Head Full of Steam
Our Enigmatic Mustang Power Brokers (at Last)

By Ro McGonegal

From the outset, our ’97 4.6L SOHC Mustang had more or less ignored the cursory bolt-on parts we’ve put to it.  The initial chassis dyno test revealed 180 hp at 4,200 rpm and 250 lb-ft torque at 3,400 rpm.  In an effort to augment those meager figures, we added underdrive pulleys (10hp), removed the silencer from the air box, installed a K&N filter element (5hp), and finally attached a Borla stainless steel Cat-Back exhaust system (5hp at power peak and 15hp at 5,000 rpm).  Proprietary items included a B&M Ripper shifter and 3.73:1 gearset (see “SOHC ‘Stang: The Sequel,” Sept. ’98).

In all, we conservatively estimated the work to be worth at least 20hp—rather unjust compensation for the expense and the effort involved, we’d say.  Disgruntled, we decided to attack the Mustang’s suspension in hopes of a tangible reward (petulant swine, ain’t we?)  We outfitted it with Eibach Pro Kit lowering springs (1.5 inches), HP Motorsport camber plates, Koni adjustable shock absorbers, and sticky Yokahama 40-series A520 rubber (255 inches and 285ZR) on 9.0- and 10.0-inch-wide forged Fiske Mag wheels (see “Looker,” July ’99).

A few months behind the wheel of the corner carver showed us the conversion’s weak points, ones we summarily ignored in lieu of out excitement over the Mustang’s enhanced handling capabilities.  With the current backspacing, the wheels are the maximum width, and maybe there’s just a little bit too much of a good thing going on here.  The 285 tires are a hair to wide and occasionally rub the fenders when the suspension compresses quickly over uneven pavement. 

At less than highway speed, the ride is harsher than stock, but the faster the Mustang goes, the better the chassis feels.  We’re still experimenting with shock valving, but there’s strong suspicion that the A520’s extremely stiff sidewalls are the culprits.  As an example, our ’96 car ran an identical suspension combination save for the tires, which were 245  and 275 BFG’s, and returned a smooth ride that felt better than stock.  So there is a real trade-off going on here.  While the Mustang’s cornering and handling ability is impeccable and frighteningly high, we’re not apt to use this capability daily—except in an emergency situation.  Most of our driving is done on the freeway, where comfort and smoothness reign supreme.

So there we were, all spiffed up and no place to go.  Though the slam job and the fat rubber had upped the intimidation factor ten-fold, we were still wheeling a stylish, red paper tiger, quite certain that it would only be a matter of time before a 5.0L (or worse yet, a snotty Honda) took us out.  Arrgghh!  We grabbed our recalcitrant pony by the ferlocks and dragged it out to Mark Sanchez’s Advanced Engineering West to get the goods.  Sanchez is SVO’s tacit performance arm in SoCal and was ready to apply the Ford Motorsport parts to the top of the engine.  Engineered as a combination, these components are most effective installed as a package (see “SVO Hot  Links,” May ’97).  Included are a revised intake manifold and throttle body, cylinder heads with larger valves (intakes increase from 1.73 to 1.84 inches, and exhausts from 1.33 to 1.41), steel “headers,” and an ECU that tolerates this tomfoolery.

As we chatted with Sanchez, we spied a Roots-type supercharger similar to the Eaton unit that SVO markets for the 4.6L single-cam engine.  The curious thing about it was the liquid-to-air intercooler atop the blower assembly.  “Yeah,” said Sanchez, “Allen Engine Development makes it.  That one came off a Thunderbird, but it’ll go on the Mustang, too.”  Then it occurred to us that most people would probably go right for the supercharger anyway, so let’s run the Allen blower first, with no other changes.  When we’re through with that part, we’ll come back with the full-on SVO treatment but without the blower.  For the final installment, we’ll put the Allen combo to the SVO parts along with Sanchez’s custom ECU calibration and then commence to find some lips sorely in need of slapping.

Prior to the conversion, Allen Engine’s Jim Sanborn and Scott Graves baselined the engine on Alex Borla’s roller dyno.  The result was 183 hp—AED had removed the underdrive pulleys prior to the dyno test; where the “increase” from the less restrictive air intake and the Borla Cat-Back exhaust went is anyone’s guess.  Maybe it was the hot weather.  After the conversion, the little engine that could produced 100 additional horsepower and put another 54 lb-ft of torque in the rear wheels.

Because it cools the intake charge air by approximately 60 degrees F at wide open throttle (200 degrees F into the engine), the liquid-to-air intercooler (50/50 water-glycol) effectively expands maximum boost to 8 psi (the SVO unit produces 6 psi and is not intercooled).  Centrifugal blowers (e.g. Vortech, Paxton, ATI) customarily provide only 1-2 psi of positive manifold pressure at 3,000 rpm, with the big numbers coming as the revs increase.  By stark comparison, the Allen puffer provides full boost at a mere 1,800 rpm.  Which one would you rather drive on the street?

Regardless, the supercharger produced the first truly satisfying results from our enigmatic pony.  It makes the engine happy and robust, and under the whip, it revs quickly and cleanly to 6,000 rpm, a joyous departure from the it’s-all-over-at-4,200-schtick we’ve lived with for two years.  That’s why we were sure it was Christmas morning the first time we stomped the loud pedal.  Acceleration is immediate and very linear.  Though the engine feels doubled in every gear, from the middle of Second on up it gathers speed, exponentially it seems, hurling you down the road with prejudice.  Undoubtedly, the mechanical advantage of the 3.73:1 axle ratio has a positive effect on this phenomenon.  The blower howls softly and is reminiscent of the sound of a Top-Fueler makes as it nears terminal velocity, and provides just the right mix of the aural and the visceral.  The loud pedal becomes addictive; not so much for the obvious but rather for the emotional joy it brings. 

Until you get on the throttle, the supercharger is absolutely invisible.  Since the Allen CARB-approved conversion is designed to work within the parameters of the stock computer and the stock engine components (factory timing, 19 lb/hr fuel injectors, and so on) all driveability circuits remain as such.  With three months on the conversion, we’ve encountered nothing but pure, saturated fun.  The car feels whole; we’ve found the missing piece and wonder what took us so long.  Credit must go to a very well engineered kit, a combination that includes the blower assembly and appropriate intake manifolding, the liquid-to-air intercooler, and the in-tank fuel pump.  Intercooler coolant is separate from that of the engine and circulates continuously via a heat exchanger and an auxiliary pump mounted next to the radiator on the driver side of the car.

A thousand millenniums ago, LACR was below sea level, but now it’s more than 2,500 feet above it.  As reference, our unblown ’97 turned a best of 15.06/90 (corrected) with the previous round of bolt-ons.

Though the fat A520’s are tenacious in the turns, their compound and construction are worthless on the dragstrip.  In their stead, BFG 275/60R15 BFG  Drag Radials inflated to 20 psi.  A bit of experimentation proved that a wet burnout followed by a long dry one prepped the tires for best possible bite.  We established a baseline (three 14’s in a row with 2-second  60-foot times), and then put a couple of bags of ice on the intercooler.  A half-hour later, we ran again, recording a best of 13.9 at 98.64.  Converting these figures for LACR’s altitude accounted for an elapsed time of 13.44 seconds and a trap speed of 101.85 mph—quite consistent with the documented power increase. (Note: This performance was produced at 75 degrees ambient, was approximately 30 percent humidity, and no wind.  The driver launched at 2,500 and shifted at 5,500 rpm).