5.0 Mustang & Super FordsHow To Engine
SN-95 Mustang Supercharger - Winds Of Change
We Change Our Pushrod SN-95 For The Better With The Horsepower Hurricane Of Paxton's Novi 2000 Supercharger
Horse Sense: Paxton's Novi 2000 has proven equally at home on the street or racetrack. Despite a helical-cut gear design that makes it nearly silent on the road, the Novi is also capable of moving up to 2,200 cfm of air, at impeller speeds up to 55,000 rpm.
Between 1987 and 1993, the aftermarket had it relatively easy when developing 5.0 supercharger kits. Despite ongoing detail changes, nothing much changed or moved around in the Fox Mustang's engine bay during that span. Lift the hood on a fuel-injected Fox and you'd be hard-pressed to tell if it's a '93, a '91, or an '89.
Then, in 1994, the SN-95 came along and spoiled all that perennial packaging consistency. Its lower hoodline dictated many underhood revisions, especially when it came to engine front dress, and it was cluttered with items such as electric fan controllers and ABS brake modules. Though the 5.0 remained its hearty old self internally, much of the stuff that hung from it, or sat on top, had to be modified or moved around to fit. This sent centrifugal blower manufacturers back to their CAD screens and CAM stations to design and fabricate all-new mounting bracketry, ducting, and miscellaneous hardware-all this for just two model years of production. Luckily, the guys whittling out the superchargers thought it worth the effort (maybe because they didn't know the modular was just around the corner).
We happen to have one of the last of the 5.0s in our fleet, a handsome but porky '95 GT convertible. Over the years, it's been gradually improved with the usual bolt-ons including exhaust, heads, and intake, but always with an eye toward eventual forced induction-its weighty 3,650-pound carcass needs all the help it can get. This gave us a perfectly rational excuse to have Joe Silva at J&P Performance install the Novi 2000 kit that Paxton Automotive developed specifically for the '94 and '95 pushrod SN-95s.
As always, we can't overstress the importance of taking a realistic view of your Mustang's ultimate use in deciding a compatible combination. The upgrades previously installed on our topless GT included Edelbrock's Performer heads and intake (ported for the street by J&P's Paul Silva), along with long-tube headers and a 2.5-inch catalyst-equipped H-pipe, from MAC. All were chosen for both blower and emissions friendliness, and for the same reasons the car also retains its factory cam.
That said, our convertible's role in life as a street-going corner carver was also an important consideration when we chose its relatively mild 3.55 gears and curve-happy Torsen T-2R differential. In other words, this is certainly no drag car. In fact, it's probably been down the strip less than a half-dozen times in as many years. So our goal was to create pulse-raising power and throttle response in typical street-driving scenarios-but we had no desire for an undriveable pig, no matter how fast.
In view of this road-going lifestyle, serious consideration was given to going the Roots or screw supercharger route for the superb, low-rpm grunt the positive-displacement blowers exhibit. In the end, we just couldn't resist the expandability of the Novi 2000 centrifugal, which, as shipped, is said to huff out around 8 psi but has the ability to deliver way more boost pressure with the simple change of a pulley. You know-just in case we ever want to seriously test the limits of our 5.0's stock bottom end.
The SN-95 Novi 2000 kit includes everything necessary for installation on a bone-stock 5.0, including a larger in-tank pump and a fuel-control unit to trick stock 19-lb/hr injectors into delivering sufficient combustible juices. Our car, however, was already producing 285 hp at the wheels and had just about maxed out its stock injectors, so we opted for a set of ACCEL's 40-lb/hr injectors, together with a Pro-M 80mm plastic mass air meter to replace our existing 75mm Bullet. Thus equipped, we thought we were reasonably prepared, but you always forget something.
Snafu On The DynoBefore the Novi 2000 came onboard, our '95 GT was good for 284.9 hp and 313 lb-ft of torque at the rear wheels. After our 12-hour install, the freshly blown ragtop fired right up and idled around the corner to Dynopower Services, where we strapped it down on Dynopower's Dynojet 248C. We were a bit surprised how well it did start and idle, con-sidering we were running without any chip at all. Clearly, the calibration by Pro-M of the company's big mass air meter was absolutely bang-on for our ACCEL 40-lb/hr injectors.
Since we had no chip, Joe set our distributor to the factory 10 degrees initial timing, and we tried letting the stock EEC IV programming dictate total ignition timing for a trial run. Since the factory timing curve assumes 87-octane fuel and we had 94-octane-plus booster-in the tank, we thought we might get by, despite the blower's boost. As usual, we were wrong. Once the Novi started doing its thing, Joe heard detonation and immediately stopped the run. He then unplugged the SPOUT connector (interrupting the timing control signal from the EEC so that no advance beyond initial is possible) and set the distributor to 22 degrees-initial and total. We knew this would hurt power and torque, but we had no choice in the absence of any form of boost retard. Conclusion number one: We need boost retard.
On the second attempt at a run, the engine wouldn't rev past 4,500 rpm, and Joe noticed the car's volt meter was reading low, meaning our relocated alternator wasn't charging (this turned out to be a suddenly faulty voltage regulator). So we hooked up a battery charger and tried again. It still wouldn't rev, whereupon Joe announced that the boost must be "blowing out" our spark, despite having gapped our new spark plugs tighter than normal. So he ran back to the shop, grabbed a capacitive discharge ignition box off the shelf, and temporarily wired it up. Conclusion number two: We need an igni-tion box.
We should also mention that we had temporarily plumbed in an adjustable fuel-pressure regulator, which Joe set at 50 psi. And since we don't yet have them in the car, boost and fuel-pressure gauges were attached remotely-their respective lines were trailing out from underhood to gauges in the hands of a couple bystanders who were drafted into eyeball service. Under these comically bizarre circumstances, Joe made what turned out to be our final pull-successful this time, at least until our volunteer on the fuel pressure gauge started motioning furiously because he saw pressure drop suddenly from 50 to just 28 psi.
We don't know whether this drop in fuel pressure was due to a deficiency in some of our factory fuel components, such as rails or lines, or something as simple as a dirty fuel filter. With a potentially lean condition, the run was immediately aborted at just 5,700 rpm, yet the Novi had already approached nearly 10 psi, and rear-wheel horsepower was measured at an impressive-especially for the goofy circumstances-435.5 hp, with torque registering at 421.5 lb-ft. Not wanting to risk our completely stock short-block, and faced with looming deadlines, we packed it in. Conclusion number three: We need to check and likely upgrade our fuel system.
So, we're not done yet. In an upcoming issue we'll address our fuel, spark, and tuning shortcomings and have another shot at it. In the meantime, we'll simply have to be good boys and limit ourselves to half-throttle. Bummer.