5. Rhoads Lifter Lowdown
Rhoads lifters are a popular way of increasing the idle quality and low-speed street manners of an engine with an aggressive hydraulic flat-tappet camshaft. At low speed, the Rhoads lifter reacts to valvespring pressure and bleeds down at a greater rate than a conventional hydraulic lifter, which can make the camshaft appear as if it were about 10 degrees smaller than it actually is. As engine speed increases, the Rhoads lifter has less time to bleed down and it begins functioning like a normal lifter above about 3,500 rpm.
If the camshaft selected for your rebuild is a bit too radical for your liking, the entry-level offering from Rhoads sells for $110 and can make your Pontiac more pleasurable to drive without compromising full throttle performance and may save you the price of replacing your cam with a milder one.
6. CNC Connection
If your intended build requires a certain amount of cylinder head airflow, but your budget can't support a set of aftermarket-aluminum castings, all is not lost. SD Performance offers an affordable CNC-porting service that increases the available intake airflow of a typical D-port cylinder head toward 250-cfm using its in-house CNC mill.
Beginning with bare castings that you supply, SD Performance modifies the intake and exhaust ports, and then completely rebuilds the pair, using top-quality components for less than $1,300. The cylinder heads are returned to you in bolt-on condition and should feed around 450 horsepower on a typical street engine.
7. Small Valve Value
In an attempt to increase the output of its performance engines for the '67 model year, Pontiac engineers increased the intake and exhaust valve diameter of its D-port cylinder heads to 2.11/1.77-inches, respectively. It seems that castings from this '67 to '72 era are most desirable for the D-port performance crowd. Similar castings were used in low-performance applications, but valve sizes were limited to 1.96/1.66-inches, which reduced peak intake airflow from roughly 210 cfm at 28 inches of pressure to about 190. However, port volume remained the same as the big-valve heads.
Most hobbyists are quick to consider Pontiac's small-valve castings worthless from a performance standpoint, and blindly discard them in favor of a more valuable large-valve casting during a build-up, but few are aware that the small-valve castings contain enough material around the valve seats to install 2.11/1.77-inch diameter valves. Simply cutting the valve seats to the appropriate sizes, like that shown here, will produce a small-valve casting, which provides large-valve performance at a fraction of the cost.
Additionally, because Pontiac's low-performance applications were often built around lesser-displacement engines, most feature combustion chamber volumes of 80-90cc, which are ideal for producing a compression ratio between 9:1 and 10:1 when building a 400 or 455ci engine. Expect to pay no more than $100 for any pair of small-valve cylinder head castings, around $250 to install larger valve seats, and an additional $125 to convert from pressed to threaded rocker-arm studs.
Note: Additional port-work like that performed to this particular head will increase overall cost.
8. Multi-Angle Mojo
Increasing cylinder head airflow is the most efficient way to improve the peak performance of any engine, but, most often, the actual port work is aimed at maximizing airflow at moderate-to-high valve lift and the task can be quite labor intensive, which can be costly. When considering said points, we found that cylinder head porting may be impractical for certain builds and/or exceed the intended budget of others.