Measduring pipe length

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Robert,

This is how I’ve measured my .21 outboard pipes - was shown years ago. They are a bit tricky with all the bends. 1) I first take measurement center of piston to outside exhaust flange on case. 2) I then use thin solder to get measurement from that point along header then pipe up to widest point of convergent (rear) cone. I carefully follow the center line of all this with the solder, especially across 90 degree bend in outboard header and throughout curve of pipe. Add these two for your final total length of pipe. For example my Rossi outboard pipe runs 7 7/8 - 8” and A tad shorter with SPP carbon pipe total lengths. Sorry I have no numbers for suggested length of a .45 set up.

Wally
 
I just use a metal ruler to measure from header to inside bend. This method does not tell you the actual length you are running the pipe but makes for easy measuring quickly and you can see if your pipe has moved from where you set it.
 
Using a piece of wire is how I do it too. Its the best way to get the initial length for sure. As Wally has instructed you, find the length using a small flexible wire or piece of solder. After getting the distance from the plug down to the header flange, you then get the length of the header pipe from the "SIDE" of the header keeping the wire positioned at the center line while bending it into shape.It may take a few tries to get it bent just right but once you have it, straighten it out and measure its length.

You can use the wire to measure your tuned pipe also but you want to do that by laying the wire on the "TOP" of the pipe and as before, keep bending it into shape until you have the wire laying on the center of the pipe and properly bent from header end to the point where the first cone (the divergent cone) ends. Your perfect length to this point will depend on the overall weight of your hull, prop size, carb size, fuel used and boat design and sea level just to name a few variables. If you have an SPP carbon pipe, contact Ron Shaw to get a starter point for your pipe length. Once you have established the length that works best for your setup, you can then use a straight ruler as suggested by Dion to take a measurement from a known point on the engine for adjustments or to just check to see if it has moved after a crash. You have watch your boat perform to tell if you have it set to perform at its peak. An afternoon at the pond tinkering with it will put you close. If you were to run into Wally or Dion at a race somewhere I'm sure they would be glad to help you get it dead on.

I hope this helps.

-Carl
 
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A good starting point for the ssp 46 pipe is 90 mm from header to inside of bend and shorten from there
 
I just use a metal ruler to measure from header to inside bend. This method does not tell you the actual length you are running the pipe but makes for easy measuring quickly and you can see if your pipe has moved from where you set it.
Nice method ;-)
 
Richard,

I used the following method to set up the Silver Bullet tuned pipe used for my Nelson .45 long stroke engine. I did not attempt to make any measurement! Instead, I made adjustments in the length of the teflon piece which connected the Silver Bullet tuned pipe to the 90* custom made header. I began with longer pieces & shortened them in 1/2' increments until I arrived at the shortest teflon piece possible. (approximate engine RPM, 28,000+) I also made sure that the area from the piston face to the beginning of the header was a very smooth transition inside. The end of the header, to the teflon piece, to the beginning of the tuned pipe is also a very smooth transition inside. Several different ID's & lengths of stingers were tested to give the maximum HP possible without excessive engine heat. (.343" ID X 4.500" long) If you were to ask me what is the tuned length of this pipe, I would not have an answer! I also believe that a proper size (.4274" bore), automatic fuel metering carburetor with a pressurized fuel system are necessary.

Jim Allen

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Robert,

The method Carl uses above is exactly how I measure my OB pipes. I have also used the solder method Wally mentions. The key is staying on the centerline of the header and pipe through the bends. Then you are good to go. Thanks.
 
Robert,

There are two different Irwin 45 OB pipes. I have never run either of them so I cant help on that particular pipe. Typical length conservative starting point for a 45 engine is 10" from center of glow plug, centerline through header, to the widest point of the pipe. If the pipe has a tuning band, (as with an Equi big belly pipe using the Irwin inboard pipe center section), I actually measure to the center of the band. You may end up closer to 9 1/2" or less to maximize performance. This should help you tremendously. Thanks.
 
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Jim,

Isn't the tuned length from the face of the piston to the start of the stinger?

Probably a much better and more accurate measurement?

This is how we are measuring pipes now. We found out that this way helped

us make more power and RPM with a certain 21-Hydro pipe.

We were way too short with the older way of measuring.

Thanks For Reading,

Mark Sholund
 
Jim,

Isn't the tuned length from the face of the piston to the start of the stinger?

Probably a much better and more accurate measurement?

This is how we are measuring pipes now. We found out that this way helped

us make more power and RPM with a certain 21-Hydro pipe.

We were way too short with the older way of measuring.

Thanks For Reading,

Mark Sholund
Mark has a point, you should always use the manufacturers "initial suggested point of reference" because they most likely have done a lot of testing prior to selling their pipe. If they say to measure to the stinger, that is what I would do. If I were to manufacture tuned pipes again I would probably use the old P.O.R. method but that is just how I have always done it.

Robert, I typically set a new style outboard pipe up to the length the designers say to use and add about a 1/4 inch to that length and then run it. If I think it is hitting too hard or if it is a complete slug, I will change it accordingly and run it again and find what length I think runs best. The initial length given from the manufacturer just puts me close to the hot zone without chopping my header too short right to start with. Every pipe I have ever run (even with my own designs) I end up setting the final length by watching my boat and listening to my engine. It will tell you what you need to do.

New modelers get nervous trying to figure out where to cut and how much to cut when it comes to outboard pipes. Since the outboard pipes typically turn 180 degrees, you can use the glow plug as a datum point to measure from after the final length has been determined and just measure from there out to the end of the stinger. That is how I like to make small adjustments to the length and is also a quick way to check the length of the pipe after a blow off.

-Carl
 
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Jim,

Isn't the tuned length from the face of the piston to the start of the stinger?

Probably a much better and more accurate measurement?

This is how we are measuring pipes now. We found out that this way helped

us make more power and RPM with a certain 21-Hydro pipe.

We were way too short with the older way of measuring.

Thanks For Reading,

Mark Sholund
The most accurate measurement would be from the piston face in the exhaust window to the middle of the "entire baffle cone length"; where it comes to a point. Two pipes that appear to be exactly the same can have very different tuned lengths when the total included angle of the baffle cone is considered.

Jim Allen

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Robert,

Be aware that on many production tuned pipes it would difficult to tell where the baffle cone starts & ends. This is why I don't bother to measure. I make the thing so that its length can be easily adjusted.

JA
 
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