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Old 03-01-2006, 04:17 PM
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HighPlains
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Join Date: Mar 2003
Location: Over da rainbow, KS
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Default RE: K&B 7.5 mini pipe

By "mini-pipe", I assume you mean the short open exhaust pipe like was used in the old Formula One engines on 65% nitro. For one of those, it can be made from 1" conduit pipe with a slight bit removed from one end on the inside to provide a lip for the O-ring seal. You should make several, as the length does matter slightly. We used to run 3.4 to 3.6" for the rpm range on the 6.5 engines (about 21.5 K on the ground, around 26-27K in the air).

One thing about the mini-pipes vs. the tuned pipes. There is no rpm limit in the air, so on a very clean airplane, the engine will rev until the drag matches up with the engine power. Whereas, the piped job will self limit at the tuned rpm, as the hp falls off rather quickly above that rpm. So diving an open pipe'd plane is quite different.