flowing, knowing and growing · flowing, knowing and growing by harold bettes 58 july-sept 2013...

56 JULY-SEPT 2013 engine professional

Power is a fairly powerful word in some circles. The word powerbrings to mind several images and means different things todifferent people. There is political power and there is peoplepower. There is also economic power. Women certainly havepower but that is way beyond the scope of this particular article.There is also power in the air. Power from the winds brought thefirst exploring sailors (whoever they were) to the North Americancontinent. However, an immediate interest gets stirred up in mostgearheads and engine builders when the term horsepower is usedwhile only some are stirred up in discussions of airflow. Therelationships of the two terms are very closely joined.

We humans are creatures that use the air to provide life givingoxygen and our internal combustion piston engines also use theoxygen in the air to help make power. It is a given that a pistonengine is a self-driven air pump and as such the more air we canarrange to get into and out of the engine, allowing it to have thepotential to make more horsepower.

The internal combustion piston engine needs three things inorder to produce horsepower and shove a vehicle against theresistances of the roadway or racetrack.

There is a critical combustion triangle of fuel, spark (ignitionspark at the spark plug), and air (oxygen in the air). All thecomponents must be present at the correct time in the combustionchamber where noise and horsepower are generated.

Yes, it is basic, but consider the four stroke cycles of a fourstroke engine: Intake (fresh air goes into the engine), Compression(where air and fuel are squeezed into a smaller volume),Combustion (where the air and fuel mixture is ignited by thespark plug and the mixture expands as it burns while pushing onthe piston), and lastly the Exhaust (where the burned gases andresidue is expelled from the engine). Yes, it is simplistic and it isbasic but kindly notice that two of the events listed previouslyhave to do with the movement of air into and out of the engine.Improving just those two cycles’ efficiency will improve thepotential to make more horsepower. If you can improve all theevent efficiencies you can make more power but improving theairflow through the engine can easily improve horsepower. If youcan capture the importance and control those events, you are wellon your way to make more horsepower. It is that simple.

If we learn some particular details about the airflowcharacteristics of the engine and its components, it is very possibleto predict with some certainty the engine’s potential to makehorsepower. A careful and deliberate study of the airflow of the

Flowing, Knowingand GrowingImproving engine airflow is a good start toward producing more horsepowerBY HAROLD BETTES

Figure 2. These intake valves are made of the same material (titanium)although shaped differently yet are the same diameters. But do they flow thesame? Only testing on a flow bench can reveal the truth and the one that flowsthe best will help the engine to produce more horsepower.

Figure 1. The airflow characteristics of engine components such as cylinderheads, manifolds, and throttle bodies or carburetors establish the capability ofthe engine to produce horsepower.

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engine and components are very beneficialand provide a platform for improving thehorsepower of the engine. The study offluids in motion (air is a fluid) and isknown by a descriptive engineering termcalled fluid dynamics.

The most common term used todescribe airflow through the engine andcomponents is CFM (cubic feet perminute) and is a volume measurementreference sometimes referred to asvolumetric flow rate. A mass flow (weightper time) reference would be somethingsuch as pounds of air per unit time inseconds, minutes, or hours. The mass flowof the running engine is dependent uponatmospheric conditions or the location ofthe testing being done. The engine’shorsepower output is sensitive to massflow while the individual components suchas cylinder heads, manifolds, carburetors,or throttle bodies are not. The assembledand running engine responds toatmospheric changes even when thecomponents bolted together remain thesame. The atmospheric effects andcomponent comparison is being testedevery day on dynamometers andracetracks. Therefore, the most commonreference in CFM can be an easy way tocompare measurement data no matterwhere the testing is being done.

Measuring the resistance to flow air isessentially what most flow benches do sothe operator can quantify and comparecomponents. The effective airflowdevelopment of the cylinder heads andmanifolds and even carburetors can beevaluated on a flow bench and is a criticalprocess in the improvement of thehorsepower of an engine.

When commercial flow benches cameon the performance scene in the UnitedStates back in the 1970s, many smallshops became more competitive withlarger and more well funded operations byhaving a way to not only check theircylinder head modifications but a new wayto improve their work. Those that learnedfaster grew in specialty applications andbecame the “go to guys” in many areas ofthe country. This was the time when it wasapparent all cylinder head work and valvejobs were not created equally. Any smallshop can fill the need and expandcustomer bases by improving quality byusing a flow bench as a pathway to greatersuccess.

Engine Airflow Establishes the Engine’sPotential for HorsepowerIf we can learn some specificcharacteristics and data about cylinderheads, it can be predicted how muchhorsepower and at what RPM it willoccur. A flow bench is the necessary andcorrect machine to use in order toaccurately measure the airflow of thecylinder heads and other enginecomponents that are in the airflow tract.

Of course there is also an initialassumption that the engine seals properly(no bent valves) or seized parts and thedetails of timing and a correct amount andtype of fuel is used and all those littlebasics have not been neglected.

