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1988 Ford Mustang 5.0 Pro Stock Build - Pro Stock Pony Part 3 - Tech
Simple Bolt-On Parts Equal Over 600-Plus Proud Ponies At The Wheels On This 5.0 Mustang.
You'll remember from the first two installments of Project Pro Stock that we set out to add some much-needed Pro to our stock 5.0 Mustang. The idea was to take a (near) bone-stock 5.0 Mustang and add a single turbo kit from HP Performance in Roswell, New Mexico. Wicking up the boost on the otherwise-stock fuelie 302, we managed to post some impressive timeslips, the best being 11.47 at 122.6 mph. This was accomplished by feeding the 200,000-mile motor 13 psi of boost, which responded with 481 hp and 545 lb-ft of torque.
In Part 1, the mods to the 5.0 included 3.73 gears, a Spec Stage 3 plus clutch for the Tremec 3550 tranny, and an MSD Digital 6 equipped with a Two-Step rev limiter. For Part 2, we stepped up the boost to 16 psi, improved the suspension with bits from Eibach and Hotchkis, and installed head studs and new Cometic gaskets after surfacing the stock heads. A tight seal is paramount to keep that boost tucked safely inside the combustion chambers. The power and suspension mods improved the e.t.'s and trap speed to 10.93 at 129.7 mph. Despite the 200,000 miles, Project Pro Stock was on a serious mission thanks primarily to the impressive single-turbo kit from HP Performance.
At the outset, we promised to add new heads, cam, and intake to the stock short-block, and in this installment we honor that promise. The idea behind the new induction system is to improve the power output of the normally aspirated motor to further enhance the power output of the turbocharged combination. The benefits are twofold. First off, improving the breathing potential of the heads, cam, and intake allows the normally aspirated engine to make more power. Obviously, the stock 5.0 heads, cam, and intake were designed with low-speed torque production in mind, to say nothing of impressive throttle response, emissions reduction, and fuel economy. Almost any set of aftermarket performance heads will offer a sizable jump in power compared to the stock E7TE castings, a fact verified in our previous "Ultimate Guide to Cylinder Heads." The same holds true for performance cam profiles and a decent intake manifold, of which there are currently a dozen from which to choose. Yes friends, despite the advent of the mod motor, it's still a great time to own an original 5.0 Mustang.
In addition to the obvious power gains offered by upgrading the heads, cam, and intake, those benefits are actually multiplied by the presence of boost. Using the old Holdener power/boost formula, we see that the power output of a 225hp 5.0 can be increased to 450 hp at 14.7 psi of boost. This is possible since a 225hp 5.0 was subject to 14.7 psi of pressure (1 atmosphere) while running normally aspirated. This, of course, assumes running at sea level at a reasonable tempera-ture and humidity, but that's not important for this example.
If we double the pressure (to 14.7 psi of boost) applied to the motor using an efficient turbo system, such as the one from HP Performance, it's possible to double the power output. This assumes a number of criteria must be met and, in fact, it's possible to more than double the normally aspirated power output at 14.7 psi, but for now we'll assume our theoretical motor simply follows the power/boost formula. If we increase the normally aspirated power of our 5.0 from 225 hp to 275 hp using heads, cam, and intake, we'll find that the new power output of the motor can be 550 hp at the same 14.7 psi. That gain of 50 hp on the normally aspirated combination translates into a gain of 100 hp under boost. Is it any wonder turbos are so popular?
The second benefit of improving the power output of the 5.0 motor with heads, cam, and intake is what we like to refer to as "shifting the torque curve." Given the massive torque production of the stock 5.0 motor, shifting the torque curve unearths a ton of extra horse-power higher in the rev range.
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Simple math from the following formula (HP=TQxRPM/5252) tells us that producing 300 lb-ft of torque at 3,000 rpm equates to 171 hp, but producing the same 300 lb-ft at 6,000 rpm equals 342 hp. Simply shifting the torque curve higher in the rev range without even increasing the peak number results in more horsepower. Obviously more horsepower equates to quicker e.t.'s and especially higher traps speeds. The side benefit of improving power higher in the rev range is that we were running out of effective rpm with the factory 5.0 induction system, and having the motor make peak power at 6,000 rpm instead of 5,200 provides an extra 800 rpm of effective gearing. Where the power curve starts to fall off with the stock induction system, the power continues to climb and allows the car to continue accelerating. The result is another 8-10 mph of available trap speed thanks to the extended operating range.
