Hi guys,

In the last few weeks I've seen several posts on whether it is ok to use 2.5" or higher piping, or if somebody could use their ITR AEM CAI as a charge pipe. I tried to help all of them best I could, but jus a short while ago I helped another H-T member out with a similar question. I searched online and used a flow calculator to help me figure out the airflow velocity for a given area and cfm. The site I used is

THIS ONE. As you guys can see it has the area in length times width instead of PiRsquare which is the area of a circle. I took the area of each pipie diameter and usd the equivalent area of a square and used those as my length and width. I made it simple and just took the area of the circle and divided by 2. The resulting number was usd as my length and 2 was used as my width.

Your actual results may vary (ie when you add an IC) so just use my numbers as sort of a bench mark to compare different piping sizes. One thing you guys will notice is that none of the velocites goes above 304 MPH or 0.4 mach. According to Corky Bell, Maximum Boost pg 61, 304 MPH or 0.4 mach is the point at which airflow meets increased resistance (drag) and flow losses are experienced.

Anyways here are the numbers I came up with. The velocities are in miles per hour and mach, and the flow rates are in cfm. Measurements for the piping are in inches.

<FONT COLOR="blue"><FONT SIZE="5">0.4 mach = 304 MPH</FONT></FONT>

__2" piping__
1.57 x 2 = 3.14 sq in

300 cfm = 156 mph = 0.20 mach

400 cfm = 208 mph = 0.27 mach

500 cfm = 261 mph = 0.34 mach

<FONT COLOR="blue">585 cfm max = 304 mph = 0.40 mach</FONT>

__2.25" piping__
3.9740625 sq in = 1.98703125 x 2

300 cfm = 123 mph = 0.16 mach

400 cfm = 164 mph = 0.21 mach

500 cfm = 205 mph = 0.26 mach

600 cfm = 247 mph = 0.32 mach

700 cfm = 288 mph = 0.37 mach

<FONT COLOR="blue">740 cfm max = 304 mph = 0.40 mach</FONT>

__2.5" piping__
4.90625 sq in = 2.453125 x 2

300 cfm = 100 mph = 0.13 mach

400 cfm = 133 mph = 0.17 mach

500 cfm = 166 mph = 0.21 mach

600 cfm = 200 mph = 0.26 mach

700 cfm = 233 mph = 0.30 mach

800 cfm = 266 mph = 0.34 mach

900 cfm = 300 mph = 0.39 mach

<FONT COLOR="blue">913 cfm max = 304 mph = 0.40 mach</FONT>

__2.75" piping__
5.9365625 sq in = 2.96828125 x 2

300 cfm = 82 mph = 0.10 mach

400 cfm = 110 mph = 0.14 mach

500 cfm = 137 mph = 0.17 mach

600 cfm = 165 mph = 0.21 mach

700 cfm = 192 mph = 0.25 mach

800 cfm = 220 mph = 0.28 mach

900 cfm = 248 mph = 0.32 mach

1000 cfm = 275 mph = 0.36 mach

<FONT COLOR="blue">1100 cfm max = 303 mph = 0.40 mach</FONT>

__3.0" piping__
7.065 sq in = 3.5325 x 2

300 cfm = 69 mph = 0.09 mach

400 cfm = 92 mph = 0.12 mach

500 cfm = 115 mph = 0.15 mach

600 cfm = 138 mph = 0.18 mach

700 cfm = 162 mph = 0.21 mach

800 cfm = 185 mph = 0.24 mach

900 cfm = 208 mph = 0.27 mach

1000 cfm = 231 mph = 0.30 mach

1100 cfm = 254 cfm = 0.33 mach

1200 cfm = 277 mph = 0.36 mach

<FONT COLOR="blue">1300 cfm max= 301 mph = 0.39 mach</FONT>

*Modified by BlueShadow at 6:55 AM 4/5/2005*