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.
One route to serious Two-Valve...
One route to serious Two-Valve performance is to build an impressive stroker and add a dose of nitrous.
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!
Yanked from a local wrecking...
Yanked from a local wrecking yard, the 4.6L used for our buildup was a high-mileage '00 PI motor.
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.
Looking to maximize power...
Looking to maximize power from the motor in normally aspirated (but streetable) trim, we first increased the displacement using a forged-steel, 3.75-inch stroker crank from Coast High Performance.
Probe Racing assembled the...
Probe Racing assembled the 5.0L short-block using forged rods and pistons designed specifically for use with the new Trick Flow Specialties Twisted Wedge Heads.
Obviously this new 5.0L deserved...
Obviously this new 5.0L deserved something more than the stock PI heads. Despite a sizable port entry, the flow rate of the PI heads was actually the limiting factor in terms of Two-Valve performance. We have to commend Trick Flow Specialties for finally offering performance Two-Valve heads. We selected a set of Twisted Wedge Track Heat 185 heads for our test motor.
The valve layout on the new...
The valve layout on the new Twisted Wedge heads is decidedly more efficient than stock.
This shot illustrates the...
This shot illustrates the offset valve location employed on the Twisted Wedge heads. Though the valves have changed position, they still utilize factory rockers and lash adjusters.
TFS offers the 4.6L Twisted...
TFS offers the 4.6L Twisted Wedge heads in two different combustion chamber volumes: 38 cc and 44 cc. We chose the 44cc chambers for our 5.0L stroker. When combined with flat-top pistons, the result is a static compression ratio of just over 11.0:1. The new heads also featured a 1.84/1.45, stainless steel valve package.
Though the new Twisted Wedge...
Though the new Twisted Wedge heads offered plenty of flow in as-cast form, we had ours worked over by the flow wizards at Total Engine Airflow. Since the new R-series 4.6L heads were not yet available, we figured the TEA-ported Track Heat heads would be the next best thing. The boys at TEA concentrated on maximizing the flow rate of both the intake and exhaust ports. When completed, the TEA-ported heads flowed 260 cfm on the intake and 215 cfm on the exhaust.
A dramatic departure form...
A dramatic departure form the wimpy factory pieces, the Twisted Wedge heads featured billet cam towers and a dual bolt patterns, allowing them to work with both Windsor and Romeo valve covers.
Ensuring we took full advantage...
Ensuring we took full advantage of the tremendous airflow offered by our new head gear was a set of XE278AH cams from Comp Cams. The XE278AH cams offered 0.550 lift and a healthy 242/246-degree duration split.