Understanding Your Engine...
The first and foremost consideration when attempting to tune your glow engine is understanding the basic parts and their functions. By understanding the fundamentals, you can better tune your engine for maximum performance while at the same time, expanding the life of your engine.
Carburetor
The carburetor is the mechanism that mixes fuel and air in very specific proportions and passes it on to the engine through the vacuum intake. The natural operation of the engines causes of flow of gases to pass through the engine (through the carburetor) and out the exhaust manifold and on to the pipe or muffler. The exact mechanism for this is unimportant for the scope of this tutorial, however it is important to realize that air and fuel pass into the engine by this vacuum method. Depending on how you adjust your carburetor, you can either adjust how much of this gas/air mixture reaches the engine and to what proportion of gas to air passes on to the engine. By reducing the amount of fuel per volume of air, you are making the mixture "lean" and by increasing the amount of fuel, you are making the mixture "rich".
The two types of carburetors are slide and barrel. The old-style barrel carburetors still dominate the market because of their simplicity in design and because of the tendency for designers to hang on to legacy design. These have been around since the beginning of glow-fuel planes. They control gas/air flow by rotating a barrel with a hole cut in either side that allows varying amounts of gas/air mixture to flow through the carburetor as the hole opening enlarges to the venturi (air shaft down the center of the carb body).
Idle-Speed Adjustment
This is the most basic and easy to understand part of tuning your carburetor. This spring-tensioned screw limits the closure of the barrel aperture. Although this doesn't affect the mixture of the fuel it does affect the idle speed. The more closed the aperture is, the slower the idle, the larger the aperture, the faster. As you close this aperture up and the idle speed decreases, you will eventually (sooner than later) stall the engine out. In order for the engine to run, it must have enough inertial energy built up in the engine and flywheel to carry it through the entire ignition cycle. Generally speaking, you want to adjust this down to the slowest idle, just before it begins to stall.
Low-End Mixture Adjustment
This adjusts the fuel mixture at or near idle. Some engines lack this low-end mixture valve for reasons of simplicity, however this makes accurate tuning difficult.
For barrel carbs, this mixture valve is generally found where the throttle-arm pivots. Some are countersunk, others are clearly visible from the outside. On slide carbs, they are generally found on the opposite side of the carb from the throttle slide shaft (has an accordion billow type rubber boot over it) next to, but below the fuel-inlet and high-end mixture valve.
High-End Mixture Adjustment
Also known as the Main Needle adjustment, this is the primary fuel mixture adjustment. This is generally found on the top end of the engine, typically next to where the fuel line goes into the engine. Some are flat-head screws like the low-end mixture, others are hand adjustable valves.
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Tuning Basics
It's important to understand that there is a reputation for glow-engines to be difficult to tune. This is a common error in thinking. With a little bit of know-how, tuning a glow engine can really be a simple, pain-free process. People that don't properly understand the basics can easily become frustrated by what should be a simple, straightforward process. Here's how you do it:
Dialing it In
For the purpose of this tutorial we are going to make some basic assumptions. First, we're going to assume that the rest of your car or truck is properly functioning and that you have everything ready to go. Second, we're going to assume that you are able to start your engine and that it at least runs for a second or so. If you can't get your engine to even start, then go back to our Engine Troubleshooting section before continuing on.
The first place to start with dialing in your engine is to make sure that you have your idle-speed properly adjusted. Your engine manual should give you specific instructions on setting the aperture gap to the minimum size. It's important that we get this resolved before continuing on. If your engine can't get enough air/gas flow then it won't start/run. A clockwise rotation opens the aperture and increases the idle RPMs, a counterclockwise slows it down.
Second, you should tune the low-end mixture valve. This is done before the high-end (main needle) adjustment because an improperly adjusted low-end can affect the high-end performance. Like most mixture valves, clockwise rotation will "lean" the mixture and a counterclockwise will "richen" the mixture.
To determine whether the low-end mixture requires tuning, allow the engine to warm up completely, and then allow it to idle, uninterrupted for one full minute. If the engine continues to run after the minute is up then your low-end mixture is correct and you're ready for the high-end adjustment. If it dies on you then there are two possibilities; either you are running too rich or too lean. To determine which is the case you must listen for how the engine dies in its idle test.
If the engine's RPM's rev up at the last second and then the engine dies than you are running too lean. To correct this, turn the low-end mixture screw counterclockwise (out) 1/8 of a turn (always make adjustments in 1/8 turn) and retry the idle test.
