Muscle Mustangs & Fast Fords
Mustang GT Boss 5.0L Block And Stroker Upgrade
Building Big With A Ford Racing Boss Block And A RGR/JPC Stroker Combination.
In 1996 Ford Motor Company transplanted its newest engine, the 4.6L modular motor, into the Mustang GT. Gone were the days of the famed and very popular 5.0L, which had a great run from the late '60s through the end of the Fox platform. The introduction of the mod motor had hardcore enthusiasts freaking out about the complex OHC design, the apparent lack of aftermarket components, and the intricate computer system controlling it all.
Thankfully, it wasn't long before aftermarket companies and enthusiasts stepped up and began unlocking the hidden horsepower. Complexity couldn't deter Mustang enthusiasts and soon the computer tuning was conquered, the voodoo of overhead camshaft design wore off, and making power was an easy thing to do thanks to power adders and then stroker kits. In 2005, Ford continued to revise the 4.6L mod motor and introduced the Three-Valve SOHC induction system on a similar short(er)-deck 4.6 mod motor.
The Three-Valve addressed many issues that Two-Valve mod motors lacked, which was a decent set of cylinder heads from the factory. SVT Mustang owners benefited from free-flowing and robust Four-Valve heads, but the base GT always suffered with the Two-Valve variant. Overall, variable camshaft timing, great cylinder heads and a high-flow intake helps the current mod motor crank out 300 hp and enables S197 Mustangs to run quickly on the track and street. The Three-Valve combo is certainly good, but is grossly underpowered when compared to the GM LS-series engines and modern Hemi competition.
We have seen people overcome the smallish cubes thanks to forced induction and various stroker engines, but the ability to build one bigger than 300ci has been rare. The mod motor simply isn't designed to handle a large bore due to the inherent design of the block. "Adding Darton sleeves allows a stock block to be opened up, but it gets costly with specialized machining needed for the sleeves," comments Rich Groh of Rich Groh Racing Engines.
The stroke has been generous and in stock trim it boasts a 3.542-inch throw, far longer than the 302's stock 3.00-inch crankshaft. The longer stroke has helped the 281ci mod motors excel in the torque department, but the narrow bore (3.552-inches) has been a major restriction in achieving big displacement.
Two years ago, Ford Racing Performance Parts released a new engine block that would allow for large bore sizes, not in the traditional pushrod small-block Ford sense, but big for the modular segment. Its name is the legendary Boss and the block was promptly run around the industry with the logo, "The Boss Is Back." Ford Racing released two versions, a 4.6L modular block and a pushrod unit (8.2-inch deck). Both blocks became an instant success.
On the modular front, it didn't take long for engine shops to shed the 298ci-302ci standard stroker sizes and go bigger. After all, bigger is better-right? The larger 3.70-inch bore allows engines to grow excessively and safely when compared to the stock block-based applications. The overall block strength increased dramatically over the factory blocks, including the popular Teksid unit.
One popular engine for stroked out maniacs has been the 322ci combination that is offered by JPC Racing and built by Rich Groh Racing Engines. The two shops have collaborated on using a Boss mod block and then combining it with a Paschal Performance 3.750-inch stroke crankshaft to come up with an LSX-slaying combination. This article focuses on a Three-Valve engine, but the short-block can be combined with any mod motor cylinder heads.
The engine featured is slated for severe street duty, which includes massive boost from a ProCharger F1R supercharger. Burcham holds this combo in high regards, "this combo made over 800 rwhp, likes to rev to 7,000-rpm, and is more than capable of cruising the streets. This piece could have been turned higher [more rpm] but the stock intake manifold limited it. The 322 is very popular amongst our customers because the larger cubic inches makes great torque for around-town driving. The price tag is higher than a standard stroker mod motor because of the block, custom billet caps, and custom rotating assembly-but it does represent the ultimate Three-Valve combination. I run this same exact engine in my '05 Stang but with a JPC intake, larger cams and a shot of nitrous. That car ran 8.48 at 162 mph, made 1,050 rwhp, and runs in MM&FF True Street," adds Burcham.
"Overall, the block is very durable except for the main cap area. Ford Racing includes beefy main caps, but are not quite enough if you are looking to go over 1,000 hp. I have even seen the caps walk in the 800 hp range with a few supercharged combos," says Groh about Ford Racing's aftermarket engine block. So, his solution is a set of custom billet main caps that feature two additional holes and he modifies the block to accept the extra main cap bolts. These precision-cut pieces require a new line hone but add considerable strength over the production configuration. The caps have been battle proven in Burcham's mid-8-second ride and several 9-second players out of the JPC shop.
The bottom-end consists of a Paschal Performance crankshaft, Crower rods, and a set of CP pistons built to RGR's specs. Moving to the topside of the engine, RGR ported a set of Three-Valve heads and used Manley valves that are slightly larger than stock. Groh spends considerable time working on the ports of the factory castings. On the flow bench, the heads move 322 cfm on the intake side at 0.500-inch lift. Moving to the exhaust port, air rushes through at a volume of 215 cfm at 0.575-inch lift. The camshafts are custom sticks cut by Comp Cams and tailored for specific applications. The head flow numbers were quoted at those lifts because the cam boasts a measurement of 0.500/0.575, intake and exhaust respectively. The variable camshaft timing (VCT) has been eliminated using Paschal Performance's cam phase eliminators. "The factory cam phasers need to be eliminated at some point because of the aggressive camshafts and heavy valve springs. The factory phasers tend to fail when under serious loads," comments Groh.
This story showcases the engine being assembled with the new JPC Racing intake manifold, but when the shop installed it in the customer's car, a stock intake was bolted on. The throttle body was upgraded to a single bore unit. Moving on to the fuel system, the car runs a JPC return-style setup with MagnaFuel fuel pump and filter, larger feed and return lines, 96-pound injectors, and JPC fuel rails. A Versafueler drives the 96-pound injectors, despite them being low-impedance units. Stock ECU boxes can drive high-impedance fuel injectors but cannot operate the low-impedance ones. "We use the Versafueler to convert the signal so we can continue to run the factory ECU and still run large injectors," injects Burcham.
The '05 Mustang GT that received this monster mod motor is no slouch. It's equipped with an eight-point roll bar and all the legal items to hit the track. The suspension fore and aft is prepared with aftermarket control arms, K-member, and anti-sway bar. Our test Stang also rolls on Bogart "big and little" slicks and skinnies. The giant stroker is backed by a TCI TH400 transmission with a healthy 4,700-rpm stall speed torque converter. The rearend is fortified with a Detroit Locker differential, FRPP 4.10 gears, and Strange 33-spline axles. On the Dyno Dynamics chassis dyno, the '05 ripped 849 rwhp and 720 rwtq, sans nitrous. Unfortunately, we don't have any track times on this combo but Burcham says the car will run deep into the 9s with just the F1R huffing boost into the engine.
If your mod Stang is lacking cubes, then it's time to start boring and stroking your way to 322ci. The Boss is certainly back!