Divorced or Bell Mouth - Subaru WRX Forum
 
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post #1 of 8 Old 10-24-2007, 07:29 PM Thread Starter
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Divorced or Bell Mouth

Just wondering some opinions on divorced waste gate downpipe rather than bellmouth.
I have a bell mouth right now that im selling but considering going to one thats divorced. anybody do a comparison or no.. any info would help (ie ) power gains-hp.tq, spiking issues, lag ?? let me know
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post #2 of 8 Old 10-25-2007, 03:41 PM
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Quote:
Originally Posted by Scooby2006 View Post
Just wondering some opinions on divorced waste gate downpipe rather than bellmouth.
I have a bell mouth right now that im selling but considering going to one thats divorced. anybody do a comparison or no.. any info would help (ie ) power gains-hp.tq, spiking issues, lag ?? let me know
Look, a true divorced setup means you should be running a divorced wastegate. These downpipes that stick a little plate in the middle until further down the pipe and are designed to attach to internally gated turbos are a joke! The gain over a bellmouth is nothing. A good bellmouth is a 4 to 4.5" bell at the top which provides excellent mixing of the main exhaust and wastgate exhaust streams for INTERNALLY gated turbos. If you have an internally gated turbo (which subarus come with stock) than you want a bellmouth. The "divorced" design won't hurt anything but it's purely cosmetic. I'd eat my hat if it gave even a single hp.

Now, divorced WASTEGATES require separate piping which means they actually have some reason to run seperate until further down the exhaust. You don't have a choice here, you can't run a bellmouth if you wanted to. Divorced is the only option so it's not really up for debate.

Review:
-Divorced Wastegates need seperate piping. They'll always have a divorced downpipe.
-Internal Wastages (like our cars have stock) are best served by a bellmouth. Putting a little metal divider sticking into the turbo ain't going to help things any.

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post #3 of 8 Old 10-25-2007, 05:32 PM
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^^^^^^^ damn, well put. finally someone that can clarify that for all of us.

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post #4 of 8 Old 10-25-2007, 06:46 PM Thread Starter
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thanks very much that does clarify alot for me
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post #5 of 8 Old 10-26-2007, 03:04 PM
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the fact that they call them divorced at all kind of bothers me. Just because they spit them on purpose doesn't mean it's a divorced setup. The wastegate is still internal! I think it's just a marketing ploy.

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post #6 of 8 Old 10-26-2007, 04:05 PM
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You are talking more about an external wastegate setup.
would`nt you be running a bellmouth down pipe even if you have an externally wastegate turbo seeing as how the bigger opening on the downpipe would`nt hurt the exhaust gas.

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post #7 of 8 Old 10-29-2007, 01:03 PM
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it could. If you allow the exhaust gasses to expand into a larger diameter and then force another contraction, it will reduce maximum flow. If the stock wastegate was bypassed and an external gate was used than the stock downpipe design would be much more reasonable. It still bends rather sharply but even the best aftermarket ones can't smooth that out too much anyway.

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post #8 of 8 Old 10-30-2007, 12:38 AM
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Afaik, separate wastegates independent of the turbine housing are only called external, not divorced wastegate. "divorced" simply means that the 2 outlets from the turbo exit through separate (or "divorced") pipes, which is true of divorced wg downpipes.

For the most part, I agree with mosc. There is little gain, if any, over a bellmouth downpipe. However, the CONCEPT of divorced is actually really good. The problem is the execution. Imo, there are 3 major problems with divorced wg downpipes.
1. Internal wastegates NEVER open all the way. At most, the wastegate "door" will only open at a 45 degree angle. This means that, instead of all the wastegate gases flowing right into its designated piping, most of the air hits the wastegate door and changes direction, running RIGHT into the dividing plate.
2. Since the dividing plate is not completely sealed, some gases are allowed to cross over into the turbine gas area (defeating the whole purpose of divorced wg), while the other gases swirl around the turbine housing until they find their way down the wastegate piping.
3. The inlet for the wastegate gases is small, and not located at the area of direct flow of the gases.

SOLUTION: this setup, while not ewg, would be truly divorced.
1. A turbo with a turbine housing that separates both outlets (such as aps turbos)

2. A downpipe with an outlet that encompasses the entire wastegate outlet (such as the aps downpipe)

3. A downpipe with a wastegate opening like the aps' that slowly tapers into a pipe, then is routed back into the downpipe further down the exhaust path (like the bpm)


You can probably tell I've thought about this a lot. Too bad downpipes like that don't actually exist... sigh. They would be expensive to make, but would definitely make more power than a bellmouth (with the right turbine housing).
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