Hi, I've searched but found nothing...

Since the stock exhaust is 2.5", what would be the effect of running a 2.5" midpipe to refrain from boost creep? Would be better flowing than 2.5" all the way with cat right?

Anyone?

 

i've never seen a 2.5" midpipe. the stock restriction in the stock system is the actual cat and not really the piping size, so i wouldn't expect a 2.5" midpipe to do much for boost creep

 

Thanks, was jus thinking about it being an improvement over stock 2.5" with cat.

Not really thinking of boost creep but a better flow... Not ready for 3" since I have a stock ecu.

Is this an actual improvement over 2.5" with cat?

 

Btw, I have a 98 jdm spec car... Stock 2.5" all the way through and replacing cat with stock siZed midpipe to improve flow...

3" in the future when supporting mods are ready but for now I don't see any creep. Just need to know if it's better than having a cat in there

 

From what I understand, you would like to improve flow to make more power. From a reliability standpoint, the cat, as long as the air pump system is in place and functioning, doesn't fail very often. For stock power levels, I would just leave the cat in. If you want to add a midpipe, you need to delete the air pump [I believe requires a tune/idler system] and PORT THE WASTEGATE. IMHO, I would just leave the stock cat on there and if you're looking to add another mod [look up the three mod rule :P], go for a catback.

Matt

 

getting rid of the cat to increase flow will introduce a boost creep problem. You should just get a 3" mp and use a restrictor to control the boost creep. I needed a 2.25" restrictor to control boost without porting the wastegate. If you dont want to mess with all that then keep the stock cat in there. A mp on a stock car is modding out of order if you ask me. my .02

 

I get it guys thanks, however I just wanted improvement on flow without worrying about creep.

Right now boost is solid 10 psi... Waiting for the chance for a pfc or safc before I head into 3" territory.

 

Can you please elaborate on why you believe that you require an ECU upgrade when changing your cat to a midpipe? What is happening to the system with the change? What is an ECU upgrade doing?

Take minute and truly ponder those questions and you will have your answer. My reasoning behind me asking you to ponder is that many people just add mods based on what the 'forum' says without truly understanding the ramifications of mods. But if you understand what is going on, you can build upon with the forum's input and choose your mods with confidence.

 

Thanks for that Montego...

I guess I just rely on info posted here, it's hard to find other info based on my main question about cats since all are doing the 3" ones.

I just wanted to free up flow by getting rid of my clogged cat, but since people say 3" will cause creep and I feel like wastegate porting will be difficult to do based on time constraints, I chose to just bolt up a straight 2.5" pipe.

My cat back exhaust is also a 2.5" so I figured a 3" DP and MP will only be useful if the exhaust is fully 3".

As for the ecu, I also relied on posts about creep and all, but with regards to my reactions having this already made I never saw creep with my straight through 2.5", and don't intend to increase boost. I know a lot of people here are being helpful to avoid others from making costly mistakes, but I don't think my mod plan is hurtful.

I do understand that I need to fix fuel settings with boost increase but since its solid 10 psi then I realized there's really nothing to worry about.

Out here in Manila it's hard to find people with the know how on this engine that's why I'm doing things carefully but then using common sense I know I shouldn't be so worried with other things that most worry about. Thanks for the input Montego, you're the kind of member I was looking for to ask questions with technical answers based on both experience and common sense.

 

My pleasure and that is exactly right. If you can control boost at 10 psi then you will not have an issue not matter what mods you have. With the stock ECU and in regards to being safe, it is all about A/F ratio. So if the boost level remains unchanged then the A/F will not be adversely affected and happy motoring.


Creep is an odd thing. Some cars experience it, others do not so one has to basically deal with on a case by case basis. If you replace the cat and precat (I'm assuming you removed the precat already) with a DP and a MP but leave the stock muffler in, I would suspect that you will experience boost spikes but not boost creep (but you never know). So you know what has changed it is a good idea to have a boost gauge in place before adding any kind of performance mods.

Boost controllers are good for adjusting elevated boost levels due to intake mods and IC mods. They are also quite handy in controlling boost spikes due to exhaust mods. However as you already know, boost creep (on a stock turboed FD) is function of the wastegate and can only be addressed by porting it.


Edit- you did say JDM fd. Those don't have a precat IIRC... But anyway the same info still applies

 

Unless the cat is really clogged, I'd leave it. They actually rarely fail on these cars. You would have better flow and more power gains with a catback exhaust as the stock muffler is extremely restrictive. I've made 360 rwhp through a stock main cat so they aren't the problem when in good shape.