nvrlft

Hello all,

My 91 964 uses 91 Octane and I am fortunate to have a Sunoco station near my home that has it. However, in the event I need to fill-up on a road trip and it is not available should I go with 89 or 93?

Thank you.

Oh, and, last Fall I read some postings about driving the C4 in snow and found that remarkable. However, after 3+ feet of snow in the DC area I am proud to say the all-wheel drive was magnificent. I will be getting snow tires next year and certainly will not be shy to drive it in inclement weather!

wellcraft290

i would go with 93 because most cars put a min octane level not max to avoid pinging

jimq

I always use 93 here in Florida. I have never tried anything lower.

BlueHeeler

+3 on 93 if 91 is not available.

I had the pcar out in the blizzard. The C4 is the best car I have ever driven in snow. These last few weeks I have had to drive around numerous SUVs and 4x4s that could not get traction on inclines or ice. I thought I was hero of the day until I saw some guy in an MGB making progress. He did look very cold though. LOL

BGLeduc

If I understand this correctly, octane of a certain level is needed for knock suppression. And the need for high octane fuels diminishes with altitude. In the Mountain West, and most of the Southwest for that matter, you will be damn lucky to find anything higher than 91, and sometimes it will be less.

When I ran the AX at the Porsche Parade in Keystone, I was running 90 Octane Shell in my Cayman because that was the best I could find on the way up. At 9,000 feet or so, it did not seem to hurt the car's performance anything more than being at 9,000 feet sure did.

You sea level guys kill me ;-)

Brian

Nine11

Use the highest you can find, and 91 is the best we got in this part of the country.

raspberryroadster

thinner air will result in lower levels of engine performance (under duress ie WOT), i am not sure that reflects a need for lower octane at altitude....but i could be wrong. a high performance car capable of rapid heat generation in the cylinder ie supercharged or turbo'd will require high octane at any altitude...and esp. if its been tuned to run in thinner air.

high octane (rating thereof) is measure of the fuels resistance to ignition.
high octane prevents pre ignition from heat generation in the cylinder (from compression & not spark)...in a regular car / car driven without duress pre iginition results in knocking/pinging....in high compression cars especially under WOT, or high performance cars (particularly turbo or SC, subject to intense heat generation) pre ignition can cause burnt / scored valve / piston.

i can source 94 locally and use that....when i travel i always carry lucas boost enhancer....likely not needed with the porsche, just a throwback habit from former vehicle (heavily sc'd muscle).

BGLeduc

This is what Wikipedia says, and we all know that whatever we read there is obviously the truth. :-)

United States - In the Rocky Mountain (high altitude) states, 85 AKI is the minimum octane, and 91 AKI is the maximum octane available in fuel. The reason for this is that in higher-altitude areas, a typical naturally-aspirated engine draws in less air mass per cycle due to the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock.


Brian

raspberryroadster

i'm glad we agree thats what i said, make less power (ie less heat generation from compression) at altitude therefore can use lower octane (also means lower performance of course).
but you are not the only area that has max as 91 octane (91/92 is becoming standard in a lot of areas....not just for alt.reasons)
but properly prepared car/running big power...at altitude or no will still require high octane (right up to race fuel....113 octane). doen't matter whether you can get it at the pump or no.