Tom Wilson
July 8, 2011
Photos By: Ford Motor Company

As RoadRunner development continued, it met an unexpected challenge: The Coyote, which was finishing up its development, was making more and more power. This put more pressure on the RoadRunner crew--most of whom worked on Coyote as well--to better themselves after just putting a maximum effort into the base 5.0-liter engine.

Mike recalled the progression of his two new V-8 engines by saying recent engineering advances mean everyone expects his teams to spool up ever-increasing power ratings, but it isn't easy.

"When we went through the product approval gateway, [the RoadRunner] was approved at 430 hp. And at that time, the base 5.0-liter was going to be 400. That 30hp delta was really where we felt [we needed to be] for a limited-edition car, and then, unfortunately we kept getting better and better on the base 5.0-liter and closing that gap. So, we just had to really... you know, the development work that went on in the end to find the last 1 or 2 hp on the dyno was pretty intensive... I think within a couple of months of the first media launch at Laguna for the historic races last year we committed to 440, and they were like, 'Well, we knew you were going to deliver that.' So we managed to scrape another 4 hp over and above my final offer--which was hard to find."

"The cool thing about doing this was that everybody was into it. This wasn't a burden to anyone. Everyone on the program--the complete Mustang Team, the complete engine team--were all fired up about doing the Boss 302 again, and that makes it really easy to get whatever you want done because people want to work on it."

Was there anything the enthusiastic RoadRunner team wishes they could have done to the Boss 302's prime mover? "People ask, 'What else would you have done?'...and there's really not a lot left."

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What sets the Boss 302 engine apart from its Coyote starting point is its high rpm. No other production Ford engine has revved this high--7,500 rpm--much less lived through Ford's rugged durability tests at such speeds. The key piece of hardware enabling the rpm is the short-runner intake manifold, but almost every aspect of the 5.0-liter Coyote was addressed to meet the RoadRunner's frenetic gait.

Another Boss 302 fundamental is higher cylinder pressures--it's simply the physics of making more power. As a consequence, in many places inside the Boss 302 not only are things happening faster due to the higher rpm, greater pressures are being generated, such as in the cylinders or at the bearings. This, too, translates into strengthened parts.

For this review, we'll use the 5.0 Mustang GT engine, the Coyote, as the starting point. If a part isn't mentioned here, such as the block, you can reasonably assume it was carried over unchanged from the 5.0. Curiously, the Coyote's piston squirters were one of the first things to go because at high rpm they resulted in massive windage. There was just so much weight of oil whipping around in the crankcase that it slowed the crank and rods, costing horsepower.

But without the piston squirters the Coyote's hypereutectic pistons were on the durability edge. Cylinder pressures were higher, plus piston temperatures climbed enough to invite a forged piston with its fine grain structure and lack of porosity. Interestingly, given Ford's immense engineering resources, short-block engineers Jay Bolyard and Claudio Battistini didn't waste time testing just how far into forged-piston territory the Boss was reaching. They knew the Coyote's hypereutectic piston was out of its league, and a forged piston could handle the Boss's pressures and stresses, so they specified a forging right away.

With a heavier piston and higher rpm, it was also obvious a stronger piston pin was required. This turned out to be no more difficult than reaching into the GT500 parts bin for the 5.4's bulldozer-spec unit. It is slightly shorter in length but slightly thicker, built from a stronger material, and nitrited for surface hardness.

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