• If you log in, the ads disappear in the forum and gallery. If you need help logging in or getting registered, send request to: webmaster@southernairboat.com

Aircraft engine fuel

J

jim

Well-known member
What kind of fuel do you run in your aircraft engine?

What engine, and what compression ratio if not stock.

Jim
 
Lycoming 0540 straight valve. 8.5/1 compression...75089 STD pistons

93 octane pump fuel most of the time with an occasional run of 100 LL. But I do have CHT gauges to monitor head temps, and I also check the plugs regularly for signs of detonation.


Kevin
 
Lycoming 4 cylinder - angle valve 170 (O320 w/O480 angle valve jugs, 8.7:1 compression)

I'm running high test pump gas and I have to say that it runs good & has a lot of power. However, if I have to really lay into it for an extended period of time, it will start losing power and missing. I suspect it's the head temp. that Kevin was referring to. I can back-off for a few seconds & it's ready to go again.

Is octane booster w/lead additive worth adding to the pump gas?
 
Rick,

You are going to get some different opinions on this one. One simple, non toxic, non corrosive way is to add 100LL avgas to it. You can experement with the amount.

Do you get backwash in that boat with a throttle chop?

Jim
 
I know I should be getting my gas at the airport and since I usually only burn 10-15 gal. a trip, it's not the extra money. It's just a hassle to go to the airport for gas.

I moved the second part of this post to the backwash topic.
 
I think "lead" is really what they need. The compression would dictate the octane. 100LL actually contains a lot of lead by most standards. I have gotten by with 93 + lead additive and octane boost---but my engine with high compression ran best on 100LL. Just my opinion---and you know what they say about them.

Harvey
 
Octane boosters can be tricky, and like cracker stated you will get many different opinions on it but here is my take.

Octane boosters work by points, meaning one bottle of booster may only increase a tank of fuel 6 to 10 points. 10 points equals 1% octane. Many gas manufactures use the same additives that are in the octane boosters (like toluene) already at the processing plants to standardize the product. How much they use in each batch is unknown to us. So if they come out with a weak blend and add a crap load of octane boosting product at the plant then we in turn add more it could cause us to run dangerously close to a melt down because these additives burn at a much higher temp.

I follow a general rule of thumb; during the winter months I will burn pump gas (93 octane) all the time. During the hot summer months if I do run my boat I will go out of my way for at lease 100 LL avgas.

Beware of bottle covers that say 104+ octane booster. Read the fine print in the back, it tells the rest of the story.

I haven't done any research on lead additives so far, but I may jump on that this week. I have access to a large chemistry lab at the office.


Just my 2cents, Kevin
 
Go to the airport to get fuel? That's crazy. I used to bring auto fuel to the airport to fuel up my airplane. Just use the highest octain your local gas station has and you'll be fine. Burning avgas is a giant waste of money.
 
kb - I would agree with you about those octane boosters. Most people misread the label, but it says you will gain 6 to 10 point per tank and people think great. But in reality, it is 1 point octane, so to boost octane from 93 to 100 you would need 7 bottles of the stuff. Add that price to the cost of 93 octane and you are at 100LL prices.

As for the use of 93 instead of 100LL, I had a friend in California that had a 540 parallel valve that was continually running on the hot side. (He had the cowling covering the top of the motor. After dealing with an A&P he spent some dollars on, they never could get the temperatures down to more than just below red line. He was running 93 octane only. He needed more power and a new stand, so he when to a 350 with a reduction gear. The fellow that got the 540 is still running it, without the cowling and only on 100LL. I have the cowling and he has a motor that is running great and within normal temperature.

Some of the Lycoming discussion site mention the same thing. Increased temperatures with 93 octane and greater potential for pre-detonation. I will stay with that. I have an old saddle tank from a tractor truck - (85 gallons which is just under the requirements for placards in TX), on a skid for the truck bed. I just pull up at the local airport and tank it off. It lasts forever. Guys doing bush pilot work in Alaska left barrels stashed at islands for emergencies. They said it would last for several years in 55 gallon barrels and that automotive gas caused all the problems due to the additives to the fuel. That is the reason that most pilots say they avoid it.

kb - I had never thought of running 93 during the winter to save money. Thanks for the great idea. :oops:
 
After 15 years or so of debating and my own personal experiences. I have used Sunnoco, Cam 2, ELF, Unocal and several others. I have run all the way up to 118 octane Pro Mod nitrous fuel. Way back in high school I tried running AV gas in my race car and my E.T. fell way off. I found that AV gas always made less horsepower in every application. Accept when a motor is running too hot or can’t dissipate heat efficiently. AV fuel has such a poor BTU value. So I spoke to someone at Unocal, we all have heard the debate about the de icier additives and bla, bla, bla. The Unocal rep informed me of three main differences. AV fuel is designed not to burn rapidly so it can prevent detonation and generate less heat. This is great with a race fuel if it produces a lot of BTU’s but AV gas doesn’t it sucks in that department. The seconded which I never heard of until I spoke with a Unocal race fuel rep was. The last thing you want in an airplane is flammable vapors so they engineered this fuel to dissipate fewer and less volatile fumes. That was the smartest answer yet I’m sure in a cockpit at 10,000 ft the last thing you want is fuel vapors. The third one which I never heard before either was most planes set for long periods of time between uses. So they added ingredients that drastically increase the shelf life of AV fuel. This additive also helps the fuel dissipate less fumes because when a fuel vapors it loses its volatility. I guess people die when they try to power up on take off with bad fuel. The rep made a good point he suggested if I have a generator or lawn mower that I only use a few times a year. I should run AV gas in it because it wouldn’t varnish up or go stale like pump gas does. I’m sure everyone knows this one but the most power you can make with any gasoline burning engine. Is by running the lowest octane fuel possible that will stay out of detonation. The lower the octane the more rapid a fuel burns and thus generates more heat. Aircraft motors are different in this matter because their not intend to remain at sea level and they don’t have a capacity to dissipate heat efficiently so they run a poor BTU fuel that helps cool the engine. Plus the higher altitude a plane goes the less power it will make due to lack of oxygen. So aircraft engines don’t generate any where near the heat and horsepower in a plane as they do in an airboat. So if you run realy hard like we all did when we were younger run AV fuel. If your wiser and don't burn up the hill hours at a time run pump gas. If she starts running to hot or pinging then switch to AV fuel.
 
That was another very interesting article. I will try to locate the BTU value chart I found that shows pump gas having a considerable amount of more power in it’s burn rate. This graph included the pressure spikes created during a burn cycle the chart also showed pump gas too be more volatile. This is one of those subjects like the JFK assignation. Never is a theory agreed upon. However every time the subject comes up there is a new theory added.
 
The theories are fine. I appreciate your insightrs into how it performs in the field.

There are contradictions there also. If you remember Mike Weaver is running a 455 Buick with long engine life, so there is no serious detonation. He got more power on 100LL with no change to timing etc, which surprised me.

I think I mentioned before that my son has a highly modified IO540 parallel valve in his aerobatic airshow plane. He is getting 400 hp on the dyno and fantastic performance without turbo or supercharger. He runs it at full throttle for the entire show except for some low speed maneuvers. He uses 100LL. However, his engine was specifically set up to run on it.

Jim
 
Didn't realize that lower octane fuels may produce more BTUs, but then never understood much about the octane ratings and how it related to HP.

Shoot, I can remember as ignorant kids we tried to get older guys we knew working with the mosquito control office to buy us 100LL thinking we would get more HP out of it. (Didn't realize we could just pull up to the county airport and fuel up.)

Thanks for the information. Pat
 
You must log in or register to reply here.
Back
Top