Big Block Cylinder Heads - Big-Block Cylinder Head Test

We set up the peanut-port heads with the same good Comp valvesprings, titanium retainers, and roller rocker arms. We also used a set of Comp 0.300-inch-thick spring seat inserts to take up the extra room created when we got rid of the stock exhaust-valve rotators.>

GM Iron Peanut Port
This cast-iron head is called the peanut port because the intake ports are not much larger than their namesake. Omar Cabrillo at Coast Motor Supply in Canoga Park, California, helped us out by supplying a pair of the heads complete with tiny stock valves, new guides, and a basic valve job. These peanut ports are roughly 30 percent smaller than an aftermarket 270cc version. There are larger factory oval-port, cast-iron, open-chamber heads at 250 cc, but the only ones we could find had been modified, which would not be representative of an OE head. But don't count these peanut clusters out. If you were looking to build a budget-oriented Rat for towing where power above 4,500 rpm was not a concern, these heads would be an excellent choice with almost 600 lb-ft of torque at 3,200 rpm. If you were to pocket-port these heads and add larger 2.19/1.88-inch valves, you could make 530-plus horsepower. That's not bad for iron castings.

GM 236 Iron Peanut Oval Port
2.06/1.72-inch valves
120cc chamber
Intake-port volume: 208 cc
Stock exhaust port location
Intake-port cross-section: 2.43 sq.in.

By Jeff Smith

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!