Engine temping tips

Engine temping tips

Bess, Stephen

PISTON POWER

EXPERT ENGINE ADVICE

Two-stroke engines require a certain amount of heat to perform well, but as mom always says, “Everything in moderation!”-and that surely applies to RC engines. Keeping a close eye on your engine’s temperature is vitally important to its reliability and performance; excessive heat may be caused by an air leak, drive-train binding or running too lean; an over-cooled engine may

be running too rich or have a carburetion problem. Either way, you need a reliable temperature gauge to determine whether your engine is getting too hot or is not hot enough. An onboard contact thermometer (such as MIP’s Temp Gauge 2 and its Traxxas-branded clone, or the Venom Temperature Monitor) is an ideal way to keep tabs on engine heating without investing in an expensive infrared temp gun. Check out the following info on the best way to use a contact thermometer.

HOW THEY WORK

I contacted Eustace Moore of Moore’s Ideal Products (MIP) for a quick overview of how a contact thermometer works. The key component is a glass temperature sensor called a “thermistor” that absorbs the engine’s heat and relays it to the electronic “brain” in the gauge’s plastic case where the reading is displayed on an LCD screen. These little sensors are surprisingly durable; although the glass sensor should not be crushed (by tightening your engine’s heat-sink head against it, for instance), it can easily withstand the vibrations caused by a 2-stroke engine. As for accuracy, the difference between a contact gauge reading and the temperature indicated by an infrared sensor is negligible. According to MIP, temperature reading variances between contact thermometers and infrared thermometers are as small as i percent when temps are taken at exactly the same point. If your contact gauge provides a different reading from that of an infrared unit, what you’re seeing probably has much more to do with positions of the sensors than with the accuracy of the sensors themselves.

MOUNTING

Contact temperature gauges make it easy to check temps, but it’s important to mount the gauge properly. As the engine’s temperature rises, the glow-plug area at the top of the combustion chamber becomes the hottest point of the engine, and this is where temperature readings should be taken. Avoid mounting the sensor loop near the exhaust port, where heat levels fluctuate most. Mount the thermometer’s wire sensor loop around the first heat-sink fin closest to the glow plug with the temperature sensor opposite the exhaust port. Gently press the sensor loop between the fins; don’t crush it between the heat-sink head and the engine block.

That takes care of the sensor; where are you going to mount the display? You can servo-tape it anywhere that’s convenient, but make sure that the sensor wire isn’t dangerously close to any moving parts (such as the spur gear). Avoid cinching the unit down with a zip-tie; squeezing the case can damage the LCD display.

GAUGING PERFORMANCE

Now that your onboard temp gauge is dialed in, how will you use it to improve performance? If you’re thinking, “Now I’ll tune my engine to run at exactly 250 degrees,” you have the concept of temperature-tuning backwards. Your objective is to tune your engine to best performance, note the temperature readings and then use them as a barometer for future runs. If your engine seems to operate best at 265 degrees, make a note in your tuning notebook (you do keep track of your setups in a notebook, right?) and tune the engine to operate close to that temperature the next time you run your vehicle. But don’t get stuck on 265 degrees as the .perfect” temperature; variables in your fuel’s nitro content (and quality), ambient temperature and humidity can affect the temperature at which your engine runs best. Just tune your engine to run its best based on throttle feel, how much smoke the engine produces and its exhaust note, and continue to make notes. You’ll soon build a library of operating temperatures for various combinations of fuel types and operating conditions. Armed with this knowledge, you’ll be able to react appropriately when your engine temp is unusually high or low for a given set of operating conditions. That’s the real benefit of a temperature gauge.

