The greatest advantage gained from using a pipe is the increase in combustion chamber pressures that are generated during the combustion process (by virtue of the denser air / fuel charge). As a general rule, a piped engine will require a higher volume combustion chamber (lower compression ratio) to reduce the initial compression. As stated earlier, heat is the greatest undesirable result of most engine modifications, the higher the compression and the higher the rpm, the more power and the MORE heat produced. Hence when engines are modified to produce more power, then modifications are also necessary to dump the accompanying increase in heat.

The most common signs of over heating are blown plugs and a ‘sand-blasted’ looking head. A sand blasted / pitted head is actually caused by detonation ... which can be caused by under compression, and running lean to compensate, or by over compression at any needle setting.

For optimum performance, the following guide may prove useful (for with or without a pipe).

Increase combustion chamber volume or head (squish band) clearance

Increase stinger diameter or decrease stinger length (to reduce pipe pressure)

Decrease prop load.

Improve cooling

Decrease nitromethane content of the fuel (if using nitro)

Decrease combustion chamber volume or head (squish band) clearance

Decrease stinger diameter or increase stinger length

Increase prop load or

Decrease cooling

Increase nitro content of the fuel (if the competition rules allow nitro)

Decrease prop load

b) Sand blasted head

c) over heating engine

d) difficult to get 'on the pipe', sensitive needle

e) excessive carbonising of the head

f) engine sags under load, ie, long climbs

g) 'Harsh' running

h) very easy on needle

i) smooth, quiet running

j) prone to burbling, rich running

k) no power

l) none of (a) to (g) above, try shorter and see what happens.

Like propellers, only trial and error will prove which pipe is best suited to your engine requirements.

It is rare that a pipe will not need adjusting in length, in fact the only way a pipe can be optimised is to vary the length to observe the changes to determine the best length. (This can also be done by varying the prop load and observing the pipe characteristics).

To shorten a pipe, remove material from the alloy header pipe, as this will lessen weight and help prevent fatigue of the alloy. Save the off-cut and use for extending the pipe.

To extend a pipe, use the header off-cut, pushed inside a 75mm length of silicon coupler. Many pilots will have three silicon extensions in their flight boxes, at say 8, 16 and 24mm lengths.

In some circumstances there will be a diameter difference between header and pipe, where possible, use the larger diameter.