Tom Wilson
December 1, 2009

It's difficult to think of mid-600 hp at the rear tires as routine, but around Kenne Bell, it's become that. Since the introduction of the modern Three- and Four-Valve modular V-8s Kenne Bell has developed the formula for making such power on 91-octane pump gas, so when the '10 GT500 hit the showrooms there was no doubt the latest Shelby would join the mid-600 club.

As it turns out, getting there was all the fun thanks to the addition of knock sensors. So, while the '10 GT500 hardware is a carryover from '09, much of the electronic strategies have changed with the move to knock sensors by Ford. In fact, this is the first time a Ford-supercharged car has used knock sensors, so sorting out the electronics was a new headache for ace Kenne Bell engineer Ken Christley.

Because the hardware is familiar to 5.0&SF readers, instead of wading through another nut-by-bolt supercharger installation in this documentation of Kenne Bell's supercharger kit for the '10 GT500, we're going to just hit the highlights, plus cover a few interesting peripheral items KB uncovered along the way.

A quick review is probably the best place to start, so let's recall the '10 GT500 uses an Eaton roots-type supercharger and air-to-water charge cooling to make 540 hp at the flywheel. Kenne Bell's kit replaces the Ford blower with their own 2.8-liter Twin Screw supercharger for greater blower efficiency and more tunability (read that as simpler pulley changes). This requires a minimal amount of hardware replacement because the Kenne Bell supercharger perches atop the stock Ford intake manifold, uses the Ford charge cooling system, belt drive, fuel system, and ignition.

In fact, the '10 Shelby system from Kenne Bell is best described as the '07-'09 Kenne Bell Stage III blower kit for GT500s with just the software and instruction manual changes required to fit it to the '10 GT500. There are no Stage I or II kits for the 2010 Shelby because Kenne Bell has hardly sold any of these for the '07-'09 Shelbys, so there's little demand for entry-level kits when it comes to GT500s. The Stage III kit includes the 2.8H high-pressure ratio supercharger, the big-twin 75mm throttle body, a cold-air intake built from a Ford GT inlet tube, 2,000-cfm air filter, and big 133mm mass-air housing.

KB is supplying the blower with a 3.250-inch drive pulley. This yields 15 to 15.5 pounds of boost, the most possible with 91-octane pump gasoline before detonation sets in. As West Coast readers know, 91-octane is the highest octane gas available on the left coast; East Coasters can run the same electronic tune with a 3-inch blower pulley for 45 more rwhp over the West Coast guys. That should put the West Coast customers at 640 rwhp while the East Coast guys are nominally at 690 rwhp although some report seeing 700-plus rwhp (and Virgin Marys in warehouse windows, for all we know).

Other Kenne Bell hardware in its '10 kit is the Mammoth blower inlet casting, DiabloSport Mafia mass-air extender, SCT Flash Tuner, and KB's dual Boost-A-Pump voltage booster for the Shelby's dual fuel pumps. There is no Boost-A-Spark as the Ford ignition is more than adequate. Because it is mechanically identical to the '07-'09 kit, '10 kit pricing is also the same at $5,999

OK, so what did Kenne Bell do to get their GT500 kit on the '10 snake? On the hardware side nothing. Well, for the first batch of kits the oval mass air meter housing KB supplies will be powdercoated gray instead of natural cast aluminum due to a cosmetic finish foul-up by KB's foundry, so there's a bit of trivia for MCA judges 30 years hence.

There are a few detail changes noted in the comprehensive installation manual. One of the more interesting is the stock air inlet featuring new ram-air tube. According to KB, Ford was unimpressed with the new GT500's performance during development, the problem being the engine was starving for air; the tight construction of the forward portion of the engine compartment doesn't let enough air into the air box. With insufficient time to engineer a new inlet a quick solution was arranged using the small auxiliary snorkel. The snorkel extends from the air box into the open grille area, which required moving the Shelby snake emblem from the driver's side to the passenger side of the grille, but it does improve performance. Kenne Bell tested this snorkel by alternately blocking it off and found it's worth 13 hp on its chassis dyno.

As for the KB blower install, the ram-air snorkel is reused, but the rest of the Ford airbox, filter, etc. is discarded in favor of the larger KB inlet. Along the firewall the electrical harness at the top rear of the engine needs to be reconfigured from below the EGR pipe to above the EGR pipe, which is no big deal. In the trunk the same fuel pumps and drivers are on hand, but are arranged slightly differently due to the '10's angled taillights, along with minor changes in the interior trim paneling. Also, the wiring color codes have changed, but all of this is accounted for in the extensive KB instruction manual.

Unlike the prior GT500 install, the large vacuum hose leading to the brake booster is too long in the '10 application, so it gets shortened about 3 inches. It's also necessary to remove and replace the serpentine belt's idler pulley to install the tensioner, so there's a couple of bolts to deal with there. And the area under the hood that needs trimming has changed slightly, but like the '05-'07 hoods, the '10 hood does require cutting a small area of the reinforcing structure for blower clearance.

That's it for changes between the Kenne Bell '05-'07 and '10 GT500 installation. In other words it's the same old job of removing the stock blower, installing the new one, fitting the Boost-A-Pump in the trunk, and driving off in search of fun. Because the GT500 is already equipped with a charge cooler and stout short-block, there's no need to spend the time or money to add them. With the nice instructions and given a few hand tools we rate the KB install as a suitable home job, but it will easily consume an entire weekend.

There are more install details in the photos and captions, along with extra dyno and supporting hardware information in the sidebars.

