Pure Stock Prep School - Part I: Engine

Cam And Valvetrain
We require the camshafts be the factory grind, or as close to the factory specs as possible. If a factory camshaft is unavailable, the aftermarket cam must fall within 1 percent of the NHRA lift spec, and duration as measured at 0.050-inch lift. For example, Pontiac's 068 cam has a duration at 0.050-inch lift of 212-degrees intake and 225-degrees exhaust, with NHRA allowed lift of 0.424-inch. Using our 1 percent rule, the aftermarket cam can have duration of 210 to 214-degrees intake, 223 to 227-degrees exhaust, and lift of 0.420 to 0.428 inch. Engines must be able to idle with 16 inches of vacuum at 1,200 rpm. (Big cammed engines like the R/A-IV are given a variance to this rule.)

We don't allow roller cams, or roller rocker arms, not even roller tip rocker arms. The rocker arm ratio must be correct for the application. We do allow the use of polylocks or crimp nuts to adjust the rocker arms to avoid lifter pump up (hydraulic cams).

Heads And Intake
Intake manifold and heads have to be the correct casting numbers. Porting or gasket matching of heads, intake, and exhaust manifolds is not allowed, not even a simple clean up. We want the castings just as they were made at the factory.

Carb
The carburetor must be correct for the year, make and horsepower claimed. Jetting and metering changes are allowed. We don't want to see the '71 Pontiac high-flow or '75-and-later 800-cfm Q-jets on engines that originally had the 750 carbs. Carbs can only be fed by mechanical fuel pumps; no electric pumps are allowed.

Ignition
We limit distributor modifications to recurving the advance and replacing the points with an electronic module that fits under the stock distributor cap. Aftermarket coils must be of the same shape and color as the factory coil. Aftermarket ignition boxes aren't allowed.

Accessories
The engine must have factory pulleys in place, and belts to run the water pump, alternator, and power steering (if optioned) at all times. The only belt that we allow to be removed is for the A/C compressor, if so equipped.

Cooling
The radiator must be correct for the year, model, and horsepower claimed-no aftermarket aluminum radiators. All cars must be equipped with radiator overflow catch cans 16 ounces or larger. The fan must be the correct factory unit for the application-no aftermarket lightweight fans.

Exhaust
We're pretty liberal when it comes to the exhaust systems. They must be routed as original, but we allow participants to upgrade to 2.5-inch mandrel-bent pipe, H or x-type pipes, and any full-bodied muffler(s). Glasspacks and straight pipe are not allowed. Of course, the exhaust manifolds must be correct for the year, model, and hp claimed, and no internal modifications are allowed. Headers aren't allowed.

Those are the basics for preparing your musclecar's engine to compete at the Pure Stock Drags. For further info, go to www.purestockdrags.com. Dan Jensen

Ram Air III Cams And Power Production
An important choice that must be made with all '69 Ram Air III four-speed Firebirds and GTOs is the cam. Early cars came from the factory with the 744 cam (224/236-degrees, 0.050 duration), but mid-year, Pontiac switched to the 068 (212/225-degrees, 0.050 duration) grind. This is an important factor. If you choose to run a lower compression motor due to the way you use your Pontiac or the availability of race gas in your area, you have to take that into account. Also, if you plan on a lot of street driving and you want a mellower rear gear, you need to choose wisely.

In this instance, the GTO was an early build car and has steep gears and the motor will be optimized for ultimate power. This in turn pointed us toward the 744 cam for its extra horsepower production and rpm potential. We will use the steep gears and compression to cover for the loss of the torque that the 068 would have given the build.

As we have built several R/A-III motors that were all dyno'd afterwards, we have a pretty good idea what to expect. For this build, we're looking for a minimum of 435 hp and 480 lb-ft of torque. The e.t. capability for this medium-optioned car is in the 12.50 range at 112-plus mph. We dyno very conservatively, which leaves us near a modern SAE Net rating. We dyno with the water pump, fuel pump, alternator (on but unplugged), exhaust pipes and air cleaner. It gives us a very representative view of a car's potential. MW