Steve Turner
Former Editor, 5.0 Mustang & Super Fords
October 1, 2009
Photos By: Stever Turner
From the moment we laid eyes on the new Roush Mustang, we appreciated the clean subtle approach of the car's new bodywork. The front fascia in particular is the perfect blend of factory quality and Roush style, complete with Cobra-like round foglights and a new front splitter. The only real critique of the car's front end is the retention of the factory fogs, which are non-functional. The front end could be even cleaner with a unique grille to complement the fascia, but perhaps that motif is being saved for a future Roush.

Roush and fast go hand in hand, but usually when it comes to the race track. In this case, that speed and a close working relationship with Ford delivered the first tuner '10 Mustang to dealer lots right on top of the arrival of the '10 Mustang GTs.

The speedster in question is a 427R. The name has plenty of historical significance, but this time around it bears no relation to the horsepower underhood. Nope, this 427R packs a 435hp, 400 lb-ft wallop in a clean, understated package.

Eagerly jumping behind the wheel, the first thing that jumps out about the Roush is not any flashy bling. Instead, it is the brightly inserted seats, but not because of their visage, but because of the pleasant, recliner plush that still provides plenty of side support. The many-logo'd Roush adornments aren't overboard, and the seat inserts were a big hit with those that came over to check the car out. From a functional perspective, the tall, retro Roush shifter makes the car easy to power shift and more fun to drive by delivering more feel in the relatively isolated '10 interior.

Once I dialed in the seating position, pushed in the easy-going stock clutch, and turned the key, the 427R ripped to life with a metallic snarl. This car looks and sounds the part-even sitting still. Finding a clear piece of road and standing on the throttle, I quickly learned the 427R runs like a self-respecting performance Mustang should. Torque comes on early and often, swelling into a fat midrange pull. Halfway up the tach, the pull is less urgent, but it keeps on thundering all the way to redline. In fact, the latest execution of Roushcharging seems more elastic on the '10 Mustang, making this car a blast to stretch all the way to the redline whenever you get the chance.

With a Roots-blown 400 lb-ft of torque on tap, starting a smoke show is just a matter of switching off the AdvanceTrac traction control and getting down to business. Our friends at Bradenton Motorsports Park were kind enough to let me burn rubber while our web producer, Greg Clark, snapped a shot. Unfortunately, the weather precluded us from running at this session. I was able to sneak in a couple passes before a Saturday bracket race, but I didn't really pull off an ideal pass-though I did manage to run potential-revealing 107 mph. You can read more of my excuses in our On the Dyno sidebar, but I did learn that with low rear-tire pressure the car refuses to go into AdvanceTrac Sport Mode. It was either On or Off.

The more consistent power delivery is likely due to 30 percent more intercooler coolant capacity and a heat exchanger with twice the surface area of its predecessor, which helps stabilize air-charge temps. Combined with the grille-fed intake system on the '10 Mustang, the new Roush does its best work moving down the road even on a hot summer day. "Both the air induction and the intercooler water changes are most noticeable in real-world driving situations that aren't captured in an SAE net-power run, where all temps are controlled to targets specified by SAE," explains Craig Barker, Roush powertrain development manager. "If SAE had a Phoenix-traffic-jam simulation, I would estimate these two improvements are worth 15 hp at redline and 20 lb-ft of torque in the midrange," So while the tuning on the new car is similar to the '09, there is more power on tap.

Getting the show on the road where it excels, the car emotes an aggressive tone to the outside world at low speeds, but in the cabin it's a dull roar. As you work your way up to cruising speed, the Roush exhaust drifts into the background. Rolling down the interstate, it's the Torch Red color, not the exhaust, that announces this 427R from a distance. This stealth bomber approach means you are quickly exceeding the speed limit without realizing it. When you finally realize where the needle is on the speedo, you regret reeling things back in, as the 427R seems built for speed.

