Project Grey Mustang 5.0: Part 4 - Improving Drivability and Reliability

by Vince Illi

The Grey Project Mustang 5.0 is still alive and kicking.  Over the past year, it’s had a lot of little things done to it to improve drivability and reliability.

Read more about the Grey Project Mustang 5.0 here!

The Mustang drove and handled great with the suspension mods performed to it, at least for the most part.  The only “problem” was throttle response.  On most newer engines, including the Coyote 5.0L found in Project Mustang, the throttle is not connected to a pedal via a cable.  Instead, the throttle plate is controlled by a stepper motor, which is, in turn, controlled by the Powertrain Control Module (PCM).  This is known as Drive-By Wire (DBW).  Instead of directly opening the throttle plate like on cable-operated throttles, the pedal simply sends an electronic number to the PCM.  Using this number and several other parameters such as engine RPM and coolant temperature, the PCM creates a torque target value.  Using this torque target, the PCM looks up values in a table to arrive at the intended torque value by changing a variety of parameters, including throttle position, spark advance, ignition timing, and cam timing.  This means that the throttle position no longer directly corresponds to the accelerator pedal’s position.

In order to make the car drivable by your average unskilled driver, throttle response is deadened and torque output is limited below 4,500 RPM or so.  (This is how a soccer mom can drive a RWD pony car that has more horsepower than the original Viper.  It is also why, around town, you can’t tell the difference between a V6 and V8 Mustang until you hammer it.)


Ford Coyote 5.0.  32 Valves.  Dual Overhead Camshafts with Twin Independent Variable Cam Timing.  430 horsepower.  Mountains of Torque.  And throttle response rivaled only by that of a 2002 Toyota Yaris.

In order to solve these problems, I ordered a new "tune" for the PCM from Ford Racing.  Ford Racing’s tunes are developed by the same engineers who designed the motor.  Because of this, all emissions functions are maintained, reliability is still as good as stock (no blown cylinders from bad tunes here!), and the factory warranty is still retained.  Also, whereas other tuners simply change values in lookup tables for their tunes, Ford Racing actually inserts and changes lines of code, meaning they can do things the other tuners simply can’t do, such as changing cam timing behavior or modifying shifting strategies on automatic transmissions.

After sending them my car’s VIN, a Ford Racing ProCal showed up at my doorstep a few days later.  Installing the new tune is a simple matter of plugging the ProCal into the OBD-II port, pressing a few buttons, and waiting about 15 minutes.  The car fired up immediately afterwards.


The ProCal is a small, handheld device that replaces the factory tune with Ford Racing’s.  The factory tune is stored on the ProCal’s memory in case you want to later return the car to stock.  It also allows you to adjust the speedometer for different diameter tires or final drive gears.

The difference in driving was immediately apparent.  Throttle response was much better—and very linear.  It felt much closer to an older muscle car that wasn’t DBW.  Flooring the pedal no longer required waiting for an electronic committee to vote on whether or not to give me full torque.  There was a nice bump in power, too.  By requiring 91 octane or higher, Ford was able to tweak the spark advance and a few other parameters, giving a claimed peak power increase of 16 horsepower and 7 lb-ft of torque.

But those peak numbers are not what make the new tune so great.  The area under the curve is the true improvement, because by eliminating torque management, the ProCal tune increases output by over 60 lb-ft of torque at 1,500 RPM.  This is like removing the seal on Pandora’s Box.  Flooring the car at the starting line of an autocross makes the horizon fly towards you at an alarming rate.  The increase of torque at lower RPMs also makes the engine very linear, which is one of the greatest advantages of a large-displacement, naturally-aspirated engine used for corner carving.  This tune was so transformative that I wished I had installed it on the second day I owned the car.  The car no longer moves; it spins the earth beneath its wheels.

After taking care of the last of the drivability issues, it was time to address several minor problems that crept up after a couple years of hard driving and racing.  Because the grey Mustang is an early 2011 model, several of the options the white ‘13 Project Mustang are equipped with were unavailable at the time, like the Torsen differential and the 4-piston Brembo brakes.


