In our August 2004 issue (#20), a new intake system and some additional tuning of the A'PEX Integration Power FC delivered an impressive 500whp on pump gas with our stock block GT-R. With this power, our GT-R propelled itself to an 11.57-second quarter-mile sprint that hit the traps at 120.3 mph. This marked a very respectable achievement for a daily-driven street car running in full street trim. However, with the ultimate goal being a 9-second pass on street tires, additional progress would have to be made. In this installment of Test & Tune, we made it…to the tune of 626whp. Even with the same 21.3 psi of boost pressure and the same 91-octane pump gas, we picked up over 120 horsepower at the wheels. We now have the power to break the 10-second barrier.

Learning Curve

As we mentioned before, every session on a dyno or visit to a dragstrip provides a performance education. We've also gained a great deal of information from the computer modeling simulations that we rely upon in our project vehicle buildups. Specifically, we use Drag Racing Analyzer (v. 3.2) and Engine Analyzer Pro (v. 3.3) from Performance Trends, Inc. The Engine Analyzer software has helped us in choosing a matched combination of parts that has met or exceeded our horsepower expectations. In addition, the Drag Racing Analyzer has helped us to determine how much power is needed to reach our performance goals. After our tuning session in the August 2004 issue, our next target would be to produce enough power to break into the 10s. According to the Drag Racing Analyzer, we would need in excess of 570 wheel horsepower to get the job done.

According to the analyzers and our own research, generating 570 wheel horsepower on the stock long block (stock short block, head and cams) was pretty unlikely on a diet of 91-octane pump gas. At most, we estimated that 520 to 540 horsepower could be made in this configuration. To get 570 horsepower or more with the factory shortblock, our hurdles to horsepower would have to be cleared.

The Players

While many people dedicate all of their attention to matching a turbo to a forced-induction engine, improvements to the flow characteristics of the cylinder head and higher-lift/longer duration camshafts can also be responsible for significant power gains. Conversely, an "un-ported" cylinder head and stock camshafts can limit volumetric efficiency and power output.

To improve the flow characteristics of the factory cylinder head, Port Flow Design addressed the shortcomings present in the factory head. Since this was a street application, attention was put on maintaining high port velocities to improve cylinder filling. Hence, Port Flow Design would not be opening up the ports significantly. The basics were covered and a "bowl job" relieved the protrusions behind the valve seats while the guides were profiled to reduce their restriction to flow. Finally, a multi-angle competition valve job was performed to ensure that the Ferrea Competition Plus alloy intake valves provided maximum flow and a good combustion chamber seal. Due to their extreme lightweight, the factory Nissan sodium-filled exhaust valves were reconditioned and installed into the cylinder head.

To orchestrate the valve's opening and closing events, we teamed a pair of A'PEX Integration bumpsticks and A'PEX Integration VMAX valve springs. Intake valve duties were put under the direction of a 270-degree, low-lift (8.9mm) camshaft while exhaust events are controlled by a 280-degree, low-lift (8.9mm) camshaft. The low-lift camshafts are designed to provide adequate piston-to-valve clearance with the factory pistons. The selection of the 270/280 split-pattern pairing was chosen to move peak power to the 8500rpm mark while providing substantial power past 9000rpm.

Since the original cylinder head would be coming off the engine, it made sense to use this opportunity to improve the combustion chamber seal. Previously, we relied upon a factory composite gasket clamped down by the factory head bolts. In Japan, tuners believe this to be a major weak link above 500whp. To eliminate the weak link, we opted for a Cometic Multi-Layer-Steel (MLS) metal gasket in a .040" thickness. Not only are these MLS gaskets much tougher, they also improve the heat transfer between the cylinder head and cylinder block. To keep the gasket between the head and block, a set of ARP Pro Series Head Studs were selected. The ARP studs are made from a premium-grade 8740 steel alloy that receives a special heat-treatment to provide an optimum tensile-strength and stretch characteristic. This translates into a more consistent clamping force that reduces the chances of blowing a head gasket. Normally, we would have opted for head bolts in place of head studs due to the cramped engine compartment. However, ARP had enough foresight to engineer their stud kit with hex recesses in the stud. This allows the head to be place on the block before the studs are installed. Then an Allen-key can be used to hand tighten the studs into place.

For more on this article and more grab a copy of DSport Magazine on newsstands and tuning shops nationwide!