In general, the stinger diameter should be approximately 20% of the pipe's major diameter. The stinger's length should be 8 to 12 X its ID. Smaller diameters & longer lenghts will raise HP amounts, but not without raising engine temperatures. Smaller diameters are much more agressive in their effects than longer lengths, therefore care should be taken when applying diameter reductions. In order for these numbers to work the chambers volume should be approximately 22 to 25 X the displacement of the engine. Sometimes, a small reduction in compression ratio will allow smaller diameters & longer lengths while HP is increasing. Chambers which are giving a good boost will show pipe pressures of 100 to 120 inches of water at wide open throttle. This pressure makes the use of .625 ID carburetor bores on .90 size engines possible. These numbers should only be used as starting points. Dyno testing is necessary to determine final numbers.
For example, my .90cuin (15cc) engine's pipe has a major diameter of 2.200", a stinger ID of .469" & a stinger length of 4.5". Fuels used range from 65% to 80% nitro.
My 1.6cuin (26cc) engine's pipe has a major diameter of 2.400", a stinger ID of .406 & a stinger length of 5.5".
The fuel is 87 octane pump gas.
