[Mr_GTO]

Could someone just explain that in detail for me. Thanks. [img]/infopop/emoticons/icon_biggrin.gif[/img]

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I am looking forward to walking to work

[Mr_GTO]

Could someone just explain that in detail for me. Thanks. [img]/infopop/emoticons/icon_biggrin.gif[/img]

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I am looking forward to walking to work

[Dave A]

I'm not 100% sure, but I recall something about the 28" H20 pressure standard for flowing heads coming from Smokey Yunich, and 28" being chosen because it was fairly close to the 'average' pressure differential actually seen by the port (28" H20 is about 14" Hg, I think). Perhaps someone else remembers better.

The tradeoff is, of course, that it takes a lot of power to generate 28" H20 pressure across a port that flows well at high valve lifts, and not all flowbenches have that kind of power. Conversions from one test pressure to another are available, but not as accurate as measuring at the desired pressure to begin with.

[pierced mikey]

Hey Chris, where did you get that from? [img]/infopop/emoticons/icon_razz.gif[/img] [img]/infopop/emoticons/icon_wink.gif[/img]



Nothing is real if you don't believe in yourself-Rocky Balboa

[Mr_GTO]

I really want to know mike. [img]/infopop/emoticons/icon_wink.gif[/img]

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I am looking forward to walking to work

[pierced mikey]

lol just curious huh? Am I being good over there? [img]/infopop/emoticons/icon_biggrin.gif[/img]



Nothing is real if you don't believe in yourself-Rocky Balboa

[Rocky Rotella]

There's a ton of good information regarding flow numbers and all associated aspects over on this site. http://www.superflow.com/flowbench/default.htm

Might be worth checking out.

[Tom Vaught]

Quote:

"Why are heads flowed at 28" of water instead of 12"?"

BRAGGING RIGHTS PURE AND SIMPLE!

The crowd will hang me for saying this but Smokey
came up with the 28" number based on some work he did as a corrolation study between porting heads and running on the dyno. He found that the head
when tested at 28" h2o would show a hp improvement
on the dyno if he saw an improvement in flow on the flow bench. This works out to slightly more than 1 psi or 2" HG (mercury) test pressure.

He would have liked to test at 5" HG like Ford did on their test stands but did not have a strong enough suction device. He ran the study to
see how close he could get.

Bob Mullins (of 392/426 Hemi fame) also had a flow
bench and he tested every head at 3" h2o. He was
considered by many, for years, to be a premium head porter for Chrysler and Pontiac heads. He did the initial work on the 455 SD heads.

Holley Carburetor and the other carb manufacturers
flowed all of their 4 bbl carbs at 20.5" h2o or 1.5" HG. 2 bbl carbs are flowed a 3" HG or 41" h2o test pressure.

Super Flow originally tested parts at 10" h2o as
the little vacuum motors they had in their SF 100 bench (yes, there was an SF 100) was not capable
of more test pressure.

John Reed of Reed Cams paid to have the first BIG
flow bench made (a Super Flow 1200) so that he could test carbs at 1.5" and 3" HG like Holley.
Super Flow has sold a grand total of about 35 in
the last 20 years. He also paid for the first Super Flow 400 bench to do head work. It was later
updated to a 600 bench by adding 2 additional motors.

Pete McCarthy flowed the heads for the Pontiac head study on Jerry's Laminar bench at 12" h2o
because Jerry originally did not use high flow Super Flow type vacuum motors and was limited to
that test pressure. Pete's first article states
that he tested at 12" HG! (This is a misprint and
the test pressure was correctly stated in the second part of the articles, (12" h2o).

All of the test pressures in the world mean nothing if the testing was done with a problem in
the flow bench. Jerry's bench was later found to
be slightly plugged by foreign material. This would cause his test results to be higher than normal for a calibrated bench. Of course the DEAD
MOUSE probably did not help either with the data.

So there you have a history on test pressures.

Tom V.

[Jack Ferris]

Tom- Isn't it harder to notice the small increases in cfm while porting using the lower test pressures? I once considered buying the SF110 bench for my own personal work but Pete McCarthy talked me out of it. He told me I'd have a hard time finding the small changes in the port work because the test pressure would have to be set so low.

