In the Feb. ’11 issue of
HPP, we presented the new Edelbrock Performer D-Port head in the article D-Port Development. At the time, the head wasn’t production ready, so our story was written based on the prototype we obtained. The heads have since gone into production and have reached the waiting hands of hobbyists and engine builders. Since the basic design philosophy, a behind-the-scenes look with Edelbrock engineers, and the specifications were discussed in this previous story (
Click Here to read the previous article), in this story, we will examine the flow potential of the heads when placed in the hands of a professional Pontiac head porter, designer, and engine builder.
Don Johnston, owner of DCI Motorsports, has been in business since the early ’80s and has been knee deep in Pontiac engines his whole life. He builds everything from stock restoration engines to all-out race powerplants.
Don also designs cylinder heads. Regular readers may recall the Oct. ’03 HPP story "Pontiac Tiger Heads--Breathe Deep" on his race heads that featured a 400-plus-cfm intake port out of the box. He is also in the process of bringing to market a modern-day version of Pontiac’s venerable Ram Air V head. With that resume in mind, we dropped in on Don at his new shop (2477 State Route 44, Atwater, Ohio) to discuss his two port designs, compare them with an as-cast port, and show the resulting flow increases on his Superflow SF-600 flow bench.
Regarding the new D-Port head, Don said, "Edelbrock fills a street/strip niche in the marketplace with this head. It exhibits much better flow, a more modern fast-burn combustion chamber, and lighter weight than a stock iron D-Port right out of the box. Of course, the fact that it will accept stock components, including a D-Port exhaust, will help keep the upgrade cost effective. With further porting, the head should be able to handle up to about 650 hp on pump gas."
In DCI’s testing, the stock intake ports topped out at 276 cfm at 0.600 lift and 177 cfm on the exhaust ports. The mild port raised flow to 303 cfm on the intake at 0.700 lift and 201 cfm on the exhaust, and the street/strip port job increased flow to 324 cfm on the intake at 0.700 lift and 225 cfm on the exhaust. Since the most work was done for the street/strip port, we will discuss DCI’s procedure for it here.
Paris Puglese, DCI’s cylinder head and engine specialist, did the head work and Don provided the explanations, measurements, and flow testing. Paris used a Fel-Pro 1233 intake gasket for the port match. "It actually matched quite well, so there was little work to do there," Don tells HPP. Next, Paris worked the pushrod bulge in the port to open up the pinch area to a total of 1.110 inch, and then he started raising the roof at the port opening, working inward to increase port taper and provide a straighter shot to the back of the valve. He followed up with blending the walls into the roof and floor.
Paris then turned the head over and blended the bowl on the long side (port roof) to the valve seat. "This head didn’t require a lot of work in that area either," Don said. Paris followed that by blending the short-turn (the floor of the port where it turns to the valve seat) to match the port angle on the long side (port roof) of the bowl as it enters the combustion chamber. Don says, "He also tried to retain the height of the short-turn while maintaining a radius in the corners to keep the mixture speed up."
Edelbrock’s latest creation...
Edelbrock’s latest creation for pure Pontiac engines is the aluminum Performer D-Port head. It’s available bare or assembled with 65cc, 72cc, or 87cc combustion chambers. Don Johnston of DCI Motorsports purchased a completely assembled 87cc head (though some items are not shown here) under PN 61579 from a supplier. He related that “the larger chamber can cause turbulence due to its size and shape and reduce flow slightly as compared to the smaller-chambered heads.” However, since 87cc chamber heads will be used most often by readers building 455ci and larger pump-gas street motors, it’s a good choice for this story.
We will discuss three ports—a...
We will discuss three ports—a stock as-cast, mild ported, and street/strip ported—how they differ, and what it took to get the higher flow numbers. The height and width of the mild ported and street/strip ports are the same, but the pinch areas are different. Notice in the photo there is a ridge that runs the length of the head just above the words street/strip. It reveals the fact that 0.050 inch of material was added to the intake flange. According to Edelbrock, this is done only on 87cc-chambered heads.
This is a 4.190-inch-bore...
This is a 4.190-inch-bore head gasket. Note the location of the valves and chamber relative to the gasket bore size, and also the small quench area on the spark plug side in the fully machined, modern chamber. Edelbrock says the head can be used with bore sizes as small as 4.06 inches.
Though Paris began the process...
Though Paris began the process in the ports, we photographed the tools while he was working in the bowl because they and the surface texture they create are easier to see. For porting, DCI employs a non-ferrous carbide burr on aluminum, which has a wider flute for a more aggressive cut than the tighter fluted ferrous burr that the company uses on iron heads. The shank length varies from 4 to 6 inches. Don or Paris periodically apply WD-40 to the burr to keep it from loading up with metal shavings.
Paris finishes up with 36-grit...
Paris finishes up with 36-grit cartridge rolls on a 5- or 6-inch shank when workin iron or aluminum. It smoothes the marks left by the carbide burr, but still leave a rough enough surface to better atomize the mixture.
Snap gauges are used to measure...
Snap gauges are used to measure progress while porting. Don explained that tapering the port size down toward the bowl area aids velocity for driveability and torque. He measures the height and width at the opening, middle, and the short turn of the port many times during the process, as shown here in the street/strip port. Since the port taper and volume requirements will be different to match each engine and vehicle application, specific taper measurements aren’t provided here.
The pinch area is the narrowest...
The pinch area is the narrowest point in the port—to accommodate the pushrods. It measures 1.00 inch in both the as-cast and the mild port versions. For the street/strip port shown here, it was opened up to 1.110 inch. Don says, “It could be opened more if we put a tube in the pushrod hole.”
Don wants to achieve a 92...
Don wants to achieve a 92 percent width of the valve in the throat area and 93-94 percent width in the area just above the throat and below the valve seat for the street/strip port. With the 2.11-inch intake valve, the target is about 1.940-inch and 1.98-inch respectively.
Once the measurement is locked...
Once the measurement is locked in on the snap gauge, it’s removed, and as was done for the ports, it’s measured with a micrometer. The width of the throat is 1.940 inch and the bowl width just under the seat is 1.989 inch (shown).