As an example, if you have an enginethat is an 8 cylinder of 389 cubic inchesdisplacement and you have some testingdone on the cylinder heads and they flow320CFM at 28” H2O test pressure at.600” valve lift. What can be predicted

from that data? It obviously has 8cylinders that displace 48.625 cubic incheseach. From the airflow data it can bepredicted that the engine has the potentialto produce 83.2Hp per cylinder or665.6Hp based on cylinder head airflow.However the engine needs to have anintake manifold and carburetor or throttlebody attached and each of those items willtypically reduce the airflow available. Forthe sake of this example, let’s guesstimatethe manifold and carburetor would reducethe cylinder head’s airflow by somethingaround 13% or 41.6CFM. So, our newcalculation of predicted horsepower wouldbe based on airflow of 278.4CFM at a testpressure of 28”H2O. Now it would havebeen better to have actually measured theairflow of the cylinder head with theintake manifold and the carburetorattached, but not many folks actually dothe detailed work that way although theyshould if they want accurate numbers.Yeah, so what is the new predicted numberfor horsepower with the changes listedpreviously? The answer is 72.38Hp percylinder or 579Hp for the entire engineworking properly. And that would happenat somewhere around 6850 RPM or so. Atleast it has that kind of potential based onthe airflow numbers given in the example.

Although the numbers listed aboveapply to naturally aspirated gasoline fueledapplications, supercharged engines orengines using different fuels can also beimproved using airflow technologytechniques gained from flow benchmeasurements.

There are many problems in notmeasuring intake manifolds andcarburetors attached to the cylinder heads.

Figure 3. A grinder is about the last thing that should be picked up whenplanning on improving the airflow of cylinder heads. First you have to knowwhat needs to be done in order to be effective and random grinding may not bethe correct answer. Often what looks good might not flow well.

Figure 4. Super Stock cylinder heads have specific rules to follow and portscan be reshaped but they must maintain mandated sizes. All exhaust testingshould use a pipe to get correct flow numbers. This 1000cfm flow benchprovides accurate numbers for developing components and keeps qualitycontrol on the heads at a high level. (Photo courtesy of Stu Zylstra.)


FLOWING, KNOWING AND GROWINGBY HAROLD BETTES


So, one has to be very wary of published flow numbers forcylinder heads and not plan on manifolds reducing the head flownumbers. It makes a difference and the only way to really knowthe airflow numbers is to measure them on an accurate flowbench.

Using a flow bench is not very difficult to learn. It is a bitmore problematic to learn how to use the data and how to applythe simple arithmetic. As with any process, practice makes thingswork more smoothly and more experience in the application ofthe test data is another effective tool in your toolbox ofknowledge.

Airflow numbers without test pressure references makes theflow numbers meaningless but many still fall for the flow numbersif they are big numbers.

Getting air into the engine has been most of the focus thus far,but the exhaust side can and should be measured also. In fact allcylinder head testing on the exhaust side should also include theuse of a pipe on the exhaust port. While not as criticallyimportant as the intake side of the engine, exhaust improvementscan enhance the performance of a cylinder head by complimentingthe intake flow particularly during the overlap event.

Camshafts and AirflowThere is no way a camshaft selection can make up for inadequateairflow for an engine. Simply put, camshafts cannot createairflow. The valve timing events can help to enhance the benefits

of whatever airflow is available, but they cannot create airflow.That is the kind of statements that stirs hate and discontentamong some. There are many myths that support camshafts as acure all for engines that have all sorts of other issues to overcome.Inadequate airflow of cylinder heads and intake manifolds is wayup on the hit parade of problems to be solved when building formaximum performance.

And the only way to check out what restrictions you have inthe airflow path of the engine is to measure each item on a flowbench. Way too many folks believe in magical methodology inchoosing camshafts while many others simply choose the last partnumber on the catalog page. With airflow based data drivendecisions, the choice of a camshaft need not be a roll of the diceor the flip of a coin.

CNC Versus Hand PortingMost CNC programs first started as a hand ported port and thenthe port is “digitized” in order to copy the shape. The uses ofCNC equipment has increased in many ways in the aftermarketindustry. The porting of cylinder heads by using CNC machines isquite popular, but is it better than hand porting? It depends. Itdepends on how well the hand developed port was digitallymeasured and thus copied by the CNC operations. Manyconsiderations used by CNC programmers and operators mightnot exactly duplicate the original hand ported configuration of agood flowing port. The CNC machined ports can be done faster

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than hand porting and everything from the coarseness(how rough) of tooling cuts and how hard the cuttingtool is forced or “crowded” causing tool deflection orwear can cause problems with the finished CNC port.However it is by far faster than hand porting. The CNCoperations allow comparatively rapid turnaround timesfrom raw casting to a finished product. However whenall is done the finished piece still needs to be measuredon a flow bench as a quality control checking item.Many CNC ports can be refined further by handtweaking the port shape and measured often on a flowbench so the progress can be tracked carefully. Noteveryone or every organization does their productdevelopment in the same way (there is more than asubtle hint in there somewhere).

