5.0 Mustang & Super FordsCar Reviews
2011 Ford Mustang 302 - Inside The Boss
How a dedicated team brought forth the greatest Mustang ever built
Imagine you are a Ford engineer and you've been hammering for months on the new 5.0-liter Coyote engine for the '11 Mustang GT. Management ordained that the new V-8 must make 400 hp, the job has to be done in a third less time than normal, costs are limited because this is a high-volume engine for the populist Mustang GT, and you and your team have been working overtime coaxing all the power and efficiency possible from the new design.
Daunting, it would seem.
Then management tells you to also create a special version of your new engine that makes at least 25 to 30 additional horsepower for the upcoming Boss 302. And hurry it up!
Would you feel a little overwhelmed?
Thankfully the Coyote team didn't mentally run off a butte because most of them segued into the RoadRunner team--what's faster than a Coyote?--to produce the 444hp Coyote derivative that powers the scintillating new Boss 302.
Furthermore, their compatriots in Vehicle Dynamics logged endless hours at the test track developing aggressive new suspension and steering packages, the calibrators worked the engine management to its limits, and the folks over at Ford Racing demanded to go professional racing with the new engine a year before customers could buy it!
That, in a lug nut, was how the Boss 302 came into the world.
This is an inside look at the process and resulting hardware. As with our major story on the Coyote 5.0 in the March 2010 issue, this in-depth look at the Boss 302 development was possible only with the extensive cooperation of the engineering teams that developed the Boss 302, an indulgence we at 5.0 Mustangs & Super Fords gratefully acknowledge.
Fundamentally the RoadRunner engine is an extension of the Coyote. By early 2009, the Coyote was prototyping, and as Ford V-8 Engine Programs Manager Mike Harrison noted, the Coyote "really had people's juices flowing, really had people interested in putting a Boss 302 program together."
So, while the Coyote had a head start, the RoadRunner's race had just begun. The idea was to extend the already state-of-the-art, not-yet-released '11 Mustang GT into a world-beating performance car channeled from the sharpest performing Mustang of all time, the legendary Boss 302. That meant the best road-holding possible, combined with an engine that lived for the lower right corner of the tach. For a performance target, Ford picked the BMW M3.
Mike explains how it got underway: "Jim Farley, who's a big Mustang nut, started pushing on the PD [product development] team and the marketing teams and the management to really start thinking about doing a Boss 302."
"We were still in shellshock from having to deliver 400 hp out of the base 5.0 liter, so we weren't quite sure at that stage of what the performance targets should be, so they just kind of did a historical look back at the old Boss 302, and obviously it was naturally aspirated. It was a bit of a parts-bin engine--right?--and it was put together by a bunch of guys who were racers... ," Mike added. "And we kind of approached it in the same way. The team that we engaged to do the planning work and then execute it were all guys that were into performance. Even the base 5.0-liter guys--but even more so with the Boss 302 guys--were into racing Mustangs and that sort of thing."
"I talked to some of the Roush guys, [including] Bob Corn," Mike continued. "He was one of the original Roush guys. He worked for Ford as an engineer back in the day, back in the late '60s, early '70s [1962-1981--Ed.], and he was one of the people that was involved in the original Boss 302. I've had an on-going dialogue with him because, you know, he's a neat guy and I just love talking to him about the old stuff."
"Bob put me in touch with Bill Barr, who was one of the powertrain engineers. He next became a manager at Ford and now he's retired," Mike said. "He lives down in Florida, comes up in summer, and... we just kind of hit it off. We went to the bar and talked on how the original Boss 302 came about ... [how] that engine was tooled, with the production one element, but then the racing models with the big ports had a lot more potential..."
