Tom Wilson
December 1, 2004
Looking as if it grew there, the Kenne Bell supercharger for Mach 1s and '99-'01 Cobras is a great fit to these exciting Four-Valve engines, as long as boost is kept at 9 pounds or less. More boost requires a prepped short-block.

When Ford bolted the Eaton Roots-type supercharger on the '03 Mustang Cobra, the '99 and '01 Cobra owners developed blower envy faster than a top fueler pegs a boost gauge. And why not? The late-model Cobra is a real battlewagon, and it has been the performance benchmark for Mustangers since the first one rolled out of a showroom.

Thus was born the current climate where early Four-Valve Cobra owners are quick to add forced induction, seemingly in an effort to keep up with their '03-'04 counterparts. Adding a blower does make a great engine, as the multivalve 4.6 is eager to handle huge air volumes at entertaining rpm levels. For years, the workable solution has been to add a centrifugal supercharger, which works wonders on the upper midrange and truly sparkles at the top end.

But now Kenne Bell has worked up a kit for the '99 and '01 Cobra (as well as the similar Mach 1) engines using an Autorotor Twin-Screw style supercharger. Broadly speaking, the new kit is Kenne Bell's existing '03 Cobra kit (see "Snake Bit Hit," Mar. '03, p. 71) modified to fit the earlier cars. Of course, the '03 Kenne Bell kit benefits from the base car already having a supercharger, so the '99-'01 version includes many more pieces-and yes, some dollars to the bottom line-to support the supercharger.

As is the Roots-type blower on the '03 Cobra, the Lysholm-screw blower of Kenne Bell's is a positive-displacement device, meaning it delivers big boost from just off-idle all the way to redline. That, in turn, means the Kenne Bell blower pumps out the same sort of muscular power as the '03 Cobra. But thanks to the greatly increased efficiency of the Lysholm screw, the Kenne Bell blower puts out much more power than the Eaton-built Roots-type blower. It would seem to be the best solution for those looking to make late-model Cobra showroom power from earlier cars.

Our subject engine was outfitted with a full suite of Kenne Bell options, including a 90mm mass airflow sensor and intercooling as indicated by the air-to-water system's fill tank.

If there is a fly in this ointment, it would be the internal specifications of the '99-'01 Cobras. These engines do not use the forged pistons and studly H-beam connecting rods or the iron block of the current Cobra. This means careful attention to detonation control is absolutely mandatory, as the mechanical strength reserve is less with the earlier Cobra engines. Furthermore, Kenne Bell cites a 9-pound boost limit on the stock Cobra and Mach 1 engines to avoid mayhem simply from increased mech-anical stresses. Any more boost requires a prepped short-block with the heavy-duty forgings.

One bright spot shines for early Four-Valve Cobra owners compared to their '03 brothers: a knock sensor. Located on the block, the knock sensor pulls ignition timing when it "hears" the vibration caused by knock or ping. It's a handy device, to say the least, but it's still not the sort of gadget you want to stake your Four-Valve's life on. There's no substitute for an adequate fuel system and intelligent engine-management software.

In fact, avoiding detonation is all about controlling combustion temperature, and the two main tools for that job are not getting overly excited with the ignition timing and supplying plenty of fuel at all times. Kenne Bell controls timing with its electronic chip. Improving the fuel system is done with the the company's Boost-A-Pump electronic augmenter on the base kit, and larger in-tank pumps and the Boost-A-Pump with some of the higher output kits. Eventually, when getting into the higher-dollar, high-output systems, Kenne Bell heavily recommends pitching all the extra pumps and simply updating to the '03 Cobra fuel system. That means purchasing an '03 Cobra fuel tank and its two in-tank fuel pumps. This gives unquestioned fuel delivery with OEM levels of quiet and fit. The parts required are as follows.

One huge plus for '99 Cobras and Mach 1s is a knock sensor. Due to the different sound signature of the Twin Screw supercharger and its drive, Kenne Bell has to recalibrate the knock sensor to work with its kit. The knock sensor is also remounted from the cylinder block to a cylinder head.
Description{{{Ford}}} Part No.Retail Price
Fuel Tank2R329002-AA$424.58
Fuel Pump2R32-9H307-AB$450.00 (incl. two-pump assembly)
Fuel DriverXR32-9D372-AC${{{90}}}.10

The cost for these parts totals about $1,000 after you add in sales tax, but they will mean the end of any fuel-delivery issues at this power level.

