5 replies to this topic

[gary76]

Can anyone give me a guide for the use of Avgas100LL as a replacement for the 'race fuels' that on the market?
I know it is commonly used in racing two-stroke engines and I have heard of the use of a 50/50 mix with super-unleaded fuel in some racing 4-stroke engines. How does the burn rate compare with super-unleaded?
In other words are there any benifits to be gained from its use apart from its higher octane value.
Gary

[cheapracer]

I used Avgas for many years, go to a small light plane airport to buy it cheap. You can buy 100 or 115 (which may vary from 100 to 115).

Same old same old, if you haven't got corresponding compression and spark advance you won't notice any difference. If you are running on hot days or hilly areas without suitable ratios then it can be an aid against pinging/knocking.

[McGuire]

There are several kinds of 100 octane avgas commercially available: 100LL, dyed blue, which is most common, and 100/130, which is dyed green. Both are leaded fuels. Aviation fuel's octane is rated under a different system and generally, 100 avgas will have a lower MON than 100 octane race gas. Under the avgas system, a typical race gasoline might test at 120/160. Avgas also has a lower specific gravity so the jetting will need to be three to four steps richer than with current racing fuels. Avgas has a number of properties that allow it to operate safely at a wide range of altitudes and temperatures, etc, while modern racing gasoline is formulated to make maximum power.

All this said, avgas has been used successfully for motorsports applications. However, this was mainly due to a lack of other options. There is no reason to use it today unless racing gasoline simply isn't available. It's certainly no speed secret as it will actually make less power.

[mariner]

IIRC in the past when very high power piston engines were in use ( e.g wartime) there were Avgas fuels available with higher octane ratings than today.

Maybe when pump fules were poor and this high octane Avgas was available it made more sense to use it. I think the use of Avgas in the 1958 to 1960 (?) F1 was as much to do with the reliable quality of Avgas worldwide as its pure octane. When the 1958 world championship was decided in Casablanca Avgas was locally available but the local pump gasoline could have been very variable in quality so the stipulation of Avgas made sense as F1 began to spread it's horizions.

[Terry Walker]

Back in the late 60s in Western Australia avgas 100 was widely used instead of pump fuel. It was allowed under CAMS rules. Like all aviation fuels, it has a sort of use-by date for aviation purposes, and out-of-date stuff was always available at the right price. My mate Jim Lush stocked drums of avgas at his gas station / garage and supplied it to quiye a lot of racers from his neighbourhood. I can't recall the octane rating of "super" grade pump fuel then, but it was pretty low - 80s? The most basic of tuning hints in those innocent days was to advance the ignition timing. I was running SUs in my racer, whicbh didn't seem to need any adjustment at all.

[Lee Nicolle]

There are several kinds of 100 octane avgas commercially available: 100LL, dyed blue, which is most common, and 100/130, which is dyed green. Both are leaded fuels. Aviation fuel's octane is rated under a different system and generally, 100 avgas will have a lower MON than 100 octane race gas. Under the avgas system, a typical race gasoline might test at 120/160. Avgas also has a lower specific gravity so the jetting will need to be three to four steps richer than with current racing fuels. Avgas has a number of properties that allow it to operate safely at a wide range of altitudes and temperatures, etc, while modern racing gasoline is formulated to make maximum power.

All this said, avgas has been used successfully for motorsports applications. However, this was mainly due to a lack of other options. There is no reason to use it today unless racing gasoline simply isn't available. It's certainly no speed secret as it will actually make less power.

Here in Oz RF100 is 100 octane Avgas though is not certified. Avgas is certified pure and clean and has a shelf life. Though unlike current road unleaded doesnt go off quickly. I have had it sitting around in the car over a year without any harm.Though I do not recomend that! ULP has gone 'off' in the vented fuel tank in a few months.
Avgas will make power in engines with only 9-1 compression without touching the engine, and advance the timing usually makes a bit more. But it really works best with 11- 12.5 to1 engines where the power is considerably better than old 98 Super. And some of those engines scarcely run with lower grade fuels.
Though some people seem to be getting fairly good results with 98 ULP with the right combustion chambers. As are a lot of people with E85 though you use a lot more of that!
The ULP98 never seems consistent though. My big old 400ci Galaxie goes ok on it one tank and bloody awful the next. Pings it self to death. And no nothing has changed tank to tank. And no the chambers really do not suit the fuel but I have to run the massive 9.2 compression on something better than normal unleaded. I used to use Avgas but the price doubled so am stuck with ULP. And have had trouble trying to get that in some country areas within 300km of Adelaide.