"What we decided... was to have the street car get a legitimate race car engine as well so that the typical customers didn't really have to do a lot of additional work to it--tear it down, port it, do all the other stuff you have to do to a hot-rod engine in order to deliver, you know, credible track performance," Mike revealed. "So, the basis for the performance development was, certainly, to have a high-revving engine. We wanted it to be around 7,500 rpm, maybe a little higher. We wanted that, but we didn't want to trade off that low-speed torque because we know that only five percent of Boss 302 customers are ever going to take them to the track day or whatever. A lot of them are only going to be driven on Sundays, gently, and preserved, and we wanted that driving experience to be pretty good, too."
As he was talking, Mike had a few Boss parts and documentation on hand. Picking up a dyno sheet, he continued: "This is the power curve for the base 5.0 liter, and as you can see, the power curve turns over pretty hard at 6,500. And then the Boss manifold with an approximately 2 inches shorter runner, it really keeps going. We rev limit it at 7,500, that's just about where it's making its peak power, but much above this, the computer system has a hard time... So, the engine's got a lot of potential, and it's that short-runner manifold that sets up the characteristic of the curve, and instead of tuning for 6,500 as peak power [in the Coyote] it tunes for 7,500. ...we have some trade-offs in the midrange torque, but it's only 10 lb-ft and it really isn't that noticeable. It feels linear. ...it's actually got more torque at 1,000 rpm--it's just the nature of the tuning. And so you kind of lose a little in the middle, and pick up some at the bottom and you pick up some at the top."
As the highest-revving production Ford V-8, the RoadRunner posed some issues. One of the first was to the development dynos. As Mike explained it, "We'd never spun anything this fast in the dyno cells and... the jackshafts and all of the system wasn't really set up to take it. I think the Ford Racing cell was--it was set up with a lightweight driveshaft and a clutch system." That Ford Racing cell used to run Formula One engines and is now used for NASCAR powerplants. It could easily handle the Boss 302 prototypes, but it was only one dyno cell, and several were needed to run the multiple-durability-test RoadRunners.
Furthermore, the RoadRunner had to pass all standard Ford durability tests. "This isn't like something we'll run for 50 hours and if it passes that it's good to go. We ran the regular fatigue tests, thermal tests, piston-scuff tests, everything like that," noted Mike. So the durability test dynos had to be upgraded. "We kind of had to do a better re-engineering of our durability cells because... Ford Racing hasn't run any long-term durability and we were just shaking dynos apart every 20 hours."
"But if the engineers in the trenches could identify the high-revving engine as a Boss 302 must-have and then design the necessary intake manifold to achieve that rpm, that didn't mean management was going to approve the intake manifold. "When all the planners saw the torque curve, they all said, 'No way. Standard manifold! There is absolutely no way we're putting that in the program. There is no way we're going to lose any low-speed torque--the driveability would be awful.'"
"So we did a stereo lith model of an early prototype [intake manifold], and just that alone, bolted that onto the engine and then I took David Pericak out for a drive--he's the chief engineer for the Mustang--and the character of the engine totally changed. You couldn't feel any of that midrange torque loss. It just felt really linear, but the top end of the engine came alive. It just uncorked it. I mean, it was like, 'Book it! It's in the program!' It was like absolutely no doubt."
"This was about the May  timeframe, and he said, 'I want an engine.' So, we had started discussions in January. In April, we drove this manifold that we had already prototyped up. In May he wanted an engine, so Tim [Vaughn] and the guys set about building something that had most of the content we had talked about, just from the prototype standpoint. At that time, we'd take a stock 5.0-liter head and CNC port it based on the port that Todd Brewer did."
Keeping with the accelerated RoadRunner development, as soon as the team had an engine to drive they took it to the track, and even got on with a bit of marketing. "We got some of the CAD profile changes, and we took that out and did that event in early August 2009 with Parnelli Jones," Mike recalled. "If you've seen the Boss 302 video, you've seen the development car out at Laguna [Seca]. ...last year  was spent polishing the development, all the tough little details. The real activity, January to August of 2009, that is when the design was made and finalized."
If finalizing the design of an all-new engine in just eight months sounds aggressive, what came next after the Laguna Seca demonstration was unprecedented.
