Optimal ID pipe pressure size?

[Bradley Maglinger]

I am building a couple boats and going to run an aluminum hard line for one of them and it got me thinking on which size to run, which I have never questioned myself. I know my Tetra fitting at the pipe is .09 (3/32) that I am using on one of the builds so I decided to use a 1/8 OD aluminum tubing to help keep it the inside clean or high and tight as some would say. Then I got looking at the (Tetra)Pipe Pressure fittings from Zippkits and the ID for that fitting is .065, then I see some 101 guys are running these really big pressure fittings, so it really raises some questions…

• So what is the optimal ID size for pipe pressure fitting and does it vary from engine size or pipe volume size?
• What is the optimal ID tubing size for tank inlet and outlet, and does it matter if there is a hopper in line or a third tank such as hopper tank with two saddle tanks? Remember we are moving liquid here, and not air.
• What is the optimal ID tubing size from tank to needle valve?
• Last but not least, you guessed it…Needle to carb optimal ID tubing size?

Educating myself and reaching out to members is one of my top 5 reasons I love this hobby, as it allows myself to really dig deep and try to figure out/understand why we use certain items. Which in turn, keeps moving the needle forward, by trying something new and or find out if I left some money on the table. Thank you in advance to everyone or anyone that would like to give their opinion or feedback on this.

 

[gilbert galli]

I use tube for the pipe pressure of 2.5mm id for the 21 engine and 3mm id for the 45 and 91 engine, the exhaust pipes are equipped with noise reducers, the limit in Europe is 80 db

 

[larcor69]

I have been thinking about this myself and was thinking using 2 pipe fittings into a Y and using 5/16 tubing in and out of my Sullivan plastic fuel tanks instead of the 1/8 inch tubing,

 

[ACTION JACKSON]

May be wrong about this but I would just try all the sizes on all pipes. A lot to consider. Could you take away back pressure from pipe with bigger hole. So you might run a single or double tank, how much line will be ran with a double tank & do you need a bigger tube from tank to 2nd tank back to normal then to motor. The other is should we or can we use a check valve going into tank to hold the pressure on the tank so not to wonder if hole size matters. Just my thought on the matter. I have never tried different sizes, but I do know this Bradley, your a family that has experimented on your boats most of your family's boating life . I have watched you all change things for the better over years. So try all diameters & see. Have an awesome boating life.

 

[dave roach]

Brad
Are you going to run one tank or two.if you run one tank1/8 pressure fitting is fine.two tanks i would run a large one. It matters on what the engine size it is.Walt told me long time ago.

Dave

 

[Samuel Hagan JR]

Brad while I was testing dual tanks in the Graham Scale I found that the pressure fitting size didn’t matter at all. That boat ran two tanks. The biggest concern was the size of the line going from tank to tank was bigger than the size of the line coming out of the tank. Just my testing from that. I think we spent all day on testing that.

We also tried running 2 pressure fittings. One going to one tank and the other going to the other tank going to a Y. Didn’t work. The tank with the less resistance drained first and left one full.

 

[Walt Barney]

Brad while I was testing dual tanks in the Graham Scale I found that the pressure fitting size didn’t matter at all. That boat ran two tanks. The biggest concern was the size of the line going from tank to tank was bigger than the size of the line coming out of the tank. Just my testing from that. I think we spent all day on testing that.

We also tried running 2 pressure fittings. One going to one tank and the other going to the other tank going to a Y. Didn’t work. The tank with the less resistance drained first and left one full.

Pressure is not not the problem most of the time , most twins and large engines need volume morhan pressure to keep the fuel flowing to the carb in a steady fashion.
Walt Barney

 

[Terry Keeley]

IIRC Jim Allen tested his 90 pipe pressure at about 3 psi so just about any tube/fitting whatever would pass that along to the tank.

Fuel is a different story, especially at the rate our little motors drink it. I like to keep the lines as short as possible and use 5/32" brass in the tank and large lines, that way the needle meters the fuel and not the line restriction.

 

[gilbert galli]

I have a FSR V 91 engine endurance imbra, the boat have 3 fuel tanks, fuel tanks left and right have a capacity of 1.8 liters and the central tank 0.6 liters for a total volume of 4.2 liters, the side tanks are pressurized by 3mm id hose with T and the fuel is pushed towards the central tank by hoses of 4mm id, the central tank feeds a tank with constant level of 4mm id and the engine sucks the fuel constant level tank by the hose of 3mm id, it is necessary to give blows of gas to maintain sufficient pressure when starting, then the boat can navigate more than 30mm without problem

 

[Brian Schymik]

Brad
This was a interesting discussion many years ago with Brian the engineer and Marty on the old site. Pipes with many pressure taps built in and testing locations and size
My real life takeaway is to use a 10/32 pressure tap on the converging cone section of a pipe with large fuel line to the tank

 

[Tim Kish]

IIRC Jim Allen tested his 90 pipe pressure at about 3 psi so just about any tube/fitting whatever would pass that along to the tank.

