Porting Expert Judson Massingill
Beneath that stern, intimidating glare and impressive stature is a man with few equals in the realm of cylinder head expertise. There are probably a few people who know more about cylinder heads than Judson Massingill, but since none of them are willing to talk, their existence is inconsequential. That's not exactly PC, but maybe it's just Judson's 100-percent B.S.-free demeanor rubbing off on us. If you want answers, this straight-shooting Texan will give 'em to you in pure, unadulterated, and unfiltered form. Best of all, he's usually right.
If you aren't familiar with the name Judson Massingill, there's no need to question his credentials. He and his wife Linda run the School of Automotive Machinists in Houston. The school's unique curriculum is strictly dedicated to the art of building high-end race engines. So successful is the program that some of the top race teams in the country, like Hendrick Motorsports, John Force Racing, Cosworth Engineering, Warren Johnson Enterprises, and DEI, all rely on Judson's graduates to put them in the winner's circle, and Nextel Cup teams enlist him to do development work on their heads.
Judson got his start like most hot-rodders, building engines in his garage and testing them on the street and at the track. Always pushing the envelope, he combined his street savvy with a university education in the quest to build more potent motors. In the heyday of the musclecar era, Judson prevailed in enough street skirmishes to pay for school with his illicit earnings. He was soon building engines professionally, but got sick of spending years training employees only to watch them quit and start their own shops. Realizing he was essentially training people for free who later became his competition, he turned that concept into a business by starting up a hard-core vocational school. Here are his words on cylinders heads, ranging from the most basic of principles to the most advanced of theories.
Which Makes More Power?
"Unless rules require it, you don't want to run an iron head," Judson says. "The only advantage is the lower cost. All this hoopla that heat escapes too quickly out of the chambers with aluminum heads compared to iron heads is pure B.S. If you're that worried about heat dissipating too quickly, just move the water jacket farther out. How hard is that? Iron is more prone to cracking and much harder to repair; you have a whole lot better chance of salvaging an aluminum head if it's damaged. You can also port aluminum twice as fast. I remember the days of spitting up black stuff for two full days after porting a set of iron heads. Another major problem with iron is that you can't weld and add metal to it, which takes away from a skilled porter's creativity in reshaping ports and combustion chambers. The weight difference isn't too bad with typical small-block wedge heads, but the penalty is significant with big-block or canted-valve heads, or anytime you raise the runners. Some circle-track guys say you need an extra 35 hp on a motor with iron heads just to make up for the additional mass, since the weight is so high up off the ground and so far forward in the chassis."
Throat Diameter
A critical aspect of maximizing cylinder head flow is establishing the proper throat diameter. Going too big or too small can seriously impede airflow, but getting it right is pretty clear cut. "The rule of thumb is that the throat diameter should be roughly 90 percent of the valve diameter," says Judson. On race valve jobs, since the seats are moved farther down near the valve, the guidelines change slightly depending on the specific valve seat angle. With a 45-degree valve seat, the throat diameter should be 0.200 inch smaller than the valve, and with a 50-degree seat, it should be 0.180 inch smaller. Stepping up to a 55-degree seat requires a throat diameter 0.160 inch smaller than the valve.