Cylinder Head Porting

When it comes to valves, Ford Motor Company has clearly concluded that three per cylinder are better than two, and perhaps even better than four, when costs are dialed into the equation. We can hardly argue their corporate logic, since it was the Three-Valve head that pushed the S197 GT to the magic 300-pony mark right out of the Flat Rock factory door. By all accounts, this is an efficient and modern head design that in stock form easily makes more power than any of the factory Two-Valve designs, and is apparently more low-rpm torque-friendly than the Four-Valve. But inquiring minds-such as those at Livernois Motorsports-needed to know if the stock Three-Valve casting left any room for power improvement. Would it respond to porting? Livernois in fact found plenty of hidden power-but using finesse rather than a heavy grinding bit.

On an otherwise stock '05 GT, Livernois Motorsports increased peaks by 40 hp and 20 lb-ft of torque with its Three-Valve head-porting program. They can do the same for you for $1,595 with your stock Three-Valve assemblies in exchange, or $2,195 outright. The price includes a three-angle valve job.

A staggeringly expensive Fadal five-axis machining center is now Livernois Motorsports' weapon of choice for all CNC-head-porting programs, including the Four-Valve head being worked on here. Letting robotics do the cutting means accuracy and repeatability, and ultimately keeps the cost to the consumer down as well.

Of course the machining center is only as accurate as the software that controls it, and that software is only as good as the hand-cut prototype pattern it digitizes. Pictured is the digitized Three-Valve twin intake port as smoothed by Rick (the colors reflect the varied "slices" measured by the digitizing hardware).

Livernois' airflow specialist, Rick Swain, eagerly took on the Three-Valve porting assignment. Rick has spent most of his professional career fussing over the oh-so-important details of cylinder-head design, including stints in Roush Racing's Trans-Am and NASCAR programs. If there's one thing he's learned, it's that bigger is not always better. Generally speaking, head "porting" is a somewhat misleading term. This is, in fact, a multifaceted art involving more than just the ports, where fine increments make the difference between a free-flowing, responsive cylinder head and a doggish piece of scrap aluminum.

Here's the as-cast finish of a Three-Valve port-gnarly looking but certainly no more so than any other factory head casting. This and core shift are the only areas Livernois' CNC-porting program addresses inside the ports themselves. Rick Swain specifically avoided any unnecessary increase to port volume in the interest of maximizing all-important flow velocity.

The time saved by not having to reconfigure the ports was instead invested in the combustion chambers. In this stock chamber, the arrows point to cliff-like "emissions masks" towering over the top side of the intake valves. These eyebrows, we understand, are intended to induce swirl to maximize homogenization of the air/fuel mixture and make the Three-Valve's breath as sweet as a baby's.

They have to go so Rick did some careful cutting to lay back the masks and unshroud the intake valves. Through experience and experimentation he arrived at the particular angle that works best-only low enough to unshroud the valves. "If they get angled too low," Rick says, "you will lose some mid- to high-lift flow." Also, the more you cut away, the more the chamber is enlarged and compression lost.

Anybody can hog out intake or exhaust passages, but it's all too common to err on the side of volume over velocity; make those ports too big and the intake charge gets as sluggish as a sloth on Prozac. Don't get us wrong: High-cfm flow capability is important at maximum valve lift, but not at the expense of the low-lift velocity that gets the intake (or exhaust) charge moving in the first place and keeps it moving as the valve closes. The speed at which flow commences as the valve begins to lift is critically important as it creates inertia that helps fill (or empty) the cylinder as thoroughly as possible, aiding torque-and power-in a big way. Our point is simply that an ideal head makeover will improve flow right across the board and not just at max valve lift.