Wang whats with all the pictures it a parking lot.....

[Skip Fix]

My machinist that did heads always used 10" and alot of the initial Superflow formulas are based on that (Hp/CYLINDER= cfm@10"x0.43). He always felt at 10" he saw things easier than at the higher flows, even when he got a bigger Superflow that did flow them.

[Dave A]

I recieved an e-mail from Mr. Jim Hand largely agreeing with Mr. Vaught's first statement (along the lines of there not being much scientific reason for testing at one pressure vs. another) - basically, that the proper conversions from flow rate tested at one pressure to another are very accurate. I stand corrected! Apparently, most of the improvement in accuracy gained from a higher capacity flow bench (talking Superflow here) is due to larger, more finely scaled manometers in the higher capacity benches.

[Jack Ferris]

On the subject of flow benches has anybody here built one using the Flow Quik set up from Audie Technologies?

Wang whats with all the pictures it a parking lot.....Audie Technology

[Pete D]

Dumb question here. What exactly does 10" or 28" mean? When a head is tested at 28" what does that imply? What is producing the 28" reading? Ok, there was more than one dumb question.

[PONTIAC DUDE]

If anyone is interested. I have installed a conversion flow chart on my website.
It's there for your use.

Build it fast, build it right, build a Pontiac.
http://PontiacDude.cc

[Skip Fix]

Pete, the inches is what pressure on the exhaust or vacuum on the intake the bench was using.More vacuum/pressure wil make more flow through the same size opening so this way each test lift is calibrated to be valid.

[Mr Dave]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tom Vaught:
Quote:

The crowd will hang me for saying this but Smokey
came up with the 28" number based on some work he did as a corrolation study between porting heads and running on the dyno. He found that the head
when tested at 28" h2o would show a hp improvement
on the dyno if he saw an improvement in flow on the flow bench. This works out to slightly more than 1 psi or 2" HG (mercury) test pressure.<HR></BLOCKQUOTE>

28" WG is closer to 14 PSI, isn't it?

EDIT--nevermind, I am thinking feet of head. About 1 PSI is correct.

David Watford
Pensacola, FL
Mr. Dave's Homepage
My Garage Sale

[Tom Vaught]

You are correct. About 2 inches of HG (Mercury)
is 1 psi. 28 inches of H2O (water column)is about 2 inches of HG. 20.5 inches H2O (what Holley flows carbs at) is 1.5 inches HG.

Tom V.

[GTO-relic]

Originally Posted by Tom Vaught

Quote:
"Why are heads flowed at 28" of water instead of 12"?"
BRAGGING RIGHTS PURE AND SIMPLE!
The crowd will hang me for saying this but Smokey
came up with the 28" number based on some work he did as a corrolation study between porting heads and running on the dyno. He found that the head
when tested at 28" h2o would show a hp improvement
on the dyno if he saw an improvement in flow on the flow bench. This works out to slightly more than 1 psi or 2" HG (mercury) test pressure.
He would have liked to test at 5" HG like Ford did on their test stands but did not have a strong enough suction device. He ran the study to
see how close he could get.

I happened to stumble on this thread/post while doing research, this needs to be cleared up. Smokey's flow bench and spintron dyno was far beyond anything anyone had in Detroit at the time. The Big Three actually all got in line, paid their money, to have Smokey flow their stuff. Let's set the record straight- his flow bench was monstrous, he chose 28" because beyond that was dwindling returns of accuracy- from Smokey's autobiography memoirs:

