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Old Jul 05, 2006, 04:46 PM
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The Toolman's Avatar
Lake of The Ozarks
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Castor oil in fuel

I bought some fuel by mistake that is a coupla % low on castor oil, 16%. I want 18-20%, and was wondering if the castor oil at the Rx is the same as they use in the fuel. If so I can just do a little figuring and up the oil content of my fuel to 20% this way.

Thanx,
Ronnie
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Old Jul 06, 2006, 04:35 AM
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Tony Oliver's Avatar
North-East England
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First pressing castor is what you want. The mathematics isn't that easy if you want to be exact, but adding 4% by volume will give slightly over what you need with no harmful effects. It's not that critical unless you are into the high technology engines where maximum accuracy of everything is needed for top performance.

There are programs around which will tell you precisely how much to add to a specific mix. Southern Modelcraft here in the UK sell their program (still on floppy disks I think) - I don't think they have either a website or email but they do go to most of the model shows in England.
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Old Jul 06, 2006, 09:55 AM
Airplane Gearhead
Central N.Y.
Joined Jan 2005
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I know that 4 oz. added to 18% brings you to a little over 20% so you'll have to add...what...about 6oz?

Check out your local motorcycle /snowmobile shop...they should have castor.

I've been told that med. castor is o.k. and then I've had others tell me not to use it, so...rather than risk maybe varnishing up my engine, I looked in the yellow pages and found a place that sells Klotz and Castrol, etc. and went there...
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Old Jul 06, 2006, 12:39 PM
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United Kingdom, England, Hebburn
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Quote:
Originally Posted by The Toolman
I bought some fuel by mistake that is a coupla % low on castor oil, 16%. I want 18-20%, and was wondering if the castor oil at the Rx is the same as they use in the fuel. If so I can just do a little figuring and up the oil content of my fuel to 20% this way.

Thanx,
Ronnie :)
5 ml castor per 100 ml 16% oil fuel will give you 20% oil. If the fuel contains nitro, then the nitro level will be reduced slightly.

Hope this helps,

Pete
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Old Jul 07, 2006, 10:33 AM
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Adelaide, South Australia
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Actually, adding oil doesn't make any difference to nitro level because when you add the oil you displace both the nitro and the methanol so the relative amounts of both of them stay the same. If your fuel had 4 parts of methanol and 1 part of nitro (a 20% nitro mix) then no matter how much oil you add you'll still have that same 4:1 blend of methanol and nitro. This blend is what the engine runs on and is what you tune the needle to get the right amount. If you add oil then you open the needle very slightly to compensate for the extra oil so the same amount of methanol/nitro still goes through the needle valve each cycle.
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Old Jul 07, 2006, 03:59 PM
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Quote:
Originally Posted by downunder
Actually, adding oil doesn't make any difference to nitro level because when you add the oil you displace both the nitro and the methanol so the relative amounts of both of them stay the same. If your fuel had 4 parts of methanol and 1 part of nitro (a 20% nitro mix) then no matter how much oil you add you'll still have that same 4:1 blend of methanol and nitro. This blend is what the engine runs on and is what you tune the needle to get the right amount. If you add oil then you open the needle very slightly to compensate for the extra oil so the same amount of methanol/nitro still goes through the needle valve each cycle.
You're correct in that the ratio of nitro to methanol will remain the same, but if you add castor oil, or anything else for that matter, the composition alters. If the 16% fuel contained 20% nitro, adding 5 % castor to bring the oil to 20% will reduce the nitro to (20X100)/105, which reduces the nitro to just over 19%. May not make a significant difference, but a drop nonetheless.


Pete
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Old Jul 07, 2006, 05:24 PM
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You can put together an Excel spreadsheet to help figure out the mix. I keep a couple fuel formulas on Excel to put together any size batch, starting with a mix of 80% nitro/20% synthetic, methanol and castor. I'll attach an example of 5% Fox Superfuel if I can.
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Old Jul 07, 2006, 05:28 PM
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Sydney Australia
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If you are having problems getting the proper castor just add a bit of synthetic 2 stroke oil compatible with methanol, I use Coolpower. Lots of fuels are available with a synthetic/castor blend of lubricant.

The amount of oil in fuel is high to allow for all the possible tuning mistakes modellers are likely to make. With a modern ballraced engine 16% should be o.k. anyway provided you do not run the mixture too lean. - John.
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Old Jul 07, 2006, 06:56 PM
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The Toolman's Avatar
Lake of The Ozarks
Joined Jul 2006
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Castor oil ??

Thanx all of you guys!!!!
I found what I think will do on the SIG site about the middle of the page. They also have the proper castor I'll need.

http://www.sigmfg.com/cgi-bin/dpsmar...01F.html?E+Sig


Thanx Again,
Ronnie
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Old Jul 07, 2006, 08:30 PM
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Adelaide, South Australia
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Quote:
Originally Posted by JoeHW
if you add castor oil, or anything else for that matter, the composition alters.
It's kind of a tricky point to explain but think of it this way. I mix a batch of fuel using just methanol (to make it simple) with 15% oil (85% of the fuel is methanol) and tune the engine to peak. Now it's got the exact right amount of methanol going through for the correct air/fuel ratio but maybe not quite enough oil. So now I double the amount of oil to 30% (70% is now methanol) and restart the engine. Now it would run lean because there's more oil in the fuel so I open the needle until it's peaked again and the air/fuel ratio is once again correct. In both cases the amount of methanol (the only thing the engine uses to actually run on) flowing through the needle valve is the same. If there was an amount of nitro in the original fuel then the same principle would apply after the oil was added.

You're correct that if calculated in the accepted way then the nitro (and methanol too) content would seem to be slightly less but oil isn't a fuel. Now if you'd added acetone or petrol (which is a fuel) then the nitro and methanol contents would be diluted.

It's only a minor point but too many people risk ruining their engines by thinking that if they reduce the oil content then they'll get more power. They won't, it just means there'll be a little bit more actual fuel in the tank (because there's less oil taking up space) so it'll fly for maybe an extra 10 seconds.
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