Tune Pipe Pressure

[Piston1]

I am looking for the correct tune pipe fitting diameter for adequate fuel tank pressure. Big and small bore engines. I know this information is some where here but I can not find it.

JOSE

 

[steve wood]

mac's products make the only usuable fittings, that i know of. they make straight and 90 degree ones. only one size hole though. you can buy aeromarine water fittings and adapt them to the mac's pipe fitting to fit a larger hose, which i have done, but you don't need the larger hose for pressure,medium is fine

 

[waltr]

For big bore motors I use the CMDI big bore fittings, but am not aware of a chart or posting the sizes.

http://www.cmdracing.com/updated/hardware.htm

 

[tnrcboatracer]

Aeromarine also makes straight pipe fittings. I have about 150 of them on hte work bench.

 

[Piston1]

In reference to "F" size engines, I guess what I am looking for, is the bore of the CMDI Big Bore fittings. I have a theory that I am trying to "prove or disprove". On launch when you are trying to pull a high load prop (rigger), when the prop bites and RPM drops momentarily if you don't have sufficient flowpath through the fitting, then tank pressure will drop faster than what the fitting allows passing to quickly makeup therefore causing a momentary lean condition that kills the motor. I think every motor goes through this transition period that becomes more noticeable when you try to increase the prop load (pitch/dia.). Note that I am also playing with the stinger diameter and length in this project. Hope the above makes sense.

Jon when you going to come play with us Knoxville model boaters. We had roughly a crowd of 20 - 25 boats playing yesterday.

 

[Ray Sametz]

Correct me if I'm wrong, it's more volumne than pressure. A small fitting can maintain fuel flow with a full tank, the larger fitting is needed to maintain pressure with the larger vol. of air in a 1/2 empty tank. That's my story and I'm sticking to it.

 

[Piston1]

Thanks for all the answers, I think I got this case solved. Ray I think we need to use the big bore fitting.

JOSE

 

[Joe Warren]

Thanks for all the answers, I think I got this case solved. Ray I think we need to use the big bore fitting.JOSE

Jose I will forward the Large CMDI pipe fittings tomorrow USPS & check on the pipes you ask about. If I have them they will ship also. Will advise later tonite. jw.

 

[Mike Rappold]

Thanks for all the answers, I think I got this case solved. Ray I think we need to use the big bore fitting.JOSE

What is the ID of the big bore fittings (CMDI) for reference? Would like to compare this to the MACS type.

Thanks in advance.

Mike

 

[waltr]

The CMDI fittings have a .086 ID

 

[Joe Warren]

I am looking for the correct tune pipe fitting diameter for adequate fuel tank pressure. Big and small bore engines. I know this information is some where here but I can not find it. JOSE

Pressure fitting bore is 3/32. No Pipes - try Aeromarine..... But the fittings are on the way........postal. jw

 

[tnrcboatracer]

Jose, I'll PM you about running in Knoxvegas. It's the same as Huntsville as far as distance from Chattanooga; 100 miles either way.

One thing to remember; when the tanks are 1/2 empty, there is more air volume; and air is compressible. So my theory is that the potential for the lean condition you describe is more apt to happen with a completely full tank. THe half full tank has an expansion volume of air to help get through the momentary tansition. To check it out, try launching with the tanks 1/2 full, and see what happens. Let us know your results.

 

[tnrcboatracer]

Thought about this some more on the drive home; what size is the fuel feed tube and the tank hard tube? You may be experiencing line losses that don't allow the fuel feed to respond to the instantaneous load increase.

 

[Piston1]

Jose, I'll PM you about running in Knoxvegas. It's the same as Huntsville as far as distance from Chattanooga; 100 miles either way.
One thing to remember; when the tanks are 1/2 empty, there is more air volume; and air is compressible. So my theory is that the potential for the lean condition you describe is more apt to happen with a completely full tank. THe half full tank has an expansion volume of air to help get through the momentary tansition. To check it out, try launching with the tanks 1/2 full, and see what happens. Let us know your results.

Jon good point. I will try it. We are practicing tomorrow.

Jose

 

[Piston1]

I am looking for the correct tune pipe fitting diameter for adequate fuel tank pressure. Big and small bore engines. I know this information is some where here but I can not find it. JOSE

Pressure fitting bore is 3/32. No Pipes - try Aeromarine..... But the fittings are on the way........postal. jw

Thanks Joe I will call you.