"Everyone [was] getting all excited. I came back [to Dearborn] and Brian Wolfe and Jamie [Allison] pulled us into the offices of Ford Racing and said, 'We want to go racing' and we were like, 'That's great!' Then, "'We want to go racing in January.'"
We hadn't built any durability engines or anything like that at that time," explained a still awed Mike. All he had was computer data that said he had a good engine, plus the single hand-built prototype that had done well so far, but nothing had been proven. Test engines built faithfully to the CAD files hadn't even been assembled. But just prior to Thanksgiving weekend, RoadRunner' Lead Program Engineer Tim Vaughn delivered the first production-spec engine to Ford Racing.
"And then we had a regular flow of engines and we got--what was it? Five engines?" Mike said. "But we literally hadn't run any durability testing at all on a dyno whatsoever. They [Ford Racing] got the first full prototype built, before even the vehicle team did. [It takes] you know, really good engineers in the company to put something like that together and go racing for an entire season and not have a failure. Be right the first time....That was really cool to actually race them before we actually did any of the development work."
As Mike put it, "It was fantastic, and a real confidence builder, too. And we were able to take the data from the Daytona race, then put that in our dynamic cell in the dyno building and run that simulation on the dyno, transiently."
Besides running the exact racing profile on the dyno in real time, the RoadRunner team subtracted all the idling and other low-load portions of the race experience, to "shorten it down to the stuff that's going to do damage to it," as Mike put it. This allowed accelerated wear testing, the equivalent of 275 Grand Am or 150 Daytona 500 races, without a failure.
"No race team would ever go that long without rebuilding it," Mike said. "So no customer is ever going to be able to break it from a fatigue standpoint, unless they start doing things like raising the rev limiter to 9,000 rpm or something silly."
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."
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.
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.
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.
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.
"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.
Along the same lines, cutting material from the backside of the exhaust valve head helped because the team could see the airflow was more sideways, across the valve head, rather then the textbook example of bending around the head in a classic tulip shape.
Of course, valves are part of the valvetrain, which was handled by a separate team of engineers, principally John Carter, Mark Nowak, and Kevin Shinners. Their story is similar to the rest of the RoadRunner team. Having just finalized the Coyote valvetrain, they turned right around and re-engineered it for the Boss 302's higher rpm and loads, plus accommodate its more voluminous breathing.
It really didn't take much new hardware to meet those goals. Of course, the Coyote valvetrain architecture had just been well laid out for performance to begin with. Or, as Kevin put it, "Once you have a valvetrain architecture, you just can't change it to get another 5 hp."
One of the more important points is the Coyote was designed to accept up to 13 mm of valve lift but used only 12 mm, so there was a spare 1 mm of valve lift available. Kevin laughed, recalling the extra capacity the Coyote team had built-in. "Someday we'll use this," he recalled thinking. "And someday turned out to be much sooner than we expected!" It's a good thing the RoadRunner team delivered a solidly stable valvetrain because it could easily have been a mechanical rpm limit. Without a stable, high-rpm valvetrain all of the 7,500-rpm intake tuning would have been for naught. Because the induction benefitted so much from the new intake manifold, the cylinder head and valvetrain didn't require much. The porting was optimized, as we just heard, but the intake valves were simply hollowed to reduce weight.
To keep pace, the exhaust valve diameter was increased 0.8 mm and it's face angle lowered from 45 to 40 degrees, both to improve breathing. The exhaust valve was also hollowed to help the valve-springs at high rpm, but a little weight was regained with sodium filling for cooling.
Titanium was briefly considered as a valve material, but it proved too much for multiple reasons. "We looked at titanium," said John Carter, "but there was a packaging issue and timing of the program; trying to keep some of the other carryover components, we couldn't package titanium. It was around getting a lash cap on the [valve] tip. The keeper grooves were pretty close to the top; I didn't have any room to make the rocker arm any wider." Tim added, "There are not a ton of people who are going to do titanium in our volume," which is a good illustration of just how much high-end technology Ford is delivering in the Coyote and Boss 302 for the money.