TECH Q & A

Q I’m having trouble keeping my T-Maxx running past h tank of fuel. I have a nearly stock T-Maxx with a stock fuel tank, a Novarossl CX-12 pull-start engine, a Kyosho fuel filet fitter mounted on the front shock tower and Aer end fuel tubing, and I run 20– percent Trinity Monster Horsepower fuel. I’ve changed the glow plug, cleaned the air filter and tested the fuel tank for leaks. I’ve even replaced all the fuel tubing on the truck, yet it continues to flame out once the tank goes past 3h full. The carb is tuned property, and the running temperatures are in the mid-200-degrees F range, so I know I’m not running the engine too lean. What’s the deal? [email]

Robert Grant

A Robert, your T-Maxx’s problem isn’t uncommon, First, let’s talk a little about 2-stroke engines and how they operate. A 2-stroke engine relies on the suction created by an engine’s compression, as well as exhaust pressure, to draw fuel into the carburetor, Eliminate the suction pressure or the exhaust pressure that pressurizes the fuel tank, and your 2-stroke engine won’t have the ability to draw enough fuel into the carb to keep itself running. Basically, these pressures allow the engine to “drink” the fuel through the fuel lines in the same way you drink a soda through a plastic straw.

Now to your problem. Your engine dies around Ih tank, and you’re running a fuel filter attached to the front shock tower? To mount a filter on the front shock tower of a T-Maxx, the fuel tubing would have to be at least twice the length for normal operation! Running the tubing from the tank all the way up to the front tower, into the filter, and all the way back along the length of the chassis to the carb causes the suctioning pressure to be exponentially reduced-thus causing fuel starvation at 1/2 tank. One of the reasons that your engine runs until 1/2 full is that gravity causes a full tank to empty itself because of the fuel’s weight Also, there’s less empty volume inside the tank to pressurize when the tank is full, so even weak pressure will easily force fuel into the curb. But once past 1/2 tank, the pressure is gone, and the engine starves.

Think of it this way: you can drink a soda through a 10-inch-long straw quite easily, but how difficult would it be to drain the can through a ii-foot-long straw? Chances are, the liquid will never reach your lips (and you’ll look like a freak). Reduce the fuel tubing to a maximum 8-inch length from the tank to the carb, and find a better place to mount the filter. Keep the pressure line from the pipe to the tank equally short. and your engine will run until the last drop of fuel. Problem solved!

FOR NITRO

PT 2000XS .21

The 2000XB is Megatech’s newest .21 buggy engine. That means it’s designed for big low-end punch-exactly the sort of power that heavy, 1/8-scale buggies need for the constant acceleration and braking seen in off-road racing. The XS has a 7-port, chrome-plated sleeve, an 11-fin head with a separate glow-plug “button” and a three-needle slide carb. There are also some neat internal features that you can see in the June 2002 issue of RC Nitro (on sale now; go get yours), which has a complete dyno test of the PT 2000XS. In case you’re wondering, it cranked out 1.73hp at 22,700rpm, with a practical rpm range of 2,500 to 28,200.

Megatech PT 2000XS .21-item no. MTCPT-05; $270.

TRINITY

Monster Horsepower Nitro

Starter Kit

Trinity offers two versions of the starter kit. One version comes with the items shown here (500ml fuel bottle, glow-starter with wall charger, 4-way wrench, Nitro Blast spray cleaner and one quart of 20-percent Monster

Horsepower fuel), or you can opt for the T-Maxx version, which adds a MOmAh battery (to power the Man’s EZ-Start unit) and a bottle of after-run oil. The Maxx kit is also great for the EZ-Start-equipped Traxxas Nitro Stampede and Nitro Rustler, as well as Kyosho’s QRC vehicles and MegaForce with Touch-Starters.

Trinity Monster Horsepower Starter Kit-item no. RC8110: $45.

Monster Horsepower Starter Kit for T=as T-Mac-RC8111: $50.

SOURCE GUIDE

MIP (626) 339-9007; miponline.com.

TRINITY PRODUCTS INC. (732) 635-1600; teamtrinity.com.

CONTACT THE PISTON POWER SOURCE

Send your “Piston Power”questions and comments to Stephen Bess, stephenh@airage.com.

Copyright Air Age Publishing Jun 2002

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