In the previous issue, we spoke with a number of well-respected companies that market high-flow Pontiac cylinder head packages, and each shared with us the detailed specifications of those aimed at enhancing the performance of moderately-sized street and street/strip engines. We also learned that the round-port castings Pontiac produced during the late '60s and early '70s were each designed to complement its specific application.
This installment will follow suit, except we'll explore the specialized offerings from a wider range of companies. While most are designed to maximize the performance of street/strip and full-race engines displacing more than 450ci, there are certainly a number of hobbyists using them successfully in dedicated street applications. The companies have shared with us their casting's major advantages, installation requirements, and expected performance levels. Follow along as we conclude our two-part series.
SD Performance offers three...
SD Performance offers three CNC-machined Edelbrock cylinder heads with varying airflow. The base package provides 310 cfm for $2,300, while a wide-port version, boasting peak airflow in excess of 370 cfm, starts at $3,000.
SD Performance's Moderate Monsters
Dave Bisschop of SD Performance in Chilliwack, British Columbia, has developed a strong reputation for his moderate approach towards serious performance. The company's cylinder head packages are a key element of that success, and SD Performance has recently incorporated a computer-controlled mill to increase internal efficiency. Bisschop has not only created successful porting programs for various cast-iron D-port cylinder heads, but also for the aftermarket Edelbrock aluminum casting.
Few would disagree that in box-stock form, a basic Edelbrock cylinder head is adequate for many mildly-built, moderate-displacement Pontiac mills, but Bisschop says that today's trend leans toward large-displacement, pump-gas engines, and he feels that a stock Edelbrock casting can sometimes become a limiting factor in those applications.
"Today's hobbyists seem to enjoy driving their Pontiacs on the street during the week, and then going to the track and running well on weekends-and the most reliable way to achieve that balance is with a large engine. Displacement starts around 470 ci when adding a stroker kit to an otherwise typical 400 rebuild, and it can reach well into the 500s with an aftermarket block. We've found these engines typically respond favorably to additional airflow, so we developed bolt-on CNC-ported Edelbrock packages for them."
The oil return holes are polished...
The oil return holes are polished to promote quicker drain-back. SD Performance also offers CNC port-matched intake manifolds that perfectly mirror the cylinder head variations.
SD Performance markets three distinct packages that begin life as a semi-machined 72-cc Edelbrock casting. "We CNC-machine its intake and exhaust ports, and enlarge the combustion chambers as necessary. Our basic 310-cfm package increases as-cast intake port volume from 215 cc, to 235, and boosts airflow from roughly 280 cfm, to 310 at 0.600-inch, at 28 inches of pressure. Pricing starts at $2,300 per pair. Our 330-cfm casting, which peaks at 0.700-inch, starts at $2,400 and is probably our most pop-ular. Many hobbyists recognize its economic value and are willing to spend the extra $100 for 20 additional cfm."
According to Bisschop, both packages boast of such standard features as 2.19/1.77-inch stainless-steel valves, multi-angle valve seats, dual valve springs suitable for either type of flat-tappet camshaft, or a hydraulic roller, and include a host of other top-quality valvetrain components. Solid roller valvesprings are optional on the 330-cfm casting only, and add $100 to the final cost. The exhaust port of either casting typically flows 70 to 75 percent of the intake port.
A heart-shaped chamber adds...
A heart-shaped chamber adds $300 to the final cost. Dave Bisschop says testing with otherwise identical 330-cfm castings indicates that his modified 72 cc chamber (shown) produced 9 additional horsepower with 2 degrees less spark lead, when compared to a typical 72 cc Edelbrock chamber.
The third CNC-ported Edelbrock package SD Performance presently offers is its wide-port casting. "We typically limit it to competition applications," says Bisschop. "Measured airflow is at least 370 cfm at 0.750-inch lift, and base price starts at $3,000. The castings feature 2.25/1.74-inch valves, and the intake ports, which measure 267 ccs, require the use of a 11/42-inch offset rocker shaft system and our similarly-modified Victor intake manifold, or a cast-aluminum unit from BOP Engineering-all of which we offer at extra cost."
Combustion chamber volume is one area of any Edelbrock package that's machined to customer order. "We've developed CNC programs that can increase the volume of a 72-cc casting towards 90 for $150, and have just released our "heart-shaped" chamber option. We weld mat-erial into an otherwise typical chamber, and then machine it into its final shape, which measures in the low 70s. Our testing indicates a definite efficiency improvement."
Bisschop tells HPP that he's happy with the dyno testing results so far, but expects to extract additional horsepower from his castings in the future. "We're finding our 330-cfm casting is presently generating around 700 to 750 horsepower on a 470ci engine with 12.5:1 compression, a solid roller camshaft, and a Victor intake manifold. Increase displacement to 541, and compression to 14:1, and we're consistently producing anywhere between 850 to 900 horsepower with our 370-cfm wide ports."