Agustin Jimenez
Technical Editor
August 21, 2015
Photos By: Ricardo Topete

There’s an old saying when it comes to building a fast car: “There’s no replacement for displacement.” But we beg to differ. While adding cubic inches is a great option for making power, adding boost can make any mildly built engine scream like Godzilla with a thorn in his foot. Of course, it never hurts to start off with a great platform that is proven to make serious horsepower, and what better than a 2003-2004 Mustang SVT Cobra, aka the Terminator Cobra?

The Terminator Cobra rolled out of the factory packing a supercharged 4.6L DOHC engine that made music to the tune of 390 hp. The engine was very different from the previous models in that it featured a number of improvements, such as a heavy-duty cast iron block with stronger internals consisting of forged Zolner pistons and Manley H-beam connecting rods with a revised wristpin oiling hole to help the new engine withstand the force-fed power of the Eaton M112 Roots supercharger, which made 8 pounds of boost.

These cars were truly the kings of the road, but as with all good things, we can never have enough. It was only natural for the aftermarket to step up to the plate and deliver performance parts that made them go like stink. Naturally many enthusiasts quickly embraced the aftermarket’s offering of bolt-on superchargers, like Kenne Bell’s 2.4L Twin Screw supercharger. Of course, it wasn’t long before horsepower junkies were overcome with the need for more power.

So what do you do when you already own a great supercharger but you aspire to four-digit horsepower numbers? You bite the bullet and list your old huffer on the classifieds and hope your significant other doesn’t bat an eye! The best part about our horsepower-junkie friend’s addiction to boost is that one can easily pick up a seasoned supercharger for one hell of a smoking deal and make more tire-shredding horsepower on a modest budget.

That’s exactly what Joel Rivera had in mind when he picked up a used 2.4L Kenne Bell Twin Screw supercharger off of the online classifieds. He wanted to give his drop-top Terminator Cobra a little attitude adjustment. The factory Eaton M112 supercharger was already equipped with a smaller-diameter pulley, which was paired with some mild bolt-ons to help the stock engine pump out 458 hp to the rear wheels. Of course, it just didn’t seem right to call it good enough, so Joel enlisted the help of GTR High Performance in Rancho Cucamonga, California, to help his Cobra lay down significantly more horsepower as well as some faster track times with his new-to-him 2.4L Kenne Bell supercharger.

Follow along as we show you what’s involved in slapping on a used 2.4L Kenne Bell supercharger onto a budget-built Terminator Cobra that won’t blow through your wallet.

1. When it comes to making big power with a Terminator Cobra, nothing’s quite like swapping to a bigger blower. This 2.4L Kenne Bell Twin Screw supercharger was just the ticket to get this wild steed to power levels above 600 rwhp. To complement the looks and performance of the Kenne Bell supercharger, owner Joel Rivera used a BilletFlow Terminator throttle-body as well as an SCT Performance Big Air mass air meter and housing. Of course you can’t forget the fresh Kenne Bell synthetic supercharger oil to keep the Twin Screw supercharger humming like a song.

2. Before the guys at GTR High Performance delved into the 2.4L Kenne Bell supercharger swap, we decided to strap this steed down to find out just how much power the stock Eaton M112 supercharger was making with the common smaller pulley swap as well as a set of JBA headers that Rivera picked up for cheap through an open box online deal. Our baseline test for this car yielded an impressive 458 rwhp at 6,150 rpm, while our torque output was a stout 460 lb-ft. Interestingly enough, the torque band was fairly flat between 2,500 rpm all the way up to 6,000 rpm where it finally dropped below 400 lb-ft of torque.

3. Pedro Pasoldan (on the left) and Ricardo Topete (on the right) of GTR High Performance wasted no time disassembling the factory supercharger system. Pasoldan removed the factory throttle-body plenum as well as the intercooler coolant supply hoses while Topete got the injector harness and vacuum hoses out of the way to make way for the supercharger’s final voyage before being shelved indefinitely.

4. Once the intake plenum was unbolted, the supercharger unit was lifted high enough to slide a short 2x4 block of wood under the plenum to make it easier to remove the intercooler coolant-supply manifold.

5. With the intercooler coolant manifold freed, the stock supercharger can be unbolted from the intake plenum and removed.

6. A quick yank and the guys at GTR High Performance had the factory supercharger jumping out of the engine bay to make room for something bigger and better.

7. With the supercharger removed, Topete was able to focus on cleaning the supercharger mounting surface on the intake plenum. The intake plenum is retained with the 2.4L Kenne Bell supercharger, so be sure to clean off any old gasket material that might be left behind.

8. Take care when handling the factory intercooler if you are reusing it like we did with the Kenne Bell 2.4L supercharger. It’s also worth mentioning that the 10 bolts that hold the intercooler onto the supercharger are notorious for snapping when being removed. One neat trick is to add a little heat to the bolts with a propane torch to help the bolts break loose without snapping in half.

9. Here you can see the business end of the Eaton M112 supercharger. While the supercharger helped deliver decent power thanks to a smaller-diameter supercharger pulley, it had reached its performance limit.

10. A nice utility blade will allow you to scrape off most of the excess RTV silicone left behind on the intercooler.

11. Right off the bat, it’s easy to see the difference in size as well as aesthetics between the Kenne Bell 2.4L Twin Screw supercharger and the Eaton M112.

