When you come down to it, what Ford did to develop the Coyote head into the RoadRunner head from a power-making perspective is little different than what a race shop would have done. What is utterly fascinating is how they did it. A race shop would have used their experience and a few specialty tools such as a flow bench to increase airflow through the ports. Ford did the same thing, but they had the jaw-dropping, God-like power to visualize what the air was doing particle-by-particle via sophisticated three- dimensional computer modeling. Yes, like a race shop that grinds ports then tries them on the flow bench and dyno, there is endless trial-and-error in Ford's computer-modeling, but the difference is it's all done inside the processors at what we still call Ford's ominously-named Numerically Intensive Computer Modeling Laboratory.
Another difference is a typical hotrod shop might have a single porting guru, whereas Ford has teams of them. For example, the Boss 302 head followed Ford's normal practice of having the Performance Development group of engineers develop the almost purely academic aspects of making power in the Boss's combustion chamber, plus another crew that did the hands-on development of the combustion chamber and port shapes, and yet another crew that handled the valvetrain. These areas are all intricately inter-related and several key people are on more than one team, but the point is there is no shortage of talent developing these engines.
Some of these people you met in our Coyote coverage a year ago, some are new to us. Jim Froling rode herd on the head architecture team. In Ford-speak, he "released the cylinder head" for production. Calvin Tran handled all the computational flow dynamics computer modeling of the ports; Todd Brewer designed the intake port; John Riegger developed the exhaust port; and Adam Christian provided the ethereal values of where, when, and how much port flow was required.
These guys had essentially just finished developing the Coyote when tasked with bettering it with RoadRunner. This helped in that it was a rare second chance to clean up what wasn't possible the first time around, plus move the design forward. Calvin, for example, had about one month of computer time on Coyote, but lavished nine months of modeling on RoadRunner. Hair-splitting details became important to this motivated group, and it got to where Adam was keeping daily score on who was ahead in the race to make more power--Todd on the intake or John on the exhaust.
Because the Boss 302 is a...
Because the Boss 302 is a low-volume car it was assumed the intake would be aluminum, a heavier, lower-performing-but-much-cheaper alternative to a modern plastic manifold. A supplier came through with a tooling bid close to the aluminum price and the Boss gained a much better intake. Note the rounded “belly” in the bottom floor of the intake runners; it was carefully designed as its shape and placement proved critical.
Ramping the floor of the plenum...
Ramping the floor of the plenum down in the rear and up to the inlet in the front helped to even flow from runner-to-runner, but that bump under and behind the throttle body was a nasty tuning issue as it tended to channel air to one side or the other of the plenum. The notch in the top of the plenum is for strut-tower brace clearance. Curiously, it has no appreciable affect on plenum airflow or performance.
Larger throttle bodies were...
Larger throttle bodies were tried but returned almost nothing for what would be a huge investment, so the Boss continues with the Coyote’s 80mm unit. Incredible work went into placing the “secondary gas” bungs, seen like whiskers around the inlet’s toothy snarl here. These seemingly meaningless minor inlets for things like the charcoal canister purge, brake booster air, and oil vapor, can disrupt the inlet’s airflow tremendously, hence the months of computer work getting their placement just right. It can take four days of 32 computers running 24/seven just to model a single bung’s placement, and hundreds of placements are tested! It took longer to get this aspect of the intake optimized than making the power development.
"I actually tracked the horsepower for each change," Adam said, "basically to a tenth of a horsepower on each change. And we literally clawed our way from nothing to about 10 hp for the whole head assembly, intake, and exhaust. And it's almost 50-50 [intake to exhaust]. I think Todd [Brewer] won, but not by much." In any case, it is clear to us that they had a lot of fun doing it.
One point illustrates the power of Calvin's computer modeling. As one team member put it, "One thing new on this program was all the CFD was run at high pressure and high temperature... we didn't try to simulate a flow bench. We tried to simulate what was going on in an engine."
"So the exhaust port geometry turned out quite differently than what you would come up with on a flow bench. And so if you flow these heads on a bench, there are actually some lift regimes where these will look worse than a Coyote, whereas on a running engine they actually out-perform it."
The counterintuitive area was the exhaust port floor, right in the throat of the port outside the valve seat. This area was choked, and the computer "actually told us to open between the guide and the short turn, which we could only do by pushing the floor lower. This would have looked worse on a flow bench," but it definitely made more power.