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.

[3WayStunna]

If its a JDM engine always run 91 or higher...Anytime i let my engine run with anything less there was always a drastic loss of gas milage..Btw 95 is just fine for it....wouldnt go higher than that though unless you have other reasons...

[Authentic]

Sweet as, cheers dude. I get roughly 650Kms to a tank of 91 so I'll see how this goes.

[Galcobar]

Make sure you're talking about the same scale when discussing octane.

North American pumps display octane rating based upon (R+M)/2), which is the average between the Research Octane Number and the Motor Octane Number. Japan, Europe and Australia use the RON alone -- New Zealand uses RON. The same gas rated in RON would have a number 4 or 5 higher than on rated in (R+M)/2 -- so "regular" New Zealand 91-92 octane would be the equivalent of "regular" 87 in North America.

That difference is the source of a lot of confusion, especially since many Japanese engines do need gas with higher octane values. It's conflated though with engines which use the same fuel, but appear to have different octane needs because the fuel is labelled differently. If it's the same engine, it'll use the same fuel (certain high-performance exceptions exist but they're rare).

The 3SFE, like its successor the 5SFE, is an economy-oriented engine and runs on "regular" fuel, which in Japan/New Zealand would be 91 octane (same as 87 octane in North America). The 3SGE and 3SGTE are performance-oriented engines with higher compression ratios (11.0 and 10.3:1 versus the 3SFE's 9.5:1 or the 5SFE's 8.5:1) and therefore need the higher octane values in premium gas.

This post has been edited by Galcobar: Mar 2, 2012 - 3:19 AM

[Authentic]

Woah thanks man, that has taught me a lot. I always thought that there would be some sort of difference in measurements between America and Aus/NZ/Japan in terms of octane, since we are different in the way we measure almost everything else.

So for the 3S-FE engine, will I see any change (better or worse) in performance or mileage by using 95 RON?

[ruckusas]

I'm running a 3S-FE in my Curren. I found that when I put 95 in it, it seems to drive alright but it felt a bit rougher when I went to turn it off, like it was 'running-on' a wee bit, when I reverted back 91 the car felt a bit smoother. That's just what it feels like in my car but it could well be different for you.

[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