378

My Feedback: (4)

Fuel's pretty cheap for me, 25 bucks a gallon or so, but I'm still considering blending my own as obtaining it requires driving 25-30 miles. I've got two applications, a .18ci car that runs best on 20%, and a .46ci plane that runs fine on 10-15%. I want to blend two fuels, obviously.


Car fuel: 20%N, 15% O(75/25 synthetic/castor blend to keep the mess down)

Plane fuel: 15%N, 18% O(72/25 castor/syn, reversed from the car fuel, as it's not going to collect half of Tennessee on the undercarriage)


I need to know yall's thoughts on these blends, as well as where in the Nashville, TN area I could obtain the ingredients.

1QwkSport2.5r

There's a ton of good information about this subject here: http://www.rcuniverse.com/forum/m_10531813/tm.htm

I've been making my own fuel for over a year. There are numerous other threads on the subject around the forum, so look around. The hardest part is finding methanol. I bought mine from a local oil company. For what you're paying for pre-mix, it will cost you about the same or a little less to mix your own. Castor oil is half the price of the average synthetics and synthetic blends. For this reason I run all castor in my car engines and my airplane engines. Airplane fuel around me is $32 a gallon and car fuel is about $34 a gallon. My homebrew airplane fuel is $10-12 a gallon, and my car fuel is $18-20 per gallon. I use 20% nitro/12% oil in the cars and 5% nitro/20% oil in my airplane engines. My engines run significantly better on my homebrew fuel than off the shelf fuel.

378

My Feedback: (4)

I want to try to keep the castor to a minimum in my car because if I run the stuff I end up with half of Tennessee glued to the side of the engine, exhaust, right rear tire/suspension, inside of the shell, air filter housing, carb, pull starter, diff case, chassis, and pretty much every other part from the stinger back that doesn't spin fast enough to sling the stuff off. It's horribly annoying to clean. Synthetic burns, so it won't collect quite as much nitro mud after an hour's run. I'd love to run a pure synthetic blend but these engines do like a little castor, and my after-run procedure consists entirely of running it out of fuel, setting it to BDC and plopping it up on the shelf.


I'll thumb through that thread and see what I can find out there.

1QwkSport2.5r

I totally understand the synthetic/castor bit. I personally don't want to pay for the $50 a gallon oil. The oil is as much or more than the nitro. In my cars, I don't see much more mess than with the blended oils. Running 12% castor allows a leaner mixture which means less oil out the muffler.

My Mach 427 lst2 gives up wheelies on my 20% homebrew, but took 25% nitro premixed to give wheelies.

Nitrovein

If you compare premixed with homebrew there is a difference in how they measure the nitro. Premix with 25% by weight will be somewhere around 20% by volume depending on what oil is in the premix and how much.
Density:
Methanol=0,79g/ml
Nitro=1,138g/ml
Oil=0,9-0,99g/ml

1QwkSport2.5r

Though the chemical densities are different, most fuel companies mix by volume anyway. There's no sense making it more complicated. My engines don't seem to care much, I can't imagine anyone else's will either.

Nitrovein

Well there is a difference in calculate and measure, I don´t know how they measure. Some fuel manufacturer sell both way, but on the fuel calculated by volume they advice that you use colder plug and re-shim the head.
When mixing your own fuel I would like to think volume is the easier way to go. But when comparing fuel "A" to "B", it doesn't hurt to know that there is a difference.

1QwkSport2.5r

Volume is far easier. Though measuring by volume usually means oil flow is reduced versus measuring by weight. I do agree it doesnt hurt to know the difference. I dont know for fact which companies use which method, but given most pre-mixed fuel is a synthetic/castor blend I would have to assume they would mostly mix by volume. It would get awfully complicated to mix by weight using blended oils.

I have never heard anyone say to use a colder plug and shim the head when using fuel mixed by volume. Considering no fuel company comes right out and says which method they use, I can't see this as being common practice.. at least not here in the U.S. If you have a link to some information talking about this, please post it. I'd like to read into it a little.

Nitrovein

As you say, in the U.S. I believe the standard is by weight and in Europe by volume (in general). But even if most engine brands come from Europe, most of the fuel come from the U.S.
I unfortunately can not find more than one brand at the moment and that site seems down for the night... http://www.gt-racing.de/ I will get back when my memory serves me better.

