BAROMETRIC PRESSURE
The pressure (force per area) created by the weight of the atmosphere, measured by a barometer. At higher elevations, the atmospheric pressure is lower because there is less air.

BASE INJECTION-TIMING
The base injection timing is calculated directly from the load signal and from the injector constants, and defines the relationship between the duration of the activation signal and the flow quantity at the injector. This constant thus varies according to injector design. When the injection duration is multiplied by the injector constant the result will be a fuel mass corresponding to a particular air mass for each stroke.

BIG TWIN
Refers to the relatively large size of almost all other Harley-Davidson engines when compared to the Sportster® engine. Sportster® models currently have 883 or 1200 cubic centimeters whereas most other Harleys have 1340 cubic centimeters. The single exception to this rule is the V-Rod® which currently has fewer cubic centimeters (1130 cc to be exact) than a large Sportster, yet is widely considered to be a big twin. Who knows, maybe in a few years' time we'll have to come up with a new phrase to separate the larger motorcycles from the smaller motorcycles…

BLOCKHEAD
The Evolution® engine (V-Twin, produced from 1984 – 2000).

BMW
A brand of motorcycle. BMWs were first made in 1923 with the R32 boxer. If you mention BMW to most non-riders, you will almost always hear, "I didn't know BMW made motorcycles." Actually, they made motorcycles before they made cars.

BMW K-bike
In the early '80's, BMW decided to revitalize their motorcycle line up by replacing all the old Airhead R-bikes with a new style of bike that had an inline-3 and inline-4 engine, and many advanced features. The result was the K series of bikes (the K100, K75, etc.) These motorcycles have inline engines (the cylinders are lined up in a row, like many automobile engines), fuel injection, advanced suspension design, etc. All the latest greatest technology. The K-bike line was the first in the world to incorporate Anti-lock Brakes, in the eighties.

K-bikes are sometimes called "flying bricks" or "whining bricks" due to their brick-shaped engine, and the Jetson's-hovercar whining sound they make. The engines, while very advanced, powerful, and fuel efficient, are nearly impossible for an amateur mechanic to do much with. They are therefore a trade-off for those of us with a more limited budget.

Boost Pressure
The increase above atmospheric pressure produced inside the intake manifold by any supercharger. It is commonly measured in psi, inches of mercury, or bar.

BOOST-PRESSURE CONTROL
Boost-pressure control mechanisms that rely on pneumatically-triggered mechanical layouts use actuators (wastegate) that are directly exposed to the pressure in the impeller outlet. THis concept allows only very limited definition of torque response as a function of engine speed. Load control is limited to the full-load bypass. There is no provision for compensation of the full-load boost tolerances, and at part load, the closed wastegate impairs operating efficiency.

BOOST-PRESSURE SENSOR
In order to regulate boost pressure, this must first of all be measured. This function is taken over by a pressure sensor with a measurement range extending up to 250 kPa.

BOTTOM-FEED INJECTOR
The "bottom-feed" injector is intergrated within the fuel-rail assembly, where it is constantly immersed in flowing fuel. The fuel supply enters the unit from the side ("bottom-feed").

Boxer
The term "Boxer" refers to an engine style where a pair of cylinders are horizontally opposed to each other -- if you look at the two cylinders from the top, they're almost on the same line, on either side of the engine. When they fire, they do so on opposite strokes, but both cylinders move in towards the crankshaft and out away from the crankshaft at the same time. The result, at least in theory, is a vibrationless engine.

Brake Horsepower (bhp.)
The measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. The actual horsepower delivered to the driving wheels is less.

Breathing (engine)
A term used to describe an engine's ability to fill its cylinders with air-fuel mixture and then discharge the burnt exhaust gases. In general, the more air-fuel mixture an engine burns the more power it produces.

BUELL
A brand of motorcycle produced by Harley Davidson.