Figured i'd start this one off, Seems like alot of racers choose different spots to get pressure to thier nitro tank, So which is the best, Heard of guys pressurizing off the band on the tuned pipe, heard other guys drilling on the other side of the header and getting thier pressure there. Any suggestions on how to avoid water entering the pressure line.
I have tested, by measuring with an inches of water gage (0 to 200 inches of water), pressures developed by many different stock & custom pipes at many different points; from the exhaust flange to the baffle cone. The pressure is never constant, but does reach a certain range of values according to the RPM of the engine. The pressure is not higher or lower at any particular point. Tests were made with various size stinger lengths & diameters. The following information was found to be repeatable:
1. Most stock pipes do not develope pressures above 80 inches of water at WOT.
2. Pipes that gave readings of 90 to 120 inches of water gave the highest boost.
3. No single or two stage diffuser type pipe gave a reading of more than 80 inches of water.
4. Pipes with tappered exhaust nozzels that had a venturi in the exhaust duct work the best.
5. Greater exhaust time area numbers greatly improve any pipes performance.
6. To acieve pipe pressures of 100 to 120 inches of water requires the pipes volume to be a minium of 28 times the engines displacement, have a tappered header, have multiple angles in the diffuser & have a stinger whose length is at least 13 X it's inside diameter.
On a nitro engine I take the pipe pressure at the header. On a gas engine I take it at the flat spot on the chamber. This is done because the measured external exhaust gas temperature taken at the header on the 26 cc gas engine at WOT is 750+ deg F. It is 450+ deg F at the flat spot. The external temperature taken at the header on the .90 cuin nitro engine is 475+ deg.
Jim Allen
