Here are the old small valves...
Here are the old small valves inserted into the heads after the seats were cut for the larger valves. You can see how much the area was increased.
Big-cube performance is very popular with hobbyists, and for Pontiacs that usually includes a 400 or 455ci engine. When attempting to extract maximum performance from such combinations, many owners opt for aftermarket high-flow cast-aluminum cylinder heads. And while that can raise the cost of an already-expensive rebuild by a couple thousand dollars, it can easily translate into 500 hp or more.
Not every owner needs 500 hp, however, nor do all rebuilds require aftermarket cylinder heads to generate stout performance. As proven in "Rehabilitating A Wounded Warrior" (HPP, Nov. '10), the mostly stock '67 400 we rebuilt generated 400 hp using its original No. 670 D-port cylinder heads. We're confident that any reader could attain similar performance from his or her 400-inch-or-larger Pontiac using most any large-valve Pontiac D-port. Such castings are, however, becoming increasingly scarce and costlier to purchase, particularly those from the late-'60s and early-'70s, which are popular for their relatively small combustion chambers and 1.77-inch exhaust valves.
Small-valve Pontiac D-port...
Small-valve Pontiac D-port cylinder heads were once considered worthless, but they can be modified to accept larger 2.11/1.77-inch valves, allowing them to perform just as well as the most desirable large-valve D-port castings. Chuck Willard of Willard Auto Machine (WAM) uses his Serdi 3.0 valve-seat cutter and a 75-degree carbide cutting bit to widen the ports to accommodate larger valve seats. A significant amount of material is removed from the intake port, but it doesn’t grossly affect total port volume. The exhaust is much simpler.
So what can Pontiac hobbyists on a budget do? There's a cylinder-head market that's virtually untapped, and it consists of low-performance Pontiac castings of that same era that were once considered worthless. For a few dollars more than the cost of a performance valve job, most machine shops can easily modify an original small-valve casting (1.96/1.66-inch) to accept 2.11/1.77-inch valves, creating big-valve-cylinder head performance at a fraction of the cost. Here's how it's done.
Pontiac Cylinder Heads
The intake port of a typical D-port Pontiac casting usually displaces between 150 and 155 cc's depending upon the original application. Intake airflow capacity with a 2.11-inch-diameter intake valve typically peaks between 205 to 215 cfm at 28 inches of pressure. Low-performance castings usually contain a 1.96-inch-diameter intake valve, and though port volume doesn't deviate far, the smaller-diameter intake valve tends to limit peak intake airflow to around 190 cfm.
Once the intake port is sufficiently...
Once the intake port is sufficiently widened, Willard machines the valve seat using a specific cutting bit, adding a multiple-angle valve seat in the process. For Pontiac applications, his performance valve job typically includes a three-angle seat with a 30-degree seat angle for 2.11-inch intake valves and a 45-degree seat angle for exhaust valves. A performance valve job runs $225. Modifying the castings for larger valves adds just $75 to that.
Savvy Pontiac hobbyist and builders have found that the Division's small- and large-valve D-port castings are very much the same from a production standpoint. Additional material was cast around the small-valve bowl and seat area, and removing that material can allow the installation of larger-diameter valves. The process was once more involved and it included removing bowl and seat material by hand, but the same modern valve-seat cutting equipment that has greatly improved productivity and consistency of valve jobs has made enlarging the seat and bowl area a much simpler and more reasonable process.
Modifying A Pontiac Casting
Elsewhere in this issue we shared the effects that a performance valve job can have on airflow. Using the same '70 No. 15 casting featured in that story, we had Chuck Willard of Willard Auto Machine (WAM) in Omaha, Nebraska, further modify its existing 1.96/1.66-inch valve seats to accept 2.11/1.77-inch valves using his Serdi 3.0 valve-seat cutter. He first used a 75-degree carbide bit to remove any material within the intake and exhaust ports that might shroud the valve and limit airflow, and he then followed that with a multiple-angle valve seat.
Most engine rebuilds include...
Most engine rebuilds include new valves, and purchasing new 2.11-inch intake and 1.77-inch exhaust shouldn’t cost any more than new 1.96/1.66-inch units. These two particular valves are stock replacements from Sealed Power, and a complete set of 16 costs less than $150. The 2.11-inch replacement (left) is considerably larger than its 1.96-inch counterpart (right). That translates into greater airflow capacity.
The result was an 87cc Pontiac D-port casting that was functionally identical to the highly desirable '70 No. 64 casting used on that year's high-performance 455, but it's just as capable as any other 2.11/1.77-inch casting, for that matter. A subsequent airflow test session with our Superflow SF-110 flow bench substantiated that claim. The casting once peaked at 192 cfm of intake airflow, but is now capable of flowing more than 210 cfm for just $75 more than the cost of a performance valve job.
Conclusion
Small-valve D-port castings are generally easier to locate and much cheaper to purchase than large-valve counterparts, and for less than $100, yours can perform on the same level as any D-port originally fitted with 2.11/1.77-inch valves. Once modified to accept large valves, the original small-valve castings respond favorably to additional port work, which might further improve your Pontiac's performance, if additional airflow capacity is required.
If low-buck performance is appealing to you and you're of the opinion that rare and desirable cylinder-head casting numbers are best left to the restoration crowd, then such a conversion may be in your future. Since any cylinder head you begin with, regardless of valve size will likely require a complete valve job and new valves, the money saved purchasing a small-valve casting won't likely be completely consumed by adding larger valves, which may increase the budget available for another area of your project. There's no doubt it's an easy way to achieve large-valve performance on a small-valve budget!
We measured the airflow capacity...
We measured the airflow capacity of the ’70 No. 15 casting before and after the valve enlargement using our Superflow SF-110 flow bench. In completely stock form with a 1.96-inch intake valve, intake airflow peaked at 192 cfm. That increased to approximately 200 cfm after WAM’s performance valve job was performed. The addition of a 2.11-inch-diameter intake valve further increased capacity to more than 210 cfm.
Beginning in ’67 and until...
Beginning in ’67 and until midyear-’73, the only Pontiac D-port cylinder heads that received threaded rocker arm studs were those destined for performance applications. All others used pressed rocker studs, and small-valve castings are no exception. Any original-pressed-stud casting can easily be converted to accept threaded rocker arm studs, however. It involves pulling the pressed studs and tapping the existing holes for ½-13 threads. WAM offers this service for an additional $75.
These ARP rocker arm studs...
These ARP rocker arm studs are specifically designed for Pontiac cylinder heads originally equipped with pressed studs (No. 290-7201). Featuring ½-13 base threads and 7⁄16-20 upper threads, they accept any common 7⁄16-inch lock-type rocker nut and cost less than $100. The rocker studs’ bottom threads may have to be trimmed slightly, and the guideplate bolt holes may need to be elongated some, but converting from pressed- to threaded-studs will complete your D-port’s transformation into high-performance casting.
| Airflow at 28 Inches of Pressure |
| Valve lift | Baseline with
1.96/1.66-inch valves* | With 2.11/1.77-inch
valves* |
| 0.05 | 38/28 | 42/27 |
| 0.1 | 73/54 | 79/55 |
| 0.2 | 142/97 | 144/107 |
| 0.3 | 173/124 | 186/126 |
| 0.4 | 196/151 | 202/155 |
| 0.5 | 202/155 | 211/159 |
| 0.55 | 204/157 | 213/167 |
| * With a performance valve job |