Muscle Mustangs & Fast Fords
Brodix LH 17 Degree Cylinder Heads - Head Hunting
Picking The Right Size Cylinder Head For Your Stroker 5.0-Liter Engine.
One of the most important pieces to the engine-combination puzzle is the cylinder heads. But navigating through the 30-plus offerings (for the small-block Ford) can be overwhelming. There are cylinder heads suitable for use in stock rebuilds, Outlaw-style engines making upwards of 2,000 hp, and every combination in between. Factor in ported-head options, and it could make one's head spin around like a scene in The Exorcist.
This month, we ventured to JPC Racing, where Burcham had a supercharged 5.0-liter Mustang ready to show the effect of improperly sized cylinder heads. We'll sample the Brodix LH 17-degree cylinder heads, which fit a variety of combinations. The LH heads are available in two different intake port volume sizes (195cc and 210cc)-both styles feature a 17-degree valve angle. The two different sizes allow this head to be useful in a variety of applications.
The '89 coupe features a Ford Racing 331ci short-block based on the Ford Racing Boss 302 block, and it's been punched out with a 4.125-inch bore. The folks from Ford then filled it with an Eagle 3.100-inch-stroke crank, Eagle steel rods, and Mahle forged pistons. The short-block is durable, and boost is provided by a Paxton Novi 2200 supercharger system.
Initial dyno-testing showed the car was producing 477 rwhp when equipped with a pair of 170cc cylinder heads from another manufacturer and 10 psi of boost. While the baseline heads are great, the runner size was not large enough for a stroker, let alone one capable of withstanding a lot of boost.
No matter what combination you are building in terms of cost and performance, you need to be armed with information, and it has to be more than just cubic-feet-per-minute flow numbers. The flow numbers are only part of the story; port volumes play an important roll in performance, as shown by the new the Brodix LH heads.
"There are so many variables when picking a cylinder head: flow numbers, port size, combustion chamber, quality of the head, intention of your combination, and of course, retail cost and budget," said Justin Burcham of JPC Racing. He summed up the major downfall in the cylinder head department: "Bigger isn't always better. The engine size, combination, and level of competition/use (drag racing, street-use, circle track, autocross, and so on) has a bearing on which cylinder heads are correct for your application."
Jason Neugent of Brodix heads offered some insight in selecting a cylinder head based on the port volume. "If it is a small-cubic-inch engine with low compression, I suggest you look for a smaller intake runner. The small intake runner will keep the torque healthy and perform well across the board. If you run a small engine with lots of compression, then more cylinder-head intake volume is required to fill the cylinders. The same goes for larger cubic-inch combinations."
A typical street engine in naturally aspirated trim (mild hydraulic roller camshaft, good intake manifold, and properly sized exhaust system) should generally require a 170-200cc runner for 289-347 ci and 195-225cc for 347-440 ci, according to Neugent. "Of course, there is a gray area, so to speak," he added. Those gray areas include high-rpm applications that require a larger intake port to feed the engine, which usually comes with the sacrifice of low-end torque. Supercharged combos can also benefit from a larger set of heads due to extra airflow being shoved into the engine.
"Experience with different combos and testing numerous size cylinder heads on a variety of applications is priceless. We can hypothesize all we want, but real-world testing is the only true test," noted Burcham, who also discussed the bigger isn't always better cliché. "If you put a 225cc intake runner on a 306ci, then the engine would seriously lack bottom-end and mid-range horsepower and torque. It would, however, scream at 8,000 rpm (given the proper valvetrain and intake manifold). But if a 306ci engine with the same 225cc intake runner had some sort of forced induction, then the port size would have a less negative effect on the bottom-end and mid-range results.
Neugent agreed about the lazy low-end with large cylinder heads on a small engine, and went on to tell us about the opposite side of the equation. "The same goes for an engine that has large cubic inches and small cylinder heads. The engine would have tons of torque but run out of power on the top-end. You can only pump so much air through a small head. It would be the same as trying to pour five gallons of water into a one-gallon bucket." That was exactly what was happening with our test engine‚the intake runners were too small given its 331ci size and the supercharger huffing in more air.
The Brodix 195cc heads use a 2.02-inch intake valve and the 210cc features a 2.08-inch valve; both heads rely on a 1.60-inch exhaust valve. Burcham chose the Brodix LH 210cc heads, which come fully CNC-ported by noted engine-builder Keith Craft. Brodix lists the heads as KC-LH-F 210cc, noting the style of head and its CNC port job. He selected the heads for the large intake runners and significant flow numbers over the un-ported, baseline 170cc heads that had just come off the test engine.
A cylinder head's airflow is also critical when selecting heads for your engine, and there is a relationship to the intake port volume. Burcham explained, "The intake and exhaust port sizing is important for port velocity, which is based on the runner's size. A smaller cc port that flows 300 cfm will normally help the engine make more horsepower than a port that is, for example, 10cc bigger and flows the same 300 cfm." Burcham told us that the higher air speeds and velocity fill the cylinder better, which allows the engine to accelerate quicker and ultimately make more power.
The Brodix LH 210cc heads we sampled flowed 298 cfm at 0.500-inch lift and 317 cfm at 0.600-inch lift on the intake side. We didn't flow the ports at higher lift ranges as our application features a mild hydraulic camshaft that checks in at 0.560/0.570-inch lift. Those results are 2 cfm less than the flow numbers shown on Brodix's website. The difference is probably due to variations between the flowbenches.
Moving to the exhaust, our independent testing showed the exhaust ports flowing 217 cfm at 0.500-inch and 221 at 0.600-inch lift. Typically, as the bore size increases, so does the cfm flow as it unshrouds the valves by moving the cylinder wall away from them. We didn't test a set of LH 195cc heads, but Brodix touts them as moving 287 and 294 cfm at 0.500- and 0.600-inch, respectively. The exhaust ports in the 195cc version flow less due to less porting-209 and 213 cfm at the two big lift numbers of 0.500- and 0.600-inch.
"Pay attention to the flow numbers in the mid- and low-lift areas when selecting a cylinder head. Too often people focus on the peak number, which is usually at 0.700-inch lift. That result doesn't matter when your cam has a max of 0.500-inch. The mid- and low-lift results are more important-during combustion a valve travels past the 0.100, 0.200, 0.300, and 0.400 ranges twice and only hits the peak once," notes Burcham.
Another nice aspect of the Brodix LH heads is the valve angle. "The valve is at a 17-degree angle in relationship to the bore or piston travel," said Neugent. The stock 5.0-liter heads feature a 20-degree valve angle, and Brodix stood the valves up by 3 degrees to help the air and fuel distribution. But Neugent cautioned that it isn't as simple as just moving the valve angle in the head. The port locations are also critical in distributing the air and fuel into the combustion chamber.
The guys at JPC Racing bolted the heads back on with a few extra parts and pieces needed for the installation. Cometic provided its MLS (multi-layer steel) head gaskets, and a set of replacement intake and exhaust gaskets. The heads were secured to the Boss 302 block with ARP 1/2-inch studs, which we procured from Summit Racing. Comp Cams came through with a set of its 1.6 roller rocker arms and new pushrods.
The swap was straightforward, and before we knew it, the car was back on the dyno. The new heads helped the engine breath easier, and Burcham dialed in the tune using a DiabloSport chip in the stock A9L computer. The result was a better 508 rwhp at 6,400 rpm and torque of 425 lb-ft. The better flowing heads helped feed the hungry 331ci, and also showed that better flowing heads also make a difference in a supercharged application.