"In 1951...I came to an opinion. No one in automotive industry really understood anything about air/fuel flow in both induction/exhaust systems. I next visited any/all engine test facilities I was permitted to examine. I really got a shock. Most all systems were different from each other, or didn't exist. Chevy air flow equipment up to 1960 was a 10hp motor driving a 6-71 supercharger. I talked to many engineers looking for guidance to build a machine to examine/test real movement/quantity of air/fuel. Well, I wasted a year. All guidance differed. I decided to continue completely on my own. This took me on a 30 year, $350,000 journey.
By 1957 after 1,000 man hours building various concepts, I'm down to $150,000 in motors, chambers, custom hardware to fit various engines. I decide to work on engines from 50 cid to 1800 cid. I've decided best info was obtained by high negative pressure 28" of water h2o. An air pump big enough to do this and associated hardware is $80,000 and weighed 3.5 tons. It's big, heavy, and now consumes 600 square feet of space, and is 15 feet tall indoors. The power necessary to drive the air pump is 100 horsepower, 440 volts, 200 amps for a Roots design blower. This is very noisy, requires a huge muffler system weighing 3,000 pounds, and was 20 feet tall. A 4" iris valve is used from early camera for perfect solution, for linear very sensitive air flow control- it came from a huge camera. I chose 4" as size for all conduits from air pump to any functions, and 4" laminar flow element- all air flow measurement equipment from Meriam Instruments, good stuff, very expensive. Barometer, inclined manometer, very accurate pressure instrument for negative pressure readout.
This equipment works slick as a whistle. We run it 18 hours a day uncovering 100's of unknown idiosyncracies that occur to the working fluid due to pressure, temperature changes incurred as the velocity, pressure changed due to orifice size, shape. NOW I COULD FLOW ANY CYLINDER HEAD VERY ACCURATELY AND I GOT ENOUGH BUSINESS FROM DETROIT TO KEEP THIS MACHINE WORKING 7 DAYS A WEEK.
At this point I added transparent ports, colored smoke. Now we have substantiated investment in the glass 'see in' manifolds, adapters, sample intake runners. The manifolds, with windows to observe colored smoke, travel in multi conduit models that showed fuel fallout due to design errors. (later in 1960's Chevy showed how to duplicate our flow equipment for $1 million cost)
1970 I decided to prepare a complete engine so it could be air/fuel flowed in both dry and with fuel, through all its components, i.e. air cleaner, carb, induction, camshaft, cylinder heads, exhaust system. This showed airflow of a cylinder could be very misleading, incorrect. We had engine on stand, complete with air cleaner, carb, intake manifold, cylinder heads, sealed oil pan, timing cover, crankshaft/rods, pistons with many holes for air passages equal to what flow should be. We put crankshaft in position of maximum cam lift and flowed each cylinder. On intake flow, oil pan had 4" hole with air tight joint. Carb in wide open position with 4" adapter to laminar flow element. By pulling on the pan we measured airflow though combustion chamber, complete induction system, each conduit individually.
I motored the engine when measuring flow. After 6 months of back to back testing, decided "holey" pistons were a negative step, removed them. I stopped motoring the engine, simply opened valves with precision adjustment.
We adopted .650" as optimum opening at 28" of water. We used to flow at .050" increments from .050" to .650" IN THIS TIME FRAME WE ABANDONED ALL FLOWING EXCEPT .650" AT 28" OF WATER BAROMETRIC PRESSURE. These changes produced a very stable result. ANY INCREASE IN AIRFLOW ALWAYS PRODUCED AN INCREASE IN HORSEPOWER, providing the intake/exhaust system was sized in correct proportion to each other. (Example: 1.58" exhaust and 2.05" intake valves in 1975 was ideal for a 350 cid small block Chevy).
By 1975 this flow bench had shown no cylinder head available had big enough intake ports, and the small exhaust port/valve were nearly ideal- but we had to confirm this with dyno and track testing. The flow bench taught us size/shape of ports and sizes relative to intake/exhaust changed with intended use. In 1978 I discovered cylinder wall interference and reduction of actual air/fuel flow as valve moved to increase lift. This changed our ideal valve motion, to a valve moving away from cylinder wall shrouding.
Development of total air/fuel flow consumed 50 man hours a week for 30+ years, plus electricity to run flow bench, materials, adapters. My experience in carbureted air/fuel flow pointed out some advantages of fuel injection. The machine taught further that the Otto cycle engine is a series of compromises, to extend rpm range and maintain maximum torque is NOT POSSIBLE, but what is do-able is maximum torque at a chosen rpm range, say 3000-6000 rpm. Air/fuel flow technology singularly is a life's work for an engineer, and still in its infancy. Huge rewards still remain to be discovered"- Smokey Yunick, 2001

[GTO-relic]

ps- we are all just a child compared to what those before us did. no other individual in history invested as much personal time, money, effort, thought into flow technology as that. corporations may have, but no other single individual has ever.

[VCho455]

Best Damn Garage in Town!