Catted vs catless DP - Page 2 - Subaru WRX Forum
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#16 Old 02-04-2014, 10:40 PM
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Originally Posted by arcticscythe View Post
The idea behind a divorced setup is to direct the gasses down the same path and create a more laminar flow of exhaust and vented boost. It wasn't designed to separate the gases entirely, only to prevent turbulence. CATs work best under laminar flow, meaning that the exhaust gasses are flowing in a straight line rather than bouncing off the walls of the exhaust.
Except the market is filled with shit "divorced" downpipes and the bellmouths do a wonderful job of merging exaust streams to achieve laminar flow with minimal backpressure.

Basically, a divorced downpipe is a marketing gimic from people trying to stand out from the ubiquitous bellmouth downpipe. Most run a tiny little side pipe out of the wastegate for a few feet and then merge it in to the main stream at a ####ing right angle (terrible) long before the end of the exhaust. The wastegate flow is disruptive to the main exhaust flow and when the wastegate is fully closed, it STILL causes a disruption because it has stagnant air, cooler air, sitting off the stream.

Bellmouths have a very spacious mixing chamber where the airstreams meet at a near perpendicular angle and are gradually reduced into one stream. In other words, it's about the best you can do short of a truly divorced wastegate stream (commonly called external wastegate but really that's whither it's internal to the turbo, not how it's dumped. They're unrelated).

There are some divorced downpipes I've seen that don't suck. You could also make one yourself. They merge in the two exhaust streams into a fat ass piece of pipe and reduce it. They may even be slightly better at it than a bellmouth design, there's just not much gain there and more likely something marked "divorce downpipe" is an inferior product to a standard bellmouth.

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#17 Old 02-05-2014, 02:11 AM
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^^^this^^^ marketing gimmick !
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#18 Old 02-09-2014, 09:40 PM
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So is this invidia catless divorced dp not a good option if I don't have an external waste gate? My dude told me to get the bell mouth unless I get one which sucks because the invidia catless is under $300

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#19 Old 02-09-2014, 11:49 PM
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So is this invidia catless divorced dp not a good option if I don't have an external waste gate? My dude told me to get the bell mouth unless I get one which sucks because the invidia catless is under $300

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Either one is fine but a divorced wastegate pipe is kinda pointless when using a external wastegate.

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#20 Old 02-10-2014, 05:57 AM
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Either one is fine but a divorced wastegate pipe is kinda pointless when using a external wastegate.
Would a divorced dp work without an external waste gate?

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#21 Old 02-10-2014, 09:58 AM
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My memory of the Invidia "divorced" downpipe is that it's a bellmouth with a metal shiv half way through the bell that they claim helps airflow. I don't think it does much, might do more harm than good but hard to prove. It's not a bad piece. I'd call it a divided bellmouth if you want to get technical, referring to it as divorced is marketing.

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#22 Old 02-10-2014, 12:50 PM
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Catted vs catless DP

Mosc is correct. I run the Invidia and it's a "divorced" bellmouth. It's only a small 1.5" or so shim in there.

I too would agree it's not doing a whole lot...


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#23 Old 02-10-2014, 10:38 PM
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Mosc is correct. I run the Invidia and it's a "divorced" bellmouth. It's only a small 1.5" or so shim in there.

I too would agree it's not doing a whole lot...


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so as far as running without getting an external wastegate, i should be fine? with stock exhaust?
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#24 Old 02-10-2014, 10:40 PM
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or should i just go with a full bellmouth?
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#25 Old 02-11-2014, 12:11 AM
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The invidia pipe IS a full downpipe. The metal divider isn't changing that. Using the turbo's internal or external gating is not a decision that has much to do with your downpipe. External gating is a lot of work, if you're going through that the downpipe is the least of your concerns. Bellmouths are designed for internally gated turbos.

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#26 Old 02-11-2014, 06:45 AM
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Catted vs catless DP

Absolutely Ryan. Def no need for an external setup regardless of the DP design you go with. That's more of a needed mod after stage 2 type HP. My internal stock gate is fine at stage 2 with a rare exception during "Mountain Run" conditions. And going with a bellmouth DP will allow you in the future to go external if needed. If you went with a "divorced" DP from say..Nameless you'd run into problems going external in the future due to fitment issues. I too do not agree with the way they merge divorced pipes like Nameless' back together either due to the angle they do it at. It makes zero logical sense to merge the two exhausts back together at that angle. Although a cool "thought" a bellmouth is the way to go IMO.

Just do yourself a favor though and stay catted. It's worth the extra money I assure you of that. Cobb and Invidia make quality DP's for bellmouth designs. Cobb's DP does not have the "divorced" shim just FYI if you wanna go that route. Either one of those will do you just fine. I don't know what you're getting back for taxes, but a catless DP is gonna require the protune like mentioned. That would put you over $1400 with the AP/Protune and DP. You can get the AP and catted DP for around $1100 and get a protune when you have the extra money, save $300 for now, and have a DP that'll never cause problems for you. Running OTS maps anything past stage 1 is not my long term recommendation, and a Protune should be your next investment IMO if you can't do it all at once. Although I'm just saying it's cost saving initially and ok for short term depending on how much you're looking to spend with tax money. But also keep in mind a Protune is only gonna be around $450 for your AP. That's only $150ish more than if you had initially gone catless. That $150 more is a no brainer investment IMO.

Just my .02 on things...

What's your budget with things anyway?

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#27 Old 02-11-2014, 04:47 PM
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I planned on getting a stage 2 tune with the catless dp, a shop by me does tunes around $500 so it'd be around 800 for it, probly not over 1000 would be my budget

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#28 Old 02-11-2014, 05:46 PM
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Learn something new everyday, today its the marketing hype around divorced pipes. I was looking at the invidia divorced pip and @mosc your definitely right, just a nice belmouth with a steel spacer welded in. Im not on the road to stage 2 (that I know of) but ill definitely be recommending bellmouth from here on in.

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#29 Old 02-11-2014, 07:04 PM
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I planned on getting a stage 2 tune with the catless dp, a shop by me does tunes around $500 so it'd be around 800 for it, probly not over 1000 would be my budget

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So he's going to do an Open Source Protune I'm taking it? I don't see on your profile you already have an AP.


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#30 Old 02-11-2014, 08:22 PM
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Yea I don't have an AP

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