Calibrating new bench

[coulterracn]

I have a three inch orifice plate inside the cabinet. According to spreadsheet calculations Is 298.9 CFM. My incline manometer is level and the scale is dead on '0'. My vertical manoneter is dead on '0'. I mounter a 1.525" ID orifice plate that was calibrated on a SF-600 bench @ 28" = 166.51 CFM.

I turned on the bench in intake flow mode and at 28" my incline scale reading was 60%. Do the math and that is 179.34 CFM. Could the 3" orifice be flowing more than the spreadsheet calculation? If so how do I go about calculating this number?

Ray

[jfholm]

Ray,

Let's stop and analyze this whole thing out. First did you measure the i.d. of the orifice and is it indeed 1.525"? If it is then the SF 600 was very close as I calculate that size orifice with a .62 cd to flow 166.859 CMF at 28" H2O. Let's assume that it is correct.

Now if I remember correctly you are running a inclined manometer that is 20" long with a 6" rise. Also I think you said that you are using Dwyer or Merrimum gauge oil which is only .826 specific gravity. I do not know what the resevoirs and tubing is on the manometer but will take a guess. Your Delta P is not 6" which is the rise of your manometer. Take Ed's inclined spreadsheet and input your manometer settings. I came up with a Delta P of 5.41" H2O.

On Ed's inclined manometer spreadsheet the Delta P you use to calibrate is the third column of the blue numbers under Inclined Manometer Scale at the bottom. It would be the last reading to the right of the 100% reading. In you case that would be 5.41" H2O NOT 6".

Next step is to use the spreadsheet to calculate the 3.00" flow at 5.41" and if it is a "sharp" edged orifice use .609 for the cd and you get 278 cfm.

Now what is 60% of 278 cfm? comes out to 166.8 cfm and that is right where the Superflow is. I will bet you a coke that your bench is right on the money. You just have to calibrate your orifices inside the bench with 5.41" not 6".

John

[jfholm]

Maybe a little more explaination. Your rise on your manometer is 6" it does not matter the length of the scale as you are still just raising the level 6". You are probably asking why then do you not just use 6" for your delta p?

If your fluid was water then it has a specific gravity of around 1.00. So not including you resevoir diameter or id of your tubing it takes 6" h2o to raise the water 6".

Since you are using red gauge oil that has a specific gravity of .826 it take less "suck" "pressure" whatever to raise it the same 6" height. It is a "lighter" fluid and raises easier.

But taking into consideration for resevoir id and tubing id (which I tried an educated guess) is how I came up with the 5.41" h2o using Ed's spreadsheet as a calibration delta p for your flow bench orifice.

John

[coulterracn]

John

I now have a much better understanding of what values to use for the calculations and why.

The reservoir on the Dwyer incline manometer is .750" id. I'm not sure of the tubing size id. I had to remove the drain plug to lower the fluid level and the drain plug is about the size of a #10 screw. I can drain the gauge and measure the size of the tube if that will get us any closer to perfect.

I like the idea of being dead on perfect if I am able to do so. That way when you give the customer an astimated et (elapsed time) or horsepower rating and they run the car/bike and are almost dead on you gain a lifetime friend/customer.

There is a well know engine builder on the Mississippi Gulf Coast area whose Dyno is inflated by 75hp and his Flowbench is calibrated to give higher flow numbers. He has alot of repeat business but they are disappointed because their cars won't run as fast as they're told.

Thank you for explaining the finer details of the calculation,
Ray

[coulterracn]

John

I do know the calibrated orifice is 1.525"id. A friend had it calibrated on Larry Meaux's SF-600. Larry measured the Orifice and wrote the formulas and values on the orifice plate. I transfered that same information to the notes section of a book I purchased about flowbenches and cylinder heads. I feel that would be the best way to keep up with the information for future reference.

I had the 3" orifice plate cut on a plasma cutter at a local shipbuilding industry. I checked it with my digital calipers but will check it again to validate the measurement.

Ray

[coulterracn]

Hey Guys

I used some modeling clay to make the radius entry on the 'As Cast' intake port of a Trick Flow Twisted Wedge SBF head. I recorded CFM numbers very close to Trick Flows advertised numbers. I recorded some good CFM numbers on the mildly ported intake port on the other head.

I'm very satisfied with the capabilities of the PTS flowbench. Great job on the design Bruce.

I will post pictures taken of the head on the bench during yesterdays flow test.

Ray

[thomasvaught-1]

The inclined manometers from Dwyer come calibrated for a correct reading of 6" (H20) at full scale (100%) with the .826 manometer fluid. That is built into the design of the part and the scale. When the manometer is level and properly zeroed the delta P WILL be 6" at
full scale. You can easy check this by hooking up a 'U-Tube" manometer in parallel with your inclined manometer (using pure water) and when the one leg is 3" up from the at rest position (the other leg will be down 3" for a total of 6" delta P. The inclined manometer will read 100 percent. You can check this easily using a hand vacuum pump to move the fluid.

Tom Vaught

[jfholm]

Tom,
That is a great way of doing it. It is so simple! and it proves your Delat p, correct?

So after I get my home made inclined done I can just do what you have stated and it will give me the true delta p, Am I correct in assuming this?

John

[coulterracn]

[thomasvaught-1]

Yes John.

And if the incline is not at 100% on the scale you can easily adjust the incline angle to get exactly at 100 % = 6" or what ever number you choose.

Ford did this for years in their Carburetor Flow Stands.
Their Inclined manometers allowed vernier adjustment for exact calibration on their flow stands.

Tom Vaught