I come from a nitro plane background (and electric helis) and have only recently started to get into nitro buggies.
When flying planes I pretty much used FAI mix (4:1) or perhaps 5%-10% nitro and that was it.
Initially I thought buggies could just use the same fuel....
Just as a general starting point for my understanding, can we start of by talking about why different models require different fuels?
Cooling is the main reason...right?
Plane motors are generally going flat out but have good airflow.
Heli motors are generally going flat out but have relatively poor airflow, compared to a plane.
Boat (inboard) motors are very variable in their throttle, have no airflow, but do have water cooling, which is not as good as air cooling?
Buggy motors also variable in their throttle, have reasonable airflow.
So I guess Helis/boats have the most oil, followed by planes, followed by buggies?
Most Heli motors have a ducted fan as part of the system and get plenty of air. I would say way more than a buggy gets. I think it comes down to power requirements more than cooling, A heli engine for instance, needs loads of torque and power, something a high nitro content can help with. I have a guy that mixes the fuel how I want it and I have experimented with different "brews" some of which seem counter intuitive, but my best brew was a 30% nitro content with 15% oil, a mix that did not affect engine life adversly and provided excellent power (mach .28 engines). Heat was never a factor, i was just trying to get the engine to honk harder, nitro was the answer
Right. That makes sense (I forgot about the fan on nitro helis; I only fly electric helis myself). With a heli you want to keep the weight down as much as possible; adding more nitro (within reason) is a good way to get more power without adding any further weight (i.e. using a larger sized engine). Correct?
So, while we're on the topic of flying things, the primary difference between plank and heli fuel, as a generalisation, is that heli fuel contains more nitro to get more oomph without adding any further weight? I know from flying planes that the pilots wanting more oomph with their planks were adding nitro for, for example, pylon racing etc, but generally speaking FAI (0%) or up to say 10% was usually plenty for plank needs.
Still talking about flying things, oil content for me was always 20% castor. I know that some people preferred all synthetic because it was cleaner (didn't make the engines go all brown from burnt up castor oil), some people liked a mixture of both caster/synthetic. Do planks and helis use about the same amount of oil? I'm guessing so.
Moving on to buggies now....I'm reading that buggies use fuel with nitro contents from about 10% - %25. I understand that more nitro gives more top end speed (up to a point obviously; and the engine has to be designed to handle it). Is there any particular reason why a buggy can't run on 0% nitro fuel? I keep seeing these "DO NOT use aircraft" fuel messages - why? It's the oil content isn't it? Too much oil in aircraft fuels? So what's wrong with the oil? I've read somewhere that too much oil in buggy motors can actually increase heat, rather than reduce it. This has me a bit confussed?
Finally - boat motors - what's so special about them?
There will be a certain percentage of castor oil in the fuel, for instance my fuel had 3% castor and 12% synthetic oil. I am no expert on fuel but I do know these vary according to the application, as per my previous post, I believe the nitro is a power thing more than a heat thing, but oil also helps to cool the engine. I chose to run a lower percentage of oil as too juicy of a mix will just sap power, but on the flip side will provide less lubrication and also can affect the cylinder seal, issues which didn't arise for me. Basically, they put the warning on there as a fuel formulated for buggy engine with 18% oil and 25% nitro might not be great for something requiring 20% oil and 15% nitro.
What is the primary difference between Castor oil and synthetic oil?
Castor Oil is a vegetable fatty acid based oil, similar to many other vegetable oil derived oils from the beans of plants.
Synthetic oil can be derived from nearly any source e.g. crude oil, vegetable oils, petroleum wax, pyrolysis of waste materials. Synthetics are termed such due to the altering of the base structure to create a set of molecules that retains advantages or improves on them but minimises the disadvantages of a simply processed oil. Castor Oil would be considered a simple processed oil.
Why use Castor oil?
Castor oil has been used as a lubricant for decades. Its chemical structure allows it to polymerise at high temperatures to form a sticky wax type material often referred as castor varnish. This wax still has lubricating properties. In the event of oil starvation the wax still separates the metal surfaces for a short time.
Why use synthetic oil?
Synthetic oils typically offer high film strength without the wax formation. Wax formation can be undesirable in ringed engines where the wax build up can result in ring sticking which will lead to a ring failure and subsequent engine failure. Synthetic oils also tend to keep the insides of the engines cleaner which results in more consistent combustion.
Can you switch from running an engine on a fuel containing Castor to a fuel containing synthetic? Or vice versa?
Yes, Castor oil is compatible with all Synthetics, especially the Poly glycols and Di-ester types used as engine oils for RC engines. When switching from castor oil to synthetic lubricant, it is not atypical for an engine to pick up rpm as there is less viscous drag with synthetics than there would be with castor oil. What also often occurs is removal of the castor varnish due to the high solvency of the synthetic oils.
Is one oil better to use with a 2-stroke engine? 4-stroke engine?
There is a lot of debate around this question in RC forums, often resulting in the closing of threads because people are really passionate about what works for them. There is also a lot of misinformation around synthetics. When considering an engine oil for an rc engine, the first thing to consider is the mechanical design. Is the engine an ABC/ABL type engine or does it have a compression ring?
