Pure Stock Prep School - Part I: Engine

Pistons
Pistons can be chosen from several NHRA-approved sources and really come down to personal choice. The two best options are hyper-eutectic or forged. Hypereutectic pistons generally have decent strength and dimensional stability. They require additional care when following the ring gap instructions. Any deviation from their proper setup has been known to shorten their life span. Another item to note is that hypereutectic pistons don't transfer heat as readily as cast pistons and may have your motor running at higher temperatures.

We prefer to file-fit our rings for a more accurate and customized fit. By doing so, we're trying to increase our sealing performance. You may also buy pre-sized rings. There is likely very modest performance difference between the two types of rings, but again, we're trying to leave no stone unturned in maximizing our power potential.

Balancing
With the additional performance all of the above machining has provided, we don't want to skip this important process. We like to have all our piston/rod sets balance within one gram. It takes time, but the motor will spin free and easy when you're charging down the track.

Oiling
Adequate oiling has three components:1) make sure casting flash isn't interrupting the oil's ability to return to the block; 2) a windage tray will help control oil frothing and ease the load on the crank's ability to turn; 3) don't put too much oil pump into your motor. Too much psi not only costs a great deal of power, but will also prematurely wear your distributor and cam gears.

We've gotten around six horsepower in the past by lowering the psi from 80 to 65 pounds. A safe guideline is to make sure you have 10 pounds of pressure for every 1,000 operational rpm.

Assembly
When assembling the motor, we adhere to Pontiac's factory specification for clearances. For example, all Pontiac motors, except the 455, use main bearing clearances of 0.0002-0.0017 and rod clearances of 0.0005-0.0025. We would look at these specs, then run on the loose end of the spectrum to try and maximize performance by lessening friction. If your project car will see more driving than the typical race car, you may want to run a bit tighter clearances than we use.

Cam And Valvetrain
Before we choose a final installation position for the cam, we check and see if it really does match the manufacturer's cam card by degreeing it. Most cams arrive slightly off due to their build tolerances. Take note of any discrepancies and make adjustments as necessary.

When installing the camshaft, there are two options. If we're running a 3.23 gear with an automatic and 9.5:1 compression, it makes little sense to retard the camshaft to create more top-end hp when what we really need is additional torque to get the car moving quickly. Advancing the cam two to four degrees will help create more bottom-end response.

Conversely, if we have 11:1 compression, a four-speed and 4.33 gears, we consider retarding the cam for more speed at the traps. A good starting point for most builds is to install the cam straight up as directed by the cam manufacturer. Remember, as the timing chain breaks in it will automatically stretch, which creates one to two degrees of retardation on the cam.

Heads
Pure Stock racers aren't allowed to alter the valve seat angles. Most Pontiac heads have 30-degree intake seats and 45-degree exhaust seats with the notable exception of the SD-455, which uses seat angles of 45 degrees on both valves. This doesn't mean we don't want to have accurately machined seats. This actually is one of the areas that will pay off with lots of power, if the machinist is careful. A proper seal with the valve and seat is crucial. This is helped along by not skimping on valve choice. We primarily use Manley valves, but there are other high-quality valves out there. The valves must match the factory items for stem and head diameter. Under no circumstances are lightweight valves, such as titanium, allowed.