DEM:

Obviously, I don't know your car, but I'm still inclined to agree with Silver here. You can do a lot of changeable software things via the ECU, but you can't alter the physical reality of engine controlled by that ECU (compression ration, valve sizes, intake shape, etc.). Likewise, most changeable parameters can only be adjusted within the bounds of practical reality. If this were purely a linear "math problem," I could calculate how much extra advance I could program in while using 200 octane gas, and we'd have the plugs firing somewhere during the previous exhaust stroke. A silly example, for sure, but made to illustrate that there's just no getting past certain physical "reality factors." Now, if you manage to get more air into your cylinders, that's something your ECU can actually sink its teeth into.

 

Sorry for the long post, but instead of trying to sound like an expert, I will just post what I read from them.

Taken from the June 2006 Sport Compact Mag on the top tuning myths. (tuner car used was a 350Z)

MYTH #5 HIGHER OCTANE FUEL PRODUCES MORE POWER.THE TRUTH: The issue here is detonation threshold and power potential; a higher-octane fuel allows more power to be made; but does not make more power by itself.

Once again, power comes from a mixture of air and fuel that is shoved into a cylinder and ignited. The more air and fuel there is, the more power is made. There is a limit, however. The more air and fuel jammed into a cylinder, the higher the cylinder pressure. Higher-compressed air and fuel mixtures tend to ignite or detonate on their own under the heat of compression. This is a bad thing. Using a higher Octane fuel makes the mixture less prone to this auto-detonation, meaning it’s safer to shove more air in, i.e. “turn up the boost” And therein lies the potential for more power.

But while higher-octane fuel is a step toward great power output, the detonation resistance it provides isn’t always necessary. Some pro Honda racers prefer to use 87-octane fuel for their naturally aspired, mild compression engines. The tendency of lower octane fuels to be less stable and burn faster means that more chemical energy is used while the charge is expanding in the cylinder before the exhaust valve opens. Fuel still burning in your header doesn’t do much but keep the cats warm.

THE FIX: Forget about power for a minute and think about protecting your investment. Cars that have been heavily modified towards high compression (anything over 10:5:1) need the good stuff to prevent detonation. Follow the manufacture’s fuel recommendation for stock or lightly boosted factory turbo- and supercharged cars. However, if you plan on stressing your engine, via racing or a night at the drags, your engine would love a few gallons of the highest octane you can afford.

In certain situations, however high-mileage low compression engines do run better on high-octane fuel. Older engines build up carbon inside the cylinder, which stores a lot of heat. When air and fuel is compressed, these hot spots will cause detonation, even on low compression motors. That’s why older cars run smoother and better on higher-octane fuels.

The flipside of this myth is the contention that you can use low octane fuel in a high output, naturally aspired engine designed for high-octane fuels without any problems. Many enthusiasts say they do it without issues. In fact, they are leaving performance on the table because today’s highly integrated engine control systems have anti-knock provisions. The ECU will pull timing out of the motor when the knock is detected, which takes away performance. -JC

 

chernmax thanks for the write-up.

 

Thanks bro, just doing some reading and sharing the info...

 

I think my gas mileage dropped from the 100 octane mix. Is this to be expected?

 

Instead of going out your way to find 100 octane at a gas pump, just goto a hardware or paint store. Xyelene or Toulene added to gasoline can make a nice jump in octane levels and it's cheaper than race gas sold at the pump or track. You also know what your getting and it's safe for o2 sensors and cats because pump gasoline already contains a percentage of these chemicals.

But to be honest I've used various combos of higher octane stuff for my car and seen no major difference under normal driving conditions. The only time it detonated was using 108 leaded racing fuel and with the ECU tuning stuff I have. Even with octane that high you can still detonate from an overly aggresive tune and hot/humid weather.

 

It is not unexpected. Remember that it will likely take your VQ's computer about 300 miles to properly adjust for higher octane. And even then it may not be able to adjust for octane above 91 (R+M)/2 octane. Your 100 Research octane fuel is about 95 (R+M)/2 octane.

If you try the trick of putting straight Toluene or Xylene into your gas tank, I'd stick to Toluene. It was and still is the more common blend stock for premium gasoline. Blending it into your tank could also cause starting problems on very cold mornings -- not likely a problem in California, but could be in the colder northern states or Canada.