2.5" or 3" DP for my setup?

[Prodigyman]

Got my 97 GSX and getting it to custom exhaust shop on Monday, here are the parts I’ll be giving them
MagnaFlow Cat Part #94009 (3")
MagnaFlow Muffler #14828 (3" inlet and 4" outlet)

So what I am wondering what size pipe going from Turbo to CAT should be? 2.5" or 3"? I want to avoid boost creep so I read somewhere 2.5" to CAT and catback 3" but I am not sure.


Turbo I have ATM is stock but very soon be getting FPBig28 (next week or so) form forced performance.

Current Setup
High Flow Intake
Getting quite large FMIC with upper and lower piping (lines will be custom finished at the same exhaust shop)
Greedy Type S BOV
Greedy Profec B Spec 2 Boost Controller
I’ll maybe getting 190 GPH pump and/or 550s inj

Any suggestions will be appreciated. Thx

 

[memory-x]

im buying a tial external wastegate, welding flange to mani, port mani etc., for my small 16g with 3 inch 02 elim(cause i know i will go with a bigger turbo soon or later). should have no creep at all for $220 , just a suggestion.

 

[Lordpaxin]

2.5 would be adequate, but 3 inch is always better.
more flow is never bad, you may get a little more chance at creep, but thats up to you.

a small16g is a creepy turbo. gives me the shivers!!!

I got a 3 nch 02 eliminator on my evoIII16g @ 19psi and creep notta bit til 6500rpm and it may slide up a psi or so. hardly noticable.

 

[memory-x]

Lordpaxin do you have internal gate ? flapper mod ? im about to bolt up my setup once i get my exhaust from rnr. im going to run the small 16g for awhile since i got it for $200. i will move up to a evo3 or 50 trim later though.

 

[CyberEye]

I have a 16g (not sure if it's small or big, came on the car). Will a 3" downpipe bolt right up to my O2 housing? Can I port the O2 housing enough to match 3" dp, or is there even enough metal on it to do it

 

[sweet97]

Most 3" down pipes are not 3" at the 02 housing though they can be had. Most neck to 2.5" at the 02 housing. My EVO3 02 is 2.5". Not sure the 2g can be opened to 2.5" because I drive a 1g. mark

 

[Prodigyman]

Well guys i am not getting 16G turbo... i am getting FPBig T28 .... and the exhaust shop can custom make me any size pipes for me! So 2.5" to cat will be better for me?

 

[NOSNUSE]

It really depends on the amount of boost you are going to run, but mine was 2.5" to the flex section of the DP then 3" all the way back. You want to keep the first 12" or so at 2.5" so the heat will keep the exhaust gases moving fast as they cool they expand henceforth why 3" after the flex section. The best way to eliminate boost creep that I have found was with a dump tube on the O2 housing, but that was just me and my car.

 

[Prodigyman]

It really depends on the amount of boost you are going to run, but mine was 2.5" to the flex section of the DP then 3" all the way back. You want to keep the first 12" or so at 2.5" so the heat will keep the exhaust gases moving fast as they cool they expand henceforth why 3" after the flex section. The best way to eliminate boost creep that I have found was with a dump tube on the O2 housing, but that was just me and my car.

sweet thx! so i'll go with 2.5" from Turbo compressor to CAT (3" cat) and then 3" catback

thx guys!

 

[Attack Eagle]

go RRE style: 2.5 to the flex section and then 3" the rest of the way.

I have the RRE piece and the smaller 2.5 up front really does give much better clearance.

Going from a stock dp and cat to the RRE and 3" cat was a noticable difference.