12. Make sure you apply a small bead of RTV silicone on the Kenne Bell supercharger before dropping in the factory intercooler. Keep in mind that the intercooler bolts are only torqued down to 48 lb-in (that’s the equivalent of 4 lb-ft) so it’s a good idea to use a pound-inch (aka inch-pound) torque wrench.

13. Since the larger blower allowed us to venture into big power territory, the stock injectors just weren’t up for the task of our new fuel demands. Luckily, Joel was able to pick up a set of Ford Racing 80-lb/hr injectors for a measly $250 on eBay.

14. Topete carefully installed the new Ford Racing injectors into the intake manifold to help feed this boosted snake’s engine.

15. With the injector upgrade out of the way, Topete installed a Kenne Bell Boost-A-Pump in the trunk of the Terminator. The Boost-A-Pump allows the stock in-tank fuel pump to deliver the extra volume of fuel needed with the upgrade.

16. Once our fuel delivery issues were wrapped up, Topete went ahead and added a bead of Motorcraft gasket sealant to the supercharger seal as well as the mating surface on the intake manifold.

17. It helps to have an extra set of hands when dropping in the Kenne Bell supercharger, but just in case you’re working on your own, be mindful of any vacuum hoses or other objects that could get pinched between the supercharger and the intake manifold.

18. Once you’ve mated the supercharger to the intake, go ahead and slide the block of wood back in under the intake manifold so you can install the intercooler coolant-supply manifold.

19. The next step is to snug down the bolts on both the supercharger and the intake manifold.

20. The intake bolts are torqued to 89 lb-in (not lb-ft) and then tightened 90 degrees.

21. With the new supercharger properly installed, the coolant hoses can be connected and the degas bottle can be installed into its stock location.

22. The owner of the Cobra was able to pick up a BilletFlow throttle-body from a Mustang forum member for less than half the price of a new throttle-body.

23. In order to take full advantage of the 2.4L Kenne Bell supercharger, an SCT four-bank ECU chip was purchased for the sum of $75 off an online forum member. The SCT chip allows the stock computer to accept a tune customized for the type of use the car will see.

24. The final step was to install the new supercharger drive belt while checking for proper tension and fitment.

25. With the hard part out of the way, we moved onto the meat and potatoes of the 2.4L Kenne Bell supercharger swap. The guys at GTR strapped the budget boosted Terminator onto the Dynojet dynamometer to see how far we could push the power on pump gas.

Dyno Runs

Here you can see our official dyno pull numbers. You’ll notice that the first run (RunFile_001) is our initial baseline with the stock Eaton M112 supercharger. Once we finished the Kenne Bell supercharger install, the guys at GTR High Performance swapped in a 3-inch-diameter supercharger pulley and used one of Kurgan Motorsports’ aggressive street tunes to help the Terminator Cobra make a hair over 18 pounds of boost. If you’ve been in the late-model Mustang hobby long enough, you know that Bob Kurgan is one of the most trusted and respected names in high-end power tunes. We were pretty pleased to see the rollers spin to a whopping 619 rwhp at 6,650 rpm. The torque output, on the other hand, peaked at 548 lb-ft at 5,000 rpm, but it never dropped below 500 lb-ft of torque between 3,000 and 6,500 rpm. Now that’s what we call a fire-snorting snake!

Clutch Work

While the clutch seemed to be OK during our initial test of the budget boosted Terminator, GTR installed a Zoom Twin Disc clutch and flywheel into the Cobra to ensure that all the power was getting to the ground. An interesting side note is that the difference in weight between the two clutch assemblies was significant enough to reduce parasitic power loss compared to the stock unit. The OEM Ford flywheel and clutch kit weighed 36 pounds, while the complete Zoom flywheel and twin-disc clutch assembly tipped the scales at just 29 pounds.

Final Tune

Since Joel’s Terminator Cobra still sees regular street time, GTR went ahead and gave the car a more conservative tune that only boosts up to 16 psi with a 3 1/4-inch-diameter supercharger pulley. GTR tells us this tune is a lot more street friendly while still putting out 600 rwhp safely on pump gas. GTR tells us they would prefer to run 17 psi of boost, but since we didn’t have a pulley available to achieve that boost level, the final street tune was done conservatively. GTR also recommends running a splash of higher-octane race fuel in your gas tank if you plan on running the smaller supercharger pulley to increase the boost.

Total Cost

Part List Price Price Paid
Kenne Bell 2.4L (now replaced by 2.6L) $3,300 $2,200
BilletFlow throttle-body 200 429
Reische 170˚ thermostat 63 56
JBA shorty headers 749 242
Ford Racing 80-lb/hr injectors 389.99 250
SCT Performance Big Air mass air meter 230 150
SCT Performance 4-bank ECU chip 269.99 75
Zoom Performance twin-disc clutch kit 1,100 512
Ford Racing throw-out bearing (M-7548-A) 55.95 51
NGK TR6 spark plugs 24.99 15
OEM Ford gaskets for Kenne Bell swap 80 80
Total $6,462.92 $4,060
HP gained over stock (390 to 619 hp) 229 HP 229 HP
Cost per HP gained in dollars $28.22 $17.72
Note: Retail prices based on American Muscle’s online prices.