Yes, we know there are no valves in the head.
Part I: Street/Strip Pump Gas Applications
While it's true that an engine inhales and exhales through its cylinder heads, simply enlarging the intake and exhaust ports does not always yield airflow improvements. Such action can, in fact, degrade airflow and/or port velocity so much that a casting can be rendered useless in short order. Fortunately for hobbyists, a number of performance-oriented options exist today, and we'll explore several in our two-part story.
We contacted companies that are presently producing or uniquely modifying Pontiac cylinder heads and requested information about the specialized castings each offers. In this issue, we'll discuss the entry-level heads, which may be best suited for street-driven combinations that operate through a wide RPM range in myriad driving conditions, as well as hear some insider information about round-port development within Pontiac.
SD Performance has offered ported D-port castings at an affordable price for several years, but only recently has the company begun using a CNC mill to perform the port work on most any D-port, including low-performance, small-valve castings with prices starting at $1,195. Like most others in our story, this particular casting is shown disassembled for photographic reasons, but would otherwise arrive completely assembled, and ready to bolt on.
SD Performance Cast-Iron CNC-Ported
Pontiac's basic cylinder head with D-shaped exhaust ports debuted along with the V-8 in 1955, and the same general intake and exhaust port configurations were utilized on most production engines through the end of V-8 production in 1981. Dave Bisschop of SD Performance in Chilliwack, British Columbia, has greatly simplified the art of porting D-port castings and he has created a new avenue for hobbyists seeking affordable performance while maintaining stock appearance.
"We've written CNC programs for virtually every D-port casting Pontiac produced from 1967 forward, and our basic package starts at $1,195 when using your castings, or $1,395 if we supply the cores," Bisschop says. "We start with bare D-port castings, and after a few hours in our CNC mill, we end up with perfectly ported cylinder heads that flow 250 cfm at 0.550-inch valve lift, at 28-inches of pressure on the intake side, and an exhaust port that flows at least 75 percent of that."
He continues, "We finish them with top quality valvetrain components such as stainless-steel Ferrea valves, Crower springs, Manley retainers, and Comp Cams locks. Spring pressure is set for the type of camshaft that's being used (hydraulic or solid flat-tappet, or hydraulic roller). The castings also receive full bronze valve guides, new pushrod guide plates, and 7/16-inch ARP rocker studs. Simply stated, everything is new, but the actual cylinder head castings."
Though some hand touch-up is performed, the entire SD Performance porting process is fully automated. There's also a specific program for the closed-combustion-chamber '67 No. 670 castings (not shown), which includes relieving the intake valve and spark plug. This gives the chamber somewhat of a heart-shaped appearance.
Port velocity is a critical element in the performance of any street engine, and Bisschop says that he commonly focuses on maximizing throttle response in such applications. "Velocity is very important, especially with a 400," he explains. "The long-stroke 455 is less sensitive to port velocity changes, but throttle response can still suffer. The intake ports of our 250-cfm heads measure around 165 ccs, which keeps velocity high, making them an excellent choice for low-to-moderate rpm 400 and 455ci engines producing between 400 and 475 horsepower on pump gas."
A limited number of extra-cost options are available for the cast-iron heads, and those include hardened valve seats, elongated pushrod holes, and three flange surfacing. "We also offer a 260 cfm program for those wanting slightly more airflow, and that adds $200 to the cost of the 250 cfm package, but once we push horsepower toward 500, we start looking at other options including the various aluminum castings presently on the market," he says.
When asked for his thoughts on the thermal efficiency differences between cast-iron and aluminum, and its effects on performance, Bisschop replied, "There's no doubt that aluminum is less efficient than cast-iron. We've found, with all variables being equal, that an aluminum head needs roughly 3/4 of a point more compression to generate the same power as a cast-iron head. We regularly shoot for a compression ratio of 9.5:1 with iron heads and 10.25:1 with aluminum heads on our pump gas engines."
Kauffman Racing Equipment developed its aluminum D-port to maximize the performance of dedicated street applications. The casting contains small, high-velocity intake ports that flow around 260 cfm as cast and bolt-on packages start at $1,750 per pair. The company has also developed CNC-porting programs that incrementally increase airflow to a maximum of 340 cfm.
Kauffman Racing Equipment Aluminum D-Port
Any performance enthusiast with a finger on the pulse of the Pontiac hobby knows the excitement coming from Kauffman Racing Equipment in Glenmont, Ohio. Within the past few years, the company has developed and released a new cast-aluminum D-port cylinder head to achieve maximum performance from specific applications. Jeff Kauffman says the endeavor has been a huge success.
"We developed our heads for the simple fact that we wanted a high-performance, aluminum D-port for street engines," he says. "Many customers already had D-port headers on their cars, so we basically filled a market void. Since port velocity is so important in any street application, we kept intake port volume relatively small, measuring 185 cc, which promotes high velocity. That brings torque in quickly, and we build horsepower off that."
According to Kauffman, the basic casting consists of intake ports that flow approximately 260 cfm at 0.550-inch valve lift, at 28 inches of pressure, exhaust ports that flow 70 to 75 percent of that, and a combustion chamber volume of 65 cc. "The basic bolt-on package starts at $1,750 per pair, and that includes 2.11/1.66-inch diameter, stainless-steel Ferrea valves, Crower valve springs, and new pushrod guideplates and rocker studs."
Another key feature of KRE's castings is the modern fast-burn style combustion chambers. "The chamber shape works very well," says Kauffman. "Dyno testing shows that the heads produce peak power with just 30 to 32 degrees of total spark lead, and any variance outside that range usually causes power to fall off. We can enlarge the combustion chamber volume to 74 or 85 cc using our CNC mill, which increases base price to $1,850 and $1,950, respectively, but doesn't have any effect on spark lead requirements.
KRE incorporated a modern fast-burn style combustion chamber into its aluminum D-port, and in as-cast form, it displaces 65 cc. Optional CNC milling can increase volume to 74 or 85 cc. Standard valves are 2.11/1.66-inch, but larger options are available upon request.
"Though we intended for these heads to be high-performance stock replacements, we have customers who use them in street/strip, bracket race, and dedicated race applications. We've developed CNC-porting programs to boost airflow to 290-, 310-, 325-, and 340-cfm for those that might benefit from it. Other extra-cost options include larger 2.19-inch intake or 1.77-inch exhaust valves, and valve springs to accommodate a solid roller camshaft."
When asked which castings sell best, Kauffman replied, "We see a 50/50 split for orders of as-cast intake ports and those with CNC-porting, but chamber volume is a little different. There might be a stretch where 85 cc castings sell best, and then 74 cc castings will sell better. It really depends on the combinations that are hot at the time. Right now, 461 to 467ci stroker engines running on pump gas are very popular, and we're consistently making around 500 horsepower with our as-cast (260 cfm) 85 cc castings and a mild hydraulic flat-tappet camshaft in those types of applications."