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 pitot vs orifice?? 
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Joined: Sun Feb 02, 2014 10:57 pm
Posts: 14
Location: iva sc
im new to this board, I have sum accuracy q's, first off I have a jkm 600 pitot style bench, one thing I have come to realize over the past 10 years is the superflow sf600 compared to my bench ( I have compared #'s on many) the sf orifice style seems to start inflation around 180-220 cfm and grow expinitialy from there, example, trick flow sbc 200 cc heads (hack job ported) customer brings them in for flow testing, so I flow them, @600 lift something like 270cfm, he said there suppose to flow 310@700. first off in my expiriance not many heads will flow over .600 lift, so he takes them to clements race engines for a retest and on there sf 600 thay flowed to .700 and did not lose any cfm at .800, I have seen this many times over the years, I think the orifice plate may be leaking or something? a sf 1020 will not give the same #'s as a sf 600 that should b a red flag in itself. say a head gives up @.600 lift and u open the valve to .700 and the test pressure stays the same are increases that head is dun! no matter what style, so something is leaking somewhere to gain flow? just my thoughts ( be easy on me, I just made it to the 8th grade)!!


Tue Feb 04, 2014 10:32 am
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Joined: Fri Feb 19, 2010 7:36 pm
Posts: 1628
Location: Grantsville, Utah 45 min west of Salt Lake City
powellmachine wrote:
im new to this board, I have sum accuracy q's, first off I have a jkm 600 pitot style bench, one thing I have come to realize over the past 10 years is the superflow sf600 compared to my bench ( I have compared #'s on many) the sf orifice style seems to start inflation around 180-220 cfm and grow expinitialy from there, example, trick flow sbc 200 cc heads (hack job ported) customer brings them in for flow testing, so I flow them, @600 lift something like 270cfm, he said there suppose to flow 310@700. first off in my expiriance not many heads will flow over .600 lift, so he takes them to clements race engines for a retest and on there sf 600 thay flowed to .700 and did not lose any cfm at .800, I have seen this many times over the years, I think the orifice plate may be leaking or something? a sf 1020 will not give the same #'s as a sf 600 that should b a red flag in itself. say a head gives up @.600 lift and u open the valve to .700 and the test pressure stays the same are increases that head is dun! no matter what style, so something is leaking somewhere to gain flow? just my thoughts ( be easy on me, I just made it to the 8th grade)!!


First of all let me say that your reasoning powers are pretty darn good for an 8th grade education! ;) You are doing great and welcome aboard. First let me show you where to download a tool that will be very good for you to use. You will need a spreadsheet program like Excel to use it though.
http://www.flowbenchtech.com/forum/viewtopic.php?f=14&t=73
from the very first post download the flowbench calculations.xls as it will be very valuable to you.

I personally prefer the orifice bench over the pitot, just not the SF ones. I had a pitot style bench and found that the flow element being just 2" limited my capacity at higher lifts and flows. Mine always flowed less than the other benches at the higher lifts and cfm readings until I added a second 2" flow element and used 2 flow elements at the same time. But found calibration was a bugger so I went with Bruce's plans and built a version of the bench and it worked perfectly.

What I would do is use that spreadsheet that Ed made to determine what size calibration orifices you need and either make yourself some or tell Bruce what sizes you need. Bruce's are the nicest I have seen. If you have all the time in the world and cheap aluminum plate and a way to make a precise neat hole then you can make them yourself. Sometimes you can make more money doing something else and then just pay Bruce to make them, your choice though.

Then test your bench through-out the whole range to see how it coincides with the calibration orifices on your bench then you will know for sure.

John


Tue Feb 04, 2014 4:22 pm
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Joined: Sun Feb 02, 2014 10:57 pm
Posts: 14
Location: iva sc
thanks! I will sifer on that formula, I have a full cnc machine shop ( only thing I cant make is money!! lol)


Tue Feb 04, 2014 7:06 pm
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Joined: Thu Mar 04, 2010 9:01 pm
Posts: 274
jfholm wrote:
First let me show you where to download a tool that will be very good for you to use. You will need a spreadsheet program like Excel to use it though.
http://www.flowbenchtech.com/forum/viewtopic.php?f=14&t=73
from the very first post download the flowbench calculations.xls as it will be very valuable to you

John


For those without Excel, it works with Openoffice as well.


Tue Feb 04, 2014 8:56 pm
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