yakfish

My Feedback: (27)

I am in the research stage right now considering making my own home brew nitro fuel. I would like to hear some veiws and opinions about nitro and oil content. what are the pros and cons to higher/lower nitro %. I have always run 20% O'Donnel race blend in my cars since that is what my hobby shop carries and it has never given me a problems but I would like to know if I should change the blend once I start making my own fuel. I have seen people running car fuel with a little as 12% nitro and as high as 40%. Any imput will be appreciated.
Thanks

1QwkSport2.5r

Well, I'll give you my take on the subject. I've been using my own homemade fuel for a year now in car engines and airplane engines. I have almost always ran 20% nitro 12% oil in my car engines. I dont race, so the "speed blends" that use 10% oil or less are not for me. The more nitro you add, the faster the engine will consume it. Most car engines will run fine on 10% nitro up to 30% nitro, with a little less performance on the lower nitro content. Being that Nitro is right around $50 a gallon, a homebrewer will want to keep this in mind. A gallon of 20% nitro fuel will need 25.6oz of nitro. Drop down to 10% nitro and you only need 12.8oz. You just went from making 5 gallons of fuel from 1 gallon of nitro to 10 gallons. Less nitro often requires a hotter glow plug to keep the idle relatively stable.

So.. Nitro is expensive, use what you need to if you're just into backyard bashing. 10-15% is more than enough unless you want a little extra kick.

Next decision is oil.. What to use? Depending on what your'e willing to spend, there's three options. All castor which is $23 a gallon + shipping, Synthetic/Castor blend (Klotz Super Techniplate for example) is $47.12 a gallon, and lastly is pure Synthetic which is (Klotz techniplate as an example) $48.34 a gallon.

Synthetics run cleaner because more of the oil burns. For the advanced tuner, this isnt a big deal because you'll keep the mixture a tad richer. Synthetics do not give the lean-run protection Castor oil does. A very good product, but one must be a little more careful with it. If using all synthetic oils, you must use an after-run oil to prevent rust and corrosion inside the crankcase!

Castor makes a bigger mess since most of the oil is simply blown out the exhaust instead of getting burned. Castor oil also "sticks" to metal better, provides superior lean-run protection, and requires no after-run treatment to prevent corrosion. Downsides with castor is its thicker, so in colder climates the fuel may thicken slightly. Not a real big deal if the fuel tank is behind the engine because the head from the engine will keep the fuel somewhat warm. I run engines in the winter all the time and I've never had a problem with fuel flow. Also, Castor oil tends to make the fuel foam up a little more in the tank. I use a squirt or two of Armorall Original to keep the bubbles at bay.

Castor/Synthetic blends kinda give the best of both worlds. The fuel will burn cleaner than all castor, and at the end of the day will not need after-run treatment usually. If storing for long periods of time, run all of the fuel out of the engine and give a good dose of ARO as a precaution if you wish.

For the simple cost of it, I use all castor oil. Its cheap, gives great after-run protection, and it smells better. My car engines run better and longer on my homebrew fuel than they did on store-bought fuel.

Some synthetic/synthetic blends have defoaming agents in the oil so any extra defoamers may not be needed.

At the end of the day, a gallon of 20% nitro/12% oil costs me $10-12 less per gallon than buying it premixed. My airplane fuel (5% nitro 20% oil) is even less, roughly $20 a gallon cheaper.

Methanol and Nitromethane are dangerous. One must exercise caution when mixing fuel - any static spark can start a fire. Alcohol fires are almost impossible to see so mixing inside a building is not advised. These 2 chemicals also evaporate very quickly which increases the risk of fire that much more. You must be careful. Aside from all of this, its nice knowing what exactly is in the fuel. You can custom mix a quart to test out (maybe more nitro or a little less oil for example) or just make a gallon at a time. Its fun for me.

yakfish

My Feedback: (27)

Thanks, lots of great info there. I also like the idea of knowing what is in the fuel I am using that and the ability to keep cost lower are the 2 main reasons I am looking into this.

I was also going to ask about the glow plug but you have already answered that for me. When changing nitro/oil contents do you need to adjust the head spacing (compression) by either adding or removing a shim?

Thanks for the help!

1QwkSport2.5r

Nope. Car engines are usually shimmed for right around 20%, sometimes requiring a shim for 30%. I don't run that much nitro, it's just a waste for a basher rig. If you really wanted to go cheap, you could modify the engine to run zero nitro to have the same performance as 20% nitro. This requires milling the sleeve and the head though.