Using a Flow Bench to Improve Quality and PerformanceThe use of a flow bench can certainly improve thequality of work any shop or individual produces. Properapplication of the data collected can also improveperformance and increase the power potential of thetested parts. Simple flow testing cannot by itself provideany performance gain, but can provide data in order toimprove the parts tested. If nothing else, flow testingparts can help to select the parts or modifications thatprovide better flow characteristics. It is very rare thatbetter flowing parts don’t provide reliable potential forincreased horsepower. The flow bench can help to findthe parts that can make building more horsepowermuch more likely. A flow bench is much less expensivethan a dynamometer and takes much less floor spaceand support, so it becomes an easy choice as a piece ofequipment that can pay for itself over a sensible periodof time.

It is the shape of the air flowing duct (port) that ismuch more important than size (volume), so justmaking a huge port is not the best answer. How doesone find the balance of shape and size? Straight answeris: With flow bench testing experience and accumulationof shaping experience. Try to get started accumulating

Figure 5. This shows the rows and rows of cutting tool paths of aCNC machined intake port. How can you know if the port flow isany better or worse than a hand developed port? The CNCprogrammer might or might not have an interest in airflow but theCNC machined heads can be produced much faster than doing thejob by hand.


both as soon as possible. The goal shouldbe to create a shape that flows wellwithout being too big and that issometimes a tough balance to control.

How does a combustion chamber’sshape affect airflow? It can be tested onthe flow bench. Have you ever taken alook at the combustion chamber shapethat has a “laid back” wall directlyopposite the intake flow path? Perhaps itwas developed on after a flow test showedit improved the intake airflow. One cannotguess so it must be tested.

Buzzwords, Attitudes, and Knowing WhatYou Are Talking AboutThe late great American physicist RichardFeynman stated, “I learned very early thedifference between knowing the name ofsomething and knowing something.” Soperhaps buzzwords and the like are notnearly as important as those that use themmake them out to be. There are a verymany buzzwords and some verbalshorthand concerning racers and racingand gearheads in general, but when itcomes to airflow it sometimes gets out ofhand. Sometimes the buzzword of theweek gets tossed out and something elsereplaces it for no reason other thansomeone else’s new comment or opinion.Or perhaps it comes from lots of opinionson the various uses of the internet. So,how do you get to understand all thisstuff? There is not a real need to doanything special relative to “airflowlinguistics” other than just call items asyou learn about them. As an example aport does not “back up” as it has noreverse gear. The clumsy term simplymeans the port flow is decreasing as the



Figure 6 & 7. The combustion chamber on the intake side is of a laid back design that probably enhances the airflow path from decreasing the shrouding of theintake valve. The only way to be sure is to measure the results on a flow bench.

Figures 8 & 9. The very critical area over the short side radius is hard to get to but very important to shapeproperly so intake flow does not separate from the turn. Here the place is pointed out by using a 3/16”flow ball. An assortment of flow balls and flow flags should be within reach of any flow bench testing(inset photo). Very handy tools for airflow development projects.

Figure 10. Here is a single-cylinder rapid prototypeplastic head for a new cleansheet of paper design 60degree V-12 engine. Foraviation use, airflowdevelopment data from flowbench work indicates800+Hp at 4600RPM for thenaturally aspirated versionand the turbocharged modelis targeted for 1600Hp at6000RPM. (Photo courtesyof EPI, Inc.)


valve is opened. Just say something thatcan be understood by a twelve year oldkid. How about “pinch point”? Makesyou want to watch out for your fingers forsure, but it is clumsily describing the portarea near the pushrod on a pushrod engineor perhaps it means the point of minimalcross section somewhere in the port if theengine is an overhead cam setup (thus nopushrod). The term “stall” means the portdoes not gain flow with more valveopening. The short side radius is a fairlydescriptive term and is an important partof a port’s configuration. Learn where it isand why it is important.

An attitude of desiring to learn andperhaps apply that learning to improvingyour business or perhaps even to start abusiness based on what you learn isworthwhile but not necessarily an easypath. The flow measurement path is theknowing path toward success.

Sometimes it is more cost effective touse a model cylinder head for airflowdevelopment and rapid prototype piecescan be generated if budget is available

before a final design is settled on. Asensible approach to airflow developmentsaves countless hours and errors. Anindividual or a small shop can work onbroken heads or manifolds before a finalproduct design is decided speeding up thedevelopment process. The inertia of alarger shop can be a detriment to success ifinnovative and results oriented personnelare not in the cylinder head department.

Try your very best to keep learning andto help others to learn. Watch out withairflow however, as it becomes quiteaddictive in a very good way. There ispower in the air but it is up to you to notjust find it but to apply it as part of yourbusiness plan or racing program.�

Harold Bettes is author of Engine Airflow and co-authorof Dyno Testing and Tuning. He has been a mechanicalengineer for over 40 years and has been involved inmotorsports in one fashion or another for more thanhalf a century. Harold is a recipient of many awards forhis contributions in furthering mechanical engineeringin the motorsports industry and aftermarket. He is anactive consultant on test facilities, equipment andracing engine configurations and designs. He is alsowriting a novel about experiences in Southeast Asia,Mexico, and Texas.



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flowing, knowing and growing · flowing, knowing and growing by harold bettes 58 july-sept 2013...

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