| A max flow rate that the engine can allow is ideally what you want. Turbo size, intercooler size and volume. The size and specifications of a vehicle's turbocharger system are dictated by the engine's characteristics. It's not the case that a larger turbo or larger intercooler will always make more power. Sometimes smaller turbochargers and intercoolers are a better fit for an engine to produce the most horsepower. Turbo size:
The most important factor deciding your turbo vehicle's horsepower is the engine itself. Smaller displacement engines often are fit with smaller turbochargers, as larger turbos require much more exhaust pressure to spool. By analyzing engine displacement and exhaust pressure, a smaller turbo can be fitted to an engine to give it a wider power band with more midrange torque in comparison to a large turbocharger. Many other engine characteristics have an important role in the horsepower produced by a turbocharger, notably intake temperature and piston compression. A larger turbo may produce hotter charged air than a smaller unit. Certain vehicle's simply will perform better with small turbochargers due to the fact that they can cool the charged air and engine bay more efficiently. Also, the higher an engine's compression, the less turbo boost pressure it will need to produce horsepower, though it also will be less reliable than a properly built low-compression turbo engine. Many factors, aside from size, contribute to deciding a turbocharger's ultimate performance. More complex spool and flow characteristics also must be considered. A smaller turbo that spools quickly and flows best in your engine's peak power rpm range can make more power than a less-efficient large turbos at specific rpm's and power bands where it's needed the most. Intercooler size:
Larger is not necessarily better (not what she said). The larger the intercooler the more volume of air is needed. In boost applications, you are trying to achieve a larger amount of air density which is obtained by air pressure and temperature. Up to a certain point a larger intercooler is best for cooler temperatures (and density). After a certain point, a larger intercooler is no longer providing any additional flow than the engine can accept. A smaller intercooler takes less time to charge to max psi. A larger intercooler take more time and if too large, the time it takes to charge will diminish the max psi during flow release. This is referred to as the pressure drop. An intercooler with a large flow rate and larger release opening will have a larger and quicker pressure drop than a smaller intercooler with a smaller release opening. But how critical is this pressure drop? How much drop is there at the rpm band that provides you the most power when/where needed? How much is to much? The engine can only take in so much air. You can provide an ocean size amount of air but you can only put in so much into the cylinders during the intake cycle. Here is a formula to find max air that the engine's intake can consume. Engine (ci) X rpm / 3456. Our engine is a 3.0L. Converted to ci = 183ci so in our engines to find the max amount of air intake at a specific rpm would look like this. Max rpm example:
183 X 7000rpm / 3456 = 370 cfm (or cubic feet per minute). This example is basically the max amount of air that can enter the engine at max rpm and WOT. But what about between the most used (and needed) rpm ranges.
Example of low to mid range air intake volumes:
183 X 2700rpm / 3456 = 143 cfm (or cubic feet per minute).
183 X 3000rpm / 3456 = 159 cfm (or cubic feet per minute).
183 X 3500rpm / 3456 = 185 cfm (or cubic feet per minute).
183 X 4000rpm / 3456 = 211 cfm (or cubic feet per minute).
183 X 4500rpm / 3456 = 185 cfm (or cubic feet per minute).
183 X 5000rpm / 3456 = 265 cfm (or cubic feet per minute).
183 X 5500rpm / 3456 = 291 cfm (or cubic feet per minute). Now what about a turbo Z? You might ask, if the turbo is pumping air into the intake wouldn't there be more air then? The answer is yes but no. Volume is the total area. The cylinders can only hold a certain amount of volume (or air) which never changes. What turbos provide is more dense air. The volume stays the same but the oxygen content goes up in turbo charged engines by compressing the air molecules. You can increase the flow rate capability of an intercooler all day long but the engine will only accept so much air at any given time. How does flow rate help then? The faster the engine revs (rpm's) the faster the air is needed to enter the cylinders. A better flow rate provides more air faster. The question is, what should the specs of the components in a turbo, intercooler intake system be to produce maximum efficiency. It's all splitting hairs and depends on what your setup is made of.
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