But if we toy with the idea of mixing fuel with 25% Nitro and 10% Oil, and use a density of 0,79g/ml for methanol, 0,95g/ml for oil and 1,138g/ml for nitro then that would look like this:

1000gram = 1147,72ml
Methanol 65% =650g = 822,8ml or 71,69% by volume
Nitro 25% =250g = 219,68ml or 19,14% by volume
Oil 10% =100g = 105,26ml or 9,17% by volume

1000ml = 893gram
Methanol 65% =650ml = 513,5g or 57,5% by weight
Nitro 25% =250ml = 284,5g or 31,85% by weight
Oil 10% =100ml = 95g or 10,63% by weight

But as you say, they probably don´t mix oil by weight, my guess is on the heavy expensive ingredient.

downunder

The only commercial fuel that was found to be mixed by weight (from evaporation tests) was Byron but that was many years ago so it's possible they're doing it differently now and not short changing on oil and nitro percentages. Mixing by weight is certainly the more accurate way to commercially blend fuels on the proviso that the end result is equivalent to a fuel mixed by volume at a standard temperature (in America this would have been 60F). For home blending there's no need to complicate the process by using weight because no one blends at temperatures that would have any noticeable effect on the final volumes of each component.

1QwkSport2.5r

After doing some math, I've concluded most fuel companies in the U.S. must mix by volume predominantly. Reason being is this: If they sold a 5% nitro 20% castor 75% methanol pre-mixed product mixed by weight, there would only be 112 fluid ounces of product. Being that they sell it by the gallon mainly, which is 128 fluid ounces, Either they are further diluting the nitro and oil with more methanol or just selling 112fl oz. of mixed product.

5% nitro by weight is 5.6oz = 168ml
20% castor (using .96g/ml) by weight is 22.46oz = 674ml
and 75% methanol by weight is 84oz = 2520ml
Added up = 3362ml.
1 Gallon = 128fl oz = 3840ml

My homebrew 5% nitro 20% castor 75% methanol mixed by volume yields 6.4oz nitro, 25.6oz oil, and 96oz methanol. Their weights as a percentage respectively would be 7.6%, 23%, and 69.9% Which ends up being just a tad over a gallon (128.64oz)

I hate converting from imperial to metric measurements since theres a great deal of fractions so I did some rounding to simplify things a little.

I probably overthought this, but in hindsight, it is far easier to mix by volume. If one needs to be dead-on exact, then mixing by weight is a better route. As I said before, my engines havent been all that picky up to this point with what I've ran through them so I'll keep doing what I've been doing.

My homebrew 20% nitro 12% castor 68% methanol by volume = 25.8%, 13.07%, and 61.06% by weight respectively.

Give or take a little.

1QwkSport2.5r

The only component I see benefiting from mixing by weight is the nitromethane since it is over 1g/ml and its the most expensive component unless you use a lot of synthetic oil. (Klotz Super Techniplate is 80/20 syn/cas I believe and is roughly $54 a gallon whereas Nitromethane is $42-$55 a gallon roughly depending on the supplier.)

Nitrovein

Not sure how you´re thoughts went on that one... If you have 128fl oz in a jug, then 128fl oz is 100%.

Anyhow, I don´t think most people care about these things. But for me it came hand in hand with mixing my own fuel, toying with numbers.
But what´s worth thinking about is that if you have say 200ml in a tank, then you´re fuel will be the methanol % of that 200ml, the rest is lube etc. (VERY simplified)
When someone say that their new fuel will make you go 1min extra, then there is most likely (not certain) more methanol in that fuel. (Again, VERY simplified)

Nitro sure is cheap in U.S. I pay 170$ a gallon... [] I think that I should go through the hassle of mixing by weight.

1QwkSport2.5r

If nitro was that expensive here in the U.S., I'd be using FAI in everything. If thats 170 Swedish Krona, then thats only $25.52 US. If you meant $170 US, then I can see your point with mixing nitro by weight.

Nitromethane is not as easy to get as it used to be so I hear, some idiots like to make bombs with it or something. All these hazmat regulations really put a crimp in the hobby. Thats why model engine fuel in my area is $32-$38 per gallon (US).

Nitrovein

Unfortunately it is U.S. $. I think one problem is that it´s not allowed here to have larger canisters than 1liter with nitro at home, larger quantity would be cheaper to buy. (1liter=300Skr/$45)
But, there are ways to get it cheaper, but no where near the U.S. price.

1QwkSport2.5r

If there was a way I could help another fellow modeler in other parts of the world obtain the stuff cheaper, I would. I wonder what the shipping price would be per quart to ship from me to you. I'd be willing to do it if it could be done (legally). I had gotten some nitro that was diluted down to 80% nitro with 20% methanol for about $13.50US per quart to avoid hazmat fees. I just dont know if it would end up being worth it shipping overseas.

Nitrovein

That´s very kind that you want to help a less fortunate modeler. I will send you a Pm and explain my situation a little better.

1QwkSport2.5r

Excellent. I consider myself an avid modeler, and I've got about 14 years of car engines under my belt, and almost 2 years with airplane engines. I try to help whoever whenever I can. PM me and we can sort it out.