A simple, yet effective way to improve overall airflow is with multiple-angle valve seat cuts, as opposed to just one, when rebuilding a set of typical cylinder heads. The various angles can be depicted here as rings in different shades around the seat. As air begins flowing past the valve as it opens, the varying seat angles tend to smooth the transitional flow into or out of the port, and that can improve low-lift airflow by a few cfm over stock, generally slightly improving low-speed performance.
Additional blending into the bowl area with a grinder and modifications to the valves can yield further increases that can equate to as much as 10 to 15 cfm over stock at low-and-moderate lift values. The airflow gain from such work diminishes as the valve progresses toward peak lift, since the seat and its angles become less of a factor and the actual port shape comes into play.
In today's hobby, it seems that three is the minimum number of multiple-angle valve seat cuts used when preparing cast-iron Pontiac cylinder heads, and it's referred to within the industry as a "three-angle valve job." One should expect to pay around $225 to have such a valve job performed to a typical set of heads.
9. Rocker Arm Affordability
The stamped-steel rocker arm assembly found on every Pontiac V-8 from its introduction in 1955 was developed by Pontiac engineer Clayton Leach. The simple design proved very effective, and other manufacturers, in one form or another, adopted it within a few years.
Over time, the aftermarket developed a variation of it that included a roller tip and trunion, aimed at reducing overall friction, and today roller rocker arms are commonplace in virtually any performance rebuild. The added cost over a traditional stamped steel rocker isn't within every budget, however.
Performance Racing Warehouse in Placentia, California, offers its own entry-level rocker arm for budget-minded rebuilds. Its Sportsman Steel Roller Tip Rocker Arms use a main-body cast in 4340-steel and feature a roller tip to minimize side loading on the valve stem. Unlike most stamped, cast-steel, or aftermarket rockers, PRW's units include 7/16-inch positive-lock nuts for accurate valve setting.
Available in 1.52:1 or 1.65:1 ratios, PRWs are an excellent alternative when replacing worn, stock 1.5-ratio rocker arms or to gain some additional lift from an existing camshaft. A complete set retails for less than $100.
Note: Be sure to clearance the cylinder head's pushrod guide tubes if 1.65:1 units will be used now or at any time in the future.
10. Iron Intake Exclusive
Even today, one of the most common modifications hobbyists first make when attempting to improve the performance of a vintage vehicle is to replace its factory-installed intake manifold with an aftermarket replacement. While that might be wise for other brands, Pontiac's cast-iron four-barrel is a solid performer for street applications, and is many times a better choice than an aftermarket unit.
If the engine you're rebuilding isn't already equipped with a factory-cast unit, finding a '68-'72 iron four-barrel manifold (or '67 Q-jet) at a relatively affordable price shouldn't be overly difficult. Because of the addition of EGR on the '73-'74 manifolds and the overall restricted appearance of the '75-'78 units (shown), these iron intakes are often cast aside, but testing has shown that the effects on airflow are limited-especially for a moderate street build.
Expect to pay no more than $100 for any '68-'72 cast-iron four-barrel manifold and substantially less than $50 for any '73-'78 emissions-era casting.