Quote:
Originally Posted by RingMeister01
Larger diameter pipes (as this system) are ideal for SC cars that push much more volume through the exhaust than NA. Its an appropriate assumption that systems like the Akra Evo were not engineered to be paired with a SC. Though the Akra Evo is less restrictive than the stock system, it has its limitation due to diameter size. I'm not convinced that this system would be ideal for NA, as I've seen over large diameter piping cause power loss, especially on the low end on a NA motor.
Impressive to say the least!  |
The gains seen by the MRF Engineering mid-section has very little, if any to do with the piping diameter selection. We have noticed many comments and responses with respect to system diameter and wanted to take this opportunity to dispel some misconceptions.
The Akrapovic Evolution and GT4 mid-sections are not 2.25" I.D. systems. They are 2.375". The MRF system is for the most part a 2.5" I.D. mid-section. In regards to volumetric flow and capacity, dual 2.25" pipes are more than capable of handling over 600 RWHP.
The volume of an exhaust pipe is calculated as a cylinder. To calculate the volume of a cylinder, the formula is:
V=
πRē x H (in this case, H will be Length and represent the length of the exhaust system)
Known variables:
Length = 80" (length of mid-section)
Radius = Diameter/2 = 1.125"
And of course, the mathematical constant of Pi
TOTAL VOLUME = 318 (now this must be multiplied by 2 because there are 2 pipes) = 636 (for comparison sake, a single 3" exhaust which can handle 575 RWHP happily, has a total volume of 565.)
Volume of a SINGLE 3.5" exhaust: (which many of us engine builders know that its capable of handling 700 RWHP easily)
Known variables:
Length = 80" (length of mid-section)
Radius = Diameter/2 = 1.75"
Mathematical constant of Pi
TOTAL VOLUME = 769
Volume of a 2.5" I.D. mid-section (again dual pipes)
Known variables:
Length = 80" (length of mid-section)
Radius = Diameter/2 = 1.25
Mathematical constant of Pi
TOTAL VOLUME (must be multiplied by 2) = 784
Volume of Akrapovic Evolution/GT4 mid-section
Known variables:
Length = 80" (length of mid-section)
Radius = Diameter/2 = 1.1875"
Mathematical constant of Pi
TOTAL VOLUME (must be multiplied by 2) = 708
Now with all this said, the point here was not to demonstrate the differences in volume, it's only to help understand what each diamter means in regards to total volumetric capacity in the system. 2.25" dual systems are more than adequate for the 4.0L S65 M3, even when highly strung out. Now, lets make this clear, the Akrapovic is not 2.25", it is 2.375". The stock M3 mid-section is an odd size, it is somewhere between 2.375" and 2.5", it is also not 2.25". The factory mid-section has one part that is 2.25", and that is the first 2" coming off the front flange to create room for the o2 sensor bung.
Now back on topic to the MRF Velaforza mid-section..... The pipe was designed for N/A applications and we also knew and tested it on high forced induced applications to see its capabilities. As mentioned earlier in my first post, we tried larger diameter piping on S/C'd cars (3") and saw no appreciable gain, and only lost low end torque. In N/A form, the car simply did not like the 3" version.
In N/A form, comparing peak RWHP and peak RWTQ, produces 28 RWHP and 22 RWTQ over stock, and in the mid-range, produces a delta of more than 32 RWHP and 40 RWTQ. The most produced by any E9x system we are aware of.
If some are experiencing that 2.5" systems are not sufficient for their cars power output, I suggest looking at replacing your rear section exhaust system with something that retains the volumetric capacity of the mid-section, as many of the systems out there shrink down the perforated sections inside the muffler assemblies to reduce drone and unwanted frequencies. The Akrapovic rear section does a great job at maintaining this capacity.
-Malek