Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!

Never run lower octane fuel than is recommended by the vehicle's manufacturer. If the vehicle manufacturer recommends 89 octane gasoline, this means that the engine has been tuned to perform optimally without detonation on 89 octane fuel. Once you've done some modifications to your engine, the manufacturer's recommended gasoline may no longer suffice. Obviously, if you can hear detonation inside your engine in the form of pinging or "knocking", try a higher octane fuel. You will also need to run a premium grade fuel (91+ octane) if you have a supercharger, turbocharger, or if you have an ignition programmer that advances your ignition timing.

04 6MT Coupe
35% Madico smoke tint /CF Hood /Injen Cat-back

 

most places here (NY) don't offer 91 either. 87, 89, and 93. I use 93 most of the time. If I happen to have a little more than half a tank I'll use 89 to get a mix at 91. And prices for 93 have been around 1.95 - 2.00 lately.

'04 Red/willow 5a, all but navi

 

I alternate between 91 & 94, depending on gas price fluctuations.

04 G35c 6MT Ivory/Graphite
HRE 448R 19x8.5,19x10 full polish/clear coated
Gallery of My Babies

 

In response to SoCal...

Im not going to claim to be a mechanic or even knowledgable enough to diagnos a problem in a car, other than the common battery, alternator, spark plug, etc. but i would like to comment...

First, you said "If the vehicle manufacturer recommends 89 . . ." and just in case u were refering to our Gcoupes...they recommend 91 and i think the sedan recommends 89.

Second, the ECU does detect the octane of the fuel you are currently running. And while everything u said may normally be correct, our engines will run without knocking at a lower performance using 87 or 89 octane. Conversely running 93 will NOT offer a higher performance but I have been told it is better on the engine and therfore since most gas stations offer 91 OR 93 but never both...i use whatever they sell (usually 93)

'03 G35 Coupe | Black on Black | Performance | 20% tint | Clear Corners | http://www.cardomain.com/id/dabomb3

 

dabomb, just to clarify, the ecu does not detect octane, it detects knock.

2004 G35C 6MT Black. Sweet.

 

well am I safe in saying that 87 and 89 will probably cause slight knock and then to compensate the ECU would lower the performance of your engine?

'03 G35 Coupe | Black on Black | Performance | 20% tint | Clear Corners | http://www.cardomain.com/id/dabomb3

 

dabomb,

If you run 87/89, the knock sensors may detect knock and retard the ignition timing. This would lower your performance. Since the coupe is tuned for 91, it is more likely the knock sensors would kick in running 87 octane then on a car tuned to 89.

Running 87/89 octane fuel on an engine tuned for 91 only promotes detonation. Just like higher compression, higher temperature, lean A/F, etc. You might get away with it but you shouldn't risk it.

04 6MT Coupe
35% Madico smoke tint /CF Hood /Injen Cat-back

 

I get pinging even with 91...

 

HAHA same here. Wherever i am, I always go for 76 peremium.

 

Curious. What the difference bewteen 87 and 91 octane? Is this rating linear?