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Could someone just explain that in detail for me. Thanks. [img]/infopop/emoticons/icon_biggrin.gif[/img]
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Could someone just explain that in detail for me. Thanks. [img]/infopop/emoticons/icon_biggrin.gif[/img]
------------------------------ I am looking forward to walking to work |
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. |
Hey Chris, where did you get that from? [img]/infopop/emoticons/icon_razz.gif[/img] [img]/infopop/emoticons/icon_wink.gif[/img]
http://kurtsplates.homestead.com/files/428LMNS.jpg Nothing is real if you don't believe in yourself-Rocky Balboa |
I really want to know mike. [img]/infopop/emoticons/icon_wink.gif[/img]
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lol just curious huh? Am I being good over there? [img]/infopop/emoticons/icon_biggrin.gif[/img]
http://kurtsplates.homestead.com/files/428LMNS.jpg Nothing is real if you don't believe in yourself-Rocky Balboa |
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. |
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. http://kurtsplates.homestead.com/files/UR2SLO.jpg |
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..... |
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.
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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.
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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 |
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. http://forums.performanceyears.com/g...icon_smile.gif
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If anyone is interested. I have installed a conversion flow chart on my website. http://forums.performanceyears.com/g.../icon_wink.gif
It's there for your use. http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g...on_biggrin.gif Build it fast, build it right, build a Pontiac. http://PontiacDude.cc |
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.
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<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 http://home.sprintmail.com/~mrdave/lemanssigpic.jpg |
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. http://kurtsplates.homestead.com/files/UR2SLO.jpg |
Quote:
"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 |
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.
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Best Damn Garage in Town!
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Just keep in mind that a highly developed induction system on a pro stock motor or a Indy cars motor can see up to a 120” H2O depression.
But this has to be tempered with average numbers also. I don’t know if they still do, but Ford has tested at 65” which is in my opinion why they thought that the oversized intake ports on a Boss Cleveland head where the way to go on street 302 cid motor. Pontiac at least though that those same size ports where good for a 303 motor that could buzz to 8200, but even that was wrong! Just keep in mind that a steady state flow bench test does not show the effects of the cycles that a running motor places on an induction or a exh system. A good marker for making HP in regards to induction system that’s tested at 28” is that for every 100 hp your looking to make you then need .100” of lift at the valve. |
Smokey's home made bench could pull 1500 cfm at 28" back in the 1960's. He had the most powerful flow bench in the entire USA. There was no shortage of flow capacity power whatsoever. The machine was a monster. Another description made 1998:
"I went to Detroit on Hudson business and get to examine equipment used to check various parts for air flow. I want to buy a book with pictures, dimensions...that tells me shapes, sizes. I'm shocked to find out some manufacturers don't own or use air flow equipment. Some like Buick, Olds use equipment that ain't worth schit. Chevy air flow bench 1958 was a 6-71 supercharger driven by 10hp electric motor- so help me God. I sat down called every place that had anything to do with air flow equipment, even the aviation engine people. No one made anything that was acknowledged accurate in a 7,000 rpm range. I bought 5 SAE papers on air flow- but I became confused, all were different from each other. By 1960 I decided nothing published could be proven correct...decided to figure it out for myself. I decided to be my own counsel in the experiment- discussions with peers distracted, confused me. Back to the peyote. I decided to get a pump big enough to flow 1500 CFM of air at 28 inches water, negative pressure, vacuum mode. I got this CFM number guesstimating the biggest engine/highest rpm I would ever test. In next 2 years more shock treatment- a company called Stuterbuilt makes such a pump, but it takes a 100 horsepower electric motor to turn it, and $25,000 to own one. Well I've sold an invention and got $50,000. One year fast forward- flow bench is complete- dry flow/wet flow. I can handle stuff up to 75 cubic inch per cylinder, 8,000 rpm. $85,000 is now gone. BUT I'VE GOT THE BIGGEST, MOST POWERFUL, MOST ACCURATE FLOW BENCH IN THE UNITED STATES. THIS FLOW BENCH RUNS DAMN NEAR YEAR ROUND FROM 8AM TO 2AM FOR 20 YEARS, 7 DAYS A WEEK. This SOB makes so much noise, it takes a pair of mufflers that weigh a ton each to half way quiet it down to about 100 decibels at 20 feet. I quickly learned best control valve was like a camera iris, the best port was straightest, that air flow around a valve was controlled by subtle things like radius, sharp edges/angles were better than a radius alone