The following is from NissanPerformanceMag.com - January 2004, and is presented here for archive purposes.
Project Pathfinder
Part 8: Headwork
By: Mike Kojima
As we have reached the limit in bolt on potential for Project Pathfinder we now delve into building the ultimate tow motor. The ultimate tow motor is probably the ultimate off road motor and perhaps the ultimate motor for a heavy clumsy SUV. Our motor will be built to emphasis low-end torque, better for pulling, good fuel economy and the ability to run on lower grades of gas. Since we are cheap bastards and this is just our tow/daily transportation vehicle, we placed additional emphasis on staying away from exotic and expensive parts, rummaging in our spares bin of factory Nissan parts.
Or first element will be the cylinder heads. We started with the late VG30E heads. These castings were made from 1987 to the present. The late casting feature smaller in cross section but better flowing intake ports. These ports produce substantially better low-end torque with no loss of top end power.
For our port work we turned to DPR Racing. Dan Paramore of DPR has many, many years of experience in the realm of modifying heads and engine development. Dan listened to our requirements and went to work. First Dan inspected the head valves and valve guides for wear and proper clearances. Since our head came out of a wrecked Xterra with only a few hundred miles on it, Dan pronounced that the heads condition was fine. However normally VG cylinder heads do not wear their valve guides and stems much and the need for replacement is rare. Dan also checked the head castings for basic soundness and cracks. Of course our heads passed with flying colors.
After inspection Dan ported the intake and exhaust ports. Dan concentrated with straightening and cleaning up the ports while removing a minimal amount of material. The idea was to keep the port volume down to keep the velocity up so as to enhance low-end torque. The gains in flow will also help peak power. The short side radius of the ports was cleaned up and some minor kinks were straightened. After porting Dan polished the ports with 220 grit cartridge rolls, the engine being port injected doesn't really need much roughness in the intake port.
Stock Exhaust Port Exhaust Port Finished
Dan then removed some material from the combustion chambers to unshroud the intake and exhaust valves to help improve low valve lift flow. After this he polished the chambers to reduce carbon build up and to get rid of any sharp edges where hot spots and detonation could propagate.
Stock Intake Port Intake Port Finished
The valve seats were treated to a 3-angle cut. 3 angle valve jobs reduce shrouding of the valves and greatly help low valve lift flow. 30 degrees on the chamber side, 45 degrees on the valve seat and a 70-degree port side cut was used. The port and combustion chamber cuts were hand blended into the port wall and the combustion chamber bowl to make a smooth radius. The valves were given a 30-degree backcut on top of the 45-degree seating surface to help low lift flow as well.
Stock Chamber Chamber Finished
This is a rather basic and inexpensive port job that we feel will be beneficial for both power production and fuel economy. Almost any engine build up can benefit from mild porting like this as there are really no negative tradeoffs in powerband, fuel economy nor engine life.
Stay tuned, next month we dive into our engines bottom end. Our goal of producing the tow power of your typical half-ton small V8 truck is becoming a reality.
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