octane

[Ron Coleman]

Here is a serious question about gas.
In many older automobiles there are instructions in the operating manuals for changing the ignition timing for various octane ratings. Some engines have a plate on the distributer marked for octane ratings from 73 to 100 octane and the included angle is significant. Many of these machines were from 1936 to 1959. This is the same era and same technology used in the Continental engine used in our airplanes.

Why don't we have to change the ignition timing (the mag setting) when we go from 80 octane to 100 octane?

?
RonC

[Howard Wilson]

Re: octane

Interesting question, When did they standardize aviation fuel grades? What was commonly available at the flying field back then?
Don't see any mention of this kind of thing in the old tractor operator and maintenance manuals either, Even for our 1940 Farmall 'H' that started on gas, then when it warmed up could be switched over to run on the distillate tank???...

[crispy critter]

Re: octane

Guys,even back then they were using distributers not magnitos. The distributer didn't put out as much spark as the mag therefore timing and octane are critical to each other.....at least that's how I was told and it makes sense.

[Howard Wilson]

Re: octane

Oops, forgot to mention the 'H' has a mag.

[Hank Jarrett]

Re: octane

A little more information.
A lot of people think higher octane makes the fuel more powerful. It doesn't, in fact high octane fuel has LESS energy than low octane fuel. The reason you use high octane fuel is it explodes (not burn, explodes) at a higher pressure. That lets you pack much more fuel and air into the chamber without knocking. You get more power from the engine at the expense of EVEN MORE fuel. If you put high octane fuel into a low compression engine you actually get LESS power. It doesn't "hurt" the engine, but the efficiency actually drops. Now if you put a turbo or super charger on the engine (raising the compression ratio) the high octane will let you get more power without knocking (letting the fuel explode instead of burning).
Adding alcohol also increases octane, but it has even LESS energy than the old TEL (Tetra Ethyl LEAD) for each point of octane increase. That's why you get less mileage in a car the more alcohol it has in it. Alcohol also INCREASES the cost of gas, so you get a triple hit. Less power, more cost and worse mileage.
Don't make fuel from Corn, EAT IT! (Or for field corn, feed it to a steer and EAT HIM). Cows make better gas anyway.
Hank
If we could only pipe it to the carb!

[Howard Wilson]

Re: octane

"If we could only pipe it to the carb"
Well it would just be a slight alteration to the seat(s), but I would stay away from any hard landings

[Ron Coleman]

Re: octane

here are a couple of examples of insructions for dealing with variations in octane ratings of gasoline. Circa 1938 to 1959.