Which octane is best for the 3S-FE engine? Options

[Authentic]

Hey everyone,

So I've been on this forum for a little while now and I've figured solutions to most of my questions from seeing previous threads, however I couldn't get the search to work for this particular question I have.

So for the people with the 3S-FE engine, I was wondering which octane you run. I have been using 91 since I bought the car in November, and my Dad said that he ran our old 5th Gen Celica GT-R (3S-GE I think) on 91 also, however I decided to try 95 today since I was driving on the fuel light. I had a short drive home from the petrol station so I haven't had chance to see any difference yet.

So yeah, let me know which you use and feel free to yell at me if I've done something wrong, cheers.

[Galcobar]

Higher octane may force the engine to adjust its ignition timing -- octane prevents premature detonation by making the fuel less likely to combust from compression. Higher performance engines run at higher compression, so need higher octane to prevent detonation before the spark begins combustion. Running higher octane in an engine not designed for it at best doesn't do anything, as the ECU compensates for it -- a spark will ignite the fuel even with high octane.

Potentially, running a higher grade of gas can help the engine, but not because of the octane content. Instead, the higher level of detergents usually added to higher octane gas can keep the engine cleaner -- those cleaning agents are a large part of why gum and varnish buildup don't cripple modern engines with very tight tolerances. However, ethanol in your gas does the same job. That's actually why regions often report a lot of damaged engines after ethanol is added to the gas supply; the ethanol dissolves the accumulated gum and varnish, sending it through your fuel system all at once. It's the deposits loosened by the ethanol which do the damage (unless your fuel system is built with natural rubber, though most automakers stopped using natural rubber by the early 1990s), usually by clogging up fuel lines, filters or injectors. Thus if your regular gas has ethanol in it you won't gain any real cleaning power from higher grades either, which leads us back not there being no advantage in using more expensive gas than the engine design requires.

This post has been edited by Galcobar: Mar 4, 2012 - 6:45 PM