**Re: Forced Induction FAQ *NEW* (herbehop)**
How to read a compressor map

Posted by:

O2VW1.8T
taken from honda-tech

using a map of a T04E 60 trim I will explain all the numbers on the map

1-left side, PRESSURE RATIO

(14.7 + amount of boost) / 14.7 = PR

so to figure out the PR for 8 PSI

(14.7 + 8) / 14.7 = 1.54 PR

2-bottom side, AIRFLOW RATE UNDER BOOST (LB/MIN on this map)

Most methods of calculation your engine's airflow rate will give you the answer in cubic feet per minute (CFM). However most compressor maps measure airflow rate in pounds per minute (LB/MIN). As some of you may know the weight of air varies with the temperature. To convert CFM to LB/MIN use the following numbers.

@ 48 degrees F : (CFM * 0.078125) = LB/MIN

@112 degrees F : (CFM * 0.070318) = LB/MIN

@175 degrees F : (CFM * 0.06251) = LB/MIN

Say for example our airflow rate is 500 CFM , and the temperature is 112 degrees F.

(500 * 0.070318) = 35.16 LB/MIN

*For those of you that know anything about ideal gas law, if you know a better way of explaining how to convert CFM to LB/MIN, your input would be appreciated. But please explain it in "laymans" terms, so that everyone can get a grasp on it.

3-dotted line on far left side of "ovals", SURGE LIMIT

It is important to try and keep yourself on the right side of this dotted line whenever possible. If you fall to the left of this dotted line you will experience compressor surge. This type of compressor surge will occur when there is too much boost, but not enough airflow through the system, usually this is between idle and the point at which full boost is reached. The chirping sound that can be heard is a result of the oscillating air. This sound is often described as a "Snakelike" sound or a che-che-che sound.

*staying in the "surge limit" area for too long could possibly damage your turbo.

4-numbers on far right, 46,020, 69,640, 83,972 etc, COMPRESSOR RPM

This is RPM at which the compressor fans will be turning. an average RPM is between 90,000 and 130,000. The line that branches out from each of these numbers that goes towards the surge limit line shows you the RPM range of the compressor fan across the entire compressor map.

5-78%,75%, 74%, COMPRESSOR EFFICIENCY

This is related to the temp of air and how much it is being heated up as it is being compressed by the compressor. A low number (60%) means that the compressor is heating the air more a high number (78%) means the air is not heated as much when it is compressed.

6-"Ovals"

I you look closely you will see that the compressor efficiency numbers usually sit right on top of one of these Oval lines. These Ovals show you the boundaries of the compressor efficiency at the different percentiles. Think of it as a topography map that shows you different elevations or changes in elevations. The innermost Oval on the sample T04 E 60" is not labeleb but it is probably 79% or 80%, so any where inside that Oval and you would be operating in the 80% range of that compressor.

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how to choose the right IC piping

Airflow velocity for different intercooler piping diameters (2.0 2.25 2.5 2.75 3.0 inches)

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