Working with the comfy seats is a suspension that is taut and neutral, but doesn't beat you up. A great combo, and one that's tuned to work with all of the Roush wheel packages. Gone are the days of multiple Roush suspension packages. Now there's just one, and it's a good one. "We used a digressive-dampening tuning approach with the new 2010 Roush Mustang. What this means is that there is aggressive low-speed damping to get good body control and response, and then allowed the wheels to move over higher velocity events such as pot holes and bumps," says Terry Hendricks, Roush chassis manager. "Additionally, we carried over the stiffer Roush Stage 3 antiroll bars from the previous model to provide good roll control and handling balance."

Out back, the three-piece rear wing steals the show, as its wraparound design really softens the factory styling a bit, and greatly improves our least favorite view of the '10 'Stang. The lower rear valance is an all-new Roush piece built from OEM-spec ThermoPlastic Olefin, and while it is more aggressive in its visage, it still dominates the rear of the car like the stocker. The Roush exhaust is installed post-title at the dealership.

Balance is the essence of the Roush 427R. It packs equivalent levels of power, handling, and braking and keeps the ride quality and comfort even on the other side of the seesaw. Sure a bit more power would always be nice, but at the end of the day, the 427R is more than enough Mustang to rock your world.

On The Dyno
I absolutely love chassis dynos as they take me out of the testing equation. When it comes to driving, I'm anything but repeatable while the chassis dyno is known for repeatability. Once the car was strapped down to the Mustang Dyno at Moore Tuned in Lakeland, Florida, we learned that Roush really has the tuning dialed in on the '10 427R. After a normal morning drive, I let the car sit for 15 minutes before making a pull on the dyno. Our corrected baseline numbers were 339.6 hp and 316.3 lb-ft of torque.

Those familiar with other chassis dynos-like the inertial Dynojet models-already know they often result in slightly higher numbers than the eddy-current Mustang units, which load the vehicle based on its weight. We once compared the two, and our testing showed about a 13-percent difference between the Mustang and Dynojet, so our Mustang 339.6 hp pull would be about 383.7 hp on a 'Jet, which sounds about right for a car with 435 at the flywheel.

Thanks to a big leap in the quality of the stock interior, there isn't much sprucing needed to really doll things up. Headlining the improvements in the 427R is the optional Roush Sport leather seating, which amplifies the stock seats with increased padding and a vibrant, body color inset. Of course, the Roush-logo'd release button on the armrest rounds out a flurry of logos from the floormats to the pedal covers, all confirming the 427R is no mere Mustang. As always, the familiar high-leverage Roush retro shifter adds a bit of visceral personality to the driving experience.

After working the car on the dyno to build up heat, Allen made a second heatsoaked pull, and power only dropped off to 336.8 hp; torque actually jumped up a bit to 318.3 lb-ft. "The Roush low-temp radiator gain also isn't captured in a formal SAE net power run," says Craig Barker, powertrain development manager at Roush. "The larger water capacity can absorb more heat, and the larger frontal area of the low-temperature radiator (a.k.a. heat exchanger) will remove the heat faster. This will be most noticeable in lower average water temps during a road-racing situation, more so than a short drag race, and not noticed at all in a formal dyno run." So while the new system can produce a lower average air-charge temp in driving situations, it seems the tuning doesn't aggressively roll back timing based on air-charge temperature, as is common factory practice.

Roush engineers are pretty keen on the factory airbox, but caution that its grille-fed induction doesn't come into play on the dyno. "The net effect of the new 2010 air induction increases as vehicle speed decreases, a gain not captured during a formal SAE power run on dyno because induction air is always controlled to 77 degree Fahrenheit dry air on a SAE dyno run," Craig explains. "Vehicle speed does not play a role in the formal power rating on dyno."

That said, we couldn't help but try and see what the induction system would do without sucking through the factory filter and airbox. Allen simply popped the lid off the stock airbox, and propped it up so there was a small gap for the inlet to breathe through. On the earlier cars, the filter played a vital role straightening the air for the mass-air sensor, and they would run poorly without the filter. Not so with this '10. Though running the car this way leaned out the air/fuel mixture slightly, it wasn't to a dangerous level, and the power really jumped up. Our open-airbox run resulted in a corrected 351.3 hp and 322.5 lb-ft of torque at the wheels, so there may just be some power from a freer-flowing airbox, especially when you start dialing up the boost.

