Ok, I have an '89 GXE, and when it was my dad's car he filled it up with 93 octane I believe. I've been filling it up with 89 octane (the manual says 87-92). Which is the better choice. Will 93 cause engine knock?

 

If you go above the recommended octane, you will get a marginal increase in performance and fuel economy. Running a gas with too low octane will cause knocking, but there arent any bad effects from running high octane. I think that using 87 octane should be just fine for your vg unless you advance the timing.

 

Grr....I wish we had 93 octane where I live. If you go to any gas station in Colorado, 91 is the highest they have here. The regular is 85. I remember in when a few of my friends and I took a roadtrip to Cali, at a 67, I saw some "Racing Octane", 100 octane.....I was like....gaw gaw gaw....LETS PUT THAT IN THE VAN! But we never did....

 

On most cars lower octane is better at higher altitudes.

 

I disagree.

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

 

Maybe you can confirm this, but I've heard that high altitude operation makes the required octane lower. It's counter-intuitive, because cars already don't run as well at high alititude, but it has something to do with atmospheric pressure, I think. So, your car may run as well in colorado on 91 as it would in Kansas on 93. But I could also be an idiot.

 

In the October issue of SCC, the 350Z was dynoed on 91 octane gas and then 100 octane. The Z showed a gain of 5 peak hp and 2 lb/ft of torque. According to your ftc article, "The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel." The Z didn't knock on 91 octane, so does that mean that it shouldn't use the 100 octane? I think that it's the owner's value judgement, and although I agree that using high octane gas in our vg's is a waste, unless you have dynos and mpg ratings that contradict me, I stand by my earlier statement.
Miles

 

Haha! I remember reading that too, good point. You may or may not know it but a higher octane could increase engine performance. I used to put 89oct in my 90gxe because I had advanced the timing and was playing it safe.

Also I read that older engines have more of a chance for the use of higher octane gas than the same engine new. This is because over time carbon deposits build up in the cylniders making a slightly higher compression than 100k miles ago. If this is just bs someone please inform me.

 

yeah,It would be nice to get a concise answer. I don't know what to listen for (never had to) so somebody help me.

 

I understand you point(s). But, if you search the net, there is far more information on NOT using "performance" and high octane gas on cars that dont require it, than to the contrary.

There are also a ton of variables. Engine condition, altitude, atmospheric pressure, etc. In my opinion, premium gas is a waste of money on a "normal" car that does not require high octane.

I am just as guilty as anyone else. I used to run Super in my 79 Supra because I thought it helped. Yeah right.

Like you, I would also like to see dyno numbers on the different octanes, but I dont think anyone wants to waste $75 on a dyno run for just that. Any takers?

 

I have been using 93 gas ever since I got this car in 95. The only differnce I noticed is the gas mileage when one day I accidentally pumped the 91 gas...

I was told that 93 is good for the fuel injector or some other stuff. Is it right? Or shall I stop using 93 because it didn't do any good other than a slightly difference on the gas mileage?

 

Try starting with this and draw your own conclusion.

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

 

according to my manual it says Premium. I live in NYC, so 93 or 91. I have 92 GXE.

 

I would agree with that if that's what the manual says. On cars with knock sensors the timing will retard if the car is detonating. So, instead of a "gain" in power like some have mentioned, they are actually running the car at optimal power by using premium.

We should all be glad we dont live in Europe and pay their gas prices.