Let's talk about Avgas (100LL)

[BikeRacer]

To begin, I'm for and against the use of Avgas. I was turned on to it by a friend in order to lower our engine temps. He purchased an engine that was run on 100ll with quicksilver 100:1 and still looked new inside. So I figured what the hell; I couldn't find the right oil so I just stuck with my redline at 50:1. I made the stupid mistake of changing the day before an IMAC contest. I flew last weekend in Sherman, TX with my EME-120. It started fine in the morning, of course it still had my old 87 octane in the carb. As the day progressed and into the contest on Saturday, it became extremely difficult to start when cold, and would bog very badly on transition until it ran at least a minute, then it would clean up and run like a champ until I landed and cooled it down. Another guy was having the same problem and he too was using 100ll. He decided to switch back to pump gas and his problem went away. 

   I haven't changed fuel yet because I was afraid to change again during a contest. My thinking is: if the engine doesn't need high octane, don't run it. I believe that when the engine is cold, it won't fire right, just like having low compression. I will change back to 87 this weekend and post my results, I'm gonna run one more tank of avgas and then change over and let it cool and see how it does. 

  Had any one else had results like this, I would love to hear more since I've heard several people that rave about avgas.

 

[Patroller]

My concern for Avgas is the lead. That and the regular non ethanol gas I can get down the street works just fine. 

 

[BikeRacer]

I also share a few doubts regarding the lead, but in reality, it's very low and I'm more asking about how it runs in our planes. Race gas would be another contender in this thread. The lead was the main reason we wanted to use it, there was the rumor of lower engine temps and the use of less oil for a cleaner and stronger running engine. Do I need it? Absolutely not, but I would like to get some real feedback on it for others to use because well... I'm curious.

 

[thurmma]

I just double checked the compression ratio and the manual states 7.6 to one. This is very low when considering the use of a high octane fuel. I am not an engineer by any stretch of the imagination, but I do know that the higher octane fuels are formulated to not burn until a higher pressure, hence the use of high octane fuel in high compression engines. With this in mind, running the 100ll on this engine is probably not compressing the fuel enough to properly burn, especially when first starting it. The bog is more than likely more side effects of the lack of complete burning of the fuel once ignited.

I have a 3W-150 TOC, that I run 98 octane no lead, real gas in and it is a beast. The compression ratio on it is stated at 10.5 to one, which is providing plenty of pressure to heat the fuel before ignition for a clean burn. If I run 91 in the engine it will not run the way it does with the 98 I am assuming because the fuel may be starting to burn prior to the spark, thus giving me detonation, an engine killer if let run wild, and a lack of power. The engine runs quite a bit hotter with the 91 also. I assume I could back the timing down a degree or so and probably get away with running the 91, but as long as I have 98 reasonably close, I will just buy it 5 gallons at a time and run it

With that said, I also have a newer 3W-106, non TOC version that runs great on the 91 and provides no benefit at all running 98 in it. The compression ratio for this engine is stated at 10 to one. One major difference between the two engines, beside displacement, is I have a CH Ignition on the 150 and the standard 3W ignition on the 106. I noticed a big difference when I replaced the ignition on the 150 so I am thinking the timing curve is more aggressive on the CH ignition than the 3W one.

Ok, I will stop now. Hope this helps a bit.

 

[thurmma]

@BikeRacer just switch to 91 no lead, no ethanol and you will likely see a reduction in temp and a smoother idling engine. It does cost a few more cents per gallon, but it will be well worth the piece of mind when the temps stay down

 

[thurmma]

BikeRacer said
I also share a few doubts regarding the lead, but in reality, it's very low and I'm more asking about how it runs in our planes. Race gas would be another contender in this thread. The lead was the main reason we wanted to use it, there was the rumor of lower engine temps and the use of less oil for a cleaner and stronger running engine. Do I need it? Absolutely not, but I would like to get some real feedback on it for others to use because well... I'm curious.

I haven't ran the 100LL, but was thinking about it until I talked to DA and Geahart at Aircraft International, 3W rep. Both companies said that the LL would leave deposits in the engines and could possibly void the warranty should they fail. This was from 2 completely different companies with no ties at all and their answers were almost like listening to a recording, so I listened

I do smart things once in a while.

When I asked about oils to run, they both said to stay away from Amzoil because of the junk it leaves in the engines and that Redline is the preferred oil to run at this time. I had been running Amzoil and noticed that I always had black junk all over the bottom of the plane and my landing gear and it wasn't from running super rich either. All engines were running very nicely. After a couple of tanks of Redline at the same ration, amazingly no more black junk and the engines seemed to be running smoother. I run 50:1, but you need to run what your engine manufacturer recommends or what you are comfortable with.

Man, I am long winded today, somebody stop me!

 

[BikeRacer]

I looked up the EME and its compression ratio is 7.6:1 which is definitely not enough to warrant the use of 100 octane fuel. I'll try some 89 or 91 in the future and see how the temps and ease of starting are. I was going to try his in my da 170 but think I'll steer clear after hearing of the deposits from the lead. Oh, and don't stop! The more the better!

 

[Capt.Roll]

thurmma said
BikeRacer said
I also share a few doubts regarding the lead, but in reality, it's very low and I'm more asking about how it runs in our planes. Race gas would be another contender in this thread. The lead was the main reason we wanted to use it, there was the rumor of lower engine temps and the use of less oil for a cleaner and stronger running engine. Do I need it? Absolutely not, but I would like to get some real feedback on it for others to use because well... I'm curious.

I doubt its the LL Avgas that is directly causing the deposits. Most likely it is the combination of the leaded gas along with the chemistry of the current two cycle oils that are formulated for use with unleaded and E10/unleaded gasolines. No data to back up my statement but our small 2 cycle engines really don't require a leaded gasoline.

 

[orthobird]

bikeracer, any updates? 

 

[BikeRacer]

Sorry, no updates yet. I only flew once since the last contest and didn't have time to change my fuel back out. I've been on vacation in Florida and will be back this weekend, so I'll try to fly one evening next week or next weekend. I'll be sure and run a tank of the 100ll, then let it cool down and try the plain ol' 87 octane no ethanol and see what happens. In the end, I may just use a blend for additional cooling in the hot summer, if that doesn't become too troublesome...