# 100 Octane



## MeanGoat (Jan 4, 2006)

Driving home today and the Sunoco in my neighborhood has a sign out for 100 octane.

I have not put this in my goat yet and I was looking for feedback from someone who has. Couple questions:

1. Noticeable power increase?
2. Will my goat become "spoiled" and prefer the higher octane?

I want to fill her up with a tank and check it out this weekend, but my baby is my baby and I don't want to break something that's not broken. Only plan to do the one fill up so want to make sure I can go back to 91 when it burns out.

On a trip back from Ohio one time I filled up with this stuff in my Isuzu Rodeo and the PCV valve just happened to go when I got home. Can't say that the problem was related, but I never rule it completely out. Obviously a POS Rodeo is not a performace vehicle so just looking for some tips from those that have used in their goat.

Grassy-arse


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## jacobyb (Jan 2, 2006)

I did a masive report on this for an online automotive website about 4 years ago. Basically the short and skinny is this. Higher octane does not mean more power. In fact it can mean the opposite if your car is not set up for it. 

The lower the octane, the bigger the burn. Lower octane fuel combusts much easier then higher octane. Octane is the label that describes a fuels _resistance_ to ignite. Like a diesel, high-compression vehicles need higher octane because as cylinder pressure increases, the fuel will try to ignite. (Diesel engines have no spark plugs due to the massive ammount of compression. The fuel ignites itself).

So, in real-world terms this means that anything over say, 93 octane on a stock (no internal mods/blower/turbo/nitrous/mega-advanced timming) is actually going to give you a net loss in power and economy. People have a hard time wrapping theor minds around this sometimes because the oil companies have done so well marketing the higher octane fuel as a magical power increaser. It is just the opposite. 

What I am trying to say is that you should save yourself a $1 or so a gallon and just stick with the standard premium unless you are modded as stated above. I am sure there are going to be people here that are going to disagree with me, but you can research it yourself and see that I speak the truth.


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## Ironmancan (Feb 11, 2006)

Jacoby is right just to add a little. In case your wondering why drag racers use the higher octane fuel primarily its because they are running higher compressions. Higher compressions dictate higher octane fuel. Theres are alot of articles out there about this on the web. Read up


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## GasTiresandOil (Aug 2, 2004)

Unless you have a modified tune to compensate for the added octane, it is worthless to put into your car. Your stock tune has the fuel tables and advance needed for 91 octane. If you add 100 octane, you will have to retune the fuel tables and advance your timing.


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## MeanGoat (Jan 4, 2006)

Thanks guys. What's funny is that now that I think about it, I should have known this one.

History channel's got a great special on petroleum refining that explains the differences between octane, heptane, why lead was added to gas back in the early days etc etc.

On the way home, I was already thinking about the octane/heptane relationship and which one was more combustible at different pressures, what the octane rating means (percent octane versus heptane) and so on. Even thought of the diesel engine comparison.

I guess when you get power hungry again it's easy to overlook the facts and have hope in marketing ploys. 

_Man_ I can't wait for the damn tax check to come for some mods....


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## C5ORGTO (Dec 30, 2004)

I've heard on various discussions on the forum that anything over 92 Octane doesn't do much, but then again thats just what I heard.


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## fergyflyer (Apr 18, 2005)

The LS2 has 2 fuel maps plus a cold start map that the computer follows. When you start the car and until the coolant temp is above a certain temperature (I think 160), the computer follows the cold start map. It is a rich set-up and the timing is not advanced very far. After the certain temperature is detected the computer listens for knock. If it detects knock it will switch to the low octane table. In that mode is reduces timing but will vary down from that number if knock is detected. The timing map that advances timing to full advance and produces the best performance is the high octane map. That map on the LS2 is set up for 90 octane fuel. Before you think you can get away with mixing 89 and 91 and coming up with 90 to save money, there are a lot of factors involved that justify 91 or 93/94 super. Some gas stations cheat and put lower octane fuel in higher octane tanks. Certain engine conditions, and atmospheric conditions may require a car set up on 90 octane to have a higher octane to avoid knock. 

With the way our cars are set up we do best with 93/94 octane and very well with 91. Anything above 94 is a waste and with as high as 100 you may be on the verge of damaging the engine and losing power. 

The only exception to the above would be if the car was a Honda Civic and the gas station was giving away free decals. Then there would be at least a 5 hp gain from the 100 octane.


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## stangeater (Jan 17, 2006)

i have put 100 octane in my bike before, but like others said i didn't feel any diffrence to justify the 4.95 per gallon price tag. but on the other hand it gives off that cool high octane smell


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## MeanGoat (Jan 4, 2006)

fergyflyer said:


> The LS2 has 2 fuel maps .....
> 
> The only exception to the above would be if the car was a Honda Civic and the gas station was giving away free decals. Then there would be at least a 5 hp gain from the 100 octane.


:lol: :lol: Very funny

Informative post relative to our cars, thanks a lot for chiming in


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## Subdriver (Dec 28, 2004)

This is one of the best and most accurate threads on octane I've read in a long time. 

A key reason you want to use a good high octane fuel (like 91-93 or so) is because as Jacob mentioned, it is resistant to early detonation or knock and when the PCM senses the inception of knock it pulls timing and thus you lose power.

Adding a little bit to what fergyflyer said, the PCM is actually much more complicated than he described. Even in normal operation, if the PCM detects the inception of knock from the knock sensors, it won't default to the lower octane tables, but it removes timing from the engine, reducing power. The amount of timing it reduces can be modified with programs such as LS1 edit. I believe that if it senses enough knock, it will then assume the car has low octane fuel and switch to the low octane table which has less advanced timing across the board. 

In my Vette, my tuner tuned it for 100 octane fuel. Again, as Jacob described, the fuel itself doesn't get us any more power, but because this fuel is so resistant to knock, we can safely run more advanced timing than stock (which does net more power) and safely lower the value of timing that is pulled at the inception of knock (less power lost). :cheers


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## BigNick (Jan 7, 2005)

I have heard that 100 octane fuel actually burns slower than "pump" gas and REQUIRES extra timing advance, a different cam profile, or both. Otherwise, it may still be burning when the exhaust valves open, causing the valves to get burned.

Any truth to this?


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## CrabhartLSX (Feb 12, 2006)

You only need enough octane to keep the car from knocking. I ran 87 (silly me) in my camaro for a month or so, cold weather, so it didn't knock, although i got the crappiest mileage ever and was running very rich. 

Once it got above 70 outside i started knocking like crazy. Put some premium in and it never happened again. The cars with their compression ratios are meant to run off of a given octane rating. lower the compression, the less octane is needed because you don't have to worry about detonation as much. That's also why you get low compression pistons in forced induction cars, so when the compression is artificially increased you don't knock.


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## NT91 (Aug 30, 2005)

Thanks for the info all.


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