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Old 02-07-2021, 12:29 PM   #1
vuuli312
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Home brew fuel recipe


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Hello everyone.I'm going to mix my own fuel.I picked up the ingredients a few years back.My interest is in rc boats.I have a deep vee 46" prather powered by an os max .77 vrm engine as well as a k&b .21 outboard ( which doesn t have a hull yet). Years ago when i built the deep vee, i didnt know too much about glow engines, i used a fuel that only contained nitro methane and synthetic oil.I think i ran it too lean and scored the piston/ liner.I have now replaced the liner/ piston.I researched boat fuel formulas and it seems that 18% oil is recommended.Im looking at a nitro content of between 20% to 30%.Im just interested in sport boating.i have the following ingredients, methanol, pure nitromethane, klotz kl 198 lite techniplate synthetic oil, klotz "benol" racing castor oil (to protect against lean run).Looking for any input advice as welll as a formula on a per gallon basis.Ive got a 5 gallon can of methanol.Thanks.
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Old 02-07-2021, 12:43 PM   #2
floyd
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Re: Home brew fuel recipe

I mix my own FAI fuel as below per liter. If you ad nitro just cut back on the methanol and it should be fine. 5% nitro would be 50ml per liter. I mix all synthetic oil but I do ad an ounce of Castor 927 racing oil to the mix for extra protection. Cheers Floyd

830ml Methonol
170ml oil

Last edited by floyd; 02-07-2021 at 12:53 PM.
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Old 02-07-2021, 04:10 PM   #3
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Re: Home brew fuel recipe

I'm no expert but was into racing nitro boats 8 years ago and we where using 50-60% nitro with higher oil content if I remember correctly.
And I know your just sport boating but I found 30% was kinda of the minimum for these higher compression boat motor to run properly.
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Old 02-08-2021, 11:04 AM   #4
MJD
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Re: Home brew fuel recipe

Not a big deal really, the decisions have to do with preferences/goals:

(1) Choose oil content - 18%-20% typical. (BTW - reducing oil by 2-3% does NOT mean you are burning 2-3% more fuel per stroke and gaining 2-3% power. However some folks will insist this is so - the math totally does not work because air is ingested as a gas, fuel as a liquid. An interesting additional point to ponder, is that in bulk, oil is the most expensive of the fuel components by volume, and more oil makes messier airplanes - a cynical thought or two about profit and marketing is in order.)

(2) Of the total oil, choose the castor/synthetic ratio if you are using a blend. Note that commercial fuels commonly use 30/70 castor/synthetic mix - it's not the gospel but a good starting point, and changing from there is a decision that pretty much depends on your comfort level with synthetic oils and/or the advice of the engine maker.

(3) Choose nitromethane % - for sport boating 25-35% ought to do the job. See 4 strokers comment, the compression is generally set up for reasonable nitro % so compresison will be low for low nitro %. Also bear in mind that plug life tends to deteriorate a noticeable degree over about the 40% mark.

(4) 100% - (1) - (3) = your methanol percentage

So a 30% nitro blend with 20% total oil, 30/70 cast/syn blend would be:

6% castor oil (30% x 20% total oil)
14% synthetic oil (70% x 20% total oil)
30% nitromethane
50% methanol

And remember - fuels are always formulated and blended by volume, not weight.

Simple as that. This is likely a decent starting point for your marine blends. I run 23% total oil in my ducted fan engines (same timing/tuning and rpm range) but they are air cooled.
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Old 03-23-2021, 10:39 PM   #5
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Re: Home brew fuel recipe

If you go to the coxengines.ca website, I published a fuel blending article that you may find of some value. With care, fuel blending is not difficult. Good luck

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Old 04-04-2021, 08:30 PM   #6
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Re: Home brew fuel recipe

Hi Andre
I was fortunate and was able to purchase a Club favourite that was years ahead of its time. I decided to keep the Super Tigre 3000 in it as John (RIP) always put on a great show with it. I spent some time today learning how to mix up Super Tigre Fuel. After learning that Methanol is .791 g/ml and Synthetic oil is roughly .92 g/ml and Castor is .97 g/ ml LOL. I went with a little simpler math and used 3400 ml of Methanol, 190 ml of Castor and 190 ml of Klotz Synthetic. I'm hoping you smarter guys will agree with me as I was shooting for 10% oil mix.

I started her. What a beast. Almost broke 3 fingers lol. It stopped, dang. Restart I threw the Prop backwards against the compression, that was better. I tached a 20x10 at just under 7k.

Paul maybe a broken link at Cox.

Last edited by Hughes500E; 04-04-2021 at 08:39 PM.
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Old 04-05-2021, 07:43 AM   #7
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Re: Home brew fuel recipe

Fuel is always formulated and mixed by volume, not weight. Makes it a lot easier. 20% oil = 20% by volume. So for 3400 ml of 10% oil fuel, you would have 340ml of oil and 3060ml of methanol.

For 10% oil, use 9 parts methanol and 1 part oil. Mix the 1 part of oil any way you want, in this case if you want 50/50 then:

18 parts methanol
1 part castor oil
1 part synthetic oil

That said, your fuel is fine.
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Last edited by MJD; 04-05-2021 at 08:51 AM.
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Old 04-05-2021, 09:05 AM   #8
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Re: Home brew fuel recipe

Getting the proper ingredient is always a problem. First of all start with metal containers. I never seen a gallon of bad fuel until I came to Ontario and the fuel came in plastic jugs. You want double distilled methanol and de-gummed castor oil. I use the Sig product. The standard fuel we get here comes with 16% oil. I add 150ml of Sig de-gummed castor oil, which brings the oil content up to 20%. Methyl hydrate and pharmacy castor oil have impurities in them that that cause black carbon to build up inside the engine. The biggest problem with glow fuel is preventing it from absorbing water from the atmosphere. You can buy little round beed's to use in gasoline, is there anything that works in alcohol?
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Old 04-05-2021, 10:30 AM   #9
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Re: Home brew fuel recipe

One thing tae remember, Nitromethane has 2% methanol in it as a stabilizer. Calculate this in your measurements.
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Old 04-05-2021, 11:11 AM   #10
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Re: Home brew fuel recipe

Quote:
Originally Posted by controlliner View Post
One thing tae remember, Nitromethane has 2% methanol in it as a stabilizer. Calculate this in your measurements.
Why - it hardly throws off the formulation, it's not like the engine only works if you use whole numbers. If you blend 10% nitromethane using a 98% solution, you still end up with 9.8% nitromethane, and that 0.2% difference will not even register on a tachometer. So for all intensive purposes it is okay to ignore the 2% methanol and use it as neat nitromethane.
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