Results of running 89 oct?
 

Of course the owners manual mandates 90+ octane fuel but at todays prices, wow. What are the effects in performance, maintenance and damage of operating on 89 octane without ethanol?

Well the real reason is that the higher grade fuels prevent knock or detonation, which will make it run smoother and last longer. I'm not sure about the 924s but in 951s, the car will go into safe mode if excessive knock is present.
-Adrian

I thought the 2.5L NA models specified 87+ in the owner's manual?

I have run 10 years with 87. no trouble yet. The only difference you will see with running a higher octane would be your wallet will be lighter.

Speedy:)

the 90 octane specified in the owner's manual is the european rating, which equates to 87 octane in the U.S.

If you have a stock 944 with no chips, etc., you're fine running 87.

No issues in my 924S with the 89 octane. No knocks or pings. I would think dropping done to like 85 with ethanol might not work so well.

I don't know, but I just run 93 just to be sure, since I like to rev high through the gears and start quickly off the line alot, and it's not much more expensive than the 87 where I get it.

The '88 NA states 91 in the manual and on the gas cap. That and a Wilks chip require me to run 91 :-) All I can say is that this is going to be another Octane debate thread.

I recently installed a wilk's chipped DME and am running 87 octane in my 83 944 with no known ill affects heard. I don't think that my 83 engine has any knock sensors and wanted to know if others have tried this as well? Car still runs the same with the chipped DME as it did with the stock DME. I would think that if I was hurting my engine that I would hear or feel it.

I don't think it's a horrible idea to run 93 or 91 octane in a car as old as ours, but it does in fact say 87 octane for US models on the NA 2.5L cars.

running the higher octane will, i've heard, cause carbon deposits in your engine...
I too have a wilk's chip and use 87 most of the time..

The owners manual on my 85.5 states: Minimun octane rating of 91 RON (87 CLC or AKI rating on fuel pumps in the U.S.A.). I'm sure others have seen this too. I don't know what CLC or AKI means. Maybe somebody can tell me. I know that RON is research octane number and that the MON (motor octane number) is usually 4 points less. So if you do the R+M/2 then that spells midgrade or 89.
I would be interested to know the boundry if there is one in terms of the compression ratios and octane requirements. Is a 9.5:1 compression ratio enough to ignite ALL of 93 octane?
Regards Dietrich

probably not... but i haven't done the math...

It's my understanding that the octane has more to do with ignition timing than compression. Different octanes have different burn rates/ignition points and you have to set the timing accordingly. That's why the wrong octane will often cause spark knock until you put the right octane in it. The knock sensor will often times help the computer recalculate the timing which is what it's there for.

In layman's terms the higher the octane the slower the burn and the more stable the fuel when compressed (less likely to pre ignition) Run the cheapest gas you can that does not knock.

^ What he said. :)

indeed.. and throw in a tank of the good stuff every couple months or so just for the benefits of the cleansers in the fuel.