This is exactly why you do not want to inject meth in the CP on high HP cars. This is also the exact reason i went port injection a while back. If anyone knows how a OCC works by using velocity and change of direction will understand why CP injection is bad practice

This is not my work besides N54 calculations at the end.

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you want to run the smallest possible without going over a certain air speed. 304 MPH or 0.4 mach is the point at which airflow meets increased resistance (drag) and flow losses are experienced. Depending on which turbo your running and what hp your looking for will determine piping size. to small is a restriction and to larger is laggy. generally for the average setup 2.25-2.5" is what works here is info i found on mach speeds of certain size piping relevant to cfm flow 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 |

What you need to do is find you airflow rate based on :

Basics you will use these numbers later on

PRESSURE RATIO = (14.7 + your desired PSI) / 14.7 = PR

convert CFM to LB per MIN = CFM x 0.070318 = LB/MIN (@ sea level and 112 degrees*)

LITERS TO CUBIC INCHES DISPLACEMENT = # of L's x 61

CFM = Cubic Feet per Minute

now using my car as an example:

3.0L (183. cid), 7300 Redline, desired boost is 25 PSI

CALCULATING AIRFLOW RATE AT REDLINE and MAX PSI

cid = Cubic Inches Disp.

VE = Volumetric efficiency in percent

.5 = (given) 4-stroke engine fills cylinder only on one-half the revolutions

1728 = converts cubic inches to cubic feet

Airflow in CFM = (cid x rpm x .5 x VE%) / 1728 = CFM no boost

CFM x PR = CFM under boost

so for my N54:

PR = (14.7 + 25 ) / 14.7 = 2.7

Airflow = (183 x 7300 x.5 x .85) / 1728 = 328.56 CFM (no boost)

328.56 x 2.7 = 887.12 CFM under 25 PSI

A cubic feet of air (length+width+height) weighs different at diff. Altitudes and different temperatures. to simplify it well just assume we are at sea level and the air temp is 112 *. the conversion number is 0.070318.

so for CFM TO LB/MIN = CFM x 0.070318 = LB/MIN

887.12 x 0.070318 = 62.38 LB/MIN (most speculate the precision 6466 is a 90lb turbo, this shows how much room is actually left in it. About 30% more left in its efficiency range)

so here we have:

BASIC ENGINE FLOW RATE = 328.56 CFM

ENGINE FLOWRATE with 25 PSI = 887.12 CFM (62.38 LB/MIN)

PRESSURE RATIO (PR) = 2.7

In conclusion you can see that a 2.5” duct is enough to support 913 CFM where as my car is pushing 887. I know its border line but here are some things to consider.

Pros:

1. Drivability is more preferred

2. If I really wanted to squeeze the lemon I’m sure another .5PSI would overcome

3. The increased speed (about 50mph) has more of a “ram air” effect theoretically filling the cyl better.

Cons:

1 meth distribution has less time . (direct port would probably be more preferred) ]]>