Kenne Bell stuck close to '03 Cobra practice when packaging its screw blower to the Four-Valve engine, both because it is the obvious packaging solution and because Ford has already plowed some tough ground in that regard. No surprises then that the Kenne Bell '99-'01 kit uses a stock '03 Ford Cobra intake manifold to provide a proven, no-hassle, bolt-on interface between its supercharger and the Four-Valve engine.

Kenne Bell's intercooler pump is tightly packaged at the bottom of the system's fill tank. Jim Bell used to engineer for Rain Bird, so he knows how to move water around hoses and pipes.

Unlike Ford, Kenne Bell offers its supercharger in either nonintercooled or intercooled form. The less expensive, nonintercooled version has proven most popular because it easily exceeds '03 Cobra power (how much tire spin do you need?) for roughly $2,200 less than Kenne Bell's intercooled option. This is possible because the vastly more heat-efficient Lysholm Screw Autorotor used by the company delivers much cooler discharge air than the Roots-type blower on the '03 Cobra. And, as you'd guess, Kenne Bell simply fits the efficient '03 Cobra intercooler heat exchanger to the Cobra intake, although the fill tank pump, hoses, fittings and such are Kenne Bell parts.

Of course, there are several important details and options to the Kenne Bell kits for the early Cobra and Mach 1. Among these is a 90mm mass air meter, a cold-air kit, a larger throttle body, pulleys, gauges, pumps, and so on. To sort through the offerings, we'll review the kits here and let you choose the options as listed in the sidebar on p. 78. The kits, and logical options, are as seen in the sidebar on this page.

Clearly the big step is intercooling. Without it, the 5-psi kit makes 400 rwhp, distinctly more power than a stock '03 Cobra at 365-370 rwhp, and it'll set you back $4,299 plus installation. While only the beginning of Kenne Bell Four-Valve kits, this kit would be fine for most of us. This is also the limit for the stock 24-lb/hr injectors and the stock mass air meter, so the base kit is a definite cost-saver too. Note that the mass air meter doesn't run out of airflow at 400 rwhp; it runs out of calibration. Kenne Bell cures this with its 90mm mass air, which is calibrated to run far into the night.

Naturally, you'll eventually want to step up your program with a cold-air kit and a 90mm mass air meter to reach the 426-rwhp level. It's more expensive to buy the cold-air kit and the big mass air meter separately, as there is a discount built into the kits, and you'll also need a recalibrated Kenne Bell Switch Chip at that time, along with larger injectors-probably 42-lb/hr units that will hang in there up to 550 hp. So, if you're looking at the base kit and you think you'll eventually be hungry for more, our advice would be to stretch for the $4,599 kit if possible. That, or go for the easier 400 rwhp for $300 less and be content with that-which is difficult to do.

To control the rapid coolant temperature rise during boosted operation, Kenne Bell supplies a 160-degree thermostat. This gives an extra cooling margin for the intermittent full-power of operating this kit.

For a major step up of $2,200, intercooling awaits. The 9-psi intercooled installation is just as compact on the engine because the heat exchanger lives under the supercharger, but there is more to the installation due to the heat exchanger that must be hung and plumbed low across the radiator opening. The cooled discharge air allows more aggressive boost, however, and given a host of Kenne Bell breathing and fueling aids, it kicks up the power to mid-400hp range. And, really, this is where the party stops with the early Four-Valve Cobras and-especially, we'd add-the Mach 1s. These short-blocks can take only so much, and then it's time for a built aftermarket short-block.

By the time you obtain an all-forged short-block, and preferably with an iron block, you've effectively home-built an '03 Cobra. A suitable short-block is around $3,200 these days, to which you can add $6,800 worth of supercharger, your existing cylinder heads, and end up with about 100 more rear-wheel horsepower than a stock '03 Cobra. This will cost $10,000 plus-the plus being whatever labor you contract to assemble everything. By comparison, Ford Racing Performance Parts lists complete '03 Cobra engines for $11,999. Call it 12 grand, and keep the change.

