Very often, we come across the term "turbo boost". And it being used in such sentences as : 1. Hey, let's crank up the "boost" and make more power! 2. I'm running more boost in my engine than person X. 3. Let's put in a bigger turbo and run even more boost. And so on. Let's also put in a customary Vin Diesel pic when it comes to anything related with turbos and boosting cars. On a somewhat more serious note, let's try to have a completely layman's look at what exactly lies behind the term "turbo boost". In it's most rudimentary form, consider a turbo as a fan having blades on 2 sides of a common shaft. The exhaust exits from the engine are connected straight to the exhaust side of the turbo. The "blades" on the exhaust side are driven by the exhaust gases exiting the engine's exhaust ports which spin the shaft. This spinning of the shaft in turn spins the intake side which takes in air from the air filter and sends it into the air intake manifold at a greater volume and pressure than it would naturally. So, what is the so called "boost" pressure? "Boost", like oil pressure, is nothing but the restriction faced by the air while moving from the turbo to the intake. Higher the restriction, higher the boost pressure, harder the turbo has to work to move a given volume of air. Imagine blowing a flute with your mouth. You can blow more air through a 1inch diameter flute at a lower pressure than through a 10mm flute which will require higher pressure to flow the same amount of air in the same time. So, a higher boost pressure does not always mean a positive co-relation with power output. Why, you ask? Any machine is designed to operate in a range where it is in it's peak efficiency. For e.g. a truck engine might be designed to operate continuously at rpm's below 2500 and a F1 engine may be designed to stay continuously in the 18000-20,000rpm range. Similarly, there is a efficiency range of the turbo as well. You can only spin a turbo so much. Try to spin it too much and working against too much restriction and it will be working beyond it's range and doing nothing but sending lesser volume of air at a higher temperature. You might see higher pressure readings but witness a power drop as well. Decreased reliability in the long run is another negative consequence. So, while talking of "boost pressures", the key point to be kept in mind is not some number which has a magical co-relation with power output. A more holistic approach is needed. For e.g. you can make X amount of power at 15 psi and you can make X+Y amount of power at 15psi as well. The Y amount of power gets added when we make the intake plumbing (including the cylinder head) that much more efficient (less restrictive,better flowing) and tune accordingly. The above is just a layman's view from a person who is not even a mechanical engineer. So feel free to discuss and debate. Cheers.