Prather Tuned pipe Question

[tdi1fun]

I am building a Prather deep vee 31" boat with an O.S. .21 rg-mx. I want to use a Prather 9010 tuned pipe with the engine. The boat instruction manual says I should have 8.25" from the glow plug to the pipe cone. But my problem is that the pipe instructions say to measure from the exhaust flange to the pipe cone. This gives me a .75" difference between the two instructions. Any suggestions on what the correct measurement should be, or what other people have used?

Any help would be greatly appreciated.

John B

 

[Propjockey]

John, what header are you using?

 

[TimD]

225mm (8.85 in) from plug element to widest point -then adjust it in or out from there to suit the prop.

 

[tdi1fun]

I am using the Header that comes with the engine. The header is a 180deg design. The engine exhaust port is on the back (away from the prop) and the header curves around the left side. It's approx 4" in length.

One person mentioned shorting and extending the pipe to tune. After you cut the pipe how do you extend the pipe with out making to big a gap for the coupler.

Thanks again for all the help

John B