WTB CMDI Nitro Pipe

[Don Ferrette]

OK - everyone seems to say that drilled out pipes need to be real short.  I have tried for a long time to run my A Mono at 8 inches with the MAC parabolic pipe (the older one) with the stinger drilled out to 1/4".  It runs good in the A Mono - for a little while.  Then, after a 2-3 laps, it drops off a cliff.  Running great one minute, the next it can't even get on pipe.  Some have told me the pipe is too short, some have told me too long.  I am inclined to believe it is too short, but what do I know.  At what length would you guys run the pipe (center cylinder to weld) in an A Mono?
Would it be the same for the Sport 21?

Thanks for all the advice!

Jay

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Sounds like it's going lean. How much time on the motor?

 

[MikeP]

Jerry,

I have a pipe and header I will sell you. Nice condition not cut, has a brass tube in the stinger for noise. The stinger was opened up slightly so the brass tube would fit in.

Mike

 

[Racerdude]

Sounds like it's going lean. How much time on the motor?

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A couple of months. Probably 3 tanks of fuel a week. So probably 20-30 tanks of fule have been run through it.

I agree - it seems to be going lean. However, richen it up, and you might as well push to boat with a fishing pole because it goes soooooooo slooooooooow. I clocked it a whopping 14 mph a couple of days ago.

So, if I set the drilled out, (old) parabolic pipe to 8" and throw it on the pond rich, it will putt around out there until I lean it out with the 3rd channel. Then, it will take off like a rocket for a couple of laps, the drop off the edge, and putt around again.

 

[Don Ferrette]

Sounds like it's going lean. How much time on the motor?

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A couple of months. Probably 3 tanks of fuel a week. So probably 20-30 tanks of fule have been run through it.

I agree - it seems to be going lean. However, richen it up, and you might as well push to boat with a fishing pole because it goes soooooooo slooooooooow. I clocked it a whopping 14 mph a couple of days ago.

So, if I set the drilled out, (old) parabolic pipe to 8" and throw it on the pond rich, it will putt around out there until I lean it out with the 3rd channel. Then, it will take off like a rocket for a couple of laps, the drop off the edge, and putt around again.

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Check your bearings. Better yet replace them & get the good WIB bearings from Ron Byrd (Racecaft Bearings). I replace 21 bearings every 1 to 1/2 gallons of fuel. This was passed along to me a number of years ago by a good friend named Kentley Porter. I did not listen to his advice at first & it cost me a NovaRossi long stroke when the big bearing failed at just under 2 gallons of fuel thru the motor.

Also, if you haven't figured it out yet by previous posts, shorten the pipe & use a prop that will let the motor SING!!

BTW- sorry we highjacked your thread Jerry.

 

[Racerdude]

Hi all -

Let me second that - Jerry sorry about hijacking your thread.

Don - tonight I went back to the fat pipe at 7 1/2". I was reluctant, but I didn't have anything to loose. The boat TOOK OFF. This is my sport 20, not the A Mono. Anyway, the engine began to "sing" as you put it (the engine finally got into the top end of the RPM range), and for the first time in a while, I actually had to worry about how to keep the boat in the water. In other words, at this speed, the boat started to want to fly. That is good. That means I am at the edge of what I can do with this setup. I am sure that I can improve how it rides, but the fat pipe at 7 1/2" really seemed to work. Thanks. Now, a friend has suggested that it may not be consistently fast. I guess we'll see at the race on Saturday.

I plan to try something similar on the A Mono.

Thanks again!

Jay

 

[Don Ferrette]

Hi all -
Let me second that - Jerry sorry about hijacking your thread.

Don - tonight I went back to the fat pipe at 7 1/2".  I was reluctant, but I didn't have anything to loose.  The boat TOOK OFF.  This is my sport 20, not the A Mono.  Anyway, the engine began to "sing" as you put it (the engine finally got into the top end of the RPM range), and for the first time in a while, I actually had to worry about how to keep the boat in the water.  In other words, at this speed, the boat started to want to fly.  That is good.  That means I am at the edge of what I can do with this setup.  I am sure that I can improve how it rides, but the fat pipe at 7 1/2" really seemed to work.  Thanks.  Now, a friend has suggested that it may not be consistently fast.  I guess we'll see at the race on Saturday.

I plan to try something similar on the A Mono.

Thanks again!

Jay

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Very cool. Always glad to help. B)

I'd still replace the bearings soon as 30 tankfulls is alot on a 20 motor.

Does this "friend" who questions "consistency" have to race against you? :lol:

 

[Joe_Knesek]

Now, a friend has suggested that it may not be consistently fast.  I guess we'll see at the race on Saturday.
I plan to try something similar on the A Mono.

Thanks again!

Jay

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Jay, look at it like this. Before you shortened the pipe, you were depriving the motor of what it needs. Shortening the pipe cured that illness. I've found that my motors become more consistant running a short pipe and small prop. These motors are made to make HP not torque so let them do what they like to do.

 

[Rick Cesati]

These motors are made to make HP not torque so let them do what they like to do.

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FWIW...my racing partner recently propped down on his MAC21 powered microburst from X440/3 to X437/3 and gained several mph.

Rick

 

[Jerry T]

Mike P

I sent you an email.

Don, no problem with hijacking the thread.

The reason I want that pipe is that it will fit under the stealth cowl I want to use.