No changes were necessary to the roller-finger followers (rocker arms) or lash adjusters. "We didn't do anything unique for Boss," Kevin said. "It was already downsized [for Coyote], so low mass and good stiffness [were already available]. It would have to be really exotic to make any improvements here."
Definitely unique to the Boss, however, are the valvesprings. As lightweight as the hollow stem valves, the extra energy from the 7,500-rpm redline plus the extra 1mm of exhaust valve lift demanded more control from the valvesprings.
We should specify that for a valvetrain specialist such as John, Boss engine speeds do not end at the production car's 7,500 rpm. "We have a design guide so that if the fuel shut off is 7,500, we want the valvetrain to be stable to 400-rpm over that in case of over-speed events, missed shift on a downshift, or whatever. [This is to] make sure that if there is a momentary over-speed, the valvetrain doesn't come apart. If you throw a rocker arm or bend a valve--and it doesn't take long to do that under the wrong conditions--then you can lose your whole engine." Told that one of the Grand Am racers had managed to wing a RoadRunner to 9,000 rpm on a missed downshift with no apparent damage, Mark's commented, "I can only warranty it to 7,900, but I'm glad it worked!"
So, when Ford says redline is 7,500 rpm, their valvetrain engineers are really aiming closer to 8,000 rpm. John detailed the spring design process. "Because of higher lift, the lobe profile on the exhaust side, and the higher speed, we went to a stronger spring. To handle the stress from the higher speeds and the higher lift, we improved the grade of steel used in the spring, going to one with a higher tensile strength so we wouldn't have fatigue failure problems."
"The spring is typically designed so that at max lift there is not a lot of room for the coils to surge up and down. The base spring (Coyote) was designed for 12mm lift, and there is only another millimeter before it goes completely solid, which wouldn't have worked, so we lowered the solid height on the spring so we could get to the 13mm lift and still have a half a millimeter of clearance before it went fully solid. So in addition to the higher load, we had to take out some coils."
Like the intake valve, the intake camshaft needed no changes and was carried over from the Coyote. Only the exhaust cam needed that extra 1mm of lift, a bit of a job for cam-lobe specialist Kevin. He cited the short time available and the need to maintain all of Ford's durability requirements when taking an already aggressive cam profile and increasing its lift, while not changing its duration.
"It was a challenging assignment, but exciting to push the envelope and do something you haven't done before. ...It still meets all the durability, NVH concerns, seating velocities, roller contact forces. All the dynamic constraints we use for a normal production engine in a Taurus, Focus, or whatever, we're still meeting all of those metrics with RoadRunner."
Not because it's the first thing you see when you open a Boss 302 hood, but the Boss 302 intake manifold is the absolute key player in setting the RoadRunner engine's rev-happy personality. That's because the tuned intake runner lengths of this carefully designed, shall we say, tunnel-ram intake, set the tuning peaks and valleys the rest of the engine runs to.
Like just about anything that is involved in making things go bang in the combustion chamber, we found Adam Christian at the core of setting the all-new intake's performance goals. He identified and shuffled the available power peaks, playing a crafty game of corporate poker in the process.
"Coyote cannot make power any higher than 6,500--the intake manifold shuts it down. This one (the Boss 302 intake) won't shut it down until 7,750. And the reason that I picked 7,750 is that there are actually... you've seen the torque curves on Coyote, there are three very distinct peaks, wiggles in the curve, and I call those 'teeth on a sprocket' So they are tuning modes of the runner; if you change the length of the runner enough, you can actually move one whole tooth."
