racing gasoline

[BlackoutSteve]

It makes a lot more sense to buy a very high octane race fuel (119-120) which already contains a substantial amount of TEL, and then blend it back using some other hydrocarbon fuels. Avoid pump gas since it is so very inconsistent from batch to batch, month to month..

Apparently.. Blending leaded with premium unleaded offers a slight octane improvement over the simple averaging of the two fuel's octanes..
For example.. 92UL + 100L = not 96, but 96.5/97 octane. In the book High Performance Fuels & Fluids (ISBN 0-7603-0054-2), I read that there is a small chemical reaction between the TEL and one of the ingredients used to produce premium UL. The reaction offers about a point, but not sure how much now with AvGas only having about 0.4 grams/gal or even less today perhaps.
I recall calling Shell's tech line and they confirmed what the book said.. I'll have a better look and see if I can find what page.

[Dodge Freak]

Back when leaded 89 gas and no lead was 91 octane, the word was to fill up 50/50 and you get 93--94 octane cause the leaded gas of the 89 octane fuel would boost the no lead 91 octane up.

Lead also needs time to work, the octane numbers keeps going up the first couple of weeks it sits in the fuel. Least this is what I recall about leaded gas back when it was around everywhere and the oil companies reps were saying.

[David Redszus]

For example.. 92UL + 100L = not 96, but 96.5/97 octane. In the book High Performance Fuels & Fluids (ISBN 0-7603-0054-2), I read that there is a small chemical reaction between the TEL and one of the ingredients used to produce premium UL.

Not really true, but sometimes it might be.

TEL reacts differently to each different component in a fuel. Listed below are examples of octane improvements using 4g/gal TEL for various components.

First number = octane @ 0 TEL (g/gal)
Second number = octane @ 4 TEL (g/gal)

Aromatics
Toluene 109...114
Ethylbenzene 98...105
oXylene 100...100
mXylene 115...121
pXylene 110...122
Indolene 107...104
Paraffins
Triptane 101...120
224TMP 100...118
223 TMP 100...115
234 TMP 96...109

In order to correctly predict the octane improvement due to the addition of TEL (or the blending of any two fuels), it is necessary to know the exact percentage composition by mass, and then perform a weighted average calculation to determine the octane contribution of each component.

For example, a fuel containing 50% oXylene, and 50% 224TMP, would produce an unleaded octane blend value of 100. If 4 g/gal TEL is added, the octane value of the oXylene would still be 100, but the 224 TMP octane would become 118, for a blend value of 109. The addition of TEL did not improve the octane rating of each component equally. In fact, the addition of TEL can actually lower the octane value of certain fuel components such as isoprene and indolene.