We were certainly impressed with the results of the stock 5.0 components. After all, who wouldn't be happy with a 10-second Mustang? Now factor in that this was accomplished with a stock 5.0 motor, with 200,000 miles no less, and those 10-second timeslips look all the more impressive. Happy as we were, we were even more anxious to install our new hardware and get back on the dyno. Unfortunately for our project, winter was quickly closing in and, with it, track closures were almost certain. We were not able to run the Mustang with all of our newfound power, but the numbers alone were impressive enough to have us talking about the possibility of running 9s.
The new upgrade even took us to the limit of the standard 60mm turbo employed on the base kit from HP Performance. To combat the lack of flow offered by the 60mm turbo, we installed a 67mm unit to demonstrate the gains offered at this elevated power level. Before performing any of that magic, off came the factory heads, cam, and 5.0 H.O. intake manifold. They served us well and were now relegated to the parts bin next to the factory air silencer, where they awaited the time when they'd be the hot, sought-after item for Mustang enthusiasts wishing to restore their precious 5.0s.
In their place went a powerful performance package consisting of a Holley SysteMAX intake combo complete with 75mm throttle body, a set of Trick Flow Twisted Wedge aluminum heads, and a Lunati Voodoo cam profile. In fact, Lunati even supplied a set of its new 1.6-ratio roller rockers, a new timing chain, and a fresh set of hydraulic roller lifters. The SysteMAX intake has always proven itself a powerful design, especially when teamed up with a performance-cam profile designed to maximize power production up to 6,000 rpm. The optimized combination of runner length and cross-section, combined with a sizable plenum volume and generous throttle entry, continues to make the SysteMAX the intake of choice among 5.0 enthusiasts and racers alike. Naturally, the intake was fed not by the factory throttle body, but by a 75mm Holley unit designed to maximize airflow to the intake. Why bother with the intake if you're only going to restrict it with the stock throttle opening? In addition to the power gains, the SysteMAX intake and matching throttle body offered visual performance as well, as the Holley components were a tad higher on the cool scale than lifting the hood to reveal a stock H.O. intake.
Obviously, all that wonderful airflow supplied by the intake must find a way through the head ports as well. The E7TE heads were limiting the eventual power output of the motor, despite the benefit of having air forced through the intake ports by the HP turbo. Coming to the rescue was a set of heads from Trick Flow Specialties, which offered a multi-tude of benefits, not the least of which was lightweight aluminum construction. Right off the bat, the heads knocked more than 40 pounds off the curb weight, some of which was reinstalled with the slightly heavier SysteMAX intake (compared to the factory H.O.). In addition to the substantial weight savings, the aluminum construction improved the detonation threshold, an important consideration with a high-horsepower turbo motor. The trick Twisted Wedge design also improved the piston-to-valve clearance (compared to conventional inline heads with similar valve sizing), which allowed more lift and duration from our cam without fear of interference. It's paramount to check piston-to-valve clearance when installing a new cam profile and/or big-valve heads. The last thing you want is to ruin a perfectly good set of heads by having pistons permanently close all those shiny stainless steel valves.
The Trick Flow Twisted Wedge heads also offered improved flow rates compared not only to the stock E7TE heads, but also to the standard as-cast Twisted Wedge heads thanks to full CNC porting. The 185cc intake ports were a significant step up from the 170cc ports offered by the as-cast Twisted Wedge heads and a monstrous step from the tiny E7TE heads. The flow offered by the CNC-ported heads was right in line with the jump in port volume, as the 185 heads increased the flow rate of the as-cast heads from roughly 250 cfm to 300 cfm. The exhaust-port flow was equally impressive, as the CNC program stepped up the exhaust flow from 193 cfm to 231 cfm. These flow figures compare to just 160 cfm on the intake and 112 cfm from the E7TE heads. The numbers indicate that the 185 CNC Twisted Wedge heads from Trick Flow nearly doubled the intake flow of the stock heads and more than doubled the exhaust flow. Having successfully run 185cc heads (from various manufacturers) on many 302s, we were not worried in the slightest about excessive port volume having a negative effect on turbo response. As it turned out, the response was actually improved, and the new power offered by the heads, intake, and cam required the use of an even larger (and more powerful) turbo.
