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Divorced vs bellmouth (again)


RJS5689

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I have read the bellmouth vs divorced threads on here and don't know what to do. I am looking at some Megan and Invidia catless downpipes. The best deal I found was on an Invidia divorced downpipe (at agreat price shipped). I'm not sure what to do though. I have heard various things in different places some saying divorced is good and others saying it is bad. My plan for the car is to throw the downpipe in and go with a custom tune and be done with power mods for awhile. Will I see issues with the Invidia divorced downpipe that make going bellmouth better, or will it be too tough to notice a real difference?
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With a proper tune, there is not much of a difference between between the two. Both sets are bellmouth, it is just that some DP's have a splitter to seperate the wastegate. I recently purchased an AVO DP with a custom 3in cat, and had to order a new bellmouth(previous owner had a twinscroll). The new one will be divorced, but I do not expect to loose hp over it.
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With a proper tune, there is not much of a difference between between the two. Both sets are bellmouth, it is just that some DP's have a splitter to seperate the wastegate. I recently purchased an AVO DP with a custom 3in cat, and had to order a new bellmouth(previous owner had a twinscroll). The new one will be divorced, but I do not expect to loose hp over it.

That's exactly what I was thinking. I am planning on having an Infamous tune made for the car, but I am still aware that there could be boost creep/spike issues regardless of downpipe design. I just jumped on this deal because of the price I found it for.

 

Excuse me for asking this rather "noob" is question, but this is my first Subaru. Why do we have boost spike/creep issues so frequently? Is it because of the mechanical wastegate? I had a GTI with the 2.0T FSI engine and it used an electronic blowoff valve and I never had boost creep/spike issues; neither did my friends with the same car. Or is it something related to our turbochargers, turbo design, etc.

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how a turbo builds boost with an internal gate....there is a rubber diaphram connected to a rod which controls the wastegate open and close. a boost controller controls the pressure on the diaphram therefore controlling the rod movement and wastegate movement. once desired boost is met the wastegate diphram will hold the wastegate flap at a certain spot so enough exhaust gas will pass the turbine to create boost, with the rest escaping through the wastegate and out the exhaust. if the wastegate is too small, then exhaust that is supposed to bypass the turbine doesn't , and in return creates undesired boost.
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  • 8 months later...
Do you believe you'd still have the boost spike issue with the stock exhaust. I noticed the majority of peoples problems were with a catless downpipe and a high-flow aftermarket exhaust. I want to keep the rumbles down, so I was planning on doing a 3" catless dp with the stock exhaust. I also figured that with a little more backpressure from the stock exhuast that it would minimize the boost spiking. Any advice would be great!
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If you go with the Invidia make sure you grind down the divorcer some anyways, after reading up on it and seeing a lot of posts saying the problem with it was fixed i decided not to grind it down when i put it on my 09 LGT back in May, but ended up over boosting real bad and having to take it off and grind it down. Since I've ground it down I've had no over boost and running 17.5 psi on an Infamous1 tune. However i ground it down all the way so its basically just a bell-mouth now with a piece of metal in the middle :D
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