Identifying Flow Deficiencies at the Valve

A flow bench allows us to evaluate the flow properties of cylinder heads, but it requires a bit of intuition and a working knowledge of how air moves through a port. Head porters use pitot tubes, flow balls, wands, threads and all manner of small development tools to map and sometimes temporarily alter the flow stream to determine the most efficient path to and past the valves.

The pressure tap opening is located on the sealing face of the valve. It performs the same function as a pitot tube, but it reads the pressure change directly at the valve.

The flow bench measures overall airflow through the port at 28 inches of water or whatever test pressure is set by the operator. You get an airflow figure that can be compared to other ports, but it doesn’t necessarily tell you where the flow is efficient and where it’s lacking without considerable work with the pitot tube and the various small tools that let you visualize and/or temporarily redirect the flow to see if you can improve it. It takes a lot of patience and experience to spot flow anomalies and use the tools to help you decide what to change. The pitot tube is the go to device for measuring flow efficiency anywhere in the port, but it requires inserting the tube into the flowing port which can disrupt the airflow in the exact location you are trying to evaluate.

A few years ago cylinder head specialist Richard Touchette devised a new method that allows flow bench operators to measure airflow directly at the valve without interrupting the flow stream. Even better, it allows them to read the flow dynamic around the entire circumference of the valve via a pitot port “pressure tap” built right into the seat face of the actual valve. The pitot port in the valve head reads the pressure differential across the valve and the valve can be rotated to read a differential in any position whether it’s in the middle of the cylinder or right next to the chamber wall where the flow might be affected by shrouding. Touchette markets this system through his company RTSTooling.

An adjustable slip collar locks to the valve guide with set screws. The numbers on the top indicate the detent placement used to lock the valve in position with the pressure tap located at eight different locations around the perimeter.

Touchette calls his device the P-D Valve because it measure the pressure differential at the valve face. His company stocks pre-made valves in popular sizes and they will also make both intake and exhaust valves in the proper size for your application. In addition to the valve the kit provides a locking position collar for fitting the valve to the head, adjusting the lift and precisely rotating it for accurate measurements. The aluminum collar contains spring loaded ball detents that snap into vertical grooves on the valve stem to lock the valve in any of eight preset positions. The slip collar also works with preset height standards that allow you to set the valve opening from .050-inch all the way up to 1 full inch.

Plastic tubing connects the top of the P-D valve to the built in pressure gauge on the flow bench so the gauge can record the pressure differential at each test point. A color coordinated flow map is generated showing the lowest to highest calculated flow numbers and their location on the valve relative to their placement within the combustion chamber.

The pressure tap 0n the valve face intersects a hollow stem in the valve and a piece of flexible tubing attached to the top of the valve allows a pressure gauge to directly read the pressure differentials. To map the pressure differentials all around the valve at different lift values. The valve is rotated to each detent and a measurement is recorded. Once the eight values are recorded for a given lift value (say .100-inch), the height standards are reset to the next desired lift point and the sequence is repeated.

If you study the accompanying pressure map you will note eight separate flow regions around the circumference of the valve. They correlate to the valve's position within the combustion chamber and the flow rating when the pressure tap is rotated to that position. The pressure tap indicates the location of more or less flow thus allowing the porter to determine how best to modify the port or chamber to improve and balance the flow characteristics of each port and chamber combination.

When an anomaly or deficiency is detected, the test valve is removed, but the collar can remain on the head while further grinding or other modifications are performed. This ensure that the valve is returned to the exact same positions for further testing. Then it’s a simple matter to reinsert the valve and repeat the test to evaluate results. The kit comes with software to do the conversions so you simply input the measured values and it calculates the flow numbers for you.

The RTST kit permits precise mapping of the airflow values around the circumference of the valve at any lift value. It helps identify shrouded areas, poor performing short side radii and other obstructions such as valve stems and guides and quantifies the differences. Follow the photographs to see how the RTST tool makes port development easier. RTST can make you new test valves for any valve size you require so you can Expand your kit's capability as needed. And the software permits you to store and compare tests so you can maintain accurate records for all the cylinder heads you process.

SOURCE:

RTSTooling
www.rtstooling.com
(704) 746 9975