flow bench program
Discussion
Why exhaust ports don't need to be flowtested is explained in Part C of my treatise on valve seats here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Exhaust ports will flow like gangbusters if you just get the valve seat and port size correct. Most of inlet port flow testing is about getting the short side radius right and exhaust ports don't give a damn about that.
Finally, every percentage point in extra inlet flow will give a corresponding power gain. To get 1% more power from exhaust ports you need about 10% more flow. A poor flowing exhaust port won't actually stop the gases getting out of the engine, it'll just generate a bit of a pumping loss.
However if you really want to you can flow test exhaust ports easily enough on a bench like mine by sucking through the exhaust port rather than having the head on a bore adaptor.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Exhaust ports will flow like gangbusters if you just get the valve seat and port size correct. Most of inlet port flow testing is about getting the short side radius right and exhaust ports don't give a damn about that.
Finally, every percentage point in extra inlet flow will give a corresponding power gain. To get 1% more power from exhaust ports you need about 10% more flow. A poor flowing exhaust port won't actually stop the gases getting out of the engine, it'll just generate a bit of a pumping loss.
However if you really want to you can flow test exhaust ports easily enough on a bench like mine by sucking through the exhaust port rather than having the head on a bore adaptor.
Edited by Mignon on Tuesday 6th November 15:24
Mignon said:
pingu393 said:
You don't seem to make allowance for any changes in air density as the air is heated and pressurised.
My bench has the vacuum source downstream of the measuring orifice so no heating of the air takes place inside the bench. I calculate the air density correctly for pressure drops and ambient temperature.
I wasn't sure that my vacuum pump would have enough oomph to do that. With hindsight, it probably would as it blew the side of the box when I was testing it this afternoon
Mine is TEST ORIFICE - PUMP - MEASURING ORIFICE.
Edited by pingu393 on Tuesday 6th November 18:19
Chuffed t'bits for two reasons...
1) this version of the spreadsheet...
ISO 5167 Flow Calculator
I've done all the calculations based on ISO 5167 as my copy is more recent (2003) than my copy of BS 1042 (1981). I'm assuming that Stolz' equation has been superseded by Reader-Harris/Gallagher's equation. I have a 2004 copy of ASME MFC-3M-2004, and it uses Reader-Harris/Gallagher as well. I've included hyperlinks to copies of the ISO standards on the "Notes" worksheet.
I've done some digging and found the calculations used to find air density, dew point and to correct the ambient pressure. It is no longer necessary to look these values up in tables or on-line calculators.
All the inputs that are specific to your system are in the worksheet "Inputs - Constants".
The inputs that are for each test go in the worksheet "Inputs - Variables". The dynamic viscosity and the isentropic exponent need to be found from the internet and input in the worksheet "Inputs - Internet".
The flow rate and the value for the discharge coefficient will be calculated automatically and are to found in the worksheet "Results"
2) My system.
I ran two tests. One with an 89.5mm orifice and the other with a 29.5mm orifice. I three tests on each orifice, alternating between the orifices and the value for the discharge coefficient was 0.614 for the 89.5mm and 0.616 for the 29.5mm.
I think that to have a such a small difference in the discharge coefficient using a homemade flow bench is not half bad.
Next challenge is to use a flow straightener and to shorten the upstream pipe length.
1) this version of the spreadsheet...
ISO 5167 Flow Calculator
I've done all the calculations based on ISO 5167 as my copy is more recent (2003) than my copy of BS 1042 (1981). I'm assuming that Stolz' equation has been superseded by Reader-Harris/Gallagher's equation. I have a 2004 copy of ASME MFC-3M-2004, and it uses Reader-Harris/Gallagher as well. I've included hyperlinks to copies of the ISO standards on the "Notes" worksheet.
I've done some digging and found the calculations used to find air density, dew point and to correct the ambient pressure. It is no longer necessary to look these values up in tables or on-line calculators.
All the inputs that are specific to your system are in the worksheet "Inputs - Constants".
The inputs that are for each test go in the worksheet "Inputs - Variables". The dynamic viscosity and the isentropic exponent need to be found from the internet and input in the worksheet "Inputs - Internet".
The flow rate and the value for the discharge coefficient will be calculated automatically and are to found in the worksheet "Results"
2) My system.
I ran two tests. One with an 89.5mm orifice and the other with a 29.5mm orifice. I three tests on each orifice, alternating between the orifices and the value for the discharge coefficient was 0.614 for the 89.5mm and 0.616 for the 29.5mm.
I think that to have a such a small difference in the discharge coefficient using a homemade flow bench is not half bad.
Next challenge is to use a flow straightener and to shorten the upstream pipe length.
I've posted the algorithms for the spreadsheet on the thread for my flow bench
https://www.pistonheads.com/gassing/topic.asp?h=0&...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
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