I have a quick question.... Ive been using brand A ...15% nitro 18% oil, and gallon after gallon i rarely have to mess with the highend on any of my engines ....LHS didn't have the fuel i have been using, so i purchased brand B which also has 15% nitro and 18 % oil ........ I noticed on brand B I had to lean my high end 9 clicks on one of my engines for it to run right...

Does that mean brand B has lower nitro?

No, if it's 15%, it's 15% no matter how you look at it.

why would my high end needle change when using identical spec fuel but of a different brand?

Do you get roughly the same rpm with the same prop at the new setting with the flavor B? I am wondering if you got a bit of water in your fuel. I am assuming that the relative air density was about the same between trials.

What about conditioners, like anti-rust and anti-foam? Maybe they are not included as part of the lubrication? Then you would have less methanol and a higher nitro:methanol ratio.

Just a thought...

no i got a couple hundred lower with brand B



I am suspecting one brand is using less nitro than the other

One last question

Hypothetically speaking, if i were to be using 15% nitro fuel with HSN set optimally, and then switched to FAI fuel, would i have to lean out the high speed needle?

That is my recollection but it has been a long time since I used FAI...

Ok then that settles it...thanks guys Ill stick with brand A

I have wandering the highways and byways of the US in a RV for a couple of years and by necessity have had to use a variety of fuels and although I usually stuck to 10% I too had to fiddle with the needle most times I changed brands.

I suspect the type of oil used changes the flow rate through the needle valve. I was flying 3d so max rpm was never an issue and I never bothered with the tach to check it.

That's what came to my mind. When it says 18% oil it's an oil blend and they can all be different from brand to brand. I use Power Master 15-18 and when I went to there 20-20 none of my engines liked it, the 20-20 has not only more nitro but a bit more castor oil. {from what I was told} I can change from brand to brand on some fuels and never notice a difference but then I can go to one brand and have to do a complete tune up on my engines. I know the brand and just don't use it. I'm lucky enough to always be able to get my fuel of choice and don't run into that problem too often. A couple of weeks ago I did borrow a tank of fuel from a friend and guess what it was????

Very simple explanation. Based on the different density of the components used, Methanol, Oil and Nitromethane if a manufacturer uses percentage by weight it will be light on nitro. There is nothing that says they have to specify what method they use however Sig states it on the bottle that they use percentage by volume. Ihave tested several different fuels and seen it also.