Explain why?
Talking about oils in a wide sense is dangerous. The one oil has a much worse lubrication than the other. With other words, with some oils you need more to get a same lubrication than others.
For sure you can run on 6% oil or even lower without a problem but you will see the lifespan will be shorter and the change of a broken rod will be higher.
By the way, with boats and airplaines/heli some fuels contain up to 20% of oils

Also explain why?
You do need an amount of oil per stroke.
I can imagine the runtime on more nitro is less on a tank, calculating back to the amount of one stroke you could be right. On the other hand the more nitro will give more forces inside which does need more oil to deal with it.

Well

Nitro needs more oxygen to explode compared with methanol. An engine uses a specific amount of air at any given RPM. Now, to make the correct oxygen/fuel ratio you'll have to add much more fuel, when you run high nitro content compared to low nitro content. When you add more fuel (and oil), there will be a higher fuel flow through the engine = more lubrication. That's why you don't need the same amount of oil when you run high nitro content.

So I emailed the folks at O'Donnel and asked them if castor oil can/should be added to the Speed Blend fuel for better engine protection. Here is their response:

-Thank you for contacting product support. This fuel is designed for racing engines and provides a higher rpm. You can use a non speed blend fuel that has 18% oil content and runs as well. For*both fuels I would highly recommend using an after run oil to keep the engine clean and running longer.

Thanks,
Mike M.
Product Support Technician
Great Planes Model Distributers
PS9021

Didn't completely answer my question, but it gave me enough to make me rethink my earlier position.

Nitromethane is an oxidizing agent. The oxygen content of nitromethane
enables it to burn with much less atmospheric oxygen.
Please read all of the interesting info in the link below.
http://en.wikipedia.org/wiki/Nitromethane

Pretty much this.

14.7 lb (6.7 kg) of air is required to burn 1 lb (0.45 kg) of gasoline, but only 1.7 lb (0.77 kg) of air for 1 lb of nitromethane. Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke. Nitromethane, however, has a lower energy density: Gasoline provides about 42–44 MJ/kg whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen.

An engine sucks in a specific amount of oxygen when running. If it was a gasoline engine you would only have to add 1/14,7 gasoline to have the correct mixing ratio. With nitromethan you'll have to add nearly the same (1/1,7) amount of nitro to make it explode.

If you have tried changing nitro content you'll see, you have to retune. Lean the needles if you go from high to low nitro content and visa versa.

I attented in a race in 2009 with a RB WSIII and ran it 0% nitro, really high compression ratio and an OS 4 stroke plug! . The runtime with 25% nitro was only 7 min. With my fuel I could pit at 10 minutes due to the much leaner tune.

I emailed Byrons about adding oil to their fuel. Here is their response: I am not familiar with Blendzall oil. However, it this is a good grade synthetic oil that will blend with methanol, then you should be okay adding it to the mixture to increase the total oil content. One thing I will add is all our synthetic and castor lubricants are much higher quality than the majority of products available on the market and your 9% oil content in the Byron Fuel is probably superior to even an 11% total oil content of another brand of oil.



To be competitive on the open market, most oil blenders, Klotz included, do not provide the highest quality possible because to do so would price them out of the market. The Klotz oils we have in our fuel are higher quality than the Klotz oils available on the market and we pay the price for that.



So, if you add Blendzall to your fuel, you should do no harm. But I am not sure of the quality and I cannot guarantee adding Blendzall will increase the lubrication qualities of your Byron Fuel.



I hope this is somewhat helpful.



Best regards,





BYRON ORIGINALS, INC.



www.ByronOriginalsInc.com