"So I took the tuning peak on Coyote that was at 5,250, moved it to 6,500, took the one that was at 6,500 and moved it to 7,750. And what that did for us was... at the time we didn't know if the hardware could support 7,500 rpm. At the time we started, we thought it might be a 6,500-rpm engine. So we said, 'OK, we'll get about 4 hp from going to this style--we'll give up a lot of torque--but we'll get about 4 hp and we'll protect for 6,500 by putting the tuning peak there. But then we had this other one that's way out there. And we all kinda... I mean it was the plan," Adam said. "Basically we gave the company enough rope to hang itself. Because once they start dyno-testing and they start seeing the power out there, then there's this relentless push to get all the way to 7,800 basically. And ultimately it was the PCM that was the one thing left that couldn't take it anymore as far as engine speed.
"And so it totally worked because if I walked in and said, 'I want to go 7,750' from the beginning of the program, everyone would say, 'No way, not a chance.' But the intake is what sets where peak power is, so I gave them this ever-increasing reward for going higher and higher, and that's how it happened."
If you wondered where the RoadRunner got its legs, now you know.
Translating Adam's power peaks into hard plastic reality were David Born and Beth Anne Dalrymple, who did the hard work of designing the actual intake and pushing it on to production. Late in the program, David left the RoadRunner team for another assignment and was replaced by James Cummings, who actually shepherded the black eight-legged spider through manufacturing. Beth brought an especially potent background to the Boss intake design party. Her background is in CAD design, the nitty gritty of laying out and building intake manifolds. She also knows what it takes to get them compatible with the machinery and procedures in the manufacturing plant. It's said she's designed just about every intake manifold Ford has built in the last 20 years.
But now Beth works in CFD, computational flow dynamics, the Ouija-board computer modeling science of what the air is doing inside the intake. She took the lead on designing the Boss intake, taking it all the way from the fundamental "air core" through the final product. Her experience with all aspects of manifold production meant there were no missteps, but hundreds of computer iterations of the intake were run through Ford's giant computer lab to get the details as good as possible.
"The idea of the shape has been similar all along," Beth explained. "[The] standup runners... that didn't change. We knew we had some package issues--hood lines--to fit within, but that idea didn't change. It was all about getting the runner to be the best flowing runner, which Dave and I worked on quite a bit. And after that, we looked at the plenum and how good we could make that. ...There's a little nose in [the entry]... We worked quite a bit on that little nose, the entry."
What is critical about the entry to the Boss intake is it splits the incoming air into two major streams left and right. The "nose" is a bump just downstream of the throttle body on the intake floor. It's for packaging the carryover fuel rail, but it took careful shaping to correctly manage the incoming air. The runner entries and shapes consumed a tremendous amount of time and computational power. In the end, the runner entries molded into the floor of the plenum responded to radii much larger than what theory said, which was something of a surprise.
Another bit of work was packaging and shaping the runners. They twist from a vertical rectangle at their top to a horizontal rectangle at the bottom. David explained the labor and rewards of this runner challenge: "So we're trying to keep the [runner] areas relatively constant--that's important to us--and how that change in shape goes from this end to that end is important. So she [Beth] has some special software she uses to control that, and she picks sections along the way... We spent a bunch of time changing those sections, and in the end took one or two of them out, and let this proprietary software that we use to make the transition the way it thought was best. At one point we ended up picking up a horsepower and a half just allowing that shape to change. Overall the intake was worth 10 to 12 horsepower, so you get a horsepower and a half from just changing how you let this area develop from here to here over such a short distance--that was huge to us."
The first thing to say about the Boss 302 exhaust is it carries over the Coyote's short, tubular headers. Long-tube headers definitely help but were never seriously considered for production. The Coyote's catalytic converters were already pushed to the limit on the '11 Mustang GT, and mounting them any farther from either the engine or each other (there are two catalytic bricks nearly touching each other in one housing) is just wishful thinking.
In fact, the entire exhaust system is a carryover from the Mustang GT. The changes are slightly quieter tips on the mufflers (you won't notice) and the addition of sound-enhancing sidepipes labeled Quad Exhaust. The sidepipes are mainly the work of Noise, Vibration, and Harshness engineers Aaron Bresky and Shawn Carney, with generous assistance from Keven Soenen, an outside supplier representative and hardcore Mustang enthusiast who was critical in seeing the sidepipes through to production.
