100LL fuel on my DA 100/3W 212b4?

[FastnLow]

I fly at a full size airport so I have easy access to av gas, does anyone run it in their gassers? Advantages/disadvantages?

[TheTank]

Higher the octane, slower the burn, no advantage to it really. Plus, lead (100-low lead) slows the burn rate a little more. That type of fuel is only gonna help you in higher performance motors with high compression ratios, so that you are burning the fuel mixture rather than detonating it. Stick with regular pump gass, 89-94 octane and youll be good to go because these motors dont have higher ratios than 11 or 11.5:1.

[Kiwi]

FastnLow.

Pretty much agree with John. Theres not a huge advantage in going to higher octane ratings with low compression ratio engines.

There is however some small benefit in that your engine will likely run a tad cooler, it may actually take a sudden burst of throttle better and not tend to load up as some do.

But these are minimal advantages and likely never noticeable in the air.

Another slight anomoly is the way they rate pump gas and avgas. From memory 100LL is like 93 or 95 octane pump gas. Dont quote me on that but I remember there is some distinct differences in the way they rate them.

Kiwi

[GremlinX]

Yeah, and the Lead will eventually get in the ring lands and can stick the rings a little. It smells great,and looks tastey, but leave it for the big guys. I buy 100LL and mix it with pump for some of my street cars. Works great that way. Gets rid of a slight ping.

[kevgofly]

DA says "don't do it", it has been linked directly to problems, unfortunately, it was a while back that I was told this (by the guys at DA) and I forget exactly what the problems were. A quick phone call to them would clear it up though.

Kev

[notorious_benny]

High octane = slow burn = possibbly less power.

The only reason you would need high octane is if you are trying to prevent detonation. My DA 100 runs on KS 1060 pipes and still runs just fine on regular petrol.

[gstjohn]

I asked keith baker at BME about using 100-110 av fuel and he said why would I want to waste the money? it does not effect anything and as stated above, could lead to serious problems. Keith actually told me to use the lowest grade fuel that is available (85 octane in colorado). there is one guy here in town that has a brission single cylinder and he runs av fuel. in fact when I asked him about it he told me that he called brission, and they told him to run the highest octane he could find 110 or better, so he has 130 octane i believe (purple in color). another guy uses 100LL in his DA100 and has about zero compression left.

[tmac48]

Would like to hear from DA about this octane thing on this thread. I tried reg on my da 100,lost 100-200 rpm & it ran terrible, and less power on up- line. back to 95% got my lost rpm back, motor runs real sweat,power on up- line returned.

tmac

[notorious_benny]

Thats intersesting Terry, It makes no diff what I use, I have tried 98 premium down to regular 89 unleaded. Finally I have settled with regular premium (95 or 91 I think) purely as I have had issues in a car with dirty regular unleaded and dont trust it as a quality fuel.

[loan4utoo]

I think the quality of the fuel is the only thing. Kiwi is right about the different methods of rating the octanes, and while 100LL AvGas is a higher octane than pump gas...there really isn't a performance difference that is noticable. The big difference is a little cooler running engine...especially good for the desert SW guys in the summer. The only time I noticed a difference was last summer when it was 105 degrees and some guy on regular pump gas started losing power due to overheating and predetonation.

So, my .02, if it's hotter than sin outside, run the AVgas, if it's below 95 degrees, save your $$.

[Kiwi]

Guys,

I'll try to do a laymans explanation of the octane thing on fuel for you.

The term octane relates actually to the speed the fuel will burn. I theory the lower the octane rating the faster the flame propogates in the combustion chamber when the spark lights things up.

SO why have different octane ratings? Well there is a second factor called compression ratio that comes into play. Compression ratio should really be called cylinder pressure. That is the actual air or gas pressure in the cylinder when the piston is at the very top of its stroke. There are power advantages to be gained by raising the cylinder pressure in an engine. Its the old rule about getting more fuel and air in a smaller space. When you do that it makes a louder (more powerful) bang. Thats why you use blowers and turbos. More air and fuel in the hole to make a bigger bang.

But there is a problem. If the pressure is too high the fuel and air mixture will ignite much faster and it does actually fire before the piston reaches the top. In your old car years back you heard that happen if your rpm was too low and you gave the engine too much gas. You could hear that really loud knocking noise from your engine or in mild cases a lesser noise known as pinking. When that happens you better beleive your engine is in death throws. Its delf destructing from the inside out so we dont want that in our aero RC engines ever!!!!

So whats all this got to do with RC engines, DA, 3W, ZDZ, EVO, KROMA, ZEANOAH and a multitude of others. BME of course being another that comes to mind.

Well really it is all related to the compression ratio. If your engines are in the 7 - 9 to 1 ratio standard gas is all you need. By mixing oil with the fuel you are slowing the burn rate down anyway or raising the octane rating ever so slightly but ignore the oil effect.

What differences will you get from using higher octane ratings.

1. The higher the octane rating the lower the power on your basic two stroke RC gas engine.
2. The higher the octane rating the cooler your basic RC engine will run.

So whats the best. In my case I recommend a mid range pump gas in the 93 to 95 octane range. Now those numbers are not USA ratings, you guys are different. SO you would ideally use one of the intermediate fuels available at the gas station. What your looking for is that unique combination of power and cooling.

100LL is made for a very different purpose. In general aviation aircooled piston engines the fuel type is critical for engine reliability and cooling. The 100LL is critical to engine cooling and pre ignition (pinking) as much as anything else. Remember an gas aero engine is 4 stroke and runs at 2700 rpm max. Thats like 1350 ignitions a minute. Your DA will be doing 7000 rpm at times. Its a totally different environment thus different fuel requirements.

You cant go wrong with the midrange auto gas mixed with the best two stroke oil you can find.

If your power crazy go for the lowest octane and minimum oil mix, it will give you the maximum power. 100:1 mixes as an example.

If your a Sunday flyer like me use a mid range fuel with good oil and you will still be flying your DA in 10 years time.

But above all else read the manufacturers guide that comes with the engine. They know whats best for the engine they designed. Read it, use it and stick to it and you cant go wrong.

Hope this helps.

Kiwi

[GremlinX]

Not to mention, the lead buildup around the dome in the head and the squish area on the piston. It probably wont hurt anything in reality except your wallet and HP. BUt sustained time will build up. In Racing Karts, the last year I raced them I won a National Championship for Parilla engines(IAME company) and we ONLY ran race fuel to cool it down. Max rpm on the motor was 22,000 and was frequently above 16,500 rpms. Hurt HP? Maybe. Kept it cool? Yes. Not to mention lead is corrosive. You have to keep running them and keep things circulating. I think Amoco 93 is the best street gas you can buy. I did a test/survey on pump gas for a MOPAR website about this same issue. Of course these are 4 strokes though..