flow bench calibration

[scooter]

So I finally got my flow bench together after a year of changed plans and revisions. I ordered some test plates 100,170,280,425 I'm testing at 28" and 15" differential. I turned my orifices out of 1/8 aluminum with 45 degree back cut, I couldn't figure what exact size they needed to be so I taped the 425 plate down to the bench and kept enlarging the orifice in the lathe until I got 100% on my inclined mano, I did all the rest that way as well, time consuming but effective. now the moment of truth I taped the 280 down and fired the bench up set the pressure at 28 and got 65.6% on the incline. I got my phone out punched that in the calculator and to my amazement it was 278.8. I was blown away by the accuracy. did the same with all the rest and they were all within 2cfm. So I put a oem ls7 that I have had flowed on a sf600 and flow numbers that I found online confirm that the numbers were accurate. should flow 364cfm at .600. I could only get 329cfm out of the head. checked the test plates again still good. the .200-.300. numbers were very close on my 280 orifice. but .400 .500. 600. and .650 numbers were not in the realm of accuracy I expected. as the lift increased the accuracy decreased. I repositioned the head checked for leaks but cant seem to find any thing wrong. any advice would be greatly appreciated.

[1960FL]

if you search for Ed's spreadsheet and apply the Delta P that the orifice will be exposed to you will see the rated flow, In this you can use trial and error with different diameters to sneak up on your wanted flow rate.

Rick

[scooter]

Yes acordingx to the orifice plates I bought from Bruce the bench is within 2 cfm, but when I put a head on the bench that has a known flow number I am ways off of what the plates say I should be, the head was flowed on a 4.150 bore. I have a 4.160 bore. If I flow on 4.500 it is closer but still not in the realm of accuracy I expected

[Brucepts]

You have a way of knowing the other flowbench that tested that head was correct?

[1960FL]

should flow 364cfm at .600. I could only get 329cfm out of the head. checked the test plates again still good. the .200-.300. numbers were very close on my 280 orifice. but .400 .500. 600. and .650 numbers were not in the realm of accuracy I expected. as the lift increased the accuracy decreased. I repositioned the head checked for leaks but cant seem to find any thing wrong. any advice would be greatly appreciated.

You cannot calibrate a flowbench with a head!, this whole situation is common place in the world of head porting there is no way of knowing that your setup and methodology is the same as the other people flowing that head. What are you using for an inlet radius? also your internal plate should be at least 25 to 50CFM larger than max cfm of what you are trying to flow. Dumb question but is the sharp edge of the internal orifice pointing toward the incoming flow?

Rick

[scooter]

Was not trying to calibrate with the head, I calibrated it with the test orifices that I got from Bruce at which the bench is spot on. I then put a head on the bench and I did not get the expected results. I moved the intake valve away from the bore and picked up 3cfm moved it back and went back to original reading. I asked the guy who flowed the head if he would check my orifices and he told me no, so maybe his bench is off and he knows it. But there is a ton of info on these heads online and the flow that every one seem to get out of them is what he got on his bench. these are OEM ls7 heads. I guess I'm just trying to figure out if im doing something wrong, This is the first head I've ever flowed on my own bench

[scooter]

So the problem I'm having is with the radius entry, I'm making it out of clay and I think it's too small. I doubled it in size and was able to keep the port from going turbulent until 650. 260cc runner flowing 370 has a lot of velocity I guess. Any one have any recommendations on exacty how big my radius entry should be.

[1960FL]

So the problem I'm having is with the radius entry, I'm making it out of clay and I think it's too small. I doubled it in size and was able to keep the port from going turbulent until 650. 260cc runner flowing 370 has a lot of velocity I guess. Any one have any recommendations on exacty how big my radius entry should be.

And now the education begins, I was not saying you were tying to calibrate the bench with a head i was referring to the fact that you were questioning the bench that you new was calibrated. What you have to understand is to be successful on the flowbench you have to stop comparing your numbers to others as it only will lead you down a rabbit hole. In this i believe you will learn the a great bit about the head industry and things you see on the internet. People will claim numbers and then you look at their inlet radius and say NO WAY, some glob of putty that looks like the kids put it on there! If .010 off the short turn will move the numbers x CFM what do you think that big old thumbprint in the clay radius is doing to the air coming in?

The flowbench in the shop is a comparator not a micrometer (Until you learn it and trust it) I would suggest finding a 3/4 to 1" thick piece of plastic board (fypon they sell pvc baord at HD) etc. and build yourself an inlet radius with at minimum a 1/2 radius even on all sides, spend the time and make the tool actually make several so you have them for different port inlet dimensions you may be working with they will serve you well.

Rick

[scooter]

Thanks for the advice Rick, what would the best method to make the radius with, maybe cut and fit the hole to the head then use a radius bit in a router to shape it? I know all benches and methods are different, but once I got the radius correct the head flowed within 5cfm at all lifts of what it flowed on the sf600. I feel that is accurate enough for what I'm trying to achieve

[1960FL]

Yes i like to use a router or because my personal shop is well equipped i may turn one on a lathe or mill here is an example of one i use to flow stock port Harley heads as you can see it is a clean exact part that will promote even flow. What you will learn is that a little bump up stream can do crazy things down stream in high speed air, as you saw with this LS head and inlet.

Rick