DIY Super Accurate Flowbench

[FlowSpecialist]

Originally Posted by Stan Weiss

Isn't all flow bench testing subjective?

Especially when the flow bench isn't accurate!

Here's a very weird thing Stan. I was Googling for Pinto flow test data until someone posts what DV achieved and came up with your website. On it there's a set of standard Pinto figures showing 40, 76, 104, 119 and 127 CFM at 100 to 500 thou lift. Very peculiar I thought because all your data is stated to be at 28" and those figures are too low for even 25".

I thought no more of it for a while and then today I was going through some data stored on my pc and came across flow figures from a guy I used to work with 20 years ago called Peter Burgess who is an MGB specialist in England. Pete designed his own flow bench and wrote a magazine article about it in about 1988 and I got in touch to find out more. My first bench was a copy of his but when I came to calibrate it against orifice plates I found it didn't work at all. I investigated further and found that Pete had made various errors in the design from which I moved on to my own design with those errors eliminated.

Well before we stopped working together I entered all his flow data for numerous heads into a spreadsheet and this morning I was looking through it and came across the Pinto section. Put me in a pink dress and call me Shirley but damned if the data isn't exactly what you have on your website.

How in hell did you get an obscure little British engine tuner's flow figures for a Pinto head? What an incredibly small world it is. I can even give you the non-rounded numbers which are 40.5, 75.9, 103.8, 119.1, 127.0. Bet you a pound to a penny that's what you have in your records somewhere.

Anyway firstly they're at 25" and you haven't corrected to 28" and secondly they're all wrong. His bench is miles out. It reads too low and also has a non linear error so the error % changes as the flow rate changes. It gets closer to accurate at high flow figures but at low ones it reads at least 15%, even 20%, low. It was actually DV who helped me find one of the errors which was that Pete's pressure tapping to measure the pressure drop across the head wasn't at the top of the downpipe the head sits on. Pete had it at the bottom of that pipe and was measuring pressure recovery after the flow had stabilised again.

Here are accurate figures at 25" off my own bench for a standard early non injection head and then for a later injection Sierra head which had a nicer shortside bend and accounted for much of the 10 bhp increase the injection engine showed over the early Capri and Cortina carb engines.

LIFT...EARLY...INJECTION
100.....52.............46
200.....91.............89
300....116...........126
400....128...........140
500....136...........147

Any other figures you have from that source such as MGB will also be wrong and best deleted.

Looking forward to hearing how you got those numbers.

Dave

[Stan Weiss]

Dave,
To be honest there is data for a number of heads in that chart that I have no idea where it came from anymore. How about a Pinto Billet Head that flow 330 CFM @ .700 lift. Log inSpeed Talk
Stan

[FlowSpecialist]

Originally Posted by Stan Weiss

Dave,
To be honest there is data for a number of heads in that chart that I have no idea where it came from anymore.
Stan

Oh well. I was hoping there'd be an interesting story in there somewhere.

If you ever do recall I'd like to know.

Dave

[FlowSpecialist]

I may have the answer Stan. Seems like since I knew him Mr Burgess has written a book called How to Build, Modify and Power Tune Cylinder Heads with case studies on the Pinto, MGB, Rover V8 and others. That will no doubt have all those old inaccurate flow figures from 20 years ago in it. Does that ring any bells now?

Dave

[Stan Weiss]

Originally Posted by FlowSpecialist

Here are accurate figures at 25" off my own bench for a standard early non injection head and then for a later injection Sierra head which had a nicer shortside bend and accounted for much of the 10 bhp increase the injection engine showed over the early Capri and Cortina carb engines.

LIFT...EARLY...INJECTION
100.....52.............46
200.....91.............89
300....116...........126
400....128...........140
500....136...........147

Any other figures you have from that source such as MGB will also be wrong and best deleted.

Looking forward to hearing how you got those numbers.

Dave

Thanks Dave.
I have converted your numbers to 28" of water and added them to the table. I also added a note to the accuracy of the other Pinto numbers. I would appreciate any flow data that you would like to share. Weather it is for heads that are already listed in the table or for heads for which there is no listing.
Stan

[marti]

Dave,
Please see my message at PORTING SCHOOL #4 ARTICLE/THREAD
AUG, 24,08.
Tks,
Jorge

[marti]

Dave, please give an example of M1 and M2 readings and the CFM calculation.
Trying to understand the formula.
For 10" WC orifice target flow 137.86 change to 87.2 . Is it correct?
Is the square root just for M2/M1, not including the target CFM (103 in your example) ?
Tks,
Jorge

[Randy W.]

Dave:
If i was to build a flowbench like u describe and wanted to flow big block chevy engines with bore sizes of say 4.500", would a down pipe size 0f 6.00" be about the correct size?
Also how did u construct the orfice plate holder?
Regards
Randy