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Porting Information


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Porting is a science, not just hogging out ports and making them shine real nice and pretty.  Years ago factory iron heads were all that were available.  The guy with the good head porter made the most power.  1 out of 10 porters out there are good at porting and can make a port flow like Niagra Falls.  The other 9 are good at hacking and killing flow.  There are alot more port hackers than there are good porters.  There is a hell of a lot more to porting than hogging out ports and giving them a nice shiny finish.  Too many people think they can port heads because they bought a port and polish kit from a popular mail order catalog.  Those people usually destroy the flow in there ports and many times beyond repair.  If you don't have any experience porting heads it is best that you either leave the ports alone or send the heads and/or intake to a professional.  Real head porting takes years of practice just to be able to keep the ports proportionate and keep the vertical and horizontal lines uniform. You have to understand airflow, how it works, what it does and what effects it.  Learning how to reduce the cutter-marks to a bare minimum so that the polishing work looks nice takes good training and a considerable amount of time. It can take several years of 40 hour work (practice) weeks to become a moderately good head porter. A quality head must look good, have equally shaped intake and exhaust ports and combustion chambers that promote flow into the cylinder via the intake valve and collect the exhaust gasses under the exhaust valve and flow out of the exhaust valve efficiently. The ports must also have flow characteristics that the engine builder wants for this particular engine.  A head porter without a flow bench is a head porter that I would steer clear of and if he has a flow bench, hopefully he knows how to make proper use of it.

There are two basic types of porting.  Hand porting and CNC porting.  Hand porting is just that, porting by hand which is the basis for both types of porting.  CNC porting copies a hand port design and then is able to duplicate it over and over again, as many times as you want.  CNC porting ensures every port is the same but is mainly there for production work.  CNC ported heads will make good power but a good hand porter will get the most out of any cylinder head but you have to look at things realistically as well.  For the average Joe bracket racer or street/strip car, one off hand ported heads are not a wise choice unless you have a Pro Stock budget.  Most CNC heads are not ported to their maximum potential before being digitized for reasons such as core shift, machining tolerances and other variables.  With that being said, most CNC heads have more horsepower in them in the hands of a good hand porter.  The nice thing about CNC heads is all of the runners are almost identical and flow almost the same numbers.  CNC machines also don't get hang overs, stress or mental issues.  They don't have bad days so you can expect consistency from them day to day.  CNC porting and hand porting both have their places but like everything else it depends on the application.




As strange as it may sound there are many variable involved in porting, cylinder head selection and engine building in general.  Bigger is not always better.  Big ports and big valves can hurt power numbers just as much as they can produce power if the proper combination of parts is not used.  Probably the two most important things are how much horsepower you want to make and how much money you have to spend.  Other things that can influence your porting needs are type of cam are you going to use (hydraulic, solid, roller or flat tappet) forced induction (turbo, roots, centrifugal, screw, etc.) or naturally aspirated, nitrous oxide, type of intake, type of carburetor and how many, fuel injection systems, engine displacement and class rules (if any).

Here is a link to some popular cylinder head and throttle body airflow numbers