Exhaust - 2.5" or 3"

[VIN18M]

I'm starting to collect bits and pieces I need to make up the exhaust for my GTi (forged 93t).

I had originally planned to go 3" from the Punishment racing dump (which is 2.5") all the way back. I'm in two minds now whether it will be insanely noisy with my cams (290/290 11mm lift) or if 2.5" the whole way will mean I'm not getting the most out of the cams because the engine isn't breathing enough. Or in this case is a bit of back pressure better for low down power?

The plan is to run downpipe-flex-cat-hotdog-rear muffler.
3" will obviously create a few clearance issues but that'll just mean I need to be extra careful over bumps.

Opinions? Recommendations?

 

[khubner1]

are you chasing big power if so go 3" I've got 3" from the dump back had a 3" flange welded to the 2.5" flange (bacically they're stacked and welded) and mine isn't that loud and i don't have the hotdog if your concerned about the noise grab a varex so that you can make it quite as stock when needed and open it up for max flow. imo theres plenty of room for 3" in either awd or fwd trims.

i had 3" in fwd and it follow the stock route exactly. including humping over the rear lower control arm.

infact i still have a muffler with that bend attached to it it's a big f off cannon though

you can see the cannon and the 3" pipe attached here went in exactly the same space as stock

 

[peasoup]

I changed my 3" system to 2.5 from cat back, main aim was to quiet it down, which it did, got some good mufflers and it noticeably reduced the drone.

 

[4piknup]

3".
You could run a gsr setup or evo.
I got a 3" gsr setup and it ran fine down the body of the jumbuck.
I had to add a bolthole under the floor and remove a hanger as well. But it was perfect fit all the way to the back of the gsr fuel tank.
Yours should fit good all the way to the tank.

Oh, does yours go around the edge of the tank?
If so you will need more mods and more pipe than I did..

 

[VIN18M]

Yeah mine goes around the fuel tank on the passenger side, then over the control arms however I was going to come straight through the middle of the control arms and off to the drivers side with a straight muffler (no more cannon for me).

This is the path the exhaust runs on the GTis...


http://76.my/Malaysia/ultra-racing-side-bar-proton-putra-satria-gti-ur-sd4-228-maxaudio-0907-01-MaxAudio@126.jpg

 

[khubner1]

same as the lancer no clearence issues man

 

[CYBORG-X]

the question is not the size, more the design... for example ive got 2 mates with xr6 turbo's, both bf2, both made very close power stock... one went with an off the shelf 4in system with 4.5in dump, the other I made a custom 3.5, with separate stinger pipe 16in long, made an extra 35kw..... hmmm.... the design if I remember right is it needs to be minimum 5in till first bend with a maximum of 15deg flare from the turbine outlet, and the separate stinger should be 13-16in long... if you get the dump right, physical size wont matter (not talkin 1in pipe)

 

[JayRome]

3" and run a 08+ STI rear muffler, will keep it quiet and flow more then enough for a 1.8T (inlet on muffler on the side and 2.75", outlets are 2.25" each side)

EvoX muffler is also an idea.. but center inlet wont work well..


Just a suggestion..

 

[VIN18M]

Well the dump pipe is a Punishment Racing item which is a pretty good design with split wastegate section, they are't cheap and have a really good reputation.

http://www.punishment-racing.com/punishment-racing-stainless-steel-recirculated-o2-housing-for-eclipse-talon/

It is only a 1.8L but I'm running very aggressive cams so I'm concerned about finding the balance between noise and performance (usual story).

I think I'll go 3" and if it's insanely loud I'll just add another muffler - it's not like it's my daily anyway, it'll only be driven on weekends.

 

[caged]

What are the specs @1mm on those tomei 290's? I couldn't find them online.

 

[VIN18M]

The cams came with the engine so not 100% sure on the details, all I know is they are 1mm lift and 290 exhaust and inlet...

 

[CLuTZ]

290 is massive. What sized turbo are you using??

 

[VIN18M]

Only a 20g to begin with. See how that performs and if I need to go bigger.
They were already in the engine when I bought it so I figure I'll see how I go with them...

 

[BYBY5L]

haha 1mm lift! Think ya mean 11.1mm bud, very lumpy cam there, ya got any vids of this running? Would love to hear it!

 

[VIN18M]

Sorry, typo they are 11.1mm as stated in my original post. Car isn't running yet, hasn't been fitted to the car but hopefully in the next few weeks I'll be able to start it.

 

[BYBY5L]

yea sweet, should sound pretty tuff
and yea i was just letting ya know what ya brought as alot of the 290 tomei's are 11.5 only know cos i got offered a set a while back