Articles

Tune your GRP Engine Like a Pro. Adam Drake Shows You How

Posted:  Friday, February 13, 2009
Written By:  Adam Drake
Copyright:© 2009 Horizon Hobby, Inc.
Adam Drake

Engine break in:

To guarantee long life and top performance, each engine needs to be broken in, bearing in mind that the more careful the break-in, the longer the engine will give its best performance. Break-in must be done carefully with the engine installed on the model, in the following way:

1. It is recommended to use a heat gun to heat the engine to 160-180 degrees before you start the break-in process. Start the engine with the factory settings. It is extremely important not to accelerate the engine for a long period of time when the car model is not in contact with the ground because it can cause serious damage.

Always make all adjustments to the carburetor in one-hour increments. Imagine the slot in the needle is the hour hand on a clock. Adjust it as though you were moving the hour hand from one hour to the next or previous one.

2. When you start the engine, leave it running a few minutes with rich carburetion, with the glow plug starter connected and with the wheels turning freely off the ground. Under these conditions, the oily carburetion perfectly lubricates all the engine's internal parts.

The factory settings are very rich, so if the engine stalls during break-in you may need to lean the low speed needle a couple of hours. Idle the engine for 4-5 tanks of fuel. While idling, occasionally turn the model on its side to drain the excess residue in the pipe. This will also help the engine idle more consistently.

3. Now try the model on the track or street. If the carburetion is too rich, slowly increase the speed to keep the engine running as long as possible. If it stops because carburetion is too rich, turn the high speed needle clockwise by a third of a turn and try again.

4. If the engine continues to run even when carburetion is very rich, continue to use the model until you have consumed at least 3 fuel tanks. Then close the high speed needle by a further third of a turn and consume another 2 fuel tanks. Repeat the procedure until you have consumed at least 6 tanks of fuel. However, the exhaust pipe should continue emitting abundant smoke.

5. To stop the engine, close the throttle completely using the throttle lever on the transmitter, then plug the pipe with your Losi tuning screw driver. Never try to stop the engine by slowing down the flywheel with your fingers or other objects. After shutting the engine down, turn the flywheel to make sure the piston is at bottom dead center.

High Speed Needle

The high speed needle should be adjusted .045 in from flush. As you turn the needle clockwise (leaner), less fuel enters the engine. Turning it counterclockwise (richer) allows more fuel to enter the engine.

Low Speed Needle

The low speed needle should be adjusted .045 in from flush. As you turn the needle clockwise (leaner), less fuel enters the engine. Turning it counterclockwise (richer) allows more fuel to enter the engine.

Idle screw

The idle screw should be adjusted .030 in from flush. As you turn the screw clockwise, it increases the carburetor opening at idle and increases idle speed. Turning it counterclockwise decreases the opening and idle speed.

NOTE: Whenever any major components of the engine are replaced, such as piston, sleeve, crankshaft, bearings, etc., or if you change fuel, the complete break-in procedure must be repeated.


Break-in Fuel

We use and recommend using Nitrotane 20% or 30% race fuel to break in your engine, using the same nitro content and brand of fuel you will run when racing


Operating Temperature

Engine temperature will vary from engine to engine—depending on the air temperature, fuel, carburetor restrictor, altitude, and driving style. The proper temperature range for GRP engines is between 170-200 degrees Fahrenheit.


Airfilter

Maintaining your air filter is essential to the life and performance of every engine.
Always run your engine with an (oiled) air filter. Running an engine without an air filter, will cause engine damage and shorten its life cycle. Change the foam on regular basis.
We don’t recommend cleaning and re-using the foam. With pre-oiled air filters, it is helpful to use clean towels and compress your air filter in the towel several times to remove any extra oil in the foam. If the air filter has too much oil, it will cause the engine to run rich.


Head Shims

All GRP .21 and .28 engines come with the proper head shims for using 30% nitro. The extra shims are just replacement shims. Two-stroke nitro engines are basically air pumps. The engine takes air in, mixes it with fuel, and then the mixture is compressed and ignited. Increasing compression increases power output, but there are limits to the compression an engine tolerates. Too much compression causes the fuel mixture to combust too quickly, and causes detonation. The amount of compression is determined by the thickness of the shims between the cylinder head and the top of the sleeve. Thicker shims = less compression; thinner shims = more compression. The stock shimming on GRP engines is one thick and one thin shim.


Weather Conditions

Changes in weather, equipment and other variables mean that nitro engines must be regularly retuned. To get optimum performance from your nitro engine, you will need to slightly tune your engine every time you run it. Once the settings are close you shouldn’t need to adjust the carburetor more then a couple of hours richer or leaner on the high speed needle. Hot weather will usually require a leaner setting and cold weather requires a richer setting. Cold air is denser and packs more oxygen into the engine, so going from hot weather to cold needs an increase of fuel to balance the ratio of fuel-burning oxygen and the fuel. Humidity also plays a role in the tune of your engine. In humid conditions, you will need to run a leaner setting. Moisture in the air takes up volume that would otherwise be occupied by oxygen.

GRP .21 Tuned Engine (LOSR2000)
High Speed:
.045 in from flush
Low Speed:
.045 out from flush
Idle Speed:
.030 in from flush

GRP .21 Tuned Engine (LOSR2001)
High Speed:
.045 in from flush
Low Speed:
.045 out from flush
Idle Speed:
.030 in from flush

GRP .28 Tuned Engine (LOSR2010)
High Speed:
.045 in from flush
Low Speed:
.045 out from flush
Idle Speed:
.030 in from flush


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