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Ford Boss 302 Engine Build - Build A Better Boss - Tech
A Legendary 5.0L Upgrade
Ford guys, even young ones just cutting their teenage teeth on the Ford mod motor, should at least be familiar with the term Boss 302. Some of us may be too young to actually have driven an original Boss 302 back when they were introduced in 1969, but all Ford guys should know the history of such an impressive performer. That Ford recently revitalized the name for its latest line of 5.0L-based crate engines adds fuel to the fire, but know that the original Boss 302 was the most powerful factory 5.0L ever offered by Ford up until 2011. That being said, we still have to recognize that the late-model 5.0L Windsor-based engine jump-started the modern blue-oval performance revolution.
Designed primarily for use in the SCCA Trans Am series, the Boss 302 was a result of crossbreeding the 302 Windsor short-block with the then-new 351 Cleveland heads. Truth be told, the Boss 302 was introduced before the Cleveland, and the Boss 302 heads differed slightly from their Cleveland counterparts by way of the coolant passages. What the Boss 302 and Cleveland heads did share was tremendous airflow potential thanks to cavernous port volumes. It is this head flow that kept the Chevy (Trans Am and drag racing) motors of the period from matching the power offered by the canted-valve Boss/Cleveland-headed Fords.
Unfortunately for Ford fanatics, the Cleveland family died out after a short run of just 4-5 years. The heads carried on in their smaller 2V configuration in the 351 and 400M motors, but these were basically torque-oriented smog mills designed for heavy hauling, rather than outright performance. Properly attired, the 351 and 400M engines can be made to produce serious power, but Ford decided that the inline-valve Windsor family would carry the performance torch for Ford right through to the introduction of the now-famous 5.0L Mustang.
Until the aftermarket jumped on the 5.0L bandwagon, Ford enthusiasts were forced to make due with ported factory heads. To put this into perspective, even a fully ported, factory iron Windsor head would not flow as well as a stock Boss 302 or 351 Cleveland head. Of course, this all changed when guys like Airflow Research, Dart, and Trick Flow started offering performance aluminum heads for the 5.0L. With the aftermarket in full swing, 5.0L Windsor owners no longer starred longingly at the flow offered by their Cleveland counterparts.
With the Windsor boys finally taking point, where does that leave Boss and Cleveland fans? Actually, a number of manufacturers now offer aftermarket Cleveland heads, thankfully in aluminum. Companies like Edelbrock, AFD, Pro Comp, Trick Flow, and Cylinder Head Innovations (CHI) have all tooled up to produce aluminum heads for Cleveland applications.
If you've ever checked out the results of the Engine Master's Challenge in either of our sister books, Popular Hotrodding or Engine Master's Challenge, you've likely heard of CHI as its heads started with a Second Place finish in their first outing, and were on the winner's list twice, once in 2004, and again in 2006.
A standard Cleveland head's flow numbers of 278 cfm on the intake and 178 cfm on the exhaust are quite impressive. To better the already stout stock 4V Cleveland head, CHI not only improved the airflow, but also reduced what many consider to be an excessive (245cc) port volume. This is said to be the real key to the success of the CHI castings.