Electronic tuning doesn't get much attention in articles such as this one, but it is absolutely vital. Kenne Bell had the foresight to bring its electronic tuning in-house years ago, so it has total control over how its supercharger kits run. The company's standard calibrations strike us as combining just the right amount of caution and aggression-its race-only calibrations are optimized for high-octane race gas. These are combined in Kenne Bell's two-position Switch Chip. Both positions give the same ignition timing, but the regular drive-around-town Power setting uses a safe 11:1 air/fuel ratio, while the Shootout setting leans to 12:1. It will give up to 20 extra horsepower, but requires high-octane fuel.

As for installing the Kenne Bell kit, there is plenty of wrench work, but some of the nasties commonly associated with superchargers are avoided. For starters, Kenne Bell assembles all the major units. The supercharger comes bolted to the intake manifold, along with the bypass valve and other associated hardware. Ditto for the intercooler. The whole shebang is well calibrated (hot rodded calibrations for race gas use are available), so all the user needs to do is bolt the large assemblies to the car. There are no oil feed lines to run, and there's no punching the oil pan. Kenne Bell's huge instruction manuals are topnotch as well, profusely illustrated with pain-staking, bolt-by-bolt guidance. While an extensive job, an enthusiast with a moderate amount of sockets and screwdrivers can handle this install.

And what do you get when you're finished? Darn near an '03 Cobra that more than hangs in there at the top end with the base 5-psi kit and the same feeling-but with distinctly more oomph-as you add boost (easily accommodated by the Kenne Bell supercharger, unlike the Eaton/ Roots on the '03 Cobra). The Twin Screw supercharger is quiet, with only the most muted of whistles and gear noises occasionally coming through. Boost comes on with full throttle no matter the rpm, giving the engine that torquey, big-block feel. Tire frying burnouts are offhandedly easy, satisfying corner exit thrust is at the ready for the corner-carving crowd, and useful maneuvering power on the freeway is more easily had without a downshift. The engine is still only 281 ci, so it helps to have some rpm on the clock, but mainly a Kenne Bell blown Four-Valve has a ton of torque compared to the weak naturally aspirated configuration.

And don't forget the top end. While the positive-displacement Twin Screw doesn't ramp up power like a centrifugal, with a minimum of 400 rear-wheel horsepower on tap, you still won't overlook its top-end charge.

Kit NameBlower SizePulley RibsBoost (psi)Inter-CoolerPower RatingOptionsPrice
5-psi Nonintercooled1.7L65No400 rwhpNone$4,299
5-psi Nonintercooled1.7L65No426 rwhpCold-air kit, 90mm mass air$4,599
9-psi Intercooled 1.7L 6 7.5 Yes449 rwhpCold-air kit, BAS, inlet upgrades, 90mm mass air$6,799
9-psi Intercooled1.7L69Yes462 rwhpSame$6,799
9-psi Intercooled2.2L813-21Yes{{{600}}}+ rwhpSame$6,999

Kenne Bell Options
There's no way one or two simple kits will satisfy every market demand, so Kenne Bell offers several options for the early Four-Valve Cobra and Mach 1 kit. These are sold as stand-alone items, and they are also included in the more sophisticated kits. Note that the Boost-A-Pump on-demand fuel pump enhancer and Switch Chip are standard with every kit.

