Homemade Flow Bench

[Kelly Murray]

Here is my archived mail on flowbenches
if it helps anyone.  -kelly murray  kem at franz.com
---
Someday I'll put up a summary and pictures of my experience building
one on my website.
I can't find my old message in the dragnet archives, but I did find
Eric Moore's reply, which I've appended to this message at the end.

This is my experience:
I used the Popular Hot Rodding articles (Oct, Nov '93) as a guide, but built
a smaller, simpler, limited unit for under $150, using leaf-blower
motors.  It took a lot of time to build, mostly making the cabinet.
It also makes a huge amount of noise.  You're neighbors will hate you!
My wife eventually wouldn't let me run it when she was home!

It was useful when porting my 460 heads.
It told me attempts to improve the intake made things no better
or even worse, but showed a major improvement by backcutting the
intake valve, and using a reduced-stem diameter valve.
It showed the improvement of raising the exhaust port floors,
from which info I've sinced used to build exhaust port-plates
(though primarly to bolt-on BBC headers onto a BBF head, but
nevertheless, I wouldn't have gone this route if I didn't have that info)

The above 460 info isn't really new, many articles on 460 heads have
indicated the same thing.  However, at least one of them states
the data backwards, saying to leave the exhaust alone and raise
the intake ports, so as always in general, double check all your
information sources, mine included!

I plan to use the bench for the new 506ci heads,
which are getting bigger valves than stock, so the grinding will
be more critical to get right and the bench will come in handy.
I'll add more flow capability for this job.

I'm not racing in heads-up classes, so the truth is it was a complete
waste of time from a practical point of view.
It doesn't really matter how good the heads were improved,
or even worsened!
If they picked up .2,
it still wouldn't be worth all the time and effort to build the bench
and spend time porting and testing and porting and testing and
porting and testing...

However, it was interesting to build and learn and play with, just like
most of the time I "waste" car/engine building.
I do intend to use it for my next major project car, where it will
have a more direct benefit, which is improving gas mileage
for my daily driver project.   If I follow through on my next
life goal of learning how to build electronic devices, 
I'll add more sophisticated data collection to the bench.
A Mass Air Meter off an EFI system seems like an inexpensive way to
add a more directly measurable and recordable values.

I made copies of the PHR articles, and I'll see if I can find them
in my office.  They were probably lost when I moved from FL.
I recall the PHR article was missing critical
information about to setup and read the manometers, and for the life
of me I can't remember it either!

Finally, if you live in the SFbay area, I'd consider loaning
the cabinet out if someone want's to play with porting their heads.

Hope that helps.

-Kelly Edward Murray   kem at franz.com   Hercules, CA


Eric Moore's old post on the subject (hope you don't mind Eric..)

------
I designed a flow-bench awhile back on paper, and researched some of the ways o
ther 
people have done it. You will quickly learn that the funcionality of the bench 
is 
directly proportional to the amount of money invested. To build a commercial qu
ality 
bench, you really need to incorporate a laminar flow element such as that avail
able 
from Merriam Instruments (216-281-1100). This is a precisely built set of air 
passages whose flow characteristics are known EXACTLY. Using the characteristic
s of 
the element, two manometers (which, for reliability and accuracy should also be
 
purchased commercially as opposed to making oneself) can be used to measure flo
w 
through the port or venturi. After getting your basic setup laid out, you have 
to 
start deciding how many bells and whisltles to pay for. Bryzinski and Quadrant 
Scientific sell many of these gadgets, like swirl meters and sliders. there is 
a 
WHOLE lot to know about building flow benches, and you should find out as much 
as 
possible before diving into your project. One of the most valuable sources I fo
und 
was Jerry Goodale at SMS in Riverside California. He does contract R&D for Chry
sler 
and designed the Viper cylinder head. He designed and built his bench many year
s ago 
and has been adding to it and modifying it ever since. He said that people ofte
n 
come from other states to take pictures and pick his brain. He offered to mail 
pictures and diagrams if I sent a SASE. He would probably do the same for you. 
If 
you would rather start afresh, find a good textbook from a college engineering 
course in fluid dynamics to get the formulas required to calculate flow through
 a 
metered orifice for a specific pressure differential. 
	One tip- use enough vacuum power to measure at at least 20" of H20. Eve
n 
though there is a formula to directly convert lower differentials to higher one
s, 
figures like 25" and 28" draw a much better picture of what happens in the head
 when 
it's on your motor. If you are interested in any of these sources, mail me and 
I'll 
dig up everyone's phone numbers. Good Luck.

Erik Moore