If, on the other hand, it begins to wind down and you notice a change in how the exhaust sounds in the last few seconds, then your engine is running too rich. To correct this, turn the low-end mixture screw clockwise (in) 1/8 of a turn and then retry the idle test.
Once you have passed the idle test and are able to idle for one full minute (after first warming the engine up, of course) you are ready to continue on. You may have to repeat the above process a few times until it is properly set. Remember, only adjust the screw 1/8 of a turn. It's far too easy to go too far with the adjustment. Setting changes don't always take effect immediately. You may have to run your engine for a few minutes for the full effect to take place.
Now that you have dialed in your low end, any carb mixture problems can be isolated to the high-end (main) mixture adjustment.
Acceleration is the tell-tale sign of how to tune your high end. If you hit the throttle and it takes off suddenly but then suddenly dies or loses power then you have your main mixture set too lean. Try backing (counterclockwise) the main mixture needle out 1/8 of a turn and retry. If it bogs immediately when you hit the throttle (sounds like it's choking), then it's most likely running too rich. Try leaning the mixture out by screwing the main mixture valve in (clockwise) 1/8 of a turn.
The more accurate way of really dialing in the top-end is to take the engine's temperature. A properly tuned engine should run between 210?d 220?hrenheit. This can only really be ascertained by using and infra-red thermometer such as the type used by automotive mechanics. On-board or direct-transfer types that measure the heat from the head are inaccurate because, assuming the head is properly dissipating heat, it would reflect a lower than accurate temperature as a majority of the heat energy would be dissipated from the exposed surface of the head. By "looking" at the temperature near the core (actually, area immediately surrounding the glow plug) the temperature can be more accurately read.
The cheap but easy alternative would be to drop a bead of water down the head on the glow-plug and see whether it boils off. If it slowly simmers than it probably is running right around 212?If it boils to quickly then it's probably too lean and needs to be richened. If it just sits there and doesn't boil at all, then its running too rich and needs to be leaned out.
An engine that is running too lean will run hotter and exceed the 220?gree limit. This can significantly reduce the life of your engine. Although it may be tempting to run your engine as lean as possible (does give a short-lived performance boost), this should only be done if you are very wealthy and like swapping engines out every race. There is no quicker way to kill and engine, honest. This is simply because as you lean the engine out, it gets less fuel to the engine, and more importantly, less lubricant. Since glow fuel is the only means of lubrication for your engine, the lack of it means certain death to your powerplant.
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A few final do's and don'ts...
Give your adjustments time to take affect. Remember that most adjustments won't be immediately noticeable. You need to drive your engine through it's full range for at least a minute. Make sure you make adjustments in 1/8 turn adjustments only!
Always run on the rich side. It's far better to take a slight performance hit than to turn your engine into a paper weight. Running too lean may give you a temporary thrill, but it's short lived. Your engine must get the proper amount of lubrication at all times.
Changes in temperature affect your tuning! Whenever the outside temperature changes you will most likely need to re-adjust your engine. Warmer temperatures require a leaner setting where colder temperatures require a richer setting.
I hope that this info gets you on the right track. If all fails, it's always a good idea to get expert advice from the vets down at your local track. However, be aware of the guy that's too eager to give you advice on how to get that extra performance boost out of your engine. Unless he or she plans on buying your next engine, I would be weary of any such advice.
Good luck!
Traction Issues
Overview:
Somethings in life transcend scale. Dealing with traction (or as most people refer to it, hookup) in racing is one of them. The same problems (well, most at least) seem to apply to scale r/c cars just as with their grown-up counterparts.
Anyone who has ever raced a serious r/c car knows that traction is one of the largest obstacles to overcome. Choosing the right equipment for any particular track and environmental conditions is not as easy as it may seem at first. Any of the following can effect traction performance.
Track Conditions
racing surface type (from pavement and concrete to gravel and mud)
operating temperature
other environmental conditions (including rain, oil, dirt, etc)
Tires
makeup of tire's compound
traction pattern and width of tire surface
pre-heating tires
Drivetrain
4WD vs. rear wheel drive
side-effects of slipper spur gears
differential types (one way, ball, bevel gear, etc.)
Suspension
shocks (including spring and oil viscosity weights)
camber and toe adjustments (both rear and forward)
chassis rigidity
center of gravity
wheel-base
Radio Control Nitro
By Steve Pond
PAGE ONE (ONE)
The technology of glow plugs escapes most of us. Sure, we all know that our nitro engines need them to start and to run, but beyond that, we don't know much. Glow plugs are, in fact, a critical part of the whole performance picture.
