True Identity - Boss 340 Engine Build, Part 2

Horse Sense: In order to meet the SCCA's minimum requirement for eligibility in its Trans-Am racing series, Ford had to produce 1,000 Boss 302 street Mustangs in 1970. We've heard off-and-on musings about Ford possibly building a new Boss 'Stang (remember, the S197 is scheduled to undergo an appearance makeover in 2010), and while we honestly don't know anything official about a return of the Boss, we can't stop thinking about how bad it would be after more than 30 years of advancement in Mustang performance.

Based on feedback we receive via the Internet (e-mail, message forums, and so on) and in person, we think it's fair to say that many of you get with 5.0 Mustang & Super Fords each month to find out the latest on our various projects-large and small. We truly appreciate your loyalty to our mag, and hope that the broad range of subjects we cover for Fox-thru-S197 Mustangs is informative and encourages you to use the bolt-on parts we install in Mustangs, or the engines, transmissions, and other driveline pieces that we profile.

When it's all said and done, conceptualizing and making bad 'Stangs and pushrod or modular engines of all dimensions and performance levels are the main ideas that spin the revolving door of our cool projects. Our latest engine effort is a prime example.

If you're just joining us, last month we introduced our newest project ("The Comeback," p. 82, Mar. '08): creating a modern-day EFI Boss engine based on Ford Racing Performance Parts' new Boss 302 block. It will feature canted-valve, Cleveland/Boss-style aluminum cylinder heads from Edelbrock and Air Flow Dynamics. Using inline-valve heads has been a longtime standard of sorts for magazine engine builds, but we think the time has come to finally do something different.

What do we mean by "different," you ask? How about employing a radical alternative to inline valve heads on a Mustang powerplant that goes far beyond the accepted norm for 5.0-based street and race engines, and at the same time, pays homage to one of the baddest bullets in Ford-engine history. We realize old-school Boss 302 purists may not take too kindly to what we're doing, but to them we say, "Get over it."

In Part 1 of this series, we focused on the surface details of the engine's makeup and L&R Automotive's meticulous preparation of our FRPP Boss block. In this installment, we take a closer look at the actual hardware that comprises our Boss 340-especially the cylinder heads and intake manifolds, which are above and beyond those found on other 5.0 strokers.

This second leg of our effort took us to Probe Industries in Torrance, California, where our L&R-prepped block was waiting on an engine stand when we arrived. Probe's shop foreman, Shawn Mendenhall, has choreographed a thorough assembly plan for our Boss 340, which we will chronicle right here in these pages.

While we realize Roush now offers Cross-Boss 351R, a fuel-injected, 351ci version of the modern-day Boss engine, we're the first 'Stang mag to build one. So for now, read through the following captions as we forge ahead with this groundbreaking project, preparing our rev-happy engine for dyno flogging and installation in a full-on drag race Mustang sometime in the not-so-distant future.

Before we get into the "new," here's some more of the "old" for you. Sewer-like 2.5-inch intake ports and a canted angle on the 2.19-inch intake valves (1.71 exhaust) are two of the main characteristics that make Cleveland heads so special. Think about this in relation to the 2.08/1.65 valve sizes that have been thought of as "big" for small-block cylinder heads-for about as long as 'Stangmania has existed. The only way to fit valves this large in a cylinder head is by installing them in canted arrangement. OG Boss 302 heads, circa 1969, actually sported gargantuan 2.23-inch intake valves and closed 62cc "quench" combustion chambers, which made the 'Stang a gangster on the street. In 1970, Ford downsized Boss intake valves to 2.19 inches and reduced chamber size to 57cc.

We're closing off our engine with this aluminum Fox Drag Pro Power oil pan kit from Canton. The set features the 9-inch rear-sump pan, which includes an interior steel girdle, a pickup, and a universal dipstick kit.