It ABSOLUTELY makes a difference.
AVGAS is rated by grade according to the amount of tetraethyl lead it contains and is dyed to identify the grade. Shortly after WW2 before hairdryers became so important, there were 5 grades of AVGAS: red 80/87 octane, blue 91/98 octane, green 100/130 performance, brown 108/135 performance, and purple 115/145 performance.
With the tremendous decrease in AVGAS requirements, the 108/135 and 115/145 for big bore engines and 91/98 for smaller engines were discontinued. The TEL content for 100/130 gas was decreased from 4.0 to 2.0 milliliters per gallon, and this low lead fuel is now what we have as 100LL.
What the designations meant was the following: the first number was the octane, or performance rating of the fuel with a lean mixture. So 115/145: 115 would be the lean mixture rating. 145 would then be the rich mixture such as used for takeoff. Additionally, those numbers showcased the fuels anti-detonation properties.
What that means in plain english is you would not get the maximum rated power in a big bore radial at takeoff power with 100LL, in fact you would more likely then not be detonating away all the way down the runway. R2800s are poisioned by 100LL at high power settings, which is why many of them are limited to 52" manifold pressure using todays fuel, except perhaps while running on a race mix at the Reno Races.
Bodhi could probably fill in the gaps on what engines like best, but that is the summary of it. Bottom line, engines 60 years ago require the higher TEL content. In fact, the higher test fuels, 115/145 for instance had a lot of aromatics such as benzine, toluene and xylene to increase its anti detonation characteristics. What was found later down the line is these additives attacked rubber products in the fuel system. As time wore on and 100LL was the fuel, materials were developed that were not susceptible to aromatic compound deterioration.
Wolf
