A 30-percent Increase in Power and Torque?

It's difficult to increase horsepower in a big way without losing something on the bottom end of the torque curve. It's also difficult to enhance low-end torque without losing something at the top end. What if you could have it both ways? You can with supercharging.

Rimmer Engineering of Colorado Springs builds supercharger kits for Jeeps that claim a 30 percent increase in power and torque. Kits are available for 2.5L engines; 4.0L kits and 5.2L kits are close to completion. Owner Rick Rimmer has been in the forced-induction business since 1995, and he builds kits for a variety of cars, trucks, and 4x4s.

The beauty of these kits is that they don't negatively affect emissions, drivability, or economy. The benefits come right off idle, with boost coming in as soon as the throttle is opened. This greatly enhances low-end grunt, but the increases extend all the way to redline. (see the Forced Induction Primer sidebar for more details on how superchargers work.)

Eaton superchargers have a working life of approximately 100K miles and can be rebuilt. In fact, since Eaton blowers are used in some OEM applications (Buick, for example), an exchange program has been instituted to minimize delays. Since the impellers don't actually touch, the only wear occurs in the sealed bearings.

Before you start ripping and tearing, take a moment to mark all the hoses and wiring connections so you won't mix things up.

Remove the fuel pump relay and crank the engine over for 30 seconds to depressurize the fuel system. Then disconnect the batter and remove the intake manifold assembly.

While removing the original intake manifold, you have to unbolt the power steering pump from the manifold. The pump gets some mods. First the reservoir is removed via a clip, and then a fitting is driven into the return inlet.

Because the power steering pump will remount in a slightly different location, a new idler pulley/PS bracket is supplied with the kit.

One of the secrets to the kit is an idle bypass, which allows boost to bypass harmlessly at idle. This prevents heat buildup. Use oxygen-sensor-safe silicone sealer to mount the valve onto the intake manifold. Check for free operation after it's mounted, and then the intake manifold can be installed.

The housing must be placed to the rear of the Eaton supercharger before you bolt it up to the manifold. One of the bolts is accessible through a vacuum-fitting hole. The air-temp sensor goes into hole Number 1, the brake booster hooks up to Number 2, and the seventh injector goes into Number 3.

The supercharger goes on next. After applying a layer of silicone to the sealing surface, install the blower. Make sure you install using the short section of hose that connects the blower with the bypass valve. Note: The bolts holding the lower part of the blower are tricky to reach.

The fuel rail is installed next. You can begin to reconnect many of the fuel and vacuum lines you previously marked. A fuel line extension is used to reach around the blower unit and will tee off to the seventh injector, which can also be installed.

At this point, you can install the throttle body that you recovered from the original manifold and begin to hook up the throttle and kick-down linkages.

The new belt can be installed according to the original schematic. The slightly longer belt just makes an extra loop around the supercharger pulley. The Eaton blower draws less than the A/C compressor, so there's no major drain on the engine.

The new fuel control unit is installed and wired according to instructions. This is a separate fuel system that is piggybacked onto the original EFI system. When the new fueler senses a lean condition during high boost, it kicks in that seventh injector to richen the mixture.

The power steering pump reservoir is relocated with a new container, bracket, and hoses. It mounts to the bracket that carried the fuel vapor canister.