The Ford V-8 Engine Workshop
Tunnel Port 302
1968 Tunnel Port 302, street version prototype
Overhead valve pushrod engines face a design dilema: the pushrods compete
for space with the intake ports. Conventional design places the pushrods along
side a rectangular shaped intake port. These ports also steer around the pushrods.
The Ford tunnel-port design runs the pushrod through the center of a round intake
port, within a thinwall tube. The ports flow better due to their round
shape and straight path.
This design was first used on the 427, and then in 1968 on a special 302.
These round intake ports are 3.8 sq. in. in area at the intake manifold face. The Tunnel Port 302 cylinder heads feature 2.12" intake and 1.54" exhaust valves. By comparison, the 289 HiPerf engine used 1.78" intake and 1.44" exhaust. These large valves completely fill the wedge shaped combustion chamber. The exhaust ports are larger than normal 289/302 heads. Two 540 cfm Holleys sit on a high-rise aluminum manifold. Autolite 4300s were used on the street version.
The race version featured domed pistons, yielding a compression ratio of 12.5:1, a solid lifter camshaft and forged steel crankshaft. The nodular cast iron rocker arms are shaft mounted, similar to those used on the Y-block V-8. Lubrication for these shaft mounted rockers required a special block with revised oil passages. Also used was a special road racing style 8-quart oil pan. Some used an early transistorized ignition.
The street version used flat-top piston, for 10.5:1 compression, and a hydraulic camshaft. Notice from the picture, the engine was complete with thermactor emissions control hardware, 289 HiPerf style exhaust manifolds, and a thermostatic clutch radiator fan. 1,000 engines were required for 1968 Trans Am homologation. As used in Trans Am competition the engines produced approximately 420 bhp with an 8,500 rpm redline.