How is a head “gas flowed” ?
"Gas flowing” involves re-profiling of the inlet and exhaust ports in the cylinder head to allow the fuel/air mix to flow in and the exhaust gases to flow out more efficiently. Essentially it is a redesign of the port based on extremely accurate measurement of size and flow rates and how changes to the port affect the flow.
Of course, hidden behind the word “redesign” is a great deal of detail and pure experience of what works and what doesn’t. What is too much and what is not enough. This development process relies heavily on the experience of the expert doing the job and the measurement tools available to him.
The development process of a new head starts with a base line measurement of the standard head. The gas flow engineer then begins to modify that port by identifying possible points which could be modified by removing material and changing the surface finish and then making that change by hand using accurate hand controlled tools. This can only be done using experience (in our case over 20 years of experience). It is entirely possible to make changes that do not work or break through the head material to the water cooling circuit during development. Sometimes we have to scrap a head and start again. Knowing what works and what doesn’t is where ‘experience’ comes in.
The changes he makes can then be measured and a further cycle of modification and measurement is carried out until gas flow improvements (accurately measured) reach a point where the head can be said to be optimised (within the parameters of the head design, valve size and lift). The process is iterative and very analytical. Very subtle changes in the port make a large difference to the CFM measurement. To assist in achieving the optimum design, we use the latest gas flow bench and software to measure and record changes.
Changes we make are mainly achieved by removing material from the head which changes the shape and dynamics of the flow through the port. Some tuning shops add material (by welding or using epoxy resins) to the port to change its shape. However, although this is a valid modifcation in terms of flow improvement, most race series do not allow adding material to the port profile. Our heads are mainly aimed at racing and hence we do not add material to the port. They are fully legal for most competition uses.
The Port flow analyzer sofware we use is designed to "streamline" the recording, calculating, reporting and graphing of cylinder head flow bench data. It makes flow testing faster and more accurate and assists the experienced gas flow engineer in achieving the optimum design. It is important to realise that this technology does not do the job for the gas flow expert. In many respects it makes the job more difficult because of the sheer amount of information it can provide. However, properly used with the intuitive science of our gas flow guru, the results are outstanding.
Power improvements at the "cutting edge" of racing come from minor improvement in details. For cylinder heads, these details not only include flow, but port velocity, swirl and tumble motion. The Port Flow Analyzer software we use has options for port velocity mapping with a pilot tube, swirl and tumble measurement (using our swirl meter and our tumble adapter), port stability, etc. Using these features and the processing power of the computer (and some fairly advanced physics contained within) we are able to predict the potential power of an engine fitted with this head from the flow bench !!. This power prediction is amazingly accurate to within 1% and has been verified on our engine Dyno.