I also use the same glow plug from 5% nitro up to 20%. McCoy mc59.

yakfish

My Feedback: (27)

Ok...so I on't have to change anything on the engine to run less nitro? I heard it was reccomended to change the head spacing when going to 30% from 20% so I assumed it would be the same if going with less nitro as well. I want to try using 10-15% and see how that runs in my engines. I have been using MC-59 plugs as well for most of my engines. so I guess that won't change either.[8D]

Do you get your nitro, oil and methanol lacally or do you have to order it all online? how is shipping for these chemicals? are they considered hazardous materials? I would like to try and find them locally but I really don't know where to start looking for them?

Thanks again for all your help!

downunder

Milling (or skimming) the top of the sleeve to help raise compression isn't really a good idea because the thickness of the flange can be considered to be a strengthening rib to help keep the top of the sleeve round. Engines will run just fine even with zero nitro and stock compression but stock compression is way too low to take advantage of the compression that methanol can handle. This just means that the fuel isn't being burnt as efficiently as it could be and that's one of the reasons for less power on low or no nitro. The best (just about only) way to raise compression to high levels is by machining away the sealing area of the head/head button to get the head closer to the piston at TDC. But not too close . Some engines though need more machining than just the sealing area, it all depends on the initial set up.

yakfish

My Feedback: (27)

Most of our car engine come with shims installed between the piston sleeve and the head button. you can then add or remove a shim to either raise or lower the compression ratio without having to do any machining work.

1QwkSport2.5r

You have to understand a few things when dealing with head shims. First off, just taking a shim out (say you have 1 .1mm shim installed for 20% nitro) will change your head clearance. Head clearance is the space between the bottom of the head button/head (the bottom of the squish band) and the top of the piston. If you pull the shim out and the head clearance is too small, the piston can hit the head/head button. One must measure the head, cylinder with piston at TDC, and factor in the shim to determine head clearance.

Take a Traxxas 3.3 for example. The stock shim is .011", and the head clearance with shim installed is .014". Take out the shim and you get .003". This is the bare minimum head clearance you should have. Now, with the shim removed, the compression is raised, but not a lot. I figured one of my 3.3 engines to have 9.63:1 compression (effective, not geometric) with the shim installed and 12.1:1 compression with the shim removed. Some engines must have a shim installed to maintain the proper head clearance, with some cases having less than .003" clearance. You can just pull the shim out and run it but without knowing how much room between the piston and head you have, you could wreck the engine. Get a Vernier caliper if you dont have one. They're a valuable tool when dealing with model engines. Determining compression ratio is easier with a small 1/2cc syringe.

I do not bother taking Geometric compression into account, only trapped compression or effective compression ratio.

Nitromethane and Methanol are hazardous. I buy Methanol locally, and I ship in the oil and Nitro. Some places dont charge the hazmat fees for nitro and some do. Shipping in quart bottles usually thwarts the hazmat fees. Look up Torco Fuels on Ebay. The last time I looked, a gallon jug of 100% nitro was $42 with free shipping. Yes, I said free shipping. I got my nitro in a 80/20 mix of 80% nitro 20% methanol for $13.50 a quart from FHS Oil Supply company. I will use the Torco stuff next time I order nitro.


Downunder: I stand corrected on machining the top of the sleeve. I figured taking a small amount off the head and sleeve would leave a little more meat on the head for sealing and thermal transfer. Isnt the ideal compression ratio for zero nitro fuel somewhere around 13.5:1 to achieve similar performance to using 20% nitro?

downunder

That's something of a minimum compression ratio (geometric, not trapped) which I determined many years ago by making a special cylinder head on an Enya 60X then checking the revs as I increased the compression. Original compression was 8.75:1 and revs kept increasing as I raised the compression until there was no more gain after 13.5:1 but all of this was done with the same hot plug. Further increase in compression should have been possible by going to a colder plug which would retard ignition (raising compression advances the ignition) but I'd done what I set out to do so never experimented with colder plugs. Theoretically, methanol can handle (geometric) compressions of at least 17:1.

As you've said though, it's necessary to do some very careful measurings before trying to raise compressions because you must know exactly how much clearance there is between the head and piston and exactly the volume of the combustion chamber plus the clearance volume to get a starting point. I put these figures into a spreadsheet and then I can use the spreadsheet to do some theoretical machining which shows what the compression and squish clearance will be if I machine any amount off the head.

