Pontiac GTO 400 Engine Block Build Up - Poncho Honcho

Edelbrock's No. 60579 aluminum heads feature 87cc combustion chambers and can be ordered either bare or complete with valves, springs, and guide plates. Sherman chose the latter.

The oil pan is a Joe Sherman Racing stock-type replacement. This one is a later model that features a baffle in the bottom to keep oil at the pickup during high-g driving. That shouldn't really be a problem with the '61 Cat, however.

This 4.181x4.210 "undersquare" engine makes big torque and horsepower between 3,400 and 5,400 (max) rpm. At max valve lift, the heads flow 275-cfm intake and 185-cfm exhaust out of the box, which negates the need to port them for this combination.

Shown here is an Edelbrock bronze wall valve guide, a smooth as-cast pocket area, and hardened valveseat inserts for unleaded gas.

The 87cc combustion chambers will provide 10:1 compression when combined with the 4.181 bore, the flat-top piston's compression height and valve reliefs, 0.005 piston-to-deck height, and the volume of the head gasket. A set of 2.11/1.66-inch stainless valves is included when the assembled head is purchased.

"D"-shaped exhaust ports were proven decades ago on GM Tech Center dynos to work best on high-performance engines. Though the heads are based on the round-port R/A-IVs, the exhaust port design was changed in the Edelbrock head to this D-shape. Nevertheless, the round-port manifold or header configuration is required when using these heads.