Offering a clean install of the Roush boost gauge is a vent pod for the '10 A/C vent. While this arrangement looks great, it does give up directional control of that airflow, which can be a downside in hotter climes. Peaking at about 5 pounds, the white-face boost gauge complemented the optional Roush white-face gauges in our tester.

Once the official dyno testing concluded, Allen offered to let us make some quarter-mile passes on the dyno. As I previously mentioned, I was only able to squeeze in a couple less-than-ideal passes at Bradenton Motorsports Park before a Saturday afternoon bracket race. I'm not a talented enough driver to just rip off a great pass on my first try. It usually takes a handful of passes to figure out just the right launch rpm, shift point, and so on. I managed a 13.62 on one hit and 107 mph on another, but I couldn't quite put it all together in two passes. I think with a bit more time, I might have been able to run a 0.30 or 0.40 on the street tires if I pulled a rabbit out of the hat. In any event, the mph reveals the car is good for mid 12s if the traction is there.

On the dyno and without the worry about traction, I made my first pass, dropping the clutch at 3,000 rpm and shifting at 6,000 rpm. (I tried 1,500- and 1,800-rpm launches at Bradenton.) The tires squealed for just a second, and the result was a 12.60 at 104.68 mph. I followed that up quickly with a 5,000-rpm launch and maintained the 6,000-rpm powershifts. (I tried 5,500- and 6,000-rpm shifts at Bradenton and traction was still an issue.) This resulted in a slight spin and an impressive 12.52 at 104.47 mph. Allen says that assuming the traction is there, the dyno passes are usually within a couple ticks of a real pass, which makes the 427R a pretty impressive unit, especially considering it's built more for the street and the road course than it is the dragstrip.

 BaselineHeatsoakedOpen AirboxHS VS. OAB
TQPowerA/FTQPowerA/FTQPowerA/FTQPower
2,0002639912.32639911.927410313.1114
2,50027613011.927713111.729013712.5136
3,00028716311.528716311.629816912.4116
3,50029519611.429719711.430720412.0107
4,00030723211.230522511.331323712.0812
4,50031226711.331326111.031927212.0611
5,00030929311.130729711.131529911.882
5,50030331611.130331611.031132511.489
6,00029033111.228932911.0{{{300}}}34111.81112
6,30027432811.228033511.129134812.01113
To find out how much the 427R puts down to the wheels, we stopped over at Moore Tuned (863) 559-4344; www.mooretuned.com in Lakeland, Florida, to strap it down to Allen Moore's Mustang MD-1100SE single-eddy current chassis dyno. Allen specializes in tuning high-horsepower cars for maximum driveabilty, which makes him our kind of guy!

5.0 Tech Specs
2010 Roush 427R
Engine and DrivetrainBlock 4.6-liter 90-degree V-8
Displacement 281 ci
Rods Cracked, powdered metal with floating wristpins
Pistons Hypereutectic aluminum
Camshafts SOHC, variable camshaft timing
Heads Aluminum, three valves per cylinder
Intake Composite shell-welded single-runner, charge-motion-control valves
Exhaust Stock with Roush after-cat system
Transmission
Tremec 3650 five-speed
Rearend 8.8-inch w/3.55 gears

Electronics
Engine Management
PCM w/Roush tune
Ignition Coil-on-plug
Gauges Roush white-face gauges, Roush vent pod with boost gauge

Chassis And Suspension
Front Suspension
Reverse-L independent MacPherson strut, 34mm tubular stabilizer bar
Springs Roush Performance
Struts Roush Performance
Brakes 316x30mm vented disc, twin-piston 43mm floating aluminum calipers
Wheels Roush 20-inch cast-chrome wheels
Tires Dunlop 275/35ZR20
Rear Suspension
Three-link solid axle with coilsprings, Panhard rod, and 20mm solid stabilizer bar
Springs Roush Performance
Shocks Roush Performance
Brakes 300x19mm vented disc, single-piston 43mm floating iron calipers
Wheels Roush 20-inch cast-chrome wheels
Tires Dunlop 275/35ZR20