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Cylinder Head Install - Project Redheaded Step Child Part 6
Project RSC gets good heads.
When we last left the Redheaded Step Child-our beloved high-mileage '96 4.6 GT-we had just completed the Maximum Motorsports suspension upgrade. The Stang was also blessed with a set of 18x9.5-inch Cobra R wheels straight out of the Ford Racing catalog and grippy Nitto 555 ultra-high-performance tires. This allowed the GT to canyon carve with the very best that Europe-and America-had to offer.
The only downside to the new suspension and footwear was that the elevated handling levels made the early non-PI motor feel all the more pathetic. Despite some impressive speed equipment, the most we'd been able to muster thus far was 241 hp. The peak torque figure exceeded 300 lb-ft, but the tiny mill just did not want to carry that impressive torque production beyond 4,000 rpm, where it would provide some decent horsepower numbers.
Rather than continue to throw performance parts at the thing, we decided to take drastic measures. This entailed running the 4.6 on the chassis dyno one last time with the current configuration to reestablish a baseline before removing the tired soldier in favor of something a bit more sporting.
You will remember that the idea behind this project was to build up an early, non-PI 4.6 Two-Valve engine (normally aspirated) to exceed 300 hp, all without resorting to the use of the later PI components. While the PI upgrade is probably the preferred (and recommended) route, we wanted to see if it was possible to get there with the non-PI components.
In doing so, we could illustrate the gains available to owners of the early modulars who have decided to stick with their original equipment. Not everyone can step up financially to the complete PI swap, so this bolt-on route is a viable option. Having exhausted the list of external bolt-ons (with the exception of forced induction and nitrous, which are coming), we decided it was time to crack open the 200,000-mile mill. The next logical step in our quest for additional performance were the factory cylinder heads. Despite being down on flow compared to the later PI heads, the early units can be made to flow pretty well, certainly much better than stock.
With additional flow in mind, we shipped a set of early heads (the original '98 engine used in our "Mods for Two-Valve Mods" series) to Ford Performance Solutions. FPS subjected the early heads to the CNC machine and increased the intake flow rate from 162 cfm to 201 cfm. The exhaust flow increased as well, from 123 cfm to 178 cfm (all measured at 0.500-inch lift). The FPS-ported heads were also upgraded with a set of SI valves and Comp valvesprings.
With such impressive heads at the ready, we thought long and hard about installing them on our tired, weak-ass 200,000-mile short-block. What the new FPS heads really deserved was a fresh motor, capable of taking advantage of the extra flow and power offered by the CNC porting. In the end, our decision came down to rebuild or replace. Wanting to minimize downtime, we elected to replace rather than rebuild the existing combination. A call to Coast High Performance netted us a suitable replacement 4.6 block.
Not needing anything wild, the boys at CHP put together a freshly machined, iron 4.6 block stuffed with a cast crank (stock stroke) and a set of forged rods and pistons. Where the early factory 4.6 pistons featured an 11cc dish, the Probe Racing pistons upped the compression slightly with a 4.5cc dish. In truth, the change was not dramatic, as the FPS CNC porting applied to the early heads increased the combustion chamber size by a few ccs. All we wanted to do was maintain the factory compression ratio of 9.3:1, and we were rewarded with a final compression of nearly 9.5:1.