depressions

[nevdos]

hello all
i have a jkm pitot style bench.i was wondering if i flow a head at say 28" and record my raw cfm manometer numbers, and then flow it a 27" ,and record those they will be differnent, after they are converted from raw cfm to actual .so im thinking how much of a difference would be normal, if i left the conversion number the same ,but still figured out my actual cfm .how much lower would you expect the 27" numbers to be than the 28"numbers? .the reason i ask is, i think my bench reads a little on the high side(by about 10-12 cfm as compared to two superflow 600s ive used )this is mostly on the intake as my ehx numbers seem to be inline .so ive been flowing my heads at 27in and then converting the numbers but not compensating for the different depression .doing it this way seems to put me in line with some other benches ive flowed the same ports on.is my thinking correct or am i way off.
ive got some performance trends software to install but id like to get this figured out 1st if possible
thanks

[Thomas Vaught]

12 cfm is a pretty big error.

I would invest in a orifice calibration plate from Bruce in the range you are testing in and confirm the actual flow numbers. When we did the plate exercise most of the SF benches were very close to Bruce's plate calibration number.

JMO

Tom V.

[nevdos]

forgive me if i sound ignorant ,as im no expert here .im still trying to figure out this bench .you stated("range im testing in") as in cfm i assume?i was told to try a 2" orifice test plate ,and see what it shows on my inclined manomter ,and then give those results to kevin at performance trends .then i assume he can give me a more accurate bench calibration to go along with his software i hope how do i know that my bench is off ?could it be that their benches are reading differently ,being that there a orifice type, and not a pitot tube as mine is?i flowed some heads for a friend that someone in new york ported for him .that person also used a jkm bench ,and my numbers were within 1-2 cfm of his .so i wonder if its my bench type causing this ?.either way id like to be on the conservative side with my numbers ,but also id like to believe my repeatability also :;):
thanks

[Thomas Vaught]

Quote:

"forgive me if i sound ignorant ,as im no expert here" .

I think that everyone on this board will tell you that they learn from all of the board members daily so none of us are Experts.

Quote:

"im still trying to figure out this bench .you stated("range im testing in") as in cfm i assume?

Yes

Quote:

"i was told to try a 2" orifice test plate ,and see what it shows on my inclined manomter ,and then give those results to kevin at performance trends .then i assume he can give me a more accurate bench calibration to go along with his software i hope "

I am basically saying the same thing

Quote:

"how do i know that my bench is off ?could it be that their benches are reading differently ,being that there a orifice type, and not a pitot tube as mine is?"

The Plate testing that we did had data from both orifice type benches and pitot tube type benches. The data was
very close to for both types of benches. The data was compared to a 3 million dollar Venturi type bench which
was a third type of measurement flow bench. If the orifice
plate or pitot tube or venturi is calibrated properly then the readings will be very close.

Quote:

"i flowed some heads for a friend that someone in new york ported for him .that person also used a jkm bench ,and my numbers were within 1-2 cfm of his .so i wonder if its my bench type causing this ?.either way id like to be on the conservative side with my numbers ,but also id like to believe my repeatability also.

This man says that his JKM bench reads 11% low vs a super flow 600 bench bench:



"Jack Merkel uses a JKM Custom Flow 400 flow bench for all his testing. We've found that compared to a Superflow SF-600, the JKM bench measures about 11 percent less, so if you're comparing our flow numbers to others out there in readerland, you'll want to tack on another 11 percent to our figures to get you into the Superflow ballpark."

Personally I have seen the JKM benches be all over the map on what they say the air flow is. At first I blamed it
on the orifice vs pitot tube style of reading airflow but now
I think it is more in the calibration.

JMO

Tom V.

[nevdos]

ive actually spoken to jack several times, as i was looking for info on the bench when i 1st bought it .nice enuff guy, but hard to talk to .busy like us all i guess. lol. anyways ,thats my dilemma right now, is trying to get this bench not to be all over. my biggest gripe on this thing is its repeatability factor. hard to get what i believe to be accurate numbers all the time. i guess ill try to flow it with a known plate and go from there. you mentioned someone having the corrct orifice plate. do you know how i can reach him/her ?
thanks agian Tom V.

[Thomas Vaught]

The guy who owns this Flow Bench Forum "Bruce"
makes calibration orifice plates for people on the board. Send him a PM or just post a topic and say that you are "Looking for Calibration Orifice Plates"

Tom V.

[bruce]

[nevdos]

i must be looking in the wrong place Bruce as i see the plates in the link you sent me ,but i see no part numbers or info on ordering ?

[bruce]

I'm not some big company so you have to PM or email me with what you want. I offer my parts for the DIY'er and keep the overhead* low so I can keep my prices low so the average person can build a flowbench.

This does not mean my parts are "cheap"! I can say they can be found in some well known shops around the world as well as alot of forum member's garage/shops

*Overhead: More like to lazy to go to the trouble of setting up a shopping cart page . . . keeping up with the forum can be enough hassle sometimes!