And that was no easy task. On the Coyote the expensive headers were the highly visible target in the cost-cutters' sights. On the Boss 302, it was the sidepipes. They were an easy target. The fallback plan (the Mustang GT system) was already established, and it was far easier and cheaper to do, so Shawn, Aaron, and Keven had to protect their baby all the way through the program. As they observed, "We had to become ground clearance engineers, heat engineers, just to protect the sidepipes." Education and sticking with the pipes once they had moved on to the design and production people proved key. "You have to be a good communicator to talk to the other teammates so they understand what it is we're trying to do. You can't just throw it over the wall; you have let them know, 'I'll be with you all the way through."
Initially a dual-mode muffler exhaust out the rear of the car was considered. But this gives a quiet idle and then at some point on the tach a noticeable step-up in noise when the second sound path opens. It's a notchy, artificial solution. A sidepipe system with cutout switches (dump valves) was the next idea, but the valves were far too expensive, so they were ditched in favor of dead simple blocking plates with a small hole in it to let a little sound out all the time, but up by the occupants so they could hear it.
This proved a winner, but the team had to continuously simplify and isolate the system from the rest of the chassis to get an acceptable sound quality. A 1-inch louvered insert in the sidepipe is the main sound control element in the system, but you can make a big difference by playing with the easily modified or removable blocking plates. A quick listen to the system with and without the plate inside Ford's development garage proved the sound quality is excellent without the plate. It's aggressive, with a rumbling idle and purposeful bark, but not overly so.
For easy street/strip legality, the system was specifically designed to accept an aftermarket dump valve (from Ford Racing) that bolts right into the system. We consider it a "why not" item, one the enthusiasts inside Ford wanted you to have in the first place.
In a testament to the excellence of the refined S197 platform we call SN-10, chassis engineers on the Boss 302 program weren't so much about debuting exciting new hardware, but refining and re-tuning existing parts and systems. Still, significant improvements were realized, among them a long-standing wish for a staggered-tire fitment and a quality limited-slip differential. To a chassis engineer such as Kevin Groot, the tire is key. "... [since] long ago, we in [vehicle] dynamics have been asking for staggered-fitment tires. We realized we were lagging behind; almost everything has staggered fitment tires. And we knew that the Brake Pack and Track Pack were getting limited by the fact that the rear tire was not as wide as some of the competition."
Thankfully the Boss 302 proved the first Mustang to get the coveted treatment. The selected tires were the Pirelli PZero's in 255/40R-19 front and 285/35R-19 in back. The Laguna Seca edition got the same tire, but in an even stickier R-compound.
"Having decided to use an off-the-shelf tire [that worked and saved development time], we started to develop the chassis around that. ...Being able to walk from the '10 to the '11 [Mustangs] we could go further and we knew that, and the staggered tires opened that up in terms of chassis development."
With the tires set, the "big adjustment knobs"--springs, sway bars and dampers--are the next items to tune. "We started to work on the springs, and then all kinds of internal hurdles, like we were already maxed out on rear spring rate. So we had to do some things, like limiting rear rebound travel to keep the springs in the pockets and things of that nature. To go above where we were with the Track Pak and Brake Pak, we had to limit the travel on the rebound side for the damper. ...Luckily we had support from management because each [challenge] represents its own compromise ...but we did manage to push through all that."
"So, get the tires. Work on the springs. Work on the bars to get the balance in the car. Always our goal was to make the car driveable and fast. And approachable. You can jump in these cars and drive them hard... Early on we decided that the [BMW] M3 was our target and with the M3, you have to wring its neck to get anywhere near our lap times. With the Boss, to me, it comes easily."