I'm curious about your trapped compression figures though because they seem to be way too high. Are you only using the volume of the combustion chamber bowl in the head and not taking into account the volume of the squish clearance? Squish clearance volume is part of the total combustion chamber volume so I'd have expected your shimmed trapped compression to be more like 6 or 7:1.

1QwkSport2.5r

It seemed high to me also, but I measured it twice. I used a 1/2cc syringe to measure the volume of the head button. I got the head clearance by measuring the distance from the piston at TDC to the top of the liner. I subtracted the head button protrusion and shim separately and subtracted that from the piston to top of liner measurement to get the squish band. Adding the squish band to the head volume gave me the total head volume. I used the formula head vol. + swept vol. / head vol. I'll remeasure it for the heck of it but I believe it to be pretty darn close. The engine I measured was used so I am not sure if it had the original shim or not.

downunder

If that's the formula you used then it's geometric compression (which is what I use) so your figures would be what I'd expect.

1QwkSport2.5r

Yes, but i measured the effective stroke having the ports closed. Perhaps I used the wrong term. I determined both geometric and effective ratios but I only care about effective compression since that's the ratio the air/fuel mixture is being compressed.

downunder

I've just reading back on some engine tests where the tester (Peter Chinn) gives figures for both geometric and trapped compressions to give an idea why I was surprised by your figures. Not having a shot at you here, I'm just trying to be helpful in case something got overlooked. For instance, when you used the syringe did you fill right to the outer edge of the squish band? Most of them are tapered so take quite a bit extra to fill other than just the bowl itself. Anyway, here are some of the figures I found with geometric first then trapped and the final figure is when the exhaust closes ABDC. The closing figure is important because the higher timed the lower the trapped compression will be compared to geometric.

Super Tigre S61H...11__8__74
Super Tigre S75....10.8__7.6__75
Enya 60X....11__8__72.5
Fox 78...12.5__9.2__72.5
OS Max-40PS...12__7__93

The first 4 engines are all very much the same with a difference of about 3 between their two types of compressions and all with similar exhaust timings. The interesting one is the OS which in this case happens to be an all out racing engine with very high timing giving that difference of 5 between their compressions. Also it's designed to run on zero nitro which would make it seem that the 12:1 compression is lower than it could be for methanol but it's also designed to be run only with a full length tuned pipe which supercharges the cylinder so gives a much higher effective compression.

I guess I should add that all the above engines are around 30 years old and compressions on more modern engines have been lowered a bit since then being more like 9:1 (geometric ) or thereabouts.

1QwkSport2.5r

The engine in question here is a .20ci car engine. The squish area is not tapered. I put a rule across it before I filled the combustion chamber in the head. This engine turns over 35k on 20% nitro. I haven't had time to remeasure the engine, but the numbers I got from the second go are 12.72 geo, 9.63 trapped, exhaust closed 82. It's got a 19 degree blowdown.

Effective volume (ports closed) .146971ci
Head + squish = .017023ci
Geometric volume = .199633ci

I'll tear the thing apart and double check the head and squish volume.
The .15 cousin ( same mfg) to this .20 has a geometric ratio of 10.53 and effective ratio 8.79 and exhaust is closed at 75. 17 degree blowdown. I'll post back tomorrow after I double check the .20. I want to make sure I'm accurate.

downunder

Fair enough, I can't see anything wrong with the way you're doing it so the compression should be as you've measured it. It's quite high for a standard engine so it should run very well on zero nitro .

1QwkSport2.5r

I have my doubts so I will recheck it and do it a little differently. I think what I'll do instead is put the piston at TDC and with the head on fill the chamber with alcohol to the bottom of the glow plug hole. This will be more accurate, I think.

This engine has gobs of power, that is when the carburetor behaves. I think a better carburetor would give it better tractability.

1QwkSport2.5r

It isnt very often I quote myself.. Anyway I did a recheck of my .20ci car engine and using a much smaller syringe (1cc in .05cc increments) and using oil instead of alcohol or water I got exactly .2cc for the cylinder head only. Water and alcohol have too much surface tension, the oil doesnt.

This equates to .012204ci for the head, and the squish band of .004819ci. Same numbers I posted above. Its for real, as surprising as it is. The little .15 isnt as high, though they market the .20 as "60% more peak power".. I suppose dropping the compression with another shim using the same fuel might give a few more rpm/top end power?

