Airflow velocity for different intercooler piping diameters 2.0 2.25 2.5 2.75 3.0 in - Honda Prelude Forum

BlueShadow · 04-05-2005, 07:55 AM

Hey guys, I originally posted this on Honda-Tech after seeing a couple of ic piping threads. I figure I'd share it with you guys too.

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.

0.4 mach = 304 MPH

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
585 cfm max = 304 mph = 0.40 mach

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
740 cfm max = 304 mph = 0.40 mach

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
913 cfm max = 304 mph = 0.40 mach

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
1100 cfm max = 303 mph = 0.40 mach

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
1300 cfm max= 301 mph = 0.39 mach

BlueShadow · 04-05-2005, 07:58 AM

If any of you guys see anything wrong with any of that stuff lemme know.

TIA

Paluce · 04-05-2005, 08:10 AM

The big dissadvantage of using big pipes is more lag. Their is a lot more capacity in the intake system that needs to run through the engine and get compressed, so spool up time is increased.

BlueShadow · 04-05-2005, 08:17 AM

Quote:

Originally Posted by Paluce

The big dissadvantage of using big pipes is more lag. Their is a lot more capacity in the intake system that needs to run through the engine and get compressed, so spool up time is increased.

Yah, one guy on H-T actually wanted to use his 3" ITR CAI as a charge pipe. I had to convince him that lag would be huge. He didn't believe me until I linked him to that site aboe with the velocity calculator and I did the math for him.

BlueShadow · 04-05-2005, 08:30 AM

Oh yah, I believe that an average velocity would be the 2.25" pipe with 375-425 cfm. I believe that where your average drag or Revhard kit at 7 psi would be. For 15 psi it would be around 525-575 cfm. (That's for an H22)

tenzola · 04-05-2005, 09:16 AM

now does all this only matter if you're looking to make crazy power? i mean.. with my bone yard boost.. i used an e-bay intake tube and connected that to the intercooler.. and i need to turn down the boost on the turbo.. i don't know how lag is becuase the shop wants to tune the car with the boost turned down before i really get on it

if you could jump to the h23 bone yard boost pictures and tell me what you think.. that would be greatly apreciated

BlueShadow · 04-05-2005, 09:33 AM

I also included piping diameters and flow rates for small piping diameters too. So yes this info can also be used for low boost setups. Say you are using an Ebay intake for a charge pipie which is 2.5" diameter and you are only boosting 7 PSI. Now say for exampe that at 7 PSI you are flowing 300 CFM (just an example). Look at the numbers above and compare the intake air velocity for the 3" pipie and 2.5" pipe for 300 cfm. You'll se there is a difference, but now as far as how noticeable that difference will be I have no idea.

tenzola · 04-05-2005, 09:47 AM