October 5, 2009

When the 30-year evolution of the late-model Mustang hobby is assessed solely from a bolt-on-parts perspective, there is no arguing that a lot of progress has been made over the course of those three decades. Although literally thousands of high-performance small-block (and modular) Ford engine parts have been developed and improved on as the years have passed, there are only a select few pieces that forever will be cited as essentials for making big steam with a Mustang's powerplant. (For the uninitiated, "big steam" is big horsepower.)

Ask any hard-core, performance-minded 'Stang enthusiast for a breakdown of engine upgrades that should be made over the course of a 5.0- or 4.6-powered Pony's lifetime, and we're pretty sure that aftermarket aluminum cylinder heads--with their larger ports, bigger intake and exhaust valves, and sometimes-radical combustion-chamber profiles--will rank near the top of the assessment. As we've explained in previous reports on engine performance, air volume is a critical piece in the big-steam puzzle. Building Mustang engines with larger cylinder-bore and crankshaft-stroke sizes is a common practice, as it enables a bullet to take in and compress a larger volume of air, and thus create more power and torque.

Although they're important, of course, heads don't do everything. The real deal is they work in conjunction with intake manifolds, valvetrain components, and camshafts to round out an engine's "top half," a collection of performance hardware that we've evaluated extensively on 5.0-liter engines over the last four years using products from various manufacturers. This report is the first offering in our series on aftermarket cylinder heads for 5.0-liter powerplants. We begin our review by featuring aluminum upgrade heads for 'Stangs that fall in the street category, meaning they provide marked horsepower improvement over stock, are smog-legal (if available), and are direct bolt-ons.

Heads in this class are affordable (and in most cases, usually available with provisions for pedestal- or stud-mount rocker arms for less than $1,500 a pair). They are perfect for 'Stangbangers seeking improved performance from the bone-stock engines in their Ponys without having to deal with deciding on camshafts, rocker-arm ratios, or other engine reconfiguring. Although, stepping up to aluminum rockers is highly recommended with any head upgrade. Also, non-Twisted-Wedge-style heads with 2.02-inch intake valves require pistons with deeper valve reliefs for clearance in their pursuit of more power.

Air Flow Research, Edelbrock, Floo Tek, Patriot Performance, and Trick Flow offer CNC-ported castings that we think fit nicely in the Street class. The details on these entry-level upgrade heads can be found in the sidebars and captions. (MSRP prices listed are per pair.)

Horse Sense: Despite the 5.0-liter Mustang's lineage that dates back to 1979 and carbureted induction, the EFI GTs and LXs of 1986 and later have been the Ponys we've focused on when it comes to detailing potential upgrades. While the cylinder-head options detailed in this first report of our three-part series are categorized as bolt-on, "street" heads that don't require elaborate internal changes for an engine, it's important to note that most of the heads presented in this story are not compatible with the OEM flat-top pistons in the 5.0-liter engines of '86 Mustang GTs (unless the pistons are notched for proper valve clearance), and are not recommended for engines with camshafts that have more than 0.550-inch lift.