how to measure pipe length

[RodneyPierce]

OK guys, another question here. I was windering how to measure the pipe length on my inboard Nova SS in my whiplash. Do I go from the plug center, AROUND the 180* header, and follow the pipe to the fattest part, or do I just measure from the fattest part, or the convergence cone to the center of the motor, without going around the header, is just alogn side the pipe, and stop when it lines up with center of motor? Does that make sense? Perhaps a pic would help me out here.

 

[Ron Olson]

Rod, I know what you're talking about. Some people foolow the path of the exhaust from the glow plug to the widest aprt of the pipe and I've seen others go from the side of the engines case or plug straight back to the divergent/convergent cone. Mike "Grimracer" used to sell a great little clear plastic plate that had a hole for the tip of the glow plug and had the measurements built in on it. I've got two of them but wouldn't part with either one. They work great for Rossi's and Nova Rossi's and have used them on other engines also. I don't know if anyone is selling them or who made them for him.

 

[RodneyPierce]

Ron, sent you a PM. Here is a picture of how I assume im supposed to measure it. The pipe cleaner is what I use, then straighten it out and measure. Here is the pic:

 

[Ron Olson]

Try it from the plug now. Solder works good also.

You've got a PM.

Just a guess but it should be at around 8-1/2". Let's see if someone who knows better than I do what the length should be.

 

[Ray Sametz]

Rodney, Ballpark, measure from plug to seam and add 3-1/2 inches Ray

 

[Rick Cesati]

Rodney, Ballpark, measure from plug to seam and add 3-1/2 inches Ray

Ray,

That estimate is too short IMO. The distance in closer to 5 in. Maybe you meant to say starting plug to weld measurement should be 3-1/2 in?

Rodney, 3.5 in plug to weld is a good measurement with that OPS pipe.

Rick

 

[RCUK John]

http://www.nimrifmodels.co.uk/setup.html

Tuned Length Chart on above site - you may have to "Copy and Paste" to access web site - did not seem to want to run the link

 

[RodneyPierce]

I have the length for the OPS, I have been told to run it at 7.5 inches. So currently as it sets, it is at 8 inches, and i made it last night so the header could slide into the pipe, so its easily adjustable now

 

[Terry Keeley]

Pretty sure the length of a NR 21 header is close to 5" from the plug to "abeam" as mentioned (my Grim template confirms this too), so add 3" to that and you'll be about 8" total as if you measured straight out like for a MAC or Valvola.

I'd start around 8" for your sport hydro or a mono, 7 1/2" is a little short and would be best for a very light rigger IMHO, of course if it launches and mills well you can shorten up from there.

 

[RodneyPierce]

Thanks Terry! And the rest of the fellas here.

 

[Rick Cesati]

Thanks Terry! And the rest of the fellas here.

Rodney,

My hydro will that pipe 2.75 to 2.825. As Terry mentioned, throw it in at 3.0 and see what happens. The SS may require more length that the LS initially until you get the prop right.

Rick

 

[Ray Sametz]

Rick, You are right, a full lenght header is 5" face of piston to end. But I have found if you leave it full you have to cut too much of the pipe, cutting into the divergent cone. The pipe should only be shortened on the straight header. The coupler holds better also. Ray B) B)

 

[steve wood]

if you guys wait a little while, i have information that the grimracer pipe measuring tool will again be available. by the way, we run 8 1/8 on the ops pipe, measured with the tool.

 

[Joe_Knesek]

The pipe volume cone angle plays a big part in the proper length. 8 inches with a pipe like an Irwin S or CMDI Fat pipe would be why too long because the volume is larger & the cone angle is steeper than say an OPS.