if over 9 degrees of direction change was required. I learned there is no way to change one parameter, without adjusting every other variable. Most importantly I learned the Otto cycle engine, no matter how perfectly done, would never give maximum performance longer than a narrow rpm range- unless valve timing, port shape/size/length could be altered on the fly. I LEARNED THE OTTO CYCLE ENGINE COULD NEVER BE PERFECTED. It is a basket of flawed systems. But it's also as of today August 1998, the best most viable system known to man, considering every aspect/parameter to be met, to be state of the art of viable surface transportation. I learned the Otto cycle engine would be replaced with a machine at least 2-2.5 times better in thermal efficiency. I learned the entropy of the Otto cycle is flawed because of the tremendous increase in the size of the combustion cavity. But man...for a quicky deal about 100 years ago, we owe Otto a helluva lot more than we gave him. I've learned it's possible to have roughly no emissions, and consume nearly all the hydrocarbons (with external combustion), but in a confined environment. I learned if we don't consume all hydrocarbons completely, this world won't be fit to live in, in 100 years. You know what 100 years is in real time ? About 100 seconds. Same goes for the carbon in wood and coal, or any other combustible solid. I WANT YOU TO CONSIDER THIS ONE SENTENCE CAREFULLY. Water is wonderful as it is, and as we understand it. Maybe one day in the near future, water may contribute a solution to our current trajectory of world genocide by atmospheric pollution. Well, my flow bench got to meet many various engine manufacturers engine components regarding air/fuel conduits, cylinder heads, intake/exhaust manifolds, carburetors, air cleaners. Small, affordable flow benches are now offered to the racers. Nowadays all racers of any stature have a flow bench. So air flow is as big a topic in race publications as chassis technology. It's too bad most of it is bullschit. The technology of air flow is no different than a liquid. Air is of course not possible to totally observe visually, but the physics is the same- the difference being the specific gravity of each. I put the "what if" to it. What if you colored the air ? Yup, it worked. You can see what's happening. I could teach you in 2 days how to build correct size intake/exhaust manifolds, and correct size carburetor, if the parts were not cluttered up with pistons, cylinder walls, head bolts, water passages, push rods, and rpm range. It turns out the best pushrod cylinder head will be the best known series of compromises. Assuming all parts are not adjustable, the maximum operating range will at best be 300 RPM for maximum efficiency."- Smokey Yunick 1998 |
[QUOTE=Mr_GTO;2200399]Could someone just explain that in detail for me. Thanks. [img]/infopop/emoticons/icon_biggrin.gif[/img]
Being no one else went into detail with the OP question, I will- it's a good question, with an even better reason why, 28" became the standard. It was a long, arduous, expensive, time consuming, cut-and-try method, discovering a hidden secret of physics: how a flow bench has a sweet spot test pressure, that directly correlates with how a naturally aspirated engine inhales air/fuel, using atmospheric pressure, and creating vacuum. THEY FINE TUNED THE FLOW BENCH RESOLUTION TO THE DYNO RESOLUTION, AND MADE BOTH LOCK TOGETHER, CORRELATE. They went on a treasure hunt out of curiosity, and struck paydirt- because nobody else up to that point including the Big 3 automakers really knew how to do it: "Next thing we had to determine how much pressure depression- 'vacuum'- to use pulling air through test fixture. When we started our research, we found most flow testing at other facilities was being done at around 10"-12" of water. So we followed along with everyone else. Before long we changed our mind about this. Flow balance between all head ports is important. You want each intake port to have the same operational efficiency, so each cylinder receives the same quantity/quality of mixture. To confirm this, you must flow all intake ports and compare them. WHEN WE WERE FLOWING PORTS WITH A 10" WATER DEPRESSION, WE FOUND WE COULD MAKE VERY DRAMATIC CHANGES BETWEEN 2 PORTS, AND YET THE MEASURED AIRFLOW WOULD NOT CHANGE SIGNIFICANTLY. We then decided to undergo a series of tests to detect valid differences between ports. We started with tests at 10" water and checked airflow variations between ports that were OBVIOUSLY DIFFERENT. Then pressure drop was increased by 2" and same test performed again. This step/repeat procedure continued all the way up to maximum drop of 34". When the test series were completed, we found at any pressure drop less than 26" water, there was little discernible variation in port balance. BUT AT LEVELS ABOVE 28" , DIFFERENCES REALLY STARTED TO SHOW UP. In addition we noticed as drop was increased beyond 28" water, the percentage of change- per increase in drop- was quite small. SO WE SELECTED 28" WATER AS A BASELINE LEVEL- and started checking results with back-to-back dyno testing. We would measure flow on bench, make a change to improve flow, take the head to dyno to see if engine performance actually improved. After considerable testing we became convinced the correlation was almost totally linear. Virtually every improvement on the bench (at 28" water), would show up on the dyno as a measurable increase in engine performance. For the past 30 years, all our flow testing had been done at 28" of water depression."- Smokey Yunick 1983 |
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