Ignition Hop-Ups
While newer 4.0L engines are calibrated lean and don't really need much help igniting a stock air/fuel charge, the 2.5L engines often run on the rich side and can benefit from a good set of aftermarket low-resistance plug wires and a hotter coil. There are hand-held programmers for these engines as well as all sorts of chips and methods to advance the ignition curve. The 4.0L engines should have the fuel bumped up, whether by an adjustable fuel regulator or larger injectors, to really take advantage of a more aggressive spark advance and increased ignition timing.
Older V-8 and V-6 engines will really wake up with a custom-tuned or recurved distributor that tailors the spark advance to come in sooner in the rpm range. The result is almost always more power and mileage. Likewise, a quality set of spark plug wires and a hotter coil will help ignite the mixture from the carburetor.
Look For: For 2.5L and 4.0L coils, make sure the manufacturer offers an adapter harness to plug the coil into the factory wiring on '98-'99 vehicles. Plug wires should be a low-resistance type, with no more then 500 ohms per foot of resistance, thick silicone or other high-quality shielding, and vulcanized boots that won't separate when pulled off. There are lots of programmers out there, and we tend to favor the ones that plug into the OBDII port (for those vehicles) and that allow changes to the speedo, rpm limit, governor, and other engine management systems in addition to timing changes.
We Say: We've seen gains of 5 hp with power programmers at the rear tires. A recurved distributor and high-performance ignition on a mild V-8 can net 15-25 hp at the tires.
Nitrous Oxide
You've heard the expression "It's not the fall that kills you, it's the sudden stop." Likewise, it's not the nitrous that makes horsepower, it's all the extra fuel the nitrous allows your engine to burn. Nitrous oxide, or N2O is an oxidizer that introduces massive quantities of oxygen molecules into your engine, allowing a proportionate amount of fuel to be introduced and burned. Nitrous systems for injected engines are commonly of a wet or dry type. In a wet system, the nitrous and extra fuel are injected before the throttle body through a nozzle, and the mixture is then drawn into the engine through the throttle body and manifold. In a dry system, only nitrous is injected into the engine, and the vehicle's fuel rail pressure is manipulated to add the extra fuel necessary to support the nitrous load. For carburetors, a wet plate system is most common, in which the nitrous and extra fuel are sprayed into the intake via a plate mounted in between the carburetor and manifold.
Since the increased combustion volume greatly increases cylinder pressures it's important to pull back the total ignition timing when running nitrous as well as making sure your pistons, rods, crankshaft, and head gaskets can survive the added pressures. As a general rule of thumb, most stock V-8s can ingest a 75hp shot easily, while six-cylinders can take 50hp levels.
Look For: You want to find a complete kit for your engine type, whether carbureted or injected. Piecing together a system is frustrating and may result in a greater possibility of engine damage. Injected engines would do best to use a wet system. It's a good idea to run an electronic bottle warmer to keep the nitrous at the proper pressure.
They Claim: 75 hp, 100 hp, 125 hp, and so on, with huge torque increases.
We Say: Deduct about 15 percent for normal parasitic drivetrain losses and the figures are right on the money.
Superchargers
Whether it's a V-8, six-, or four-cylinder, a supercharger is a great way of making big power and torque across the entire rpm range. The supercharger compresses the intake charge, usually to about 5-8 psi in a street application. This forces the mixture into the cylinders, hence the term "forced induction." The upside is a great increase in torque and power. The downside is that the intake charge heats as its compressed, which can result in detonation and lower power levels than with a cooler charge. To combat this, some supercharger systems use an intercooler to chill the charge before it's introduced to the cylinders.
For carbureted V-8 centrifugal blow-through applications, in which the compressed air is introduced into the carburetor via an air horn or enclosed box, the atomization of the fuel as it enters the intake manifold chills the charge back down and helps prevent detonation. This allows for a little more boost and higher power numbers to be realized than with a regular-roots or twin-screw supercharger.
Look For: Once again, complete systems designed for your particular application will be less likely to cause engine damage and will be easier to install than a scraped-together system using whatever you find laying around. Injected applications will make better power and have higher tolerance to pump gas at larger boost levels with an intercooler. A centrifugal system allows for more hood clearance at the cost of front engine accessory drive real estate.
They Claim: 40-75 percent power increase.
We Say: Expect a true 45 percent increase at the rear tires with an intercooled system running 5-8 psi.