To help shed some light on the technology of glow plugs and for some practical information concerning their use, I consulted a few of the most knowledgeable people in the industry.
The roster of experts who lent their knowledge to this piece includes Howard McCoy of McCoy Racing, Jerry Conley of Wildcat Fuels and Alberto Picco of Picco Mfg. They all have extensive knowledge of glow plugs.
WHAT IS A GLOW PLUG?
A glow plug is the ignition system for your nitro-powered RC vehicle. Instead of a spark-ignition system such as those found in automobile engines, the remarkably simply glow plug is what we use to ignite the fuel in our engines. It doesn't have a single moving part or adjustment; its only functioning component is a simple, stationary coil of wire.
All glow plugs are not created equal. The housing, wire element, type of plating and hole size determine the relative temperature range of a glow plug.
HOW DOES IT WORK?
Starting an engine is one of the functions of a glow plug. When a glow igniter is attached to a glow plug, it causes the glow plug's coil to "glow" white-hot. This ignites the air/fuel mixture in the cylinder when the engine is started. Once the engine is running, the heat generated during compression and combustion keeps the glow plug's element hot enough to continue igniting the fuel mixture on its own without the help of an external power source. In the simplest terms possible, that's how a glow plug works.
WHAT IS A TURBO PLUG?
Glow plugs are available in two configurations: standard and turbo. Most engines come with a standard plug. They feature a straight, threaded housing that threads through the cylinder head into the combustion chamber. Turbo plugs feature a different type of housing; the end that goes into the combustion chamber is tapered. The tapered end mates with a head that is specially designed for use with turbo plugs. The head is also tapered to accept this type of plug. The supposed advantages are less compression leakage around the glow plug and less disruption of the combustion chamber. The hole in the cylinder head that exposes the glow plug to the air/fuel mixture in the cylinder is much smaller, and there are fewer rough edges to create unwanted hot spots.
The turbo plug on the left uses its tapered housing to seal it to the cylinder head. The standard plug on the right uses a copper gasket.
There are specific racing rules for using turbo plugs. Currently, only .21ci (3.5cc) engines are permitted to use turbo plugs in competition. You can certainly use turbo plugs if you are not racing; that's a matter of preference. The prevailing wisdom, though, is to stick with standard plugs whenever possible. They are more widely available than the hard-to-find turbo plugs, and they cost less.
WHICH TYPE OF GLOW PLUG SHOULD I USE?
OK; you've blown the glow plug that was included with your engine, so it's time to get a new one. Which one do you buy? You could try to find the same plug, if information about its brand and type was included with your engine. More likely, you will have to choose from the brands and types of plugs that are available at your local hobby shop.
What makes the subject of choosing a glow plug a little confusing is the variety of types that are available. Each manufacturer offers a range of plugs, from as few as three or four up to 10 or more. A plug is usually identified by a code that indicates its effective operating temperature; not the operating temperature of the engine or the outside air, but the relative temperature of the glow plug's coil. Each manufacturer has its own unique temperature-rating system, and general application recommendations are sometimes included to try to steer consumers toward the correct plugs for their needs. The process can be confusing, however, because a universal rating system does not exist for glow plugs. For example, an O.S. R5 plug is not the same as a McCoy MC-9, although both are considered "cold" plugs. A glow-plug manufacturer's guidelines will suffice for average enthusiasts who simply want their cars to run; racers and performance buffs, however, won't get the most out of their engines without a little experimentation. So what should you look for in a replacement plug?
Some general rules about plugs are determined by the size of the engine and the type of fuel used. Smaller engines usually require hotter plugs, while larger engines favor cooler plugs. Engines that run fuel containing a high percentage of nitro favor the cooler plugs as well, while those that run on less nitro prefer hotter plugs (nitro fuels for car engines typically include 10 to 40 percent nitromethane). For example, a small, .12ci (2.1cc) engine that burns high-nitro fuel would favor a warm plug in a mid-range temperature (small engine = hotter plug; high-nitro fuel = colder plug). The same plug might also be suitable for a .21ci (3.5cc) engine running low-nitro fuel (large engine = colder plug; low-nitro fuel = hotter plug).
The size of your engine and the type of fuel are easy enough to determine, so these guidelines should get you pointed in the right direction. For racing buffs who want to get maximum ponies, however, another element that's not easily determined?? should be taken into consideration??compression ratio. The compression ratio of an engine will also be a factor in choosing the proper plug. High-compression engines favor colder plugs, while those with lower compression favor hotter plugs. Engine manufacturers rarely disclose an engine's compression ratio, so it may be difficult to use this information to select plugs unless you know how to calculate compression or can measure it with a compression gauge.