JOSE

 

[Mark Bullard]

In reference to "F" size engines, I guess what I am looking for, is the bore of the CMDI Big Bore fittings. I have a theory that I am trying to "prove or disprove". On launch when you are tying to pull a high load prop (rigger), when the prop bites and RPM drops momentarily if you don't have sufficient flowpath through the fitting, then tank pressure will drop faster than what the fitting allows passing to quickly makeup therefore causing a momentary lean condition that kills the motor. I think every motor goes through this transition period that becomes more noticeable when you try to increase the prop load (pitch/dia.). Note that I am also playing with the stinger diameter and length in this project. Hope the above makes sense.
Jon when you going to come play with us Knoxville model boaters. We had roughly a crowd of 20 - 25 boats playing yesterday.

Hi Jose,

That is a very good theory you have there. I have seen the same thing myself. It is worst with bigger bore carbs that I have seen. That is why I have gone back to 0.480 bores on our twins. To easy to drop a motor on launch. I have also heard a motor stumble about number 2 bouy when I started opening the barrels and it is worse with good lean side needles. I run third channel and always richen up before launch and then lean back down these days. If your still running those HR 91's I think they have a 13mm bore or about 0.511. I think that your dead right on this and a larger bore fitting alone with 5/32" tubing in the tanks will help.

 

[Piston1]

In reference to "F" size engines, I guess what I am looking for, is the bore of the CMDI Big Bore fittings. I have a theory that I am trying to "prove or disprove". On launch when you are tying to pull a high load prop (rigger), when the prop bites and RPM drops momentarily if you don't have sufficient flowpath through the fitting, then tank pressure will drop faster than what the fitting allows passing to quickly makeup therefore causing a momentary lean condition that kills the motor. I think every motor goes through this transition period that becomes more noticeable when you try to increase the prop load (pitch/dia.). Note that I am also playing with the stinger diameter and length in this project. Hope the above makes sense.
Jon when you going to come play with us Knoxville model boaters. We had roughly a crowd of 20 - 25 boats playing yesterday.

Hi Jose,

That is a very good theory you have there. I have seen the same thing myself. It is worst with bigger bore carbs that I have seen. That is why I have gone back to 0.480 bores on our twins. To easy to drop a motor on launch. I have also heard a motor stumble about number 2 bouy when I started opening the barrels and it is worse with good lean side needles. I run third channel and always richen up before launch and then lean back down these days. If your still running those HR 91's I think they have a 13mm bore or about 0.511. I think that your dead right on this and a larger bore fitting alone with 5/32" tubing in the tanks will help.

Mark thanks for the reply. I agree with you 100%. I am setting up a new Twin rigger and it has a few different characteristics. I am testing this afternoon, hopefully (if the plant stays together). An operator tripped the reactor by mistake yesterday and now we are in a forced outage. We need you to start fabricating carburators again. I will see you in Charleston.

 

[tnrcboatracer]

Jose, do you work at Watts Bar? My neighbor retired from TVA nuc projects eng, and now works for Bechtel. He tried to get me to apply for a contractor position with Bechtel at Watts Bar, and then go with him to the APW1000 job at Belafonte (if it ever happens). Sequoyah is just up the road from me about 10 miles. Lots of nucs in the TN river valley.

 

[Piston1]

Jose, do you work at Watts Bar? My neighbor retired from TVA nuc projects eng, and now works for Bechtel. He tried to get me to apply for a contractor position with Bechtel at Watts Bar, and then go with him to the APW1000 job at Belafonte (if it ever happens). Sequoyah is just up the road from me about 10 miles. Lots of nucs in the TN river valley.

Yes, I am a Mechanical Engineer at Watts Bar Nuclear Plant. I am the Primary Reactor Containment Test Programs Engineer at WBN. Who is your Neighbor I probably know him? Are you familiar with the Westinghouse AP1000 design planned for Bellefonte in Alabama .

 

[Piston1]

Jose, I'll PM you about running in Knoxvegas. It's the same as Huntsville as far as distance from Chattanooga; 100 miles either way.
One thing to remember; when the tanks are 1/2 empty, there is more air volume; and air is compressible. So my theory is that the potential for the lean condition you describe is more apt to happen with a completely full tank. THe half full tank has an expansion volume of air to help get through the momentary tansition. To check it out, try launching with the tanks 1/2 full, and see what happens. Let us know your results.

We ran today. The increased tune pipe pressure helped but I am not completely satisfied with the launching torque of my rigger. Ran at least 10 fuel loads. I think it is time to experiment with a more broad pipe, maybe bigger TP volume and/or longer TP.