Cylinder head porting is a very touchy art, and unless you have the right tools it can seem like a black art. The holders of secrets guard them closely when it comes to producing race-winning flow numbers, but the tools and flow benches from SuperFlow remove the shadowy witchcraft veil and help engine-builders identify and optimize flow for any application.
As is the mantra, an engine is just a glorified air pump, volume and velocity are the name of the game. The more air we can cram in and push out the more power potential an engine has. Porting seeks to remove restriction and promote increased volume of air charge entering or exiting the combustion chamber. Restrictions can manifest in a number of different forms. Burs, casting defects, sharp corners, and other design flaws can negatively effect flow characteristics.
To the inexperienced hot-rodder the temptation is to hog-out ports until the walls are paper thin, rationalizing the “improvement” with the misinformed metaphor of a fire hose. If the hose is bigger diameter it will flow more, but there is a crucial second part to intake or exhaust runner design — velocity.
Pressure is proportional to velocity, but not the inverse. As velocities increase pressures decrease, per Bernouli’s law. Velocity is your friend, it promotes scavenging on the exhaust and throttle response on the intake. Indiscriminately opening a port may have unseen consequences on the velocities and pressures in different areas of the port.
When we start to look at the flow of a cylinder head on a SuperFlow bench we are looking for multiple pieces of data. Traditionally, these measurements are taken with a pitot static probe. Like the system to measure airspeed on an airplane, a pitot tube employs a protrusion into the airflow with a number of holes placed inline with, and tangent to the airflow. As air passes over the holes the pressure differential can be translated into velocity.
Because the pitot probe must be held in the flow through the port it represents a relatively large disturbance in the flow and may yield false readings. Using a pitot tube to examine flow characteristics in a port is akin to exploratory surgery. You may find obvious problems to fix, but the act of exploration may taint the results.
“Putting a pitot tube anywhere in the stream adds something to the environment that’s not normally there if the engine was running down the street or track. Also remember, there may be some inconsistencies, because I guarantee the next time I put the pitot tube back in there, I’m not going to be in the exact same spot — when I go back and forth testing I don’t know if it’s going to be comparable, I know it’s going to be close but it’s not going to be exact,” explained Mike Giles of SuperFlow.
In these videos we are presented with a different option — one that makes flow visualization easier and more reliable. A valve stem is an obvious obstruction to flow, but it will always be part of the equation. By integrating the pitot static ports into a mock valve, RTS Tooling created the P-D Valve and diagnostic software to interpret the data.
“The P-D valve takes care of both of those problems because obviously you’re measuring the pressure across the lip of the valve, and it also has the indicator ring that mounts to the valve guide and some height standards — so that each time you flow across the lip of the valve you do it at the same one of eight positions indexed around the mounting ring, and at the same lift you did the time before — taking the inconsistencies out of it,” continued Giles.
To use the P-D Valve, the cylinder head is mounted to the flow bench as in any other conventional test. This time it will have one of the valve guides filled with the probe. The kit comes with spacers to set the lift of the valve to simulate different static positions in the flow continuum. Included is a block with eight selectable detents allowing the user to spin the valve in it’s guide — examining flow at different extremities of the port.
“There are a couple of different schools of thought. Some guys want consistency all the way around, some want maximum flow at the spark plug — where the combustion is going to start is where they want the biggest charge of air. As far as interpreting what highs and lows mean in the data — it’s going to be varied based on what head, what radius comes before that etc.,” Giles relayed.
By running the flow bench and watching the inches of water rise or fall in response to pressure changes the technician can collect data. Plotting the data in RTS’ software is as simple as a basic spreadsheet. First a few details about the engine are required such as the lift, exhaust or intake valve, and valve size. Following the background info the user inputs the pressure readings at the eight respective detents and the software does the rest.
“Not only the shape of the port, the radiuses in the port, how smooth or dimpled the walls are, if the air is tumbling or not — but the shape of the valve has a tremendous impact on how much air can get into the cylinder. There’s a standard set that comes with it, or you can do a fully custom valve, ” Giles assured.
The graphic generated is a circular doughnut somewhat like a pie chart — using a color legend it is easy to identify areas of high or low flow. With this information the head can be taken back to the porting bench with a plan of attack. Specific areas and be addressed rather than chasing a flow problem around the port with little validation.
Ultimately the flow testing of the ports display more realistically and thanks to the precision instrumentation from SuperFlow, that translates the tooling’s sender unit role into a easily decipherable display.
“I don’t want to say they integrate seamlessly, but it’s pretty easy. There’s an extra pressure hook up on the flow pump on the front of all our flow benches. You just run a piece of hose from there down to the top of the P-D valve and you’re live as soon as you start flowing air. The only manual portion is that you have to input all the data into the fields to represent air flow around the valve,” Giles explained.
These days the quality of parts continues to increase as manufacturing and computer modeling technology advances. For aftermarket tuners this means we have less low hanging fruit to grasp in the horsepower department. The first few horsepower are certainly cheaper than the last, and squeezing those last few leaves us looking for solutions like the P-D valve.
“When flow benches first came the market heads were steel and cast, there was a lot of improvement you could do manually — today, heads come out of a five-axis machine and they already know what they’re going to flow because they did all the modeling on a computer,” Giles lamented.
For more information on the P-D valve and SuperFlow’s flow benches, give them a call or drop a line. With more than 7,000 units out in the field they certainly have a grasp on the market and can direct you to what best suits your needs.