Richard Holdener
January 1, 2008

Part 1
It's Possible that the Pro Stock title may be a tad presumptuous, as the '88 5.0 Mustang used for this test was a whole lot less Pro and a whole lot more stock, but we were hoping to change that in the near future. Sure, we'd never get this old Pony to run like a real Pro Stocker, but we could sure take the stock and make it rock. We've performed many 5.0 buildups in the past, and every one of them was a learning lesson on which parts and combinations work well together. With the veritable avalanche of performance parts available for the 5.0, the difficulty comes not in finding parts, but wading through the vast array.

Should we go all motor, or how about a little squeeze? Blowers are always good, especially if we combine the boost with extra displacement via a stroker combination. While all of these combinations have strengths and weaknesses, in the end, this 5.0 got a turbo.

After deciding that the boost would come from a turbo kit, we still had plenty of decisions to make. Having had excellent results in the many tests run with HP Performance in the past, we decided to take the company up on its offer to supply one of its single-turbo kits for the 5.0 Mustang. Simple and effective, the standard kit featured a 60mm turbo that offered plenty of boost and power potential. In fact, even the base 60mm turbo offered much more power than the stock (high-mileage) motor could ever hope to harness. We'll take care of that situation in Part 2 or 3 of this series, but for now, we wanted a simple kit that could be installed on our otherwise stock 5.0 motor and provide impressive boost and power numbers, all without hurting our not-so-precious powerplant.

Did we mention that the boost was being applied to a 5.0 motor with over 200,000 miles logged on the odometer? It was still in decent shape, but how long could we expect a motor like this to live? If it gave up the ghost during the first dyno run, we'd certainly understand. It had lived a long life and provided untold smiles during those many hard quarter-mile runs. That it continued to soldier on was a testament to the original design and proof positive that the legendary status of the 5.0 was well deserved.

Our idea behind this 5.0 turbo story is to demonstrate just how much power the bone-stock motor would take. If all went well, we'd baseline the normally aspirated motor, add the turbo kit, and run up the boost to a reasonable level. Then, we hoped to take the car out for some dragstrip runs to see just how the improvements in the power curve translated into changes in the e.t. and trap speed.

While you'd think every last 5.0 in existence has already been modified, it might surprise you how many people left their motors completely stock. Besides, running boost to the stock motor would allow us to demonstrate the power gains offered not only on the stock motor, but to later illustrate how heads, cam, and intake affect the power curve of a turbo motor. Would the gains be more or less than on a normally aspirated combination? Would the stock (high-mileage) motor withstand the extra cylinder pressure produced by the turbo kit? Questions like these are why we constantly run motors on the dyno and at the dragstrip.

The first order of business was to perform some prep work on the car. The '88 Mustang was equipped with a stock 5.0 motor. Being an '88 non-California car, the 5.0 was not equipped with a mass air meter. Knowing the turbo combination would certainly require tuning for proper operation, we put a mass air meter upgrade on the to-do list. Sure, we could add an FMU and adjust the static fuel pressure, but that old-school technique has some serious issues, from both a performance and safety standpoint. Adding the mass air upgrade allowed the guys at HP Performance to dial in the air/fuel and timing curves via SCT software.

The oil-sending unit was removed, drilled, and tapped to provide oil to the 60mm turbo.

The car was already equipped with a set of 3.73 gears, though we'd actually like to see 3.55s or even 3.27 gears in there, especially after we add the heads, cam and intake, since the trap speed is going to be elevated significantly. Running the 3.73 gears will mean elevated engine speeds to produce the corresponding (and desired) trap speed. In the end, we decided to just run it with the 3.73s and worry about the engine rpm once we install the top-end package in Part 2. Obviously the stock clutch wasn't going to take the torque offered by a turbo kit, so it was upgraded with a Spec Stage 3 plus. That the car was already equipped with a Tremec 3550 was obviously a plus. To improve the spark energy and aide the launch, the ignition was upgraded with an MDS Digital 6 equipped with a two-step.

Given the minor exhaust and mass air modifications on the otherwise stock 5.0 motor, we didn't expect big numbers out of the tired 302. Run on a Mustang chassis dyno at HP Performance, the 5.0 posted peak numbers of 199 hp and 243 lb-ft of torque. Given the relationship between the power and torque numbers in stock trim, we expected to see a slightly higher peak torque number, but the curve was repeatable. Now it was time to add the turbo kit from HP Performance.

The system included a single 60mm T4 turbo sized to provide both impressive response along with plenty of maximum power. Though turbo upgrades are available to produce insane power levels, even this standard 60mm turbo was more than capable of boosting this tired little 5.0 into oblivion. The key to any forced induction motor is obviously the tune. Provide the proper air/fuel and timing values, and the motor should live a long, happy life. Miss by just a degree or two and it could be "bye-bye motor." Even a new engine featuring forged internals won't stand up to detonation, but our high-mileage stocker was even more fragile than a dedicated buildup, so HP was purposely conservative with the tune.

The 60mm turbo was positioned near the factory airbox and mass air meter thanks to a set of dedicated tubular exhaust manifolds and crossover pipe. Boost was fed through a front-mounted air-to-air intercooler. Though our boost levels would certainly be conservative for street use, we planned on upping the boost for drag-strip use.

