pipe length

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john v

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Oct 10, 2007
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I have a 29 hopper with a nova rossi purple head 21 with a rody rhohm crank and pto. I am experimenting with pipes, I am trying a Irwin stamped ob pipe on there now and measuring pipe length is kinda tough, its easy on my inboards. I know 8'' is about right for the 21's. do the outboard guys measure the space between the header and the pipe?. I tried to use a piece of string 8'' long and follow the pipe but I figured there must be a better way. thanks john virgalla
 
Some just scribe a mark on the pipe near the header so you can take measurement with a ruler from the bend of the header- this also means your measurements are personalized to that engine making it hard to share pipe lengths with others. Easiest to just start long and move the pipe in. I don't run 3.5 ob but someone should be able to give you a rough starting point to get you going
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Dion
 
John,

You measure the entire length of the exhaust system as that is the length fhat the pressure waves must travel. The string is very basic but it does work. Just run it along the system along the center of it all. 8" is a good starting point to the center of the flat band of the pipe. The Irwin is a bit similar to the Hopper pipe and both use the same measurement process.
 
Measure from the center of the plug.. to the beginning of the divergent cone. I length of solder works better then string.

Start if you can at 8-1/4" and work shorter 1/8" at a time is good.

Take lap times and when your lap times start slowing down or the boat will not launch well it getting to short..

Also.. don't confuse "getting back on the pipe" with a short pipe.. it can be a lean or rich low speed mixture.

Grim
 
tried my Irwin pipe over the weekend and started long on pipe length , around 9'' and tried to shorten it up and could not get on the pipe, I have a 3rd channel mix control and tried all settings. my guess that motor doesn't like the Irwin pipe. I am going back to the equie pipe. any other pipes worth looking at?. I saw a 3280 cut up into an ob pipe that moparbarn had a picture of, looked really cool. I am going to continue experimenting trying to get a good performing pipe. thanks for all your input. john virgalla
 
John,

I have had excellent success with a Hopper standard OB pipe with a NovaRossi. Did not like the HP pipe but the standard one works very well. I have an extra one that I can sell you if you want. Need your e mail addy to send a pic if you are interested..

John
 
I made that OPS 3280 outboard pipe for moparbarn. I make alot of custom outboard plpes.i can do whatever you need.

Sent from my VS985 4G using Tapatalk
 
that job you did on that 3280 was a work of art, I am trying different pipes now before we get ice, if I need anything I will contact you bob. thanks john v
 

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