Pipe length and prop recommendation. stealth with old Rossi gold head .R21 outboard with irwin pipe.

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Davidkrienke

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Jul 7, 2018
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I wanted to get a head start if someone knows what the pipe length this motor likes I would really appreciate any info on it. Also any starting prop recommendations for it on this old Stuart Stealth hull would be great as well. I will be running 30 percent nitro .I just checked squish and its .008
I soldered the cooling outlet also to .16 thou to start and ill drill it larger from there. Also I have no idea on this carb what the low setting usually is stock. 20210517_002846.jpg
 
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jaxracer

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Joined
Jan 17, 2005
Messages
638
I wanted to get a head start if someone knows what the pipe length this motor likes I would really appreciate any info on it. Also any starting prop recommendations for it on this old Stuart Stealth hull would be great as well. I will be running 30 percent nitro .I just checked squish and its .008
I soldered the cooling outlet also to .16 thou to start and ill drill it larger from there. Also I have no idea on this carb what the low setting usually is stock. View attachment 291341
Not sure on the pipe measurement but that Rossi doesn’t have a lot of bottom end torque but loves to sing RPMs. A detongued x440 or x637 will probably be your best bets to start. If you can find one, an Irwin stamped pipe runs good on that motor.
 

Davidkrienke

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Jul 7, 2018
Messages
80
Not sure on the pipe measurement but that Rossi doesn’t have a lot of bottom end torque but loves to sing RPMs. A detongued x440 or x637 will probably be your best bets to start. If you can find one, an Irwin stamped pipe runs good on that motor.
I think my brother might have a stamped Irwin pipe that I could try. This pipe and lower on it now was one I bought from Jim Irwin at the end there when he wasn't doing much anymore ..Also I was looking through props. I have a x438 x440 x637 x437/3 and a Prather 215 none are detounged but I might have to look for some pictures on how that looks so I can prepare one to try.
 

dave roach

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May 28, 2004
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4,052
Set the pip[e from the center of the glow plug to the weld at the widest part of the pipe at 8;00 inches
 

jaxracer

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Joined
Jan 17, 2005
Messages
638
I think my brother might have a stamped Irwin pipe that I could try. This pipe and lower on it now was one I bought from Jim Irwin at the end there when he wasn't doing much anymore ..Also I was looking through props. I have a x438 x440 x637 x437/3 and a Prather 215 none are detounged but I might have to look for some pictures on how that looks so I can prepare one to try.
That Irwin lower should work well. The material makes it pretty light so easier to get the CG right. If the boat handles odd, double check the skeg as some of them did come out of the molds slightly crooked. As for prop modifications, here’s a link to an article that gives a great starting point for understanding blade modifications. The bottom right photo has the detongued x series that I mentioned. Essentially taking off that blacked out area on the leading edge of the blade.
 
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