Unfortunately, for enthusiasts, the laws of physics dictate that compression causes heat. What this means is that boost pressure heats up the inlet air temperature. Hot air increases the likelihood of detonation, so intercooling is employed to reduce the charge temperature. Testing on the ultra-efficient air-to-air intercooler provided with the kit has demonstrated the ability to reduce inlet temperatures by more than 200 degrees on a high-boost race application. Though we had no plans of running 20 psi on our stock motor, it's nice to know that the intercooler has the ability to grow with our power needs should we decide to crank it up in the future.

The turbo was fed by the pair of tubular exhaust manifolds. Air was drawn into the turbo through the MAF, fed through the intercooler, and then to the stock throttle body. The exhaust exited through a 3-inch downpipe, which splits to feed a Bassani after-cat exhaust. Also present on the turbo kit from HP Performance was a 44mm Tial wastegate and a Bosch blow-off valve.

Naturally, the additional power potential of the turbo required upgrades to the fuel system. In anticipation of the added power, both the stock fuel pump and injectors were ditched in favor of a 255-lph high-pressure in-tank pump and a set of 42-pound injectors. Larger injectors and additional fuel flow are available should they be required, but the combination was more than sufficient for the power potential of our turbocharged stock motor. The MSD was chosen both to increase the spark energy and to utilize the built-in two-step while running at the dragstrip.

The secondary section of the exhaust downpipe was set in position.

Installation of the kit was straightforward, requiring only that the exhaust manifolds (in this case, headers) be removed and replaced with the tubular exhaust manifolds and crossover pipe. It was also necessary to tap into the extension for the oil-sending unit to provide oil to the turbo. A hole was drilled into the oil pan to serve as a drainback for the turbo. The down tube featured a Y-section to connect the turbo exhaust to a conventional after-cat. After running the various inlet tubing to and from the turbo, intercooler, and factory throttle body, we were ready for the dyno.

Before getting to the power numbers, a quick lesson on horsepower and torque might be helpful. From the formula that dictates the mathematical relationship between horsepower and torque values (HP=TQxRPM/5,252), we see that gains in horsepower below 5,252 will show a greater increase in torque. Conversely, improvements in torque above 5,252 will show more dramatic changes in horsepower.

An example works well here. Using the formula, we see that increasing the power by 50 hp at 3,500 rpm will result in a jump in torque of 75 lb-ft. Increasing the torque output by 75 lb-ft at 6,000 rpm will improve the power output by more than 85 hp. Since the stock 5.0 motor has always been a torque motor (it produces a higher peak torque number than horsepower) and does so at a relatively low engine speed, adding boost to the equation is likely to exaggerate this relationship. Basically, adding a turbo kit to a motor that makes peak power at just 4,800 rpm will provide huge torque gains. If the peak torque number was higher than the peak power number in normally aspirated form, we should expect things to remain the same once we install the turbo.

True to form, adding the turbo kit from HP Performance offered not only a sizable jump in peak power, but a huge jump in peak torque. Where the normally aspirated motor produced 243 lb-ft of torque, the turbocharged 5.0 thumped out a diesel-like 493 lb-ft of torque at just 3,700 rpm. Running 10 psi of boost, the peak power output of the turbocharged 5.0 checked in at 433 hp.

We've always been amazed at the power offered by a good turbo system, and this single-turbo kit from HP Performance certainly continued the trend. The great thing about this torque monster was the immediate gratification that came from sticking our foot into the throttle. Having 493 lb-ft to play with at just 3,700 rpm means this thing builds speed like nobody's business. Even down at just 3,000 rpm, the torque output was 360 lb-ft. What this avalanche of torque means is that this Mustang gets moving, right now. Of course traction is in short supply, but it's always better to have too much power and not enough traction than the other way around.

While 433 hp and 493 lb-ft of torque was certainly impressive, naturally we couldn't leave well enough alone. Despite the high mileage, we decided to crank up the boost at least a few more pounds to see how it responded. To hedge our bets and prep for the upcoming trip to the strip, we poured in some 114-octane Rockett Brand race fuel. At this combination of timing (18 degrees total), air/fuel (11.2:1) and boost level (13 psi), the 114-octane fuel was probably overkill on our part, but we wanted to make sure we still had a healthy candidate for Part 2.

Run on the Mustang dyno once again, the additional 3 psi of boost increased the peak power output from 433 hp and 493 lb-ft to 481 hp and 545 lb-ft. With the torque output close to 550 lb-ft of torque, we were talking about some serious cylinder pressure, especially with stock head gaskets and bolts (in who knows what kind of condition at 200,000 miles). We'd not recommend running this power level on an otherwise stock motor for long, but it's nice to know that it's possible. Run at the strip at this power level and with 28x10.5-inch ET Streets, the front swaybar and rear quad shocks disconnected (but otherwise stock 5.0 suspension), the five-speed Mustang ripped off a string of mid-11s, the best being 11.47 at 122.6 mph.

Despite the stock suspension, the 5.0 managed 1.50-second 60-foot times, according to the timeslips. Even more impressive was the fact that the motor was still alive and ready for Part 2. Check back with us next month as we install a set of cylinder heads, a cam upgrade, and a new intake manifold.