measuring an outboard exhaust for nitro

[mattb]

say guys does anybody know how to measure an outboard tune pipe system besides trial and error.

 

[Jerry Dunlap]

By "measure," do you mean the length of the pipe?

JD

 

[Bob Kensill]

Go online and get yourself a copy of the Two-Stroke Tuner's Handbook by Gordon Jennings. There are several formulas for tuned pipe design and development. You will suffer brain-overload if you read the book.....,,lol

 

[Curtis Maglinger]

T

 

[Bob Kensill]

I bought John Equi's business over ten years ago and have devoured every bit of info I can find about expansion chamber design and theory. Current pipe manufacturers make their pipes to fit a range of engines. I tend to make my pipes to fit specific engines. I would love to talk "tuned pipes" with anyone who wants to.

 

[Bob Kensill]

Here are a couple of copies from Gordon Jennings

 

[lohring]

My experience is with custom pipes for gasoline engines. The big difference is much lower exhaust gas temperatures on small nitro engines. I believe around 250 degrees C versus 500 to 600 degrees C are typical. That design temperature is critical and needs to be measured on an engine under load. That means dyno testing at least in the form of a propeller or similar load. Look at Jim Allen's gallery for some advanced ideas. Nearly all the development on engines and pipes over the years was done with calibrated propellers and rpm measurement. I can steer you to pipe design details, but they would be misleading without a good, real world testing system.

Lohring Miller

 

[Carl Van Houten]

Here are a couple of copies from Gordon Jennings

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Joey and I spent hundreds of hours testing pipes when we were developing the "J" pipe before we ever landed on the final

dims that were used to manufacture our pipe. We could build a faster pipe than what we wound up with but we decided that a pipe that had some torque left in it would be the best route from a marketing standpoint because the final product had to suit a a range of setups. I read what I could back then about pipe theory and talked to as many people about volumes, angles, lengths, diameters, header dia & length, stinger dia and length, overall pipe shape, convergence and divergence angles and lengths material hardness etc.

After getting the basics down, I learned the most by starting with a base pipe design that gave (what I considered at the time), an acceptable boat speed around the track and needle range. Then made 5 or 6 slight variations of that base design. Nothing beats actual testing. After finding a design that gave acceptable characteristics, controlling engine heat was the final key. I am sure you can use equations and get close but whether you understand the exact internal harmonic dynamics of the pipe or not in the end what works....just works.

(I have actually seen pipes that were square instead of round work fairly well).

Lohring posted while I was writing this and I am sure he has much more refined ways of accomplishing what we did by trial and error years ago.

How many people have actually tried to monitor engine temp? I believe that temp spikes are what knock a lot of the fast guys out of the race.

-Carl

 

[lohring]

My first (and only) look at nitro exhaust gas temperatures was on a device that used EGT to adjust the third channel needle. The idea was to maintain the best needle despite the engine load. I found that the thermocouple was not very rugged. When it failed the needle went lean, stopping the engine.

Pipe design formulas are empirical and reflect a lot of experience as well as some theory. I don't know of any formulas that are based extensive on small nitro engine testing. Most of my exploration has been done in engine simulation programs. The one I use, EngineMod2T, now has a glow ignition module, but I have almost no experience with it. Some of the basic variables in pipe design are covered in my Propwash article Tuned Pipe Design Factors. It's about a 26 cc Zenoah pipe, but the basic issues are explained. Scott Bouche has built the most successful custom nitro pipes of anyone I know. I believe he uses the basic Blair formula for design. A free version is available here. Maybe Scott would be willing to disclose more details.

Lohring Miller

 

[Carl Van Houten]

I think that monitoring your engine temp "in real time" would be a great and a useful tool to have. You would think the FE guys would be all about that idea.

-Carl

 

[Jim Allen]

There are some basic rules that I adhere to when building high RPM or high torque type tuned pipes. The engine's exhaust nozzle should be tapered down to a smaller area from the exhaust window to its end point. The exhaust nozzle itself should also be pointed at a downward angle (approximately 15*). The first part of the tuned pipe, the header section, should also be tapered (approximately 2*to 3*) before the first section of the tuned pipe. I do not build pipes with one or two sections in the diffuser, because doing this can make it difficult to build a chamber with an area large enough for the engine in question. Baffle sections with several sections (increasing in angle) show some promise in the high end & over-rev end. All the chambers I build have displacements which are 28 to 30 times the engines displacement. If a tuned pipes volume is to small for the engine in question, the total length & diameter of the stinger will be greatly effected. I want the stinger's total length to be approximately 13.5 X it's inside diameter. The stinger's ID, not it's length, will greatly effect the engines operating temperature. The measured pressure in a properly designed tuned pipe used on a 15 cc to 30 cc engine at WOT can easily reach 120 inches of water (4.336 psi). Tuned pipes should always be as smooth as possible inside without any protruding welds or unmatched sections.

I would prefer to measure both the head temperature & the exhaust temperature at the same time. An increase in head temperature with a decrease in exhaust temperature indicates the engine is going into detonation!

Jim Allen

 

[dwilfong]

I have monitor eng head temp and ex gas temp with my Eagle tree in real time alone with eng RPM and GPS speed and course over lay on google maps.

It is not hard to set up and gives results on a boat running in the water.

