[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