How It Works?
Even if technical jargon, mathematical equations, or scientific calculations are not your thing, part II of How It Works, like the first that ran in last month's issue, should be easy to understand and apply to the daily workings of your most prized possession-your 4x4. And so you wouldn't have to go to the end of the universe to discover for yourselves the workings behind each off-road apparatus we have compiled more of the technical wonders for you to study and apply.
This second installment of How It Works is an eclectic compilation of the basic and the complex, from old school to high-tech, from just plain I-knew-that to who-would-have-thought. For each topic we've picked the brains of various on-staff and in-the-field resources. Basically it's automotive tech information that every gearhead should know. What's more is that it's more enjoyable and interesting to read than your automotive class textbook. Feel free to make up your own quiz at the end, or better yet, you can quiz your buddies.
Gear and Chain Driven Transfer Cases
Power in the form of torque enters the transfer case through the input shaft and spins an idler gear that is cut with a neutral, a low range, and a 1:1 high range ratio. The shifter lever moves two shift forks that lock a slider on the shaft into the desired position and allow the power to be transmitted through a combination of the front or rear output shafts. The combination of positions of the shift lever(s) determines which axle gets power and if the low- or high-range ratio is selected. Geardriven transfer case shifting options can include, but are not limited to, 2-Hi (rear), 4-Hi, 4-Lo, 2-Lo (rear), and 2-Lo (front).
Power in the form of torque enters the transfer case through the input shaft and spins an input gear that is surrounded by a low-range planetary assembly housed in the front half of the transfer case. A large chain connects the front output shaft and the rear output shaft. The chain is engaged by a mode fork which will lock a slider into the desired position and allow the power to be transmitted through a combination of the front or rear output shafts. The combination of positions of the shift lever(s) determines which axle gets power and if the low- or high-range ratio is selected. Chaindriven transfer cases can be modified to get the 2-Lo function, but are most commonly found in the part-time (2-Hi, 4-Hi, 4-Lo) and full-time (4-Hi, 4-Lo) versions.Rob HallAdvance Adapters
Throttle Body Fuel Injection (TBI, or Direct Injection) and Tuned Port Injection (TPI, Multiport Fuel Injection, or Sequential)Two basic types of electronic fuel injection are TBI and TPI. Throttle body injection in the early '90s became the automaker's replacement for carbureted systems. TBI is an electronically controlled system of fuel injectors that bolt directly onto the throttle body and inject an air/fuel mixture into the intake manifold.
Tuned Port Injection, or TPI as it's primarily called, has become the modern replacement for TBI fuel injection. The main difference between TBI and TPI is the mounting position of the injectors. TBI has injectors mounted at the throttle body, so both air and fuel flow through the intake (what's referred to as a "wet" intake). TPI has a fuel injector mounted at the end of the manifold runner that sprays directly into the head. In a TPI system, the incoming air passes through the throttle body and intake runners before mixing with the fuel charge in what's referred to as a "dry" intake.