Steady Flow Of Data
Cylinder-head flow is widely misunderstood in the high-performance world. Magazines are accused of promoting only the big flow numbers, but if you take the time to read, you'll see this couldn't be further from the truth. Today, most editors understand the importance of overall flow and openly talk about the big picture, not just peak numbers. With that said, many enthusiasts still make mistakes when evaluating cylinder heads because they base everything on flow. If you spent a few days at Rich Groh Racing or any professional engine shop, you would see that just slapping a cylinder head onto the flow bench and letting it rip isn't the proper way to evaluate heads. It is a process that has been standardized, and testing procedures are replicated exactly each and every time a head is tested.
It all starts with the flow bench. For many, the SuperFlow SF-600 is the bench of choice. When ordered at RGR, it was specifically calibrated for the shop location. The reason for that is the flow bench readings at a head shop in the mountains of Colorado will certainly have different readings from a flow bench at sea level. With the calibration in place, Superflow provided specific flow plates to test the flow bench to ensure accuracy.
Another useful piece of equipment that has helped bring more accuracy to the cylinder head flowing segment of the industry is FlowCom. In the early years, head porters relied on the "test tubes" on the flow bench, and they eyeballed and scribbled down the results. These days, a digital readout is provided that ensures 100 percent accuracy in the readings.
On the exhaust side of the...
On the exhaust side of the TFS heads, the ports are 95 cc and flow a maximum of 251 cfm at 0.750-inch lift. Our camshaft lifts the exhaust valves a maximum of 0.575 inch. These heads flow 230 cfm at 0.550 inch and 238 cfm at 0.600 inch through the 1.600-inch exhaust valve.
Once you have a bench that is calibrated properly, it is time to set up cylinder heads. Test equipment is sensitive to how the test subject is attached to the tool. Problems can occur if there are air leaks, as an inadequate seal will allow the results to be skewed. The most common areas for air leaks are the valves, head gaskets, and spark plug hole. Groh even said he runs the rocker arm studs when he flows the heads. He proved his point by flowing the head with the rocker arm studs in place and without. By not running the studs, the heads were down by 8 cfm. The cfm dropped because air entered the port and disrupted the airflow pattern.
These heads were flowed in 0.050-inch increments using step blocks to simulate the valve lift. Groh set up a micrometer on top of the valve and calibrated it. He used the blocks to open the valve to the predetermined lift and he took measurements. He also double-checked the micrometer so it was always set up perpendicular to the valve tip. If it is not lined up properly, the results will come out higher and be less accurate.
It's all about consistent and accurate setup techniques.