"There are also more subtle things in there--all the bushing work; we even did top mounts [for the front struts]. We never did mention that to anybody. We did top mounts in the front, which was a pretty cool improvement in its own right." The top mounts are 50-percent stiffer radially.
In the end, the Boss 302 and Laguna Seca received the following suspension hardware:
Spring rates are in Newtons per millimeter; sway-bar diameters are in millimeters. Front lower control arm bushings are common in all Mustangs; the Mustang GT uses a softer rear lower control arm bushing than all others.
Generally things get stiffer as expected when moving from a Mustang GT to the track-happy Laguna Seca, except for the lower front spring rates on the Laguna Seca. Kevin explains, noting "The Laguna tune is all about handling the massive rear tire, also, because it has a more aggressive [tire] compound, the Laguna has a little more understeer margin. That's because the tires come up to little bit different temps and you have to manage it a little bit better. If you were to make the Laguna as balanced as the base car, there'd potentially be times where novices would be in trouble. We don't want to do that, so we got a little bit more (understeer) margin in that car."
With the suspension basics set, the tuning moved on to the dampers [shocks], and finally the electric power-assisted steering, or EPAS. The shocks are five-way adjustable units sourced from Tokico, but with Boss-specific valving. The EPAS is a whole new engineer's playground full of twiddle knobs to be adjusted. After decades of a few coarse adjustments to hydraulic power steering, EPAS opens many new tuning doors.
In fact, EPAS just debuted with the '11 Mustang, so the Boss program gave EPAS specialist Steve Ferrari a second shot at fine-tuning the system. "Between the dampers and the EPAS, that's one of my favorite parts because you have five adjustments on the dampers, and you can drive it as your daily driver and the EPAS goes along with it. You have Comfort, Sport and Standard settings, so you can dial back on the shocks and dial back on the steering and relax." Or go all out.
Because the EPAS' electric motor is so tunable and the feedback each driver likes is so subjective, there's real artistry in harmonizing the steering with the shock settings.
"The neat thing about the system we use," Steve said, "is you can tune the damping independently like a shock absorber, so turning in versus turning out. You typically use more damping turning out; just like hydraulics, we're able to make it emulate the feel of the hydraulic system. We have aggressive tires and high levels of caster and camber, and it gets really snappy if you don't have control over the steering system."
Obviously the chassis guys gravitate to the track-oriented Laguna Seca. As Kevin summed it up, "[I] think what we achieved, especially with the (optional) Torsen, is reliable consistency throughout the track day. It's a 444hp car, right? And they can be nasty. But we worked hard to make it approachable and docile, yet still fast and give the experience of being fast." Just the way we like it. Thanks, Ford! 5.0
Horse Sense: It's impossible to discuss the Boss 302 engine without understanding the Coyote 5.0-liter engine it is based on. If you need to brush up on that engine, see our March 2010 issue for the 19-page "Coyote Beautiful" article. If that issue escapes you, or your friend "borrowed" your copy, we are re-running it as part of our 2011-2012 Mustang Performance special issue, which is on newsstands June 21, 2011.
Lubricating the high-rpm Boss called for detail changes from the already fast-rotating Coyote baseline. Interestingly, a new oil pump was not one of them. By deleting the piston oil squirters, the Boss oil system effectively closed eight bleed holes, thus gaining pressure and slightly restored volume to the bearings. Furthermore, the oil was thickened to a fully synthetic 5W-50 from the Coyote's 5W-30 dinosaur squeezings. Together these changes gave the pressure needed to force oil out to the rod bearings at 7,500 rpm.
Another boost came from the synthetic's better aeration qualities. Ford says they need to be under 10 percent aeration; the Coyote posts 8 percent aeration, and the Boss, 5 percent. Inevitably the high-speed RoadRunner heats its oil a little more than the Coyote, and indeed the engineers say they let the Boss's oil temp run a little warmer under extreme conditions, something synthetic oil is entirely nonplussed by.
