Forcing the Induction Issue
Q I'm considering adding either a supercharger or a turbo system to my 2.5L/4.0L for more power. Is one better than the other?
A Both a supercharger and a turbocharger do the same thing. They compress the air from the atmospheric pressure of 14.7-psi at (sea level), allowing the engine to ingest more air than it could when naturally aspirated and thereby allowing a proportionate amount of fuel to be introduced to the engine. It basically makes the engine think it's bigger than it is.
However, the way in which each accomplishes this compression differs. A supercharger is driven off the crankshaft of the engine. Since it's mechanically driven, it contributes a bit to the overall parasitic power losses the engine incurs. A turbo, on the other hand uses the flow of exhaust gasses to spin the compressor. Although it's not exactly free power, a turbo doesn't accrue the same parasitic losses as a supercharger. Both methods require some form of intercooler to reach their full potential since the intercooler will combat the inescapable byproduct of compressing air - heat.
That said, at the modest boost levels of 4- to 7-psi that most Jeep forced induction systems run, these differences between turbocharging and supercharging are minimized. Which do I prefer? I think based on its sheer capacity for power building, I'd be more inclined to go turbo. In the Jeep world, 505 Performance (505performance.com) has some pretty complete kits whipped up that make some real power. On the other hand, supercharger companies like Avenger Superchargers (avengersuperchargers.com) and Adventure Innovations (adventure-innovations.com) both have very complete, well-designed supercharger kits for Jeeps. In the end, it's up to you to pick your own poison.
No Stop
Q My Jeep has a 4:1 gearset in the transfer case and an automatic transmission. When I'm off-road in Low range I have to step on the pedal with both feet to get the Jeep stopped. What can I do to get my Jeep to stop off-road?
A This is the definition of the adage, there's no free lunch. All that awesome torque multiplication and off-idle chugability that keeps you going forward through gnarly rocks can quickly overcome even the stock four-wheel disc brake setup on a modern Rubicon.
For starters, it's probably a good idea to swap to stickier brake pads. The stock pads are geared more towards longevity than brute stopping power. Check EBC Brakes (ebcbrakes.com) for some stock replacement pads that will really put the hurtin' on forward momentum.
However, I'm sure the pads aren't going to solve all your problems. Some of the guys at Jp have had moderate success with hydroboost setups, which do away with the vacuum booster and replace it with a hydraulic booster powered off of the power steering pump. Or, replacing the stock master cylinder with an aftermarket unit with the largest piston size you can find. And while it may seem counter intuitive and although I haven't tried it yet, I'd bet junking the power assist setup altogether and replacing it with twin Wilwood or CNC master cylinders setup with 7/8-inch pistons would work surprisingly well.