This information is best used when adding or removing head shims. More or thicker shims lower the compression; fewer or thinner shims raise it. Remember: when adjusting head clearances with shims, a plug change may be necessary (this should be left to experienced engine tuners).
WHAT HAPPENS IF I USE THE WRONG PLUG?
If you have used a plug that is too hot or too cold for your application, this will be revealed in one of two ways. If the plug is too hot, the engine may suffer from detonation, pre-ignition and high running temperatures. Detonation occurs when the fuel mixture explodes quickly rather than burns. You don't want this to happen because it can damage the engine. The telltale signs of detonation are a "miss" in the exhaust tone at high speeds and a pitting of the cylinder head around the glow plug and the top of the piston. Severe detonation can cause the coil element of the glow plug to come loose, and this can severely damage the engine. The primary cause of detonation, however, is excessive compression. Simply using a hot plug will not usually cause detonation, so don't be afraid to experiment. If you're using high-nitro fuel and have increased the compression by reducing head clearance, however, a hotter plug may just push the engine too far and cause damage. At the very least, an excessively hot plug will cause pre-ignition, in which the fuel mixture begins burning well before the piston reaches the top of the cylinder.
Using a plug that is too cold will result in a loss of acceleration and top speed and will cause poor engine idle. If the plug is much colder than it should be, you might notice an excessive raw-fuel discharge from the exhaust pipe, but don't confuse this with an excessively rich fuel mixture.
WHAT MAKES A GLOW PLUG HOTTER OR COLDER?
Many elements influence a glow plug's temperature range, but primary is the thickness, length and composition of the wire used to form the coil. It will be impossible to find out anything about the composition of the wire because most manufacturers keep it a secret, but the wire can certainly be measured. Other factors that affect a glow plug's temperature include the size of the hole in which the wire is installed, the type of plating used on the glow-plug housing and the material the glow plug's housing is made of.
The plug on the left, an O.S. F, is rated "hot" for use in 4-stroke applications. The thin element wire and the large number of coils create more resistance, and this results in higher operating temperatures. The Enya no. 5 plug on the right is one step up from the coldest plug. The thicker element wire and lower coil count reduce the plug's temperature.
The best way to keep track of your glow plugs is to store them in their original packaging; the plug type is printed right on it. A visual inspection won't help you much, since some plugs don't have any temperature information printed on them; that's why the original packaging comes in handy.
IS ONE TYPE OF PLUG MORE DURABLE THAN ANOTHER?
If the fuel mixture is properly adjusted, most plugs should last equally long. When the fuel mixture is on the lean side, the hotter plugs tend to be more susceptible to damage as a result of their typically thinner elements. The quality and consistency of the material within the glow plug's element can also affect durability, and this varies among manufacturers but can be sorted out with experience. So yes; within the various brands, there are slight advantages to colder plugs, but these advantages are not enough to justify choosing them if the result is diminished performance.
These glow plugs have very different electrode designs, but despite the visible differences, electrode design has no bearing on plug performance.
BEST-KEPT TUNING SECRETS OF THE PRO'S
One of the best-kept secrets of the most experienced nitro racers and engine tuners is that you can net some serious horsepower gains by experimenting with various glow plugs. As mentioned earlier, a glow plug is the ignition system for a nitro engine. Anyone who has ever worked with spark-ignition systems knows that ignition timing can have a profound effect on engine performance. "Ignition timing" is when the fuel mixture is ignited in relation to the position of the piston and crankshaft during the compression stroke. When the piston is at top dead center (TDC) of the cylinder, the crankshaft's journal, to which the connecting rod is attached, is pointing straight up. This puts the piston at the highest point of its travel in the cylinder; therefore, the crankshaft is at "zero" degrees. The crankshaft must rotate a full 360 degrees to make a full cycle, so the amount of crankshaft rotation in degrees is used to measure the events that take place inside the engine; for example, ports opening and closing and ignition. Although you can't measure or definitively set when ignition takes place inside a nitro engine, it helps to be able to visualize what's happening when you experiment with different plugs. Let's say, for example, that the fuel mixture is ignited precisely at the moment the piston reaches the very top of the cylinder. This would effectively mean the ignition timing is taking place at zero degrees of crankshaft rotation. Installing a hotter plug in the same engine makes the fuel ignite sooner because less compression is needed to heat the plug's element to the point that the fuel will ignite. Let's say that now, ignition occurs 10 degrees before the piston reaches TDC. In ignition-engine-speak, that would mean that the timing is set to 10 degrees advanced, or 10 degrees BTDC (before top dead center). What does all this mean? Simply knowing that plug temperature will affect when combustion takes place will, hopefully, help you understand why choosing the proper plug will improve performance. Generally, it's best to try to advance the timing or flash point of the fuel??the case of nitro engines, as much as possible without going too far. If the mixture is ignited too early, then performance is lost and pre-ignition and detonation may occur. Picco's engineers don't use plugs to tune the engine; they simply find the proper plug for the application and stick with it. They haven't seen much difference in performance from changing to a slightly hotter or colder plug. They do, however, admit that getting too far away from the ideal plug temperature will have a negative effect on power production.
