I know what octane does basically; more octane, more complete burn, more fuel stability, less combustability, etc...

Can you run too high of an octane number? The reason I ask is because I found a place that I can get 100 octane fuel for not too much more money/gal than the 91 octane that's readily available here in Colorado.

I know that it's not a permanent solution, but putting an octane booster in with my fuel does stop the knocking on big hills. So, logically a higher octane fuel would help too, right?

I going to add the URD kit in a couple of months for now, I just want to avoid as much knocking as possible until I can swing the price tag of the upgrade...what do you guys think?

 

nope, the only thing too much octane will do is lighten your wallet.

 

Go for it. URD has documented the stock S/C setup lean condition. I'd consider it cheap insurance until (and maybe even after) your mods. BTW, what brand is it? The best pump gas around here is 91-92 oxygenated, you're lucky!

 

The octane of a fuel is relevant to two things. The first is how hot it has to get to burn and second, how much energy it releases when its ignited. The answer to your question is yes, you can have too much octane. If you get too much octane, your gonna get crappy gas mileage and incomplete ignition. Try putting diesel in your truck. Diesel is a way higher octane than gas. Diesel's flashpoint, or the point at which it ignites is 200 and something and your trucks compression ratio isn't high enough to cause it to burn even with a spark from a sparkplug.

 

I have heard that if you use a higher octane on a vehicle that doesn't need it(lower compression engines) all the fuel will not be burt. This will lead to excess carbon buildup. I always use Chevron 87 in my 3.4 and it runs fine like it should. My manual says to use 87 or higher and that it should not ping when using the recommended grade, unless for a short period when accelerating or going up a hill which is no need for concern. With the supercharger though i'm sure a higher octane than the minimum is recommended.

 

the highest i will run in my 4cylinder taco and my 85 runner is 89 octane. The taco runs ok on 87 but spark knocks a little when im pulling out. I run 89 in the 4runner cause i have the timing advanced about 7 degrees. Its set at 12 degrees before top dead center. Helped out the bottom end pull quite a bit.

 

I'm assuming this gas station is somewhere around Boulder, where did you find it? I want to give it a try.

 

It's at Jefco airport.

 

Say goodbye to your cat. Avgas 100LL contains some lead that will eventually play havoc with your emissions controls if they're still intact.

 

That's a good point. You deffinately don't wan't to use leaded gas in a modern vehicle unless it's racecar.

 

again would like to state too high an octane and it will hurt performance

 

If I use anything less than 91, it pings all the time. I've also noticed my mileage has steadily increased from 10mpg to around 12-13 using 91, and I've still got the same brick foot I had when I was getting 10mpg.

 

I didn't know that avgas had lead in it; not using that stuff.... I'll just keep saving up for the URD kit and get it in asap.

Thanks for all the input guys!

 

well if the higher octane helps the ping then roll with it because pings are just a way of knowing you don't have enough octane.

 

I'd be checking my timing, plugs and distributor advance if my machine pinged all of the time. Something is up and the higher octane is merely masking the problem

 

Well, let me be clear. It does not ping all the time. Only under load; like going up a steep hill at 60-80 mph. That's pretty rare, but given that I hit that hill several times a week leaving Boulder, I'm not comfortable with the problem. So, for now, I'll back off the throttle going up that hill and do a comfortable 65 until the mods are complete...

 

Knock Sensor should detect the detonation problem and roll back the timing to compensate. I'd take it to the Stealership and have it plugged in and diagnosed.

 

Actually diesel is a much LOWER octane than gasoline. Most Diesel #2 sits at around 63 octane if I remember correctly.

Diesel is NOT ignited by a spark but by compression so you need a LOW octane rating, not a high one, to induce knocking. (Diesels are SUPPOSED to knock, gas engines aren't) You dont put diesel in a gas engine because it will not idle and it's ignition temperatures arent high enough to burn the longer hydrocarbon chains... And if you COULD get it to completely burn the diesel it would be knocking like a mofo.

the higher the octane rating the longer it takes to burn the fuel charge and the more resistance there is to compression ignition. This is why a 15:1 race engine needs 115 octane. If you put 91octane in it, it'll diesel, and knock like hell.

The octane rating is the percentage of hydrocarbon chains containing 8 carbon atoms, these carbon chains are called octanes. Octane resists spontaneous combustion from compression VERY well and Heptane (only 7 carbon atoms) does not. 91 octane is 91% octane and 9% heptane.


And my 3vze MUST have 93 octane or it pings under load...

 

Too high of an octane will just be a waste. A higher octane will produce a slower/complete burn...providing your engine is capable of doing so. Don't bother with octace boosters....they don't do anything. If you need an octance higher than 91 to prevent knock, mix it with 100 to get you around 93 octane or so.

Or, you can buy toluene and mix it. Make sure you add some lubricant to it as pure toluene(114 unleaded octane) will erode your fuel lines. We use either 100 race or 114 toluene at the race track.

 

I am the fourth owner of a 97 4Runner Limited with 115,000 miles on it.
I have spoken with the previous two owners about this and we all agree
that using anything in this puppy higher than 87 octane is a waste of money.
I am getting around 20 MPG in town and about 24 to 25 on the highway.
Higher octane seems to burn much faster, killing my gas mileage and it runs quiet and smooth on regular.

Graywoulf in Western NC