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4.6L Two-Valve Stroker Motor Build - Two Can Do
Here Is What You Can Expect From A TFS-Headed, Nitrous-Injected, 4.6L Two-Valve Stroker Motor.
Why is it that the Three-Valve, Four-Valve, and (especially) Shelby GT500s get all the modular love, when the Two-Valve motors are arguably the workhorse of the family?
I know-the Four-Valve motors have, well, more valves; the Three-Valves have that cool cam phasing; and the Shelbys have displacement and boost! Heck, the new Coyote motors have more valves and cam phasing, but where does that leave Two-Valve owners?
With the recent introduction of the Track Heat heads and matching intake manifold from Trick Flow Specialties, the substantial performance gap between the Two- and more-than-Two-Valve mod motors has successfully been bridged.
Don't get us wrong-the Three- and Four-valve motors will always make more power, but Two-Valve owners can now put together a seriously stout, all-motor combination, without resorting to boost. Toss in a little go juice from Zex, as we did on our buildup, and you have supercar power from your humble GT.
When we first built and tested this engine, we subjected an otherwise-stock non-PI motor to a PI-plus upgrade. Replacing the non-PI heads, cams, and intake with a set of ported PI heads from Total Engine Airflow, a PI induction system, and a set of healthy Comp cams resulted in an increase in peak power of 130 hp. This took the non-PI motor from 260 to 390 hp, a serious jump in any book.
Impressive as that may be, there was more power to be had. We all know how well mod motors respond to blowers and turbos, but we wanted to take the all-motor route, as not everyone wants boost. A non-boosted combo can benefit from a lighter weight, less potential problems from belts and detonation, and it is of course, more affordable.
After the PI conversion, we increased the power output by replacing the heads, cams, and intake, so we decided to take a look at those components once again. In addition to these bolt-ons, we also recognized the fact that our proposed upgrades deserved something more exotic than a wrecking-yard, non-PI short-block. Besides, upgrading the short-block gave us the opportunity to further increase the cubes and compression. If 4.6 liters is good, then 5.0 liters must be even better!
It is with the tried-and-true no-replacement-for-displacement principle that we embarked on. Given the limitations of the modular family (something Ford has yet to rectify), increased displacement is somewhat limited. Unlike a 351 block that can be punched out an additional 100 ci (or more), the most common stroker upgrade for the modular motor takes the 4.6L to just 5.0 liters. Obviously, more displacement is always welcome, but we'd like to see a 6.0L (or even 7.0L) modular motor topped with Four-Valve heads. The limited bore spacing precludes any significant changes in bore diameter (which would also increase the flow rate of the attending cylinder heads), so the additional displacement comes primarily from the installation of a stroker crankshaft. Combining a stroke of 3.75 inches (up from 3.543-inches) with a 0.030-inch overbore (from 3.552 to 3.582 inches) results in a displacement of 302 ci (the magic 5.0L). Put down the calculators and keyboards, we know that 5.0 liters actually equates to 305 ci.
The 5.0L stroker short-block was assembled by the Ford experts at Coast High Performance. The Two-Valve block was cleaned and bored 0.030 over to make room for the new stroker crank, rods and pistons. The list of components included a 4340 forged steel crank and matching (6.0-inch) connecting rods combined with a set of forged flat-top pistons. Given the revised valve locations, the valve reliefs in the flat-top pistons were specific to the new Track Heat cylinder heads. The new stroker not only increased the displacement, but when combined with the new heads from TFS, produced a static compression ratio of just over 11.0:1. This represented a substantial jump from the 9.7:1 of the original 4.6L PI motor.
Naturally, the build up also included new rings and bearings, along with Fel Pro (MLS) head gaskets and a new factory oil pump. When reusing components such as the timing chains, guides and gears, make sure they are still in good condition. We reused all of the components from our donor motor (we saved yet another 4.6L from the boneyard-this time a PI '00 version).
With our stroker short-block assembled and ready for action, it was time to upgrade our power producers. You may remember we installed a set of TEA-ported PI heads, a pair of Comp XE274H cams and the PI induction system on this engine in the Nov. '10 issue. These were (excuse the pun) head and shoulders better than the factory non-PI components they replaced, but we wanted more for our stroker. To that end, we installed new Track Heat 4.6L Two-Valve heads from Trick Flow Specialties.
Even in as-cast form, the Track Heat heads offered more flow than the ported PI heads. Credit the revised port design, valve locations, and use of a 1.84/1.45-inch valve combination. Production of the overhead cam cylinder head was difficult, so we have to give credit to TFS for stepping up to the challenge. The flow rate of the new heads immediately bridged the gap between the production Two- and Four-Valve motors. Toss in some porting from Total Engine Airflow and you have the makings of a serious set of heads. In fact, the only thing holding these babies back from eclipsing the Four-Valve heads is the available bore size. Our 0.030-over motor was not sized to maximize the flow potential of the heads, but stick these on a big-bore mod motor and you're looking at near 300 cfm.
With head flow now in abundance, we decided on a set of cams and an intake manifold. Since our stroker was destined to run sans artificial aspiration, we went not only with high compression, but also with aggressive cam profiles. The XE278AH cams combined 0.550 lift (both intake and exhaust) with a healthy 242/246-degree duration split and a lobe separation angle of 113 degrees. These cams will sacrifice low-rpm power compared to some of the other milder grinds, but they offer plenty of power on the big end. Besides, our additional compression and displacement more than made up for the aggressive cam timing.
Working with the cams and Track Heat heads was another performance upgrade from Trick Flow Specialties. The Track Heat intake manifold was offered in a number of different color and throttle body combinations, but we opted for the standard single-blade throttle body with the black finish. Though less of an issue on our engine dyno, the Track Heat intake even came equipped with the required air intake system designed to connect the throttle body to the factory (or aftermarket) MAF assembly. To ensure adequate airflow, the Track heat was fed by a 75mm Accufab throttle body. A decided step up the performance ladder from the factory PI intake, the Track Heat manifold was the final element in our three-tiered approach to improving the power output of the Two-Valve.
With our 5.0L stroker ready for action, we installed it on the engine dyno at Westech Performance and equipped the test motor with Kooks 13/4-inch long-tube headers (no extensions or mufflers), a Fast XFI management system and a pan full of Lucas 5W-30 oil. Not having access to our usual Meziere electric water pump for the mod motor (the author left it at his shop in Vegas), we were forced to pressure feed the motor from the dyno (like they do with jetboat motors). The factory water pump was installed but served as a simple O-ring to seal the cooling system.
After a pair of 15-minute break-in procedures, the motor was tuned using the FAST EFI system, and we were eventually rewarded with peak power numbers of 463 hp at 6,600 rpm and 430 lb-ft of torque at 5,000 rpm. Torque production exceeded 400 lb-ft from 3,800 rpm to 5,600 rpm.
For those wanting a peppier Two-Valve, we quickly installed a Zex universal EFI wet kit with 150hp jetting. Designed with a single fogger that combined and injected both fuel and nitrous before the throttle body, the Zex nitrous kit bumped the peak power output to an amazing 604 hp and 588 lb-ft of torque. Our little Two-Valve was now ready to take on some heavy-hitters, but make sure to check back with us as Evan and the boys finally allow me to let loose with the boost!
4.6l Two-Valve Stroker NA Vs. Zex Nitrous (150hp Shot)