Very good info Dave. Some of my buddies forget to figure in the extra lower octane in the tank and I always have to remind them of this. For those that mix, it only takes a few minutes to drain your tank from the 2 bolts underneath the tank, you dont even have to lift the car. A shallow oil pan(5 gallon) works great for catching the gas. Prices on gas vary but VP is the most expensive at 10 to 12 a gallon for C116.

 

I think this is a really important point. Refineries produce a lot of stuff from petroleum depending on market demand and the kind of crude they're starting from, so the exact composition and properties of pump gas do change even if it really has a 93 AKI. I've found a lot more detailed specs on various companies' race fuels versus their pump gas. The race fuel is formulated to *be* "just so" while the pump gas is whatever is the cheapest way to meet a limited number of functional specs.

Dave H.

 

Dave is 100% on the mark but perhaps more so without actually realizing it. He / you Dave, are assuming a perfect mixing ratio for the octane. That is you are assuming 1part of 110 + 1part of 94 equals the average of the two therefore (110+94)/2 = 102.

Problem is it doesn't work that way, most of the time, because of the different methods (read chemical additives) used to increase the octane rating. I can tell you for sure that the chemicals used in race gas bare NO resemblance at all to the ones used in pump gas and when they mix it doesn't mean they add their effects to each other.

So what am I getting at ... chances are when you mix those two fuels you get an octane rating that is actually even LOWER than you might think. So instead of that 107 octane you calculated above it might actually be 103. And the 102 you "guestimated" above might be 98.

So yeah totally right and perhaps more so than you realise.

There is a reason I remember disconnecting the fuel return line from my talon at the drag strip and hotwiring the fuel pump to run till it was pushing almost all air (didn't want to burn out the pump) before I poured in race gas.

 

Had what I would call an empty tank of fuel this weekend. Needle was on the last line on the guage, no fuel light on. Manual says the car has a 14 gallon tank. I filled up and it took 12.2 gallons. This left 1.8 gallons in the tank. Keep this in mind.

David Buschur
www.buschurracing.com

 

Wow that is pretty empty actualy. Cause when my light IS ON I can only put in 11-ish gallons and I have to ride the light for a good bit before I can fit in 12+ gallons.

Just shows how uncalibrated the fuel gauge / reserve light is.

Of course that only proves your point even more so