The pressure developed by any tuned pipe will be determined by the ID & the total length of it's stinger. Both things will effect the engine's operating temperature! However, changes in the ID of the stinger will have a greater effect on the engines operating temperature than changes in the stingers length. The stinger acts as a bleed resistor, therefore a longer, smaller ID stinger, will develop a higher pressure than a shorter, large ID stinger. It becomes very difficult or impossible to use a longer length, smaller ID stinger if the tuned pipe's volume is insufficient when compared to the displacement of the engine. A volume of 26 to 32 times the engine's displacement seems to work best. A typical "measured" tuned pipe pressure for a 15 cc to 27 cc size engine should be approximately 4 psi or 110 inches of water at WOT. The "measured" pressure is the same anywhere in the chamber & it will vary directly with the engine's RPM.
Jim Allen
