"Boost" is generic for positive manifold pressure anywhere between the turbo housing and the cylinder. Like CNY said, it's important to know where, and how, to measure it properly.
You may have positive pressure all the time upstream from the throttle body/carb but downstream, between the TB and the cylinder, manifold pressure is purely a function of throttle opening and engine RPM (how much air can get in vs how much air the engine pumps at that speed).
By the way, if you ever build a blown or turbo'd engine, the goal is to make as little manifold pressure as possible for a given volume of air. Pressure builds when there is a restriction to air flow. Pressure makes heat. Heat bad. There is a point of diminishing returns for blowers and turbos on stock engines. The intake tracts are designed for N/A airflow efficiency. Overstuffing them with a turbo or blower may build more HP, but at some point the intake system simply will not efficiently support more airflow. At that point you can build all the manifold pressure you want but you won't make another nickel's worth of power. That's where you have to start digging into the engine and doing port work, enlarging throttle bodies, setting up exhaust systems, etc. A moderately worked engine will more power on less pressure than a stocker because it moves the same volume of air with less pressure and less resulting heat buildup in the intake charge. Or to put it another way, you will get more air volume for a given manifold pressure. More volume equals more power. More power gooooooood!
Brad
