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Message: [QUOTE="B585Ford, post: 382319, member: 5497"] Very interesting post. Let me start by saying that I am still learning and trying to understand the relationship between turbos, boost, EBP. My understanding of running compounds is different so hopefully some people can chime in and let me know where I am going wrong. My understanding for a compound system is that at low RPMs/low boost, the HP turbo is providing most of the air flow. In the case of a 6.4, since the HP turbo is also a VGT turbo, its duty cycle will result in nearly completely open vanes in low boost settings. Since the HP turbo is smaller, it can spool up quicker (especially with the open vanes). As boost and RPMs rise, the Atmo starts to take over (as it is becoming spooled) because it can flow more air with its bigger wheel than the HP turbo can. Also during that time (moderate boost or RPMs), the vanes are beginning to close on the HP turbo. This also helps keep the EBP reasonable. When the boost is getting higher, the Atmo has taken over providing most of the air flow and the air flow it creates actually slows the HP turbo a little. This setup provides the best of all worlds...quick spool up thanks to the HP turbo along with massive air flow when needed from the atmo. My understanding of air flow is similar to what you said except I thought the CFM ratings were always based on a standard set of parameters (certain temp, humidity, pressure ([PSI], etc.) although I don't know the exact specs. In agreement with what you said, given the same volume of air, higher boost (PSI) will provide more air. What I love about this build is that air flow is being addressed from all angles (including the heads which is often not addressed). If I understand this correctly, if someone did a build with just a ported intake manny, ported heads, and ported exhaust manny and larger diameter up pipes (with the same turbo and same fuel), they would actually produce less boost but create more air flow/power with the less boost (because the volume is now larger). A Dmax is good example. They don't run nearly the boost we do to get the same HP/torque (ignoring the fact that they have shorter rods which helps making HP but hurts torque) because their heads flow more from the factory than the stingy 6.4 heads. Sorry for the derail. [/QUOTE]