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4.6L Two-Valve Stroker Motor Build – Two Can Do

Written by Staff. Posted in How To Tutorials

Published on April 25, 2016 with No Comments

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.

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 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 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 Twisted Wedge heads is decidedly more efficient than stock.

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