Regular readers may recall an oil-to-water oil cooler was considered for the Coyote, but didn't make the cut because it was only necessary after about 20 minutes at speed on a road-racing track. Well, if the everyday Mustang GT doesn't really need an oil cooler, the race-car-with-license-plates Boss 302 demands one. The unit is fitted between the block and oil filter, and is fed coolant from the lower radiator hose. As in the Mustang GT, it's only needed for on-track action, but it's there because the Boss 302 is designed for just such fun.
More hardware changes were required when tuning the Coyote oil pan, not only for the Boss 302 engine's higher rpm, but also the Boss 302 car's increased cornering and braking loads. At high rpm, the issue is oil drain-back. The Coyote's horizontal baffle is a step for the river of draining oil to loiter on at high rpm, so the baffle was trimmed back to route the oil more directly to the pan's sump. Naturally this had a negative effect on keeping the oil in the sump when the Boss was maneuvering hard, but extensive work gained a compromise between drain back and retention.
Another pan detail, the Coyote baffling is stitch-welded in sections to the pan. During hard Boss braking, the oil fountained up between the baffle and pan, so the welds were made continuous in the RoadRunner. Tim Vaughn says that even if it's run a quart low, the Boss engine still keeps adequate oil trapped around the oil pump pickup.
Name That Tune
The Boss 302 posed serious calibration challenges due to its unprecedented high rpm. Furthermore, the previous Coyote calibration in the '11 Mustang GT was of little help because changing the intake manifold, camming, even the oil viscosity, made the Boss 302 an entirely different challenge.
Jeff Seaman, who wrote all of the Coyote calibration, did most of the Boss 302 cal but was promoted to management in the middle of the job. Ford then put two superb senior calibrators on the job, Mark Sabuda and Gilbert Fournelle. They were occasionally assisted by Dev Saberwal, Ford Racing's calibrator, who has previous calibrating experience in everything from V-6 Mustangs to Ford's Jaguar Formula 1 team. The resulting Boss 302 calibration is entirely new and unique to the Boss, but is still housed in a Copperhead module.
If daily driving mode didn't pose anything particularly difficult to the calibrators, everything above 7,000 rpm did. "Everything you do at the top end is from scratch," Jeff noted. "Spark, variable cam timing, fuel, exhaust temperature--it's all unique." Some help came from Dev as he and his Ford Racing compatriots were the first to run Coyote-based engines above 7,000 rpm. "Being able to leverage Dev's experience on this was huge," says Jeff, and it marked the first-ever cooperative calibration effort between mainstream Ford and Ford Racing. This meant another first--Ford calibrators at the racetrack, taking data and running experiments on street cars under racing conditions. Jeff directly attributes the Boss 302's unique, larger radiator to track experience because that's where the Coyote radiator first proved inadequate thanks to the Boss' oil-to-water oil cooler.
But above all, it was plain old engine speed that made tuning the Boss 302 uniquely difficult. "There are a lot of concerns when you go run at high rpm" Jeff said. "Horsepower and rpm become an exponential cost item, and it's because the challenges you start running into are immense. It's not a simple one-off like, 'Hey you know what happens is that I run out of processing power.' No, it's things like my crank signal becomes much, much harder to see with a limited wheel that has only a finite number of teeth. It's my injector pulses start to overlap each other at high rpm. It's a ton of stuff. So it's not one item that trips you and says, 'I can't run at high rpm.' It's everything."
As Dev underlined it, "It's a systems issue, not really a processing power issue."
Today the Boss 302 runs seamlessly to 7,500 rpm, but you know Ford is relentlessly searching for more rpm capability. The issue is likely as much about cost as anything. High-end automakers such as BMW routinely offer 8,000-plus-rpm V-8s, and Dev has tuned F1 engines well into the rpm teens. But as Ford moves forward with the next Cobra Jet Mustang and beyond, the challenge will be how to electronically manage such engines and vehicles without breaking the budget. And that's because we all enjoy thrashing BMW M3s with a Mustang that costs $25,000 less.