Stock Power Ratings Ford says the '07-'09 Shelby GT500 makes 500 hp and the '10 GT500 makes 540 hp. But Kenne Bell says they both make 640 hp with his blower on 91-octane fuel. How can that be? Isn't the new Shelby a more powerful engine?

In stock form it is, but the power gain Ford realized with the '10 Shelby came strictly from its electronic tuning, says Kenne Bell. To make their point, Ken Christley showed us two dyno sheets from the KB dyno. The first was from a stone-stock '07 Shelby Ken had tuned, the second was from the '10 shown in the photos. Both cars received the exact same tune by Ken, both were mechanically stone-stock, and the two dyno tests lay right on top of each other like a pair of back-up runs. That would say the GT500 mechanicals are the same, and the difference is electronic.

On The Dyno Here is the official Kenne Bell dyno sheet for the '10 Shelby GT500. It came in 14 rwhp lower than predicted-a disappointment for sure, but likely due to 3.55 rear axle gearing, cam timing, and only 400 miles on the test car.

The final drive situation is explained in another sidebar, while the cam timing is an issue Kenne Bell has heard from customers. Because Kenne Bell sells only direct, they hear constantly from their customers. Ever since the '03 Cobra, the Four-Valve modular engines have shown an occasional lazy engine, and KB says these might just lay over because of slightly out-of-time cams. KB believes this may well be the case with the '10 test car, but he figures they won't know until they can retest the car after it has around 5,000 miles on it. That would eliminate the chance this engine simply hasn't settled in with only 400 miles on it.

BaselineKenne BellDifference

Credit Kenne Bell with presenting an accurate dyno sheet when they could have easily kept mum. We've come to trust KB's dyno work and fully expect their blower to deliver a nominal 640 rwhp on the '10 Shelby.

All data was taken on Kenne Bell's Dynojet and is SAE corrected.

Knock Sensing Ford has stayed away from knock sensors on its supercharged performance cars until the '10 GT500. The difficulty for the engineers is separating the small knock noise from the tremendous amount of general engine vibrations, and with a supercharger there is that much more racket inside the engine.

What's more, as Ken Christley educated us, the knock sensors are not set at the factory for a certain frequency as we had imagined. Instead, the knock sensors are constantly being re-mapped by the computer. This is because the engine subtly changes the noise it makes due to environmental factors and the engine's lifespan due to things such as slowly changing piston ring seals. As Ken points out, listening for detonation and doing the computations to separate it from the background din consume a tremendous amount of computing power, leading to all sorts of strategy changes in Ford's Spanish Oak engine operating software that he's had to learn.

So, while the basic spark and fuel tuning required to make power on a 5.4-liter GT500 engine with a Kenne Bell blower was figured out on the previous Shelby, Ken has had to learn a whole new chapter in Ford engine strategy to implement that tune on the 2010.

It's worth noting Kenne Bell does not take the easy way out when tuning these knock-sensor cars. It is easy for a tuner to go into the Ford operating software and bypass the knock sensors; that allows tuning the spark and fuel at will. In fact, many tuners do this, but Kenne Bell refuses this tactic. With the knock-sensing safeguards turned off the engine is just one splash of lousy gas, one hot day at the track, one inadvertent miscue away from piston-melting disaster. The knock sensors are there for a reason-they allow tuning closer to the detonation edge under real-world conditions-and need to stay operational.

Geared For Power? To support Kenne Bell's contention that rear axle gearing has a measurable effect on rear-wheel horsepower when the test vehicle is in the "big-power" category, Kenne Bell supplied us with a pair of dyno tests.

All this got started a while back when Jim Bell thought he saw differences in power output depend-ing on the rear axle ratio in the car. Anecdotal evidence on this subject surfaces occasionally, but Kenne Bell went to the trouble of dyno testing the concept.

Two rear axle assemblies were used so the gear ratios could be quickly swapped. KB elected to test 3.31 and 3.73 gears in its own '07 GT500 test car tuned to the upper-700hp range, and the results indi-cate the 3.31 cogs are more efficient than the 3.73 gears. Of course the 3.73 gears provide more torque multiplication and will out-accelerate the 3.31s, but apparently not as well as they might should the gear ratios be equally efficient. The difference is notable, and while we're not completely sure why one gear set is more efficient than another (the answer is somewhere in the number of gear teeth engaged, their angle, etc.), the affect seems a factor to consider when evaluating combinations. Below are the numbers to consider.

3.31 Gears3.73 GearsDifference

Snorkeling Jim Bell never misses a chance to remind us how dyno testing with the hood open is the work of the devil. He's right, of course, because we don't drive with the hood open. We all have a tough time replicating the volume and velocity of air associated with a 112-mph quarter-mile pass when strapped to the chassis dyno, but testing with the hood closed has its issues as well.

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But Jim's insistence on considering underhood air flow makes him the perfect fellow to chase down the effects of the '10 Shelby's secondary intake snorkel, which is what he did, alternately testing with the hood open and closed, and with the snorkel taped shut or left open. And yes, all the temperatures were stabilized so the only variable was the airflow.

We're going to spare you the columns of dyno numbers all this testing generated and summarize it in a chart.


Clearly opening the hood greatly improves airflow (especially in the cramped GT500 engine compartment, which is 10 pounds in a 5-pound sack). But that little snorkel does seem to help-it scored 13 extra horses in this test, plus a slight torque gain all the way across the rpm range. The higher the rpm, the more the gain from the snorkel. We'd say this is notice to all hot rodders that there's a reward to the guy who can get real airflow to his air filter.