exhaust system size

[EC17PSE]

Ok so yet another exhaust question, but ive done my homework and read alot of posts today and im running into brickwalls and seem to get to the same ending! So i thought that i might get a better answer but i dont know so here i go!

My next upgrade is a full exhaust system, i already have PR o2 recirc housing to go with the setup and im not wanting to go cheap so full mandrel and v-bands,
now ive read many posts on a full 3" system but keep getting boost creep in every thread, and the only way cure it is porting! But im not in a position to take the turbo hotside off so im a little stuck, then i read a post about a 2.5" dp - 3" catback but then another few posts said its not the best idea and was like pissing in a funnel backwards .

My future plans are to go with a 20g or bigger and about 500 hp but thats a few years away,

So am i ok to just run a 2.5 dp and 3 catback? Oh and im running a testpipe aswell, i just dont want this boost creep or try to eliminate it as much as possible.

Im sure ive read almost every thread on this and im sorry for making yet another thread on exhausts,

Thanks for everyones help and hope im able to go this route as ive already brought an expensive 3" inlet muffler.

Bobby

 

[SHEARER_TSI]

You could switch to wither a external wastegate or a O2 dump.

 

[EC17PSE]

You could switch to wither a external wastegate or a O2 dump.

Sorry i forgot to say thats not an option either, ive just brought the o2 housing and i dont want to go external just yet aswell,

And on another note i dont want answers like just go 3" and dont look back as thats not a helpfull answer! This was NOT aimed at you SHEARER TSI just so you dont think im being rude

 

[gofer]

Running a 2.5" downpipe, a catalytic converter, to a 3" catback exhaust will be fine to get you to the 500hp goal you've got. In the mean time though, because the downpipe is a bit smaller you should have no problem with boost control. Remember, the more restriction you free up in the exhaust the better chance you'll have boost creep.

 

[EC17PSE]

Running a 2.5" downpipe, a catalytic converter, to a 3" catback exhaust will be fine to get you to the 500hp goal you've got. In the mean time though, because the downpipe is a bit smaller you should have no problem with boost control. Remember though, the more restriction you free up in the exhaust the better chance you'll have boost creep.

NO im running a cat less system! Will that make a difference?

On a side note i pm'd justin and asked him a few hours before i made this thread and he said 3" is ok as the stock t-25 is restrictive in its self and that boost will hold its self to the normal level. Untill i go tdo5 or bigger, i see the theory but i read it still happens on stock turbos still so im at the wall again :-(

 

[Alex42590]

i have a evo 3 16g with evo o2 housing to a rre long cat elim downpipe then my srs 3" ebay cat back unported and have my boost controller at 13 psi because i havent had time to upgrade my injectors or fuel pump, anyways i get boost creep to 19-20 psi it really pisses me off not being able to drive my car without worying or staring at my boost gauge........ hopefully ill port it soon and be done with it because im guessing thats my only option at this point

good luck

 

[EC17PSE]

i have a evo 3 16g with evo o2 housing to a rre long cat elim downpipe then my srs 3" ebay cat back unported and have my boost controller at 13 psi because i havent had time to upgrade my injectors or fuel pump, anyways i get boost creep to 19-20 psi it really pisses me off not being able to drive my car without worying or staring at my boost gauge........ hopefully ill port it soon and be done with it because im guessing thats my only option at this point

good luck

Is your dp 3" aswell or is that 2.5"?

 

[gofer]

Justin' correct, I just assumed you had something other than a t-25 on there. It might creep but, whatever it does creep to, it won't be so much that you'll run out of fuel.

Did you notice any rise in boost pressure after you installed the exhaust setup you currently have?

Is your dp 3" aswell or is that 2.5"?

ALL RRE downpipes are 2.5" inlet to a 3" back from the flex section. I installed one on a 16g (with no cat and a 3" exhaust) and couldn't keep boost below 26 psi it would creep so bad. My only choice was to go back to the stock downpipe/cat to regain control of boost pressure so I didn't blow my headgasket or lean the motor out.

 

[Alex42590]

Justin' correct, I just assumed you had something other than a t-25 on there. It might creep but, whatever it does creep to, it won't be so much that you'll run out of fuel.

Did you notice any rise in boost pressure after you installed the exhaust setup you currently have?