OptionDescriptionPriceNotes
Cobra cold-air kitIn-fender air filter and hose$139Recommended w/90mm mass air
Cobra 90mm mass air{{{Ford}}} '03 Cobra 90mm mass air$147Cold-air kit required
Big Oval throttle bodyOval inlet throttle body$359Not needed until 450 rwhp
Boost-A-SparkKB ignition amplifier$199 
In-tank 217 L/hr pumpHigh-capacity fuel pump$125317 L/hr w/Boost-A-Pump
7.5-in crank pulleyLarge-diameter crank pulley$125Gains apprx. 3 lbs of boost; stock is 6.5 in
Supercharger pulleysSix-rib or eight-rib$349Six-rib = 4-13 lbs/{{{Eight}}}-rib = 13-20 lbs
Pod or pillar mountFor boost/fuel pressure$ 30
Fuel-pressure gaugeElectric instrument$146
Boost-pressure gauge $ 55
Dyno Report
 Stock '03 CobraKenne Bell 5-psi Non-
intercooled
3 7/8-in Pulley
Kenne Bell 5-psi Non-
intercooled
3 7/8-in Pulley, Cold Air
RPMPowerTorquePowerTorquePowerTorque
2,500166349151318152319
2,750187356169{{{323}}}170325
3,000207363187327186326
3,250256365203329205332
3,500243364221332223334
3,750262366237332{{{240}}}336
4,000280368255335258339
4,250295365272336276341
4,500310362288337296345
4,750323356307339313346
5,000336353324340330347
5,250347347337337347347
5,500358342349333359343
5,750365332359328375342
6,000361316373327384337
6,250350294383322394331
6,500326263389315404327
6,750n/an/a397309411320
7,000n/an/an/an/a420315
 Kenne Bell 5-psi
Nonintercooled
3 7/8-in Pulley,
w/Cold-Air Kit,
90mm Mass Air Meter
Kenne Bell 9-psi
Intercooled
3 3/8-in Pulley
Kenne Bell 9-psi
Intercooled
3 1/4-in Pulley
Kenne Bell
9-psi Intercooled,
3 1/4-in Pulley,
94-Octane Gas
RPMPowerTorquePowerTorquePowerTorquePowerTorque
2,500153320178374186390182382
2,750170324{{{200}}}381209399204390
3,000188330220384230403225395
3,250206333243392253409248400
3,500224336262394275413269404
3,750{{{240}}}336280392296415292408
4,000260340303397317416314412
4,250278343325401339419332410
4,500299348339395358417351410
4,750316349363401378418371411
5,000335352382401401421392411
5,250354354400400418418414414
5,500366350411393432412432413
5,750378345421385443{{{405}}}444405
6,000398341436382453396455399
6,250396333445374461387461387
6,500402325456368469379470380
6,750417324460358472367480373
7,000n/an/a462347462346477356

All data was obtained on Kenne Bell's in-house DynoJet-a well-instrumented dyno we've used before on an '01 Cobra with only a MagnaFlow after-cat. The dyno data is a summation of the full dyno printouts, therefore some of the peak numbers do not exactly match those cited in the text. All numbers are valid, however, even if they do not appear in the lists here.

  • The benchmark of all late-model Fords and a rocket from the showroom floor, the '03 Cobra lives life with a target on its back, but what a quiet, smooth, OEM reliable accomplishment from Ford SVT. Huge torque from low to high, and just a bit of disappointment at the top of the tach after the midrange charge is what you feel.
  • As bare as Kenne Bell makes 'em-well contained, safe as houses on 91-octane pump gas-the basic 5-psi kit is slightly outgunned by the higher-boost '03 Cobra on the way to all-hanging-out rpm, where it surges ahead.
  • Adding a conical air filter and cold-air kit shows the stock air filter, box, and hose are slight restrictions at this power level. Kenne Bell uses this same cold-air kit on many combinations and found it makes power on all of them because the Twin Screw blower really doesn't like restrictions on its inlet side.
  • This power level is where the stock 80mm mass air pegs, meaning it has run out of measuring capability. Adding the 90mm mass air with its recalibrated, wide-range measuring ability cures the problem and pays off powerwise beginning at 5,000 rpm.
  • This first of the intercooled combinations really puts out 8 pounds of boost, but Kenne Bell calls it a 9-psi kit anyway. It's a big step up in price from the nonintercooled option, but a big step up in power too. We'd sleep better at night with this supercharger pulley on our Twin Screw than the "9-pound pulley" in the next test.
  • Oh, what a pound of boost will do. This is the same configuration as the previous test, but with a 1/8-inch smaller supercharger pulley for a true 9 pounds of boost. While still running on 91 octane, this is the last stop for the pump-gas gravy train and is therefore the practical limit for a street car. It's also plenty far out on the grenade pin-pulling contest with NA Cobras and Mach 1s.
  • Here's the previous combination hot rodded with a tad more ignition timing and running on 94-octane fuel. This might have some relevance to those with access to slightly higher-octane fuel, or fuel doping at the track with a hotter combination in the "Shootout" portion of their Kenne Bell Switch Chip. It's an incremental gain-useful for running against the clock but not worth the effort or risk on a street car.