Likewise the Coyote connecting rod was destined for the Mustang GT's lower rpm threshold, so an upgrade was necessary there too. The new Boss rod is identical to the Coyote rod dimensionally and is still pressed from powdered metal, but uses a higher grade metal and has been beefed up with extra material here and there. The result is said to be the strongest connecting rod in Ford V-8 history, so it ought to give super- and turbocharger hot rodders newfound confidence when trying to lift the head gaskets with boost.
After hearing the press reports that the Boss 302 wears CNC-ported heads, anyone would be forgiven for thinking the RoadRunner uses the Coyote head casting with a CNC port and chamber job. While true as far as that goes, that's hardly the full story.
Yes, the Boss 302 head is fundamentally a Coyote head. It boasts the crosshead cooling flow that's so important to even cylinder temperatures, it has essentially the same chamber design, and it oils the valvetrain from the front of each head. But it is actually a different casting, made from a different aluminum alloy, and differs in many details from the base head.
Look closely at the center...
Look closely at the center two lobes on this Boss 302 camshaft and the reverse radius of curvature flanks of the lobes are just perceptible. This is the exotic stuff of Competition Eliminator dragsters not that many years ago, and now it’s certified for 150,000 miles in a production Ford. Having a roller-finger follower helps with the aggressive valve accelerations such a lobe produces as the roller more faithfully follows the lobe than a flat-tappet.
Perhaps the best view of the...
Perhaps the best view of the intake’s layout is from the bottom. The runners are arranged like a pair of hands with their fingers crossed—too bad the top of the runners is covered by the plenum—it would be a sexy display of intake trumpets indeed. The left and right air paths through the plenum are also obvious from this view. The runner spacing at the cylinder head and all gaskets are carryovers from the Coyote, which this intake bolts right onto. It’s worth about 8 high-rpm horsepower and a real low-rpm torque loss as a direct bolt-on. To optimize the shorter intake runner tuning with the intake valve event, it’s important to close the intake valve sooner. Adam Christian says advancing the intake cam 5-10 degrees and raising the rpm limit is what everyone has been missing so far when bolting this intake onto a Coyote. That, and don’t look for any power gains below 5,250 rpm no matter what. It sounds like a real terror would be more rear axle gearing, this intake, and a centrifugal blower.
Even with quite different...
Even with quite different torsional loads coursing through the timing chains, little in the timing chain system needed to change between the Coyote and RoadRunner. The timing chains, guides, tensioner arms, and ECT units are all carryover parts. The chain tensioners, however, needed a pressure relief valve to vent oil pressure at high rpm as they are somewhat “over-pumped” at 7,500 rpm.
In fact, it was the decision to CNC-machine the combustion chamber that gave the cylinder head design teams license to develop a new RoadRunner-specific casting. Tim Vaughn explained it: "We were going to have a unique cylinder head casting anyway. The combustion [casting] core was different because we were CNCing, so we had to leave that out, and the runner cores were different. Then, because we changed the rear CNC runners, the coolant cores were different. We were changing everything anyway [so numerous other changes were cost effective]. So go ahead, let's put some money in it. Just make sure we have all the robustness covered."
A hidden benefit of slipping straight from building the Coyote head into developing the Boss head was the ability to recycle the Coyote tooling. This ultra-expensive part of manufacturing would have killed the Boss 302 head dead in its tire tracks had it been necessary to build new tooling from scratch. But with the Coyote tooling available for modification, the Boss head was enabled and time saved.
Most basically, the Boss head is cast from AS7GU aluminum--what we hot rodders know as 356 aluminum, with a little bit of added copper for increased heat transfer, while retaining the high strength properties of 319 aluminum. It's the same stuff used for the 6.7-liter diesel Scorpion heads, if that gives you a better idea of its capabilities.
In the Boss 302, the extra strength is needed both on the fire-deck side of the head against the RoadRunner's increased cylinder pressures, and on the valvespring side of the casting where the higher speeds and greater spring pressures must be resisted. This is especially true around the lash-adjuster bore that now has reduced deflection, even under the Boss's higher valvespring pressures. The faster heat transfer comes in handy in keeping the Boss cool under severe racetrack conditions.
Internally, the cross-flow cooling passages have been massaged as necessary to accommodate a larger exhaust valve and improved port shapes, and, of course, the all-important ports and combustion chamber are slightly, but significantly, re-shaped by CNC cutters.
What hasn't changed is the valves are still mounted at the same angles relative to the combustion chamber; the ports are still at the same heights, the fire deck is the same thickness, and the overall architecture is identical to its Coyote starting point. There's certainly none of that 4.6 modular nonsense of a different number of timing cover bolts from one factory to another. Thank goodness that lunacy is behind us.