This has bin around for many years now and many have played with it.

You can plug in to the boat after every run and see the results at the pond or make a file and save for later.

It take time and effort to do this and understand what it all means and how to use it.

Spent about a year messing with it and it did yield good results once I got the hang of how to interpret the info.

The problem with ex gas temp reading is it changes at different points on the course and the load the eng is under. every change in set up changes the results.

Now if you where just talking strait line and a short run it would help but on a boat running in race water where the conditions change it is not very help full.

There are to many variables in "real life" running of a boat to nail down just one thing it all has to work together.

The best help I received was from a good buddy that told me to "stop chasing the gun. You know when the boat is running good."

The best running boats are those from a person that understand the whole boat setup and can make it work.

Why do you think that some can make any combo run good???????

You cant teach a bird how to build a nest.....................................

Me and Julian where just talking about this and putting it on his twin. There is a wireless transmitter that will send info to a hand held unit. I think it will work on a smart phone now. this way the pit man can see the head temp and ex gas temps as the boat is running. With two remote needles the driver can change the tune as the pit person tells him on what motor to change the mix.

I almost have him convinced to try it............LOL

Getting board again.........need a challenge........................

Happy boating......................................

 

[mattb]

what I really wanted to know was pipe length and how to measure it ,the info is great thank you. I'm running a cmb .21 powerhead on a lawless outdrive.

 

[Brandon Atwell]

what I really wanted to know was pipe length and how to measure it ,the info is great thank you. I'm running a cmb .21 powerhead on a lawless outdrive.

seamstress tape works great, easy to flex around the header and pipe, just make sure you keep it in the center of the pipe/ header.

 

[Carl Van Houten]

I have monitor eng head temp and ex gas temp with my Eagle tree in real time alone with eng RPM and GPS speed and course over lay on google maps.

It is not hard to set up and gives results on a boat running in the water.

This has bin around for many years now and many have played with it.

You can plug in to the boat after every run and see the results at the pond or make a file and save for later.

It take time and effort to do this and understand what it all means and how to use it.

Spent about a year messing with it and it did yield good results once I got the hang of how to interpret the info.

The problem with ex gas temp reading is it changes at different points on the course and the load the eng is under. every change in set up changes the results.

Now if you where just talking strait line and a short run it would help but on a boat running in race water where the conditions change it is not very help full.

There are to many variables in "real life" running of a boat to nail down just one thing it all has to work together.

The best help I received was from a good buddy that told me to "stop chasing the gun. You know when the boat is running good."

The best running boats are those from a person that understand the whole boat setup and can make it work.

Why do you think that some can make any combo run good???????

You cant teach a bird how to build a nest.....................................

Me and Julian where just talking about this and putting it on his twin. There is a wireless transmitter that will send info to a hand held unit. I think it will work on a smart phone now. this way the pit man can see the head temp and ex gas temps as the boat is running. With two remote needles the driver can change the tune as the pit person tells him on what motor to change the mix.

I almost have him convinced to try it............LOL

Getting board again.........need a challenge........................

Happy boating......................................

Great feed back!

I know that there are a lot of guys out there that have been doing things the same way for years and will not try anything like this unless they find themselves at a disadvantage and start loosing races without it. The unit would have to be easy to use and reliable so that it doesn't add another level of complication to running a model. I think that this temp monitoring (Header, Head or Battery temp) has its place with a good dependable lite weight unit. What brand are you using?

 

[Carl Van Houten]

what I really wanted to know was pipe length and how to measure it ,the info is great thank you. I'm running a cmb .21 powerhead on a lawless outdrive.

Matt,

For aluminum pipes I use a black sharpie and draw a line down the top on the center line of my pipe and make a mark every inch to get the length of the pipe and clean it off with acetone when I am finished. Like MJ said seam tape can help measuring around bends. Some guys use masking tape and tape a small wire on top of the pipe on the center line and cut the ends of the wire, remove the tape and measure the wire. That works too. Curved header pipes have to be measured from the side (at the center line) to the length right.

 

[dwilfong]

Eagle Tree Systems R/C telemetry

Go check it out.....not that expensive and easy to set up and use.

There are all kinds of options for sensors and what you can record.

If you have the time to test and record the results it is the only way to go.

I had it setup in my .21 rigger it is that small and light weight.

 

[moparbarn]

To measure tuned pipe length, start at the cylinder centerline & measure along the centerline of the header & pipe to the seam where the divergent & convergent cones meet. Or to the center of the flat band, if the pipe has one. As mentioned, measure the engine & header & then the pipe as you will have to rotate around approx. 90° at the pipe/header junction. Add those 2 for a total length. I use a narrow (3/16" wide) tape measure, as it bends easily. I have also used solder, it works well too.

A little information overload, Matt? LOL! Great info, always love when folks post tech stuff like what has been posted here - whether it was what he was asking or not (-;!!

 

[lohring]

I did a little testing with exhaust gas temperatures with the Eagle Tree. I did both 3.5 and 7.5 outboard testing. These pictures should give you the idea.

Lohring Miller

 

[lohring]

A Blair pipe design spreadsheet can be downloaded at:

http://www.mediafire.com/download/t87d51tpgo3mbvg/BlairExhaustII.xls

Lohring Miller