Richard Holdener
August 1, 2008

With The modular Mustang world chock-full of Two-Valve motors, it's only natural that Mustang owners figure out the best way to modify them for increased performance. While it's true that the Four-Valve motors and big-inch Windsors ultimately offer more power potential, don't discount the Two-Valve motors, as they have a lot of things going for them, the most obvious being price and availability.

Production figures suggest that as many as 10 Two-Valve GTs were produced for every Four-Valve Cobra. Toss in the tremendous production of 4.6L and 5.4L truck motors, and you have an avalanche of Two-Valve motors from which to pick parts. Add to this equation that most '96-'04 Mustangs still on the road are housing Two-Valve motors, and it's easy to understand the appeal.

Lurking Inside Any stock 4.6L GT motor is a performance combination just waiting to be unleashed.

Given its continued popularity, we here at MM&FF decided to investigate the inner workings of the Two-Valve motor and offer some insight into its performance potential.There's always forced induction and nitrous oxide, but rather than take the easy way out, we decided to cater this discussion to the all-motor crowd, since that makes up the majority.

Though the topic is power production in normally aspirated trim, remember that all of this information will transfer to any buildup involving forced induction, as the best blower and turbo motors always start out with efficient, normally aspirated combinations. Additionally, what you'll learn will also translate to just about any internal combustion engine.

By Subjecting countless combinations and components to the rigors of the dyno, we've taken all the guesswork out of building a healthy Two-Valve combination.

Induction Function
For this all-motor discussion, we will begin with the throttle body and work our way back to the exhaust. Along the way, we'll cover intake manifolds, ported cylinder heads, and even displacement. Cam timing will also be covered, as well as compression and the scavenging effect of a set of headers.

In truth, the induction system begins with the air filter and includes the mass air meter and associated plumbing. When it comes to the induction system in front of the throttle body, obviously it's important to minimize any airflow restrictions. These include the filter itself, the mass air meter, and the induction tubing that joins the MAF to the throttle body. Gentle radius bends are important, not only for absolute airflow but also to minimize turbulence in and around the mass air meter. The orientation of the mass air meter relative to the flow is important, as air is not distributed evenly in a bend. If the bend precedes the mass air meter, then the meter will read only a portion of the actual airflow. If the element is positioned toward the short-turn radius, then the meter will read much lower than if it were positioned toward the long-turn (where a larger percentage of the airflow will be). Simply rotating the meter can alter the signal and therefore the air/fuel and timing specs of the motor. This can obviously have a dramatic effect on the power output and longevity of the motor. Meter orientation can be turned around using current SCT or other available software. Naturally the air-intake system should be designed to supply a source of cold(er) ambient air rather than running an open filter in the engine compartment or the more-restrictive stock airbox.

Running through the intake system, the inlet air will then come to the throttle body and intake manifold. As with the mass air meter, the throttle body should be sized to eliminate airflow restrictions, but not too big where it will cause a loss in intake air velocity, thus resulting in poor throttle response. For most normally aspirated Two-Valve combinations, the typical aftermarket 70-75mm throttle body and elbow combination should work well. There's a great deal of confusion about throttle bodies, however, as bigger is not always better.