Muscle Mustangs & Fast Fords
Porting Stock Cylinder Heads
When Aftermarket Cylinder Heads Are Not An Option, Port Your Stock Heads!
Picking Ported Heads
Most companies offer multiple levels of porting. The "bigger isn't always better" philosophy is shared by Jack, Kuntz, and Robart. "You have to know what you want before choosing a level of porting," explains Ron Robart. "Before you can even think about cylinder heads, you have to look at your goals, budget, and the rest of the engine. The engine's displacement, the efficiency of the intake manifold and exhaust system, as well as the desired rpm range all need to be taken into consideration.
"So many times, people hog out cylinder heads to get higher flow numbers," adds Robart. "Too big of a port can create thin spots [in the material], which can crack and cause failure down the road. You can make big power when the heads are matched to the rest of the combination."
"When you're building a modular Ford engine, you have to remember that the small [cylinder] bores hurt power potential," Jack tells us. "The combination of small bores and the extremely shrouded intake valves aren't great for making power. Luckily, you'll see big gains from working around the intake valves to reduce how deep they are in the combustion chamber."
Buying a set of CNC-ported cylinder heads is a big purchase for most of us. Prices can vary depending on your needs and wants. Livernois Motorsports in Michigan can supply a set of its ported Three-Valve heads using new Ford castings for just under $2,100, while Robart at Fox Lake can port your castings starting at $1,599. M2 Race Systems in New Jersey offers its CNC-ported Three-Valve heads for about $1,700, and Blow-By Racing sells its CNC-ported heads for around $1,900.
As with any big-ticket purchase, doing your homework is key. Although the casting options for modular cylinder heads are nearly non-existent, porting your stock heads is an option that offers many choices. And many companies offer ported stock heads that are ready to go. So talk to you local engine builders and performance shops-they can help figure out what's going to work best for you.
What Is A Flow Test?
In its simplest form, flow-testing consists of moving air through a cylinder head at a constant vacuum pressure, and measuring the flow rate at various valve lift positions. The vacuum is measured in inches, and is displayed on a water-filled meter that is part of the flowbench. Changes can be made to the port shape, the valve angles (known as the valve job), or the combustion chamber to alter the airflow.
When testing the intake port, air is sucked in using vacuum; when testing the exhaust, air is forced up through the mock cylinder and out the exhaust port. Often artificial material is used to smooth the airflow in and out of the ports. Clay is used around the intake ports to create a curved entry for the incoming air when the intake side is tested. For accurate exhaust testing, a pipe is attached to the cylinder head to simulate an exhaust header.
Greater airflow generally indicates a flow improvement, as long as there is no loss in velocity. Since the intake and exhaust valves are only open for a short time during each cycle, the speed of the air moving past the valves is just as important as the volume of air. Velocity can also be tested on a modern flow bench.
"Flow numbers are directly related to valve size, how much the valves are shrouded in the head, and how smooth the turns are," explains Jack. "In the end, horsepower numbers and flow numbers are directly related, but bigger isn't always better. If the ports are too big, the heads will not be efficient and you will lose all the low-end torque.
|Ford||M2 Race Systems||Fox-Lake Perf.||Blow-By Racing|
|Stock||Ported 1||Ported 2||Ported 3|
|77.1 at 0.100||85.2 at 0.100||86 at 0.100||75.3 at 0.100|
|147.0 at 0.200||177.0 at 0.200||166 at 0.200||162.0 at 0.200|
|196.6 at 0.300||233.5 at 0.300||221 at 0.300||228.3 at 0.300|
|216.0 at 0.400||260.3 at 0.400||249 at 0.400||273.8 at 0.400|
|223.2 at 0.500||272.7 at 0.500||264 at 0.500||283.6 at 0.500|
|224.8 at 0.600||282.7 at 0.600||281 at 0.600||292.9 at 0.600|
|Stock||Ported 1||Ported 2||Ported 3|
|52.7 at 0.100||46.6 at 0.100||60 at 0.100||46.2 at 0.100|
|97.8 at 0.200||99.0 at 0.200||110 at 0.200||104.3 at 0.200|
|120.2 at 0.300||129.4 at 0.300||142 at 0.300||135.7 at 0.300|
|138.1 at 0.400||153.2 at 0.400||175 at 0.400||163.2 at 0.400|
|148.2 at 0.500||171.9 at 0.500||190 at 0.500||177.0 at 0.500|
|153.7 at 0.600||188.7 at 0.600||212 at 0.600||189.6 at 0.600|
|All measurements are cfm/inch-lift.|
These numbers represent the flow of CNC-ported Three-Valve cylinder heads that are readily available from three major aftermarket companies versus the flow number of the stock Three-Valve heads. There are significant differences in the port work, and this is reflected in the flow numbers. "There is no right or wrong way to port a cylinder head," adds Kuntz. "If there was one way to port a head, they would all look and flow exactly the same."