intercooler pipe size

[Pappu1]

a mate recently bought a FMIC kit which is supposed to have 3inch piping (still waiting for the shipment to arrive)

while we were talking abt it another mate cam along nad he already has a FMIC on his v4 wrx and his one is 2.5 inch piping

anyway we all got talking and came up with this question:

if someone were to use smaller piping say 2inch how much power will that support before choking the flow...???

anyone here with some experience or theories around that?

does smaller piping have any efect on the performance?

from what i see, my factory turbo pipe is around 2inch but its a TMIC though....

[Guest S T E Y E]

3 inch would be too big bro...on a mild setup anyway..

U normally go the size of the throttle butterfly (not the joiner on the throttle body but the diameter of the throttle butterfly)

so in theory if u have a large throttle u would go to bigger piping etc...

[Pappu1]

wat abt using a smaller pipe like 2 inchs?

[Guest S T E Y E]

well the theory would be that it would speed the air up ...

the outlet of the turbo is 2 inch and the throttle butterfly is 2.5inch (standard)

so the aftermarket kits run 2 inch off the turbo untill it gets to the pod filter area...then to 2.5 inch to the intercooler...then 2.5 inch from the cooler to the throttle...

seems to work good

[Pappu1]

wat if 2 inch from turbo to fmic and all the way back to throttle where its using a joiner to get to the required size....

[Guest S T E Y E]

havent seen or tryed that on a subaru before so hopefully someone can message up and tell us whats up....

ive ran 2 inch piping on a GT starlet before....originally had 2.5 inch piping on it and it didnt perform as it should have with the turbo / suporting mods it had.. redone the piping in 2 inch and the results were improved majorly...

but this is due to the gt starlet having a 2 inch throttle butterfly

[Solja]

had these same questions awhile ago when i had to decide between 2.25 inlet intercooler, 2.5 and the 3inch inlet intercoolers and then what piping to use for a optimized setup, settled on the smaller 2.25 to keep lag down.

i then decided on 2inch piping pre intercooler to match outlet of turbo and then 2.5inch post to the throttlebody. i was reaching the flow limits of 2inch piping at around 230-240kw so have upgraded to 2.25 piping pre intercooler since.

heres some info on various pipe sizes, match it to your turbo cfm and give yourself alittle headroom but generally 2.5inch all around is more than anoth for most people

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

[ODB]

yeah was gonna say.

generally if you are gonna be anal over sizing you go 0.5 inch bigger on outlet side of the cooler.

[Pappu1]

thankd for the sizing and all but im not sure how to read.. i think the turbo is 500cfm at max (vf22)

will the 2inch work on that as the list shows mph etc..

aim is 230kw@w max (pretty much max on a vf22 i been told...)

[Guest S T E Y E]

it shows 2 inch is 585 cfm max so i guess so...

would running 2 inch all the way make less lag? in theory?

[Pappu1]

hmm so wud i be rite to addume 2 inch piping on vf22 wud eb able to flow a max of 230kw@w with no issues???

[Solja]

2inch will be fine but if you wanna do it once so dont need to revisit it again go with 2.25/2.5, using the correct size will keep the airflow speed up to help with response

[Pappu1]

the reason i wana do small pipes id want to try and get a custom piping dine and get both pipes on the left side and kinda mount the fmic so both the inlet/outlet are on the side...

just trying to sus out what is the smallest pipe i can get away with and then try bit bigger..

does that make sence?

[dubbedup]

Pappu - similar to an Evo setup?

also Sti type R on here had a mean intercooler setup, its one of the shortest i have seen without going v mount etc

[Pappu1]

Will draw a rough diagram and post wat i mean perhaps