If it is of the former type i.e. ABC/ABL, then it is wise to use some castor oil in the fuel. These engines are typically 2 stroke engines. However there are also 2-stroke engines that are ringed engines and this is typically where the debate rages into fisty cuffs and degrades into a “hand bags at dawn” type disputes.
Two Stroke methanol engines are quite tolerant of the lubricant because they are oil lubricated but fuel cooled. In the hot cylinder environment, the fuel evaporates leaving the lubricant behind to do its job. This lubricant needs to be able to separate the ring from the liner effectively. You will be surprised to know that with a ringed engine the type of oil is less critical because the lubrication comes from the ring riding an oil wave much like a water-skier being pulled over water.
This is called hydrodynamic lubrication. In ringed engines, the oil can escape behind the ring resulting in effective oil flow under ring to maintain that hydrodynamic wave. In an ABC type engine the oil is pushed away along with the piston, also hydrodynamic but the distribution of pressure in the oil is different. In the ABC type engines, the castor is beneficial here since its highly polar nature allows for it to cling very strongly to the walls of the cylinder ensuring you have that one layer thick oil film to provide separation.
Four strokes are typically ringed engines so the above applies to them as well. However we also need to consider where that oil feed comes from; the top of the piston or is it recirculated oil?
Now we know that 4-strokes draw fuel and oil in from above so lubricating the bore below the piston crown is tough. Hence it is even more important to use an lubricant that can flow past the compression ring i.e. an oil that does not get continuously more viscous and forms wax, but one that is stable under increasing temperature and pressure. Synthetics meet that need. Some 4 strokes recirculate the lube oil and reintroduces the oil via the crankcase. These are a little more tolerant of different lubes but essentially high quality stable viscosity oil is best.
Some people have argued that Castor oil is better than synthetic oil. Historically this argument stems from the manufacturing process of rc engines. Why is this?
If we consider the demographics of the RC hobby, I think you’ll find it s is mostly 40 to 60 something’s who are most active. When these folk started in the hobby, manufacturing techniques where not dominated by CNC (Computer Numerical Control) machinery but by manned lathes and mills. Engines were mostly cast and liners were not very accurate. These components were not “close fit” as they are today. The use of castor oil would result in a varnish layer on the components that effectively took up some of the tolerance and provided sealing and hence compression.
Today engines are not made this way. CNC allows millions of components to be produced within a very tight tolerance and very little deviation of dimensions from the intended specification. Modern Rc engines being close fit, actually benefit from as little varnish as possible coating engine parts.
The other dogma driving castor oil is that somehow some folk have it in their heads that castor is still in widespread use today in automotive lubricants. This is simply not true. Although vegetable oils are continuously being developed and reviewed for suitability, they see less than 1% volume use in modern motor vehicle engine oils.
Castor blend fuels often coat the inside of an engine with what is called a ‘varnish’. What is this and is it bad?
The castor varnish is essentially a polymer of castor formed by the oxidation of the castor oil. It still has lubricating properties hence people feel that this is a good thing. However in modern engines where tolerances between parts are much finer, the buildup of castor varnish can lead to a degradation in engine performance.
What is one benefit to using Castor?
It is fairly easily available over the counter and it lubricates well enough.
What is one benefit to using synthetic?
Synthetics oils tend to be more thermally stable at the operating temperatures of RC engines and they don’t leave residue behind in the engine.
Is mixing your own fuel recommended for a beginner?
Unless one can ensure a reliability of supply and quality of the components, I would advise against home blending. Varying fuel quality will lead to constant fiddling with mixture settings when what a beginner needs is stick time, not needle time.
What is the best fuel advice you can give to a beginner?
Pick a reputable brand and learn to work with your engines on that brand. Ensure that you keep Nitro, and oil content constant in the fuels to minimise the variables when tuning the engine. It matters not whether you opt for fuel with a little castor, a lot of castor and or full synthetic, just keep using the same fuel blend until you are comfortable with understanding your engines “moods”.
Q:Why use more nitro or why not...
A: Nitro is a fuel that caries its own oxygen, that is where the power comes from. You need to richen up the high speed needle if you run higher nitro contents since the fuel caries its own oxygen, you can burn more fuel and create more heat. The proper nitro content for an engine largely depends on the compresson ratio and to a lesser extent the needle settings. If your engine is not compressed for example 30% nitro, you can still run it and realize a gain in performance if you can control the detonation and excess heat. Richening up the needle to keep the heat inside its range will help you control detonation, but you may actually be chasing needle settings and be back to the performance of a lower nitro fuel. If you are going to run more nitro than what is recommended by the manufacturer, start off with the next higher nitro blend and see if it can be tuned to your engine. If you absolutly have to run more, and your engine is running unacceptably hot and/or detonating (frying egg sound) then add a head shim to lower your compression ratio.
Q: Effects of nitro content...(question from a buggy driver)
A: More nitro in the fuel means more heat produced which means more potential power. Since you are actually packing more fuel into the combustion chamber with more nitro (hence the richer needle settings) you are doing a couple things: creating more heat and burning more fuel which equates to shorter run times on a given tank of fuel. Higher nitro fuels may need a different glow plug, the higher the nitro the cooler the plug needs to be so the fuel is not pre-detonating before the piston is at top dead center causing detonation and ruining rods and melting down pistons. You may or may not need a different plug depending on how you tune the engine and how the engine is compressed.