The stock 2011+ “base-model GT” brakes are a two-piston sliding caliper type with 13.2” rotors.  Pre-2011 S197s have 12.4” rotors with the same caliper.  While more than adequate for street driving and hard stops after drag races, these brakes begin to fade, wear out, and warp rather quickly when subjected to repeated hard braking at autocrosses and road courses.
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Monday, March 03, 2014 3:17 AM
Nissan S chassis in Europe have an active diff cooler, maybe you could get one cheap from a junkyard. I know people here remove them (the car only activates it at low speed so it gets binned).

Quick question : why do you want to see the commanded AFR on the gauge ?
Dusty Duster
Dusty Dusterlink
Monday, March 03, 2014 6:52 AM
I didn't know about the active diff cooler from S-chassis. Thanks for the heads up!

As for why I want to see the commanded A/F ratio, that's just because I'm a tech geek who likes engine management systems. :-P
Monday, March 03, 2014 7:31 AM
I wonder why you are so concerned about diff temps in autocross? They'll never get high enough to be concerned about. Your car is likely better off than, say a 350Z, GTR, or Corvette on track because their diffs are tucked up farther away from ambient airflow than yours. One of the local C5 drivers with a diff temp gauge will only drive the car until the diff hits 300, then pulls off. That usually takes a 30 minute run in 95 degree heat.

How about drivability between a Trak-lok (semi-tunable) and the Torsen? I understand how their operating principles differ, but have never felt both diffs in the same car. My C5 has a clutch type diff and my Camaro has a Torsen, neither lights the inner tire leaving a corner and neither has a sudden transition mid-corner from open to locked. I just wonder if you're not splitting hairs again with respect to the heat produced from a clutch type diff vs. Torsen. Please don't take it as an attack, I want to make sure I'm not missing something here too.
Dusty Duster
Dusty Dusterlink
Monday, March 03, 2014 7:50 AM

You would think the diff wouldn't get hot during an autocross (I know I did), but there are a LOT of people who have burned through the stock clutch diff in only one or two seasons (or even less). Perusing any corner-carving S197 forum will show numerous melted Trak-Loks. Even the GT500 carbon-clutch Trak-Lok upgrade can be melted in short order if using 305-width slicks. The reason I haven't completely trashed my Trak-Lok yet is due to using 285-width street tires (as opposed to slicks) and that aluminum diff cover.
Monday, March 03, 2014 8:18 AM
Why bother with the Trac-Lok at all? Just keeping it because you've already got it, or do you prefer a clutch-type differential?

On SN95s, I've always swapped the Trac-Lok for a basic, non-preloaded Torsen T2. I didn't like the way the Trac-Lok seemed to induce understeer under lift-throttle or coasting conditions.
Mike Kojima
Mike Kojimalink
Monday, March 03, 2014 9:06 AM
You really like torsens? I hate them. One tire fire if you get them started and twitchy on high powered cars. For me clutch types work a lot better once you set up the chassis around them.
Monday, March 03, 2014 9:33 AM
In street use, yes. I just never liked driving the Trac-Lok on the street very much; always made the car feel like a total understeering pig. The Torsen definitely does make the car much more twitchy on surfaces with less than ideal traction, though.
Monday, March 03, 2014 11:16 AM
On Project S2000, I'd say the stock torsen is a bit slow to respond. Kind of like turbo lag. In auto-x in the stock class, the S2k guys have to run insanely stiff front sway bars to keep the inside rear down on the ground so that they don't lose drive.
Dusty Duster
Dusty Dusterlink
Monday, March 03, 2014 11:21 AM
I actually like the way the Trak-Lok handles, both during racing and on the street. However, I DON'T like the fact that it essentially becomes a wear item when pushed hard.
Monday, March 03, 2014 11:58 AM
@ Lemming: you sure it wasn't the SN95 chassis making it feel like the understeering pig that it was? :)
Monday, March 03, 2014 12:08 PM
Considering that the only original Fr0d suspension pieces on either of those cars were the rear axle housing and the front spindles...probably. :)
Mike Kojima
Mike Kojimalink
Monday, March 03, 2014 12:46 PM
I think the SN95 has a lot of potential!
Monday, March 03, 2014 1:15 PM
We use the stock diff for drifting on 265 street slicks, no problem at all, no oil cooling, but good blue motul.
Dan DeRosia
Dan DeRosialink
Monday, March 03, 2014 2:06 PM
Mike: Problem with the American style clutch limited slips is that there's no ramps to load the clutches - it's just a bit of spring preload, and then the spreading force on the spider gears. You get about 40 ft/lbs of breakaway torque and then stuff is slipping. The way they're set up, some you can shim to set up more like spools, and others you're stuck with it acting like a sticky open diff. Either way, they're not made to cope with torque going to the wheels at the same time as the car's rotating.