The final upgrade to our 5.0 turbo motor was a performance camshaft. Obviously, the turbo was working well with the stock cam, but there was much more power to be had with aggressive cam timing. We didn't want to go hog-wild with a solid-roller race cam, especially given our piston-to-valve worries, but we could improve top-end power, and power throughout the rev range, with the proper aftermarket cam profile. Given our concerns for piston-to-valve clearance, we went the conservative route.
Just because we couldn't run a wild cam profile didn't mean we weren't hoping for impressive power gains. The Lunati Voodoo lineup offered super-aggressive ramp rates to maximize the power gains offered for any given combination of lift and duration. The aggressive ramp rates helped improve the all-important average power production. As we've seen with this low-rpm motor, massive acceleration doesn't come from peak power numbers alone. The best motor combination is the one that offers the most power over the usable rpm range.
Given our clearance issues, we selected the smallest hydraulic roller profile offered in the Voodoo line. The hydraulic roller cam (PN 61010) offered a 0.541-/0.549-inch lift split, which allowed the motor to take full advantage of the CNC-ported Trick Flow Twisted Wedge heads. The duration figures were kept in check to ensure adequate piston-to-valve clearance. The Lunati cam featured a 211/219 duration split measured at 0.050 valve lift. Though not nearly as radical as some street grinds we have run on our test motors (on the dyno), this Voodoo profile represented a perfect street cam that offered an impressive combination of idle quality, driveability, and even fuel mileage, providing you can resist the temptation to explore the far side of the boost gauge on a regular basis.
Speaking of boost gauge, the Lunati Voodoo cam also worked exceptionally well with the single-turbo system from HP Perfor-mance. It's amazing how well a good, normally aspirated performance cam profile works on a turbo motor, this despite a lobe separation angle of 110 degrees. The cam was installed straight up using the new double-roller timing chain, something that was a necessity given the mileage on the (sloppy) factory timing gear. We also installed the fresh set of hydraulic roller lifters and new 1.6 ratio roller rockers supplied by Holley.
To say that upgrading the cam, heads, and intake was a success would be a serious understatement. This was perhaps best illus-trated by the fact that we could not compare the new Holley/Twisted Wedge/Lunati combina-tion to the factory counterparts at the boost level run in Part 2. You'll remember that we ran the boost up to a maximum of 16 psi with the stock components to coax high-10-second timeslips from the 200,000 Mustang. Attempting to run the boost this high with the new components took us to the flow limit of the standard 60mm turbo.
To illustrate the gains offered by the induction upgrade, we turned the boost down to just 10 psi and compared it to the same boost level with the stock components. Running the stock 5.0 motor at 10 psi resulted in peak numbers of 433 hp and 493 lb-ft of torque. Running the same boost level (actually an identical boost curve) with the new induction system resulted in some serious power gains. With the same 10 psi of boost from the HP turbo system, the modified 5.0 motor pumped out 575 hp and 607 lb-ft of torque. The new combination improved the power out of the stock 5.0 by a whopping 142 hp-that's what we call an improvement.
Once we generated numbers to illustrate the gains offered by the induction upgrade, it was time to see how much power was available with this new combination. Given the tremendous torque numbers being made, we were beginning to get nervous about the strength of the stock block but decided to press on with the project. Since we were effectively out of turbo with the standard 60mm unit (at 550 wheel horsepower), the guys from HP Performance decided it was a good time to perform an upgrade. Out came the 60mm turbo, and in its place went a larger 67mm unit, capable of nearly 100 extra horsepower.
Measured back-to-back at just 10 psi, the larger 67mm turbo increased the power output from 575 hp to 604 hp, though the smaller 60mm turbo was slightly more responsive in the lower rev ranges. Obviously, at elevated boost levels there would be no comparison, as the smaller turbo would continue to sign off, while the power climbed with the freer-flowing 67mm unit. With a bone-stock motor, the clear choice would be the smaller 60mm turbo, but there's a case to be made for the larger 67mm turbo on a modified motor once you get past the 550hp mark. For an honest 600 rwhp, there's no comparison, as the 67mm turbo is the only way to go. With the motor capable of producing a solid 100 more horsepower that it had when we posted high-10s, the question now is, is it capable of dipping into the 9s without splitting that fragile, stock 5.0 block right in half?
The boys from HP Performance promised to take the car to slightly sunnier Phoenix for a shot at the 9s with a stock bottom end. If they're successful, we'll be sure to let you know, but even if the stock block won't stand the abuse, we'd still call Project Pro Stock a smashing success.