CMB Pipe Performance and Matching

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BobBonahoom

Well-Known Member
Joined
Mar 6, 2009
Messages
532
We had been using Bouchie pipes on our 21 and 45 riggers. A few weeks ago we substituted CMB pipes with 707 stinger mufflers and saw what seemed like an improvement in acceleration and speed. Not a scientific test, we just put on the CMB pipes at the same length as the Bouchie's (center engine to center fat band or cone maximum) and ran them. There was however one other difference, that matching of the pipe to the header. I bought a plumber's swaging tool on Amazon and used it to expand the CMB pipes so the header would telescope. (Prior to that we were sharpening the ID of the header to reduce the obstruction to the reflected gas wave). With this tool you can get an exact match where the ID of the pipe and header match almost perfectly. Works real well if you know the length of the pipe you wa

nt to run.

CMB Pipe and Swage Tool.JPG

CMB Pipe and Header with Swage.JPG

CMB Pipe and Header Close Up.JPG
 
No heat required, just patience. Takes about 20 minutes of constant rotating and squeezing the swage. You have to be careful you don't squeeze too hard or the pipe will go out of round. Plumbers us them to solder to pieces of the same size copper pipe together without using a coupler union.
 
Bob what length did you run the CMB 45 pipe at if you don't mind saying? Ive had real good luck at 9.25 to 9.375 to the weld.
 
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David,

We were running the 21 at 8.25" and the 45 at 9.25". I have since found that I can run the 21 at 8.0" with the CMB pipe and pick up RPM with no launch problems or coming off the pipe. We were not able to run the Bouchie that short however.
 
David,

We were running the 21 at 8.25" and the 45 at 9.25". I have since found that I can run the 21 at 8.0" with the CMB pipe and pick up RPM with no launch problems or coming off the pipe. We were not able to run the Bouchie that short however.
Ok cool. I know the Bouchie pipes always liked to be a little longer but have never tried one.
 
Mike, sorry but no. We still like them for some boats. They seem to work very well on our Nova engines. Plus they are like works of art that a person just can't part with.
 
they are like works of art that a person just can't part with............
yep
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ScottBuchie_TunedPipe_CMB-.80HR_May2018_01.jpg
 
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David,

We were running the 21 at 8.25" and the 45 at 9.25". I have since found that I can run the 21 at 8.0" with the CMB pipe and pick up RPM with no launch problems or coming off the pipe. We were not able to run the Bouchie that short however.
I am at 7.5 on my set up with CMB 21 nitro pipe.
 
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