ALL RRE downpipes are 2.5" inlet to a 3" back from the flex section. I installed one on a 16g (with no cat and a 3" exhaust) and couldn't keep boost below 26 psi it would creep so bad. My only choice was to go back to the stock downpipe/cat to regain control of boost pressure so I didn't blow my headgasket or lean the motor out.

so your saying im screwed? porting wont help me

 

[EC17PSE]

Justin' correct, I just assumed you had something other than a t-25 on there. It might creep but, whatever it does creep to, it won't be so much that you'll run out of fuel.

Did you notice any rise in boost pressure after you installed the exhaust setup you currently have?

Sorry i forgot to state its a stock turbo, and ive got the stock system on at the moment! I got abit excited and added it to my list before i installed it ooops my bad. But the rest of the list is correct and spot on.

I will be getting a boost gauge aswell in the next few weeks so i can keep an eye on it in the future.

So you think im ok running a full 3"? Im more then happy to run a 2.5" dp if its a safer option to start with. I just dont want to have any issues first time round if you know what i mean. At least not yet

 

[gofer]

so your saying im screwed? porting wont help me

I'm sorry, but yes. I ported mine, it still crept, I pulled it and ported it again, it still crept. The only answer was going to an external wastegate setup or installing the stock downpipe/catalytic converter until I was ready to run that much boost.

I reinstalled my stock downpipe/cat and then ordered a PR o2 housing setup for a external wastegate, both fixed my boost creep issue.

 

[LxiMax]

Isn't the stock exhaust capable of running 11's?

 

[Alex42590]

I'm sorry, but yes. I ported mine, it still crept, I pulled it and ported it again, it still crept. The only answer was going to an external wastegate setup or installing the stock downpipe/catalytic converter until I was ready to run that much boost.

I reinstalled my stock downpipe/cat and then ordered a PR o2 housing setup for a external wastegate, both fixed my boost creep issue.

you ported the turbo and o2 housing? maybe a external wastegate and the rre downpipe woulve fixed it

 

[gofer]

Yes. Installing a external wastegate allowed me to run the RRE dp without any boost creep issues, the stock wastegate system wasn't enough to control boost no matter how much I ported it. Thats all I'm trying to say, porting everything, at least in my situation, wasn't enough to control boost.

Isn't the stock exhaust capable of running 11's?

In the 1/8th mile... Who told you that?

 

[LxiMax]

In the 1/8th mile... Who told you that?

I've seen it posted on here a few times. Not at a computer at the moment but can find the conversations later.

 

[Alex42590]

Sorry i forgot to state its a stock turbo, and ive got the stock system on at the moment! I got abit excited and added it to my list before i installed it ooops my bad. But the rest of the list is correct and spot on.

I will be getting a boost gauge aswell in the next few weeks so i can keep an eye on it in the future.

So you think im ok running a full 3"? Im more then happy to run a 2.5" dp if its a safer option to start with. I just dont want to have any issues first time round if you know what i mean. At least not yet

i wouldnt be able to tell you if porting is gonna fix boost creep but a cobination of porting and external wastegate should do it

well if your gonna upgrade your turbo eventually , go with 2.5 to 3" downpipe then a 3" catback and be sure to port while you have it off, if you get boost creep do a external wategate

 

[SHEARER_TSI]

Or sell your current o2 housing and get a dump.

 

[JOEY A]

3inch and be done with it.

Isn't the stock exhaust capable of running 11's?

Why do you want to run a stock exhaust>

 

[SHEARER_TSI]

I've never seen anyone run really run the stock exhaust usually thats the first thing people toss.

 

[EC17PSE]

Well thanks for the help guy, im going to run a 2.5" DP and then 3" from either the flex or from the test pipe back it seems to be a safer option and as many people have said 2.5" is capable if 350-400 hp and im not going close to this this year, so all i will need in the future is just a 3" DP so im cool with this.

Here are a couple of quoyes from justin that helped me decide my exhaust side,
I'd just go with a 2.5" downpipe or at least one that has 2.5" to the flex section. A full 3" exhaust is absolutely overkill for any street-driven car below 20psi and slower than a 13.0.

Back in the day (2002-2003) a good buddy of mine ran 12.69 @ 109 with a Big 16G @ 18psi, Supra Sidemount intercooler, SAFC1, 550cc injectors, 2G MAS, and a catless Buschur 2.5" turbo-back exhaust. Everything else was stock. That was a fast DSM in that era...but things were so much simpler back then.

~Jus

And this one,

It doesn't matter for a T25 because the turbine wheel is so small it has plenty of restriction. You can run open downpipe on a T25 and still have perfect boost control. It's not a problem until you reach the TD05H turbo platform and you're attempting to run low boost on a large exhaust system.

~Jus