I wish there was a way to stick a prop equivalent to the load of a car's drivetrain to find out what rpm these car engines really hit. I dont know if I trust my Telemetry in my radio and I dont think my prop tach will work on a car engine's flywheel. The crankshaft doesnt have enough of a threaded portion to even stick a 7-8" dia. prop on it.

downunder

The only relatively simple way to know how many revs a car engine actually turns on the track is a method I used with my son's car. I took a video of it then played back the video on my computer and recorded the sound. Then I ran the sound through a program (Goldwave) which showed the actual waveform. The screen grab below shows this waveform after slowing it down 100x and now the individual exhaust pulses can be seen. What's kind of neat is that by playing it back 100x slower the pulses sound a bit like flub...flub...flub.... Now looking at the screen grab and starting with a pulse that lines up with the .03 second mark and counting the number of pulses to the .07 second mark (where a pulse lines up again) there's 19 pulses in that .04 second duration or 1/25th of a second. So multipying the 19 pulses by 25 gives 475 per second which is 28,500 per minute. On another recording down the main straight his engine was turning 36,000 revs. This was with a Mach 28 engine on 80/20 all castor fuel but with compression raised to 13.4:1 in a Hyper 7.

1QwkSport2.5r

I'll look into that software. Definitely a higher-tech method than the norm, but not the instant gratification I was hoping for... I have a few other ideas I'm going to try when I get time. New family and work constraints will be limiting my free time for awhile, so this will have to be on the back burner for now.

Did you just machine the head on that Mach .28 engine?

Sport_Pilot

If you are racing use as much nitro as allowed. If not, use as much as you enjoy.

yakfish

My Feedback: (27)

I have ordered the nitro from torco fuels. 1 gallon for $49.50 shipped. A gallon castor oil I ordered from fox manufacturing for 24.00 shipped and I will get the methanol here locally for 2.69 per gallon. so I buy 5 gallons of methanol I will have enought to make 7 gallons of fuel for $86.95 or 12.42 a gallon! that sure beats spending $30 a gallon at the hobby shop!


if I was just to mix it all together I would have roughly 16.xx% nitro and oil content. but I plan to experiment a bit with different mixtures.

yakfish

My Feedback: (27)

I started mixing today! I pulled out an old airplane that has been collecting dust in the garage for a couple years. I wasn't enen sure if it ran or not. but I mixed up a blend 10% nitro, 20% castor and it stared right up! the plane needs some work before it can fly and I need to practice with it some also but the engine runs!

Then I fired up my Mugen MBX5T with a LRP Z.28 Spec 3. I had about half a tank of the 20% O'donnel race blend that I have been buying from the LHS left in it so I ran out the last of that fuel so I could get a comparison to my own 15% nitro 8% castor blend. it ran great! had lots of power. More than I expected out of just 15% nitro! It did seem to be on the rich side too so I need to tweek the tune just a bit. The LRP engine manual actually calls for 25% nitro so I might try to mix a quart of 25% and see how that runs. but I will save more money if I stick to a lower nitro content.

This is really cool mixing my own fuel! I should have started doing this years ago!

Thanks for all the help over the past few weeks!

1QwkSport2.5r

My engines seem to have more power on my homebrew fuels too. My Mach 427 LST2 would wheelie on 25% nitro storebought fuel, but not 20%. On my 20% homebrew, I get wheelies. Kinda odd, but cool nonetheless.

The castor will make more of a mess, but running only 8% oil, it probably wont be a real noticeable difference. I run 12% oil in my engines which is probably overkill, but they seem to like it.

yakfish

My Feedback: (27)

I also noticed that there is quite a bit more smoke and the smoke seems to linger. Where as before with store bought fuel that used sythetic oil the smoke would quickly dissapate. 8% oil does seemsto be a bit on the low side I might go with 10% next and see how that works. The O'Donnel race blend I was using only had 8% synthetic oil in it which is why I went with just 8% with this blend. I need to get new batteries for my temp sensor I am curious to see how warm the engines get on this homemade fuel. I am going to tweek my tune tomarrow I am expecting to see at least equal permorance compared to the store bought 20% fuel. tongiht the engine did seem a little more sluggish from a dead stop but top end seemed nearly the same. But I think it will be just as snappy once I lean it out just a bit.