Modified Mustangs & Fords
Boss 429 Engine Build - Meet The New Boss
Exploring the unrealized potential of the classic Boss 429 to build 670 horsepower
Like those classic Greek stories you read in school, the mythology surrounding classic muscle cars often strays quite far from reality--and there is perhaps no better example than the Boss 429 Mustang.
The mere mention of the Boss '9 and its infamous semi-hemi "Shotgun" motor evokes knowing nods of impressed enthusiasts. That perception is backed up with stellar values for original-condition models sold in the collector market. Unfortunately, the out-of-the-box performance of the cars has never measured up to the hype surrounding them.
Like numerous other engines of the muscle car era, the Boss 429 was originally developed as a racing engine and subsequently detuned for the street versions typically required for homologation. That meant compromises. Stuffing it into the tight confines of the Mustang engine compartment, for example, required saddling it with a slab of restrictive iron to serve as a low-rise intake. It effectively choked off airflow to the cavernous cylinder heads that were simply way too large for a street engine. Consequently, there was no velocity through the ports and low-rpm torque was almost non-existent. Another strike against the engine was a set of crimped exhaust manifolds that were designed to fit the Mustang's engine compartment rather than optimize airflow.
To address complaints, Ford instituted a midstream change from an admittedly "small" hydraulic cam to a hotter solid-lifter setup from the 429 Super Cobra Jet, but it did little to improve the situation. The early hydraulic engines are known by their 820-S engine code, while the later engines are known by the 820-T code (see sidebar). It's true that when wound up, the Boss 429 engine would pull strongly--until the factory rev limiter shut things down--but in most daily driving situations, the Boss 429 was a rather anemic street-performance engine. And a heavy one, at that.
On paper, however, the Shotgun Ford has the potential to deliver big power numbers if it could only capitalize on its attributes. Engine builders John Lohone and Adney Brown recently took up the challenge to see what a properly prepared Boss 429 street engine could do when its known deficiencies were addressed.
"With those mile-wide valve covers and distinctive style, the Boss 429 should be a great option for a Ford enthusiast wanting an alternative to cookie-cutter Windsor engines," said Brown, of Detroit-area Performance Crankshaft, Inc. (www.performancecrankshaft.com). "We thought if we could take an engine beyond the 600-horsepower level, but with good low-speed and idle characteristics, we'd have a great, contemporary combination that's competitive with modern crate engines, but one that's going to draw some 'ooohs' and 'ahhhs' when the hood is lifted."
Brown partnered with Lohone to help develop and assemble the engine, and right off the bat, they knew using an original Boss 429 block and heads was out of the question. The specific, thin-wall casting of the Boss 429 block is all but impossible to find and, given the collector value of restored cars, makes the few out there almost as expensive as the total investment in this entire project. The same goes for a set of original heads.
Fortunately, a strong block alternative is available in the Ford Racing catalog, with the basic 460 cylinder block (PN M-6010-A460). Ford engine guru Jon Kaase casts his own Boss 429 heads--appropriately named "Boss Nine"--to fit the 460 block. That's significant, because the oiling circuits were different on wedge-head blocks and the Boss versions, resulting in different oil drain holes. Kaase's heads match the oil drain holes of production-style 429/460 blocks.
Although the project engine uses all new parts for the major components, the basic parameters are very similar to the original Boss 429. Therefore, a comparison of the original production engine and this 21st century example is appropriate. In fact, the new engine uses a host of forged, heavy-duty parts, but so did the original engine--including the crankshaft, rods, and pistons.
"The bore is a little larger, but the stroke, compression, and basic setup of the engine is very similar to the original," says Brown. "We hoped to make the most of its truly impressive specifications."