Fuel is a different story, especially at the rate our little motors drink it. I like to keep the lines as short as possible and use 5/32" brass in the tank and large lines, that way the needle meters the fuel and not the line restriction.

So a fitting with .062 I'd. in theory should work on a 90 ?

 

[John Beardslee]

Brad
This was a interesting discussion many years ago with Brian the engineer and Marty on the old site. Pipes with many pressure taps built in and testing locations and size
My real life takeaway is to use a 10/32 pressure tap on the converging cone section of a pipe with large fuel line to the tank

If I remember right, they saw as high as 5 psi on the pipe pressure tap while testing on the dyno.

 

[Timbo Whalen]

I've always just kept it AT LEAST the same size as carb inlet, stock or drilled. Works for me.

 

[Terry Keeley]

So a fitting with .062 I'd. in theory should work on a 90 ?

For ***** and grins I put 24" of medium Prather line (1/8" ID) on my old school flowmeter with a standard 0.075" ID pressure tap on the end. At 10" water pressure it flowed 6.75 CFH.

I then put an 0.052" ID fitting on the end of the line and it flowed 5.75 CFH at the same pressure, only about 15% less. So yes, I would think an 0.062" ID fitting would pass enough pressure to the tank.

 

[Jeff Lutz]

If I remember right, they saw as high as 5 psi on the pipe pressure tap while testing on the dyno.

John, I’m guessing that your a little off on their findings. I’ve put pressure gauges on pipes and crankcases on numerous setups over the years. Most people will only see around 2- 2 1/2 lbs of pressure in our boat setups. In some cases 1 1/2 . On a test stand pushing it really hard maybe a little more. Jeff Lutz

 

[John Beardslee]

Maybe. They did some pipe testing as well to optimize pressure tap locations and other variables. It might have been when they were working with stinger I.D’s. Marty might chime in but he doesn’t visit here very often. He isn’t entered in the Nitro Championships this weekend but may stop by. I’ll try to remember to ask him about it if he’s there.

 

[Marty Davis]

Maybe. They did some pipe testing as well to optimize pressure tap locations and other variables. It might have been when they were working with stinger I.D’s. Marty might chime in but he doesn’t visit here very often. He isn’t entered in the Nitro Championships this weekend but may stop by. I’ll try to remember to ask him about it if he’s there.

At this low pressure I believe that the minimum diameter of the fitting is the controling factor. A larger fitting really is overkill and won't affect the result. We did some testing on the dyno years ago and found this to be true.

 

[Tom Foley]

Aluminum will work harden over time with vibration . Brass tube would be much better and weight difference would be insignificant IMHO .

 

[Daniel's Racing]

You don't want a bigger tube than you have flow to pass through it or the extras size(volume)of tubing would diminish what flow and pressure you started with.
Small size tubing seems to be fine for pressure on most all sizes of engine fuel systems. I think you get more consistant pressure with small line as well.

 

[Phil Mitchell]

I am building a couple boats and going to run an aluminum hard line for one of them and it got me thinking on which size to run, which I have never questioned myself. I know my Tetra fitting at the pipe is .09 (3/32) that I am using on one of the builds so I decided to use a 1/8 OD aluminum tubing to help keep it the inside clean or high and tight as some would say. Then I got looking at the (Tetra)Pipe Pressure fittings from Zippkits and the ID for that fitting is .065, then I see some 101 guys are running these really big pressure fittings, so it really raises some questions…

• So what is the optimal ID size for pipe pressure fitting and does it vary from engine size or pipe volume size?
• What is the optimal ID tubing size for tank inlet and outlet, and does it matter if there is a hopper in line or a third tank such as hopper tank with two saddle tanks? Remember we are moving liquid here, and not air.
• What is the optimal ID tubing size from tank to needle valve?
• Last but not least, you guessed it…Needle to carb optimal ID tubing size?

Educating myself and reaching out to members is one of my top 5 reasons I love this hobby, as it allows myself to really dig deep and try to figure out/understand why we use certain items. Which in turn, keeps moving the needle forward, by trying something new and or find out if I left some money on the table. Thank you in advance to everyone or anyone that would like to give their opinion or feedback on this.

Olav AAen was the master of 2 stroke snowmobile engines. You might look at
aaenperformance.com to see what they might say.