THE FINAL ANALYSIS
We hope you now know more about glow plugs and what to do with them. Most people don't think about glow plugs until they don't work. It's precisely then that this information should be most useful. Just keep in mind that there isn't a magic glow plug that will suddenly make your engine scream as it never has before; glow plugs are one of many elements that factor into overall performance.
Fuel and Lubricants
Nitro Engine Basics
Nitro engines run on a highly combustible mixture of methanol, nitro methane (CH3NO2) and castor or synthetic oil. Rather than using spark plugs, such as in typical 4-cycle engines, these engines use a method of combustion similar to diesel engines (granted diesels are generally 4-stroke).
Using electrical current and a glow plug, a hot spot is created in the combustion chamber. This, in addition to the compression of the moving piston, creates the combustion cycle. Within seconds, the combustion chamber and glow plug become extremely hot and maintain subsequent combustion without the need for the electrical "jump start". This is what is often referred to as "dieseling". The only thing that breaks this cycle is either lack of oxygen or fuel (or an un-timely death of the engine).
Nitro-Methane Content
Fuels are rated by their nitro-methane content, typically 10-40%. The higher the nitro-methane, the more power to the engine. Typically in 1/10 scale cars (with .12 engines), 10-20% is plenty sufficient. More than that on these smaller scale cars will go wasted, since the engines to not efficiently convert use the extra-potent fuel and the hookup (traction) is usually marginal, at best. They heavier 1/8 scale and larger cars can see significant increases in usable power by using these higher (30% and higher) nitro-methane ratings
In-Fuel Lubricants
These engines do not use any auxiliary method of lubrication. Instead, they use the same method of lubrication found in most other 2-cycle engines. Because of the physics of 2-cycle engines, the fuel passes both sides of the piston, including the crankcase. This allows a convenient method of lubrication. By actually combining the lubricants with the fuel, you can continually coat all the moving parts of the engine as the fuel makes its way to the combustion chamber. Whatever lubricants are not absorbed by the metal they come in contact with are either burned in the combustion chamber or are discharged through the exhaust port. This is why you will often see these broken down oils seeping from the mufflers or tuned pipes. It is just the normal process of cycling through the lubricants.
Most nitro-engine manufacturers recommend using a special "break-in" fuel which contain a higher percentage of lubricants for the first few dozen tanks or so. This is to insure that the engine has plenty of lubrication in order to properly break in and maintain a good seal in the combustion chamber.
This is also why we encourage users to tune their engines slightly rich (see Engine Tuning & Maintenance) so that there is a sufficient supply of these lubricants to the engine. Although running your engine lean may increase performance (temporarily anyways), it will be short lived if the engine doesn't have enough lubricant to maintain proper engine temperatures.
After-Run Lubricants
An important and often, overlooked procedure in maintaining your engine is after-run lubrication. The benefits from this are two-fold. First, as the engine cools after being run, moisture can build up inside the engine, causing corrosion. The next time it is run, the engine will typically see some undue wear from the corrosion buildup. Secondly, the lubrication process often enhances the starting ability by providing a better piston to cylinder seal. Until the engine has had a chance to warm up, this seal is often sloppy, and just like the engine in your real car, a majority of the engine wear happens in the first few seconds before the lubricants in the fuel get a chance to recoat the engine's working parts. You can find these "after-run" lubricants in your hobby store. Usually a few drops down the glow-plug hole or in the carburetor right after you have run your car can significantly add life to your engine.
I cannot stress enough how important this is. Just like running your engine rich is important for your engine's life, so is this simple process. Don't let this one go unchecked.
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