is definetly present with regular.

FWIW- every 4 months I do run a tank with Techron thru it. She likes the Techron additive with premium!! Zoom zoom! Much quicker acceleration and throttle response afterwards.

hoffman912

i wouldnt run anything but premium in any p-car.

Geo

Most correct. US pumps by law display (r+m)/2.

A good recommendation. You can find it elsewhere as well. Do a google on gasoline FAQ.

But it won't help a stock 944. It won't help a 944 with the usual NA mods either.

Not true. And how do you figure it will put more stress on the components. Only in situations and state of tune that cause pinging will higher octane help.

None of these things are necessarily true. I have experienced lower CHTs with my racing kart in true back-to-back tests between pump gas and race gas, but others have speculated other things were going on (like detonation). They may be right. I wrote to the author of the Gasoline FAQ about this very subject and he was very clear that one could not state there was a causal relationship.

How do you figure it's being "nicer" to your engine?

Octane rating or Anti-Knock Index (AKI) is simply, purely, and ONLY a measure of a fuel's ability to resist auto-ignition. Period.

Higher octane ratings (AKI) are useful when building/tuning an engine. Higher AKI fuels expand the envelop of things that will improve performance without causing detonation with that fuel. This includes ignition advance, higher compression, high boost pressures, increased volumetric efficiency, etc.

Dmitry S.

MY 88 and 89 cars had a substancial bump in the compression ratio (up to 10.2 I think). On my old 88 n/a, it would detonate on 87 and 89.

For your 89 car, I would highly suggest 91 octane. 83-87s seem to do fine on 87 octane.