The supercharger choices begin with the 2.8-liter for the 8- to 23-pound boost range, then the 2.8H variant featuring slightly different porting to favor the 15- to 28-psi boost window. For dedicated big-power applications, you can move up to the 3.6-liter for 15-30 pounds of boost, and if anyone really needs to, Kenne Bell has a 4.2-liter screw blower on the shelf that is yet more efficient at the outer limits.
From a packaging perspective, these blowers differ only in their length, which has been accommodated in the drive snout and manifolding. In other words, any of these blowers can be easily used from the kit's initial installation or retrofitted in 20 minutes.
As for adjusting boost in the field, all Kenne Bell blowers are designed for rapid blower drive-pulley changes. Most pulley swaps can be done in three minutes, 10 on the outside. The entry-level Kenne Bell 5.0 kit starts at 8 pounds of boost using a 4.125-inch pulley; the limit for 91-octane pump premium gasoline. East Coasters with access to 94-octane can step down to the 3.875-inch pulley for 10 pounds of boost (and not have to bother with re-flashing the computer's tune), and in any event, KB can supply pulleys in 0.125-inch steps until your connecting rods are scattered a hundred yards on either side of the dragstrip-call it 28 pounds of boost with the 2.8 and 3.6-liter blowers.
Note that even the 2.8-liter blower is generously sized for the deep-breathing 5.0-liter Coyote. It's loafing at 8 pounds of boost with cool discharge temperatures, so you can consider 8 psi as a minimum pulley choice for this kit. We doubt few people will ever really need the 3.6-liter, much less the 4.2. Need and want, of course, are two different matters.
Street applications drive nicely with the stock six-rib pulleys, but 12-psi or higher kits need Kenne Bell's eight-rib pulley set. Jim Bell didn't have one on hand to show us during our visit, but he's promising a trick, compact method of adding two ribs to the stock crankshaft harmonic damper/pulley sheave. The eight-rib layout will also require a smaller water pump pulley to physically clear the crank pulley.
Kenne Bell pricing reflects the inherently expensive nature of a screw blower on one hand and the fact KB sells only direct to the customer on the other. The base '11 Mustang GT kit is $6,599. That gets you a charge-cooled, black 2.8-liter supercharger without liquid cooling and an 8-pound, six-rib pulley, plus you re-use the stock throttle body to reach right around 550 rwhp on 91 octane pump gas. It's a big old kick in the rear, and if you're just giving it a squirt now and then or never going over 10 pounds of boost, you won't miss liquid cooling the blower. If you're planning on more boost in the future (who isn't?) then liquid cooling is more beneficial. It's an additional $300, or $6,899 on the otherwise base kit.
The huge KB throttle body is a $400 upgrade, the eight-rib pulley kit is $349, and polishing is $500. As you go up the Kenne Bell price list (already available on the Kenne Bell website), polishing becomes a standard feature and bundling the big throttle body is sometimes included.
Of course, you can always spend more. Step up to the 3.6-liter blower (you guys with 1,000hp dreams) and you're looking at $8,099, but that includes the big throttle body and polishing. Pricing on the 4.2-liter blower wasn't set at our press time.
Getting back to the real world, poking around the price list we see a black, 2.8-liter, liquid-cooled blower with the big throttle body ($6,999), a couple of extra pulleys ($69 each) for test and tune night, and the required pulley changing tool ($25) make a great package that will put out all the power you can handle for $7,162. That'll range from 8 to 28 pounds of boost and last the life of the car. If you want to make life easy on your wife at Christmas time, you could have her step you up to the eight-rib pulley kit or a Boost-a-Pump, so everybody wins.