Spent some time researching rear axle options for a 1st gen RX-7 that could take some torque - never came up with a good one aside from maybe a modified Toyota truck rear end with an aftermarket Mk3 Supra diff. ;)
Norm Peterson
Norm Petersonlink
Tuesday, March 04, 2014 4:37 AM
@supercharged - at autocross you're nearly always turning, and for much of that time turning under power. Keep in mind that a clutch or cone style diff wants to be locked until/unless a difference in drive wheel rpm forces them to slip instead. So when you're cornering, the LSD is forced to . . . well, do its differential speed thing, which forces slippage to occur between the clutch plates while carrying significant torque. The greater the difference in wheel rpm (read: tight turns), the worse the slippage and the greater the heat generation. For a ~50 second autocross run, I would not expect temperatures of the fluid and the friction surfaces to reach equilibrium.

Like Dan said, "they're not made to cope with torque going to the wheels at the same time as the car's rotating." For the straight line crowd who don't want much more than the ability to put parallel black lines down on the pavement or just the average driver who either coasts through turns or who (barely) maintains speed, this isn't a problem.
Dusty Duster
Dusty Dusterlink
Tuesday, March 04, 2014 5:24 AM
Good to "see" you here, Norm!

The tighter turns of an autocross course are in some ways harder on a differential than a road course. Because the turns' radii are shorter, there is a greater differential in speed between the inside and outside wheels.
Tuesday, March 04, 2014 11:25 AM
I hadn't thought of it that way, so the oil likely never gets hot overall, but locally things get cooking pretty quickly. I've never tracked or autocrossed a trak-lok, so I'm definitely missing some perspective there but the fact that it's 50-60 seconds of straight abuse to the diff, I could see it becoming a wear item which would get old quick. Also, from what I recall, the Ford clutches/steels are smaller than even what's in the Kaaz 1.5 way in my Corolla so they probably don't deal with heat very well at all.

It hasn't happened to me yet, but as Mike indicated once a Torsen unloads that's it, a total one tire fire whereas a good LSD will still have forces applied to it that are trying to put some power to the lighter wheel.
Dusty Duster
Dusty Dusterlink
Tuesday, March 04, 2014 2:22 PM
The T2R Torsen used in the latest BOSS 302R/S Mustangs actually has preload clutches, preventing one-wheel peel. It also has a much higher 4:1 bias ratio.
Grant 302
Grant 302link
Tuesday, April 29, 2014 10:14 AM
"Because the grey Mustang is an early 2011 model, several of the options the white ‘13 Project Mustang are equipped with were unavailable at the time, like the Torsen differential and the 4-piston Brembo brakes."

Brembo brakes were available on the '11 GT. I have one (option 55D) and there's a site dedicated to the cars http://brembo50.com/
Dusty Duster
Dusty Dusterlink
Tuesday, April 29, 2014 11:01 AM
There were no Brembo-equipped cars available when I purchased Project Mustang 5.0.
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