converting to 28h2o

[slowkaw]

Hope someone can help. I know there is a formula to convert a flowbench reading from 10" H2O to 28" H2O. The flowbench I have access to is 10". Thanks.

David

 

[MaxRaceSoftware]

David,

New_Flow = Old_Flow * ( New_Pressure / Old_Pressure ) ^ .5

334.664 CFM = 200_CFM * ( 28 / 10 ) ^ .5

334.664 CFM = 200_CFM * 1.673320053
===================================================

example for Holley 500 cfm 2-barrell carb
at 2-barrell rating at 3.0 inches Hg. -VS- 1.5 inches Hg
4-barrell rating

353.55 CFM = 500_CFM * ( 3.0_Hg / 1.5_Hg ) ^.5

As you can see ..a Holley 2-barrell 500 CFM carb is really a very small carb ( 354 cfm ) ..when compared to a Holley 4-barrell 500 CFM carb

Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[MaxRaceSoftware]

David , if you want to go the other way , then just calculate the "Reciprocal" which is 1/x

10 to 28 = 1.673320053 conversion factor

1 / 1.673320053 = .597614305

28 to 10 = .597614305 conversion factor


Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[GregLocock]

Hi Larry, in practice do you need to worry about laminar flow effects or other non linearities possibly caused by Reynolds number when you do a run at two different pressures? Cheers

Greg Locock

 

[MaxRaceSoftware]

Previous Post in ERROR
353.55 CFM = 500_CFM * ( 3.0_Hg / 1.5_Hg ) ^.5
===============================================

Should be
353.55 CFM = 500_CFM * ( 1.5_Hg / 3.0_Hg ) ^.5
=================================================

Greg, there is another small correction factor used by SuperFlow with the normal conversion factor
this might be a small Reynolds type correction ???

Most people just use the Test Pressure Conversion equation i just posted as its pretty close (Linear)

if you use the additional SF correction factor , its
even closer

if the Test Pressure is too low , the air speed will be low
and if theres a bad curve or any problem area in port or valve area , it won't show up at low airspeeds because air is flowing slow enough to follow bad curve , but at higher speeds (Test Pressures) , the same port will flow different numbers or in a live engine make less HP than the flow bench predicts.







Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[MaxRaceSoftware]

Greg ,
additional info ;
SuperFlow doesn't use a Laminar Flow Element
they use Orfices.

When flowtesting on SF bench
especially above 20 inches of water
the flow is always in turbulent range (> Reynolds laminar value ) Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/