Q: Effects of oil content... (question from a buggy driver)
A: Oil is Life Insurance for your engines! Although most car & buggy engines run just fine on very low oil (usually under 14%), more oil will never hurt anything. Oil does two things for your engine- it lubricates and it carries away heat. When oil content is reduced to enhance top end power (less oil means more burnable components), proper break in and needle settings become critical. When an engine is leaned out for performance, you are actually supplying your engine with less oil and creating more heat. Thats fine untill you get to a certain lean point where the heat is too high and their isn't enough oil to keep the engine from rapidly accelerating its wear or coming apart. Not enough oil between moving parts (primarly the piston and sleeve and rod journal) will cause the metal parts to actually be scrubbing against each other. Don't run it too lean and run at least what the manufacturer recommends for oil contents, even more for break in is fine. I have found that a fuel containing significantly more oil than the average buggy fuel runs just fine in buggy engines and they last a long time. Competition drivers will probably want the low oil high performance fuels but for the average sport driver the higher oil contents run great.
(This was from a buggy guy, but it applies to all ABC Type engines) Q: Engine temp...
A: Engine operating temprature is dictated by design type. Car/buggy engines are of ABC or ABC type construction. this means that there is an Aluminum piston riding in a Brass sleeve that is Chrome plated. ABC engines are of an interference fit, the cylinder sleeve is actually tapered so the piston pinches the further up the sleeve it travels. With ABC engines, you get excellent compression as long as you can maintain the tight tolerences. These engines are designed so the top of the cylinder sleeve expands faster than the piston itself so the fit is optimal at operating tempretures. The engine needs to come up to tempreture real fast in order for the sleeve to properly expand to acheive optimal fit, otherwise the piston will be wearing real hard against the sleeve and the precision fit will be lost and the engine will lose most of its compression and performance. The sleeve will start expanding to design peramiters at around 230 degrees F. Anything less the piston will be scrubbing hard against the sleeve and rapidly wear the piston and sleeve which will loose that nice tight compression. When running your engine, keep the engine at least 230 deg. Your engine will last much longer and give more performance.
Q: Needle settings...(from a buggy driver, applies to all ABC type engines)
A: When breaking in an engine, put the needles where the manufacturer recommends and use the nitro & oil content they recommend for break in. When needling an engine, never let your ABC engine run blurbbry rich- that does not allow the piston and sleeve to heat up. As far as needle settings go, when running at high speed if the engine sags or looses power you are too lean, you must richen it up some. On the other side if your engine does not clean out and is stumbling at wide open, lean it a touch. Off idle response after break-in should be crisp and even. If your are getting a slow spitting or stumbling type of acceleration you are too rich on the idle mixture, lean the idle mixture an 1/8 turn until it cleans out. If your getting a sagging response off idle where the engine sounds like its starving for fuel it is too lean, richen idle mixture about an 1/8 turn. It is important to make mixture adjustments a little at a time, especially on the idle side. Never try adjusting a carburator based on how it runs when its not to operating tempreture- you'll be chasing the needle settings all over the place. Weather changes have significant affects on the needles, changes in weather may require you to adjust the needles.
Q: Tuned pipe info...
A: Tuned pipes allow the exhaust pressure waves to actually suck more fuel mixture into the combustion chamber and scavange more exhaust out while the exhaust port is still open. Tuning the length of the pipe and having the correct volume are essential for maximum efficiency. Numerous variables have to be taken into consideration such as: engine, gear ratios, torque band
your looking for (high end, low end or mid range), type of racing or runing (or type of flying). It is sometimes best to follow the engine manufacturers and pipe manufacturers instructions for tunig a pipe to your application.
Q: Why coil the pressure line on car & buggy engines...
A: I can not think of one valid reason why. Some prominate "Car" expert probably did it just to see if everybody else would follow. Or it could have probably been cooked up by the fuel tubing manufacturers. Just my opinion. (a little humor here folks)
Q: What about break in for my car engine...
A: NEVER NEVER run your engine so rich it hardly runs. This will do more damage to ANY ABC engines piston to sleeve fit than you want. It is critically important to get that engine up to at least 230 degrees as fast as you can to minimize that wear, even on initial start-up. Do not let the engine sit and idle for the first tank. Start it up, bring the speed up (not necessarly wide open), get the temp up and get the needle to where it will hold that 230 degrees. Run your engine in short runs of 2 or 3 minutes for the first couple of tanks with letting the engine cool down completly between runs, this heat cycles the engine and makes for a longer lasting engine. You should run at least the amount of oil in your fuel that the manufacturer recommends for the first quart or so, you can even run more oil than what is recommended for break in, it will only allow your engine to last longer. Before starting your engine for the first time, take out the plug and put in 2-3 drops of oil and do the same thing down the carburator- this gives your engine some additional initial lubrication for its first startup. Always run a fuel filter and an air filter.