bellmouth dp or divorced waste gate dp?

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92whitelegacy
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bellmouth dp or divorced waste gate dp?

Post by 92whitelegacy » Wed Jan 18, 2006 10:06 pm

im gunna start tacklin my exhaust soon, 3"turbo back. I was wondering who runs bellmouth dp's and who runs divorced waste gate dp's. Which ones are better for our legacy's? and your opinions on what you have would be nice as well, O and im planning on 3" turbo back, with a highflow cat and a straight through muffler wit a 4 1/2" tip at a nice angle JDM style
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by legacy92ej22t » Thu Jan 19, 2006 12:31 am

I run the CES twin dump. LOVE IT!

Twin dumps are the best design but also the most difficult to produce and the most expensive.

Don't go cheap, the cheap ones tend to fall apart.

:)
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

92whitelegacy
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Post by 92whitelegacy » Thu Jan 19, 2006 6:23 am

on the bright side, i wanna go wit an expensive 4" invidia bellmouth :twisted: but on the frugle side i wanna 3" bellmouth. so im torn ill prolly go with some cheaper but not "cheap" stuff. im almost gunna force myself to buy a black anoed apex n1 fart can......................................you mean divorced wg, when you say twin dump? right matt?
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by gt2.5turbo » Thu Jan 19, 2006 6:46 am

im going to go divorced when i decided to do the exhaust... which hopefully will be soon
93 White Legacy Turbo Wagon: For Sale-ish
93 White Turbo Sedan: soon with a little more umf
91, funky brown purple gray color, legacy L Wagon: the "its so cheap i cant not pass it up" purchase to get me around when the others are down

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Post by dwreck30 » Thu Jan 19, 2006 6:49 am

If I was going to do it I'd go with the Invidia V3. Bellmouth+Divorced WG for around $300.
- Derek
'06 STi

Subtle
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Post by Subtle » Thu Jan 19, 2006 7:01 am

For two years I've been using a 3-inch divorced stainless DP and the MRT guys like them.

Made up in Vancouver for c$450.

Before the install, it looked like a decorative vase so I took a picture with daffodils in it :-)
Subtle (normally aspirated engines suck):
05 Legacy GT Wagon with Cobb chip.
62 Alfa Romeo Spider- had a 1.6 L with 80 hp, now 2 L with 160 torque. Curb weight 2050 lbs.
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Post by 92whitelegacy » Thu Jan 19, 2006 7:18 am

yea we'll see how much money the tax fairy brings me, that'll decided 4" or 3" and sweet apex n1 or crappy megan fartcan
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by 93forestpearl » Thu Jan 19, 2006 7:44 am

There is plenty of debate going either way. I like APS's setup the best, but whoa $$$. Cobb has a beautiful cast SS bellmouth as well. If you think about it, a separate wastegate pipe on a downpipe actually has a smaller overall volume than a bellmouth. Therefore the gasses are forced through smaller volume. The main idea is to make the gas flow as smoothly as possible. If the wastegate dump tube mated right up to the wastegate, that would be a different story, but thats not possible on a tubo with an integrated wastegate.

The reason you don't see more cast bellmouth downpipes is because casting metal for production is super expensive. It takes much less capital to cut a flange, bend some pipe, and weld it together.

When I take fluid dynamics next fall, I'll be able to tell you which is better. Or I could go talk to one of my professors tomorrow.
→Dan

piddster34 at h0tma1l d0t c0m

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Post by 92whitelegacy » Thu Jan 19, 2006 7:51 am

DAMN dan, very nice detailed reply. I thank you yea i wanna go wit bellmouth cause it just seems like it will flow better, and i want some fuckin fire(havnt decided about using a cat yet). :twisted: i wanna toast my bumber like this sweet 240/silvia i saw the other day :twisted: but not burnt to a crisp more of like a blackening 8)
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by 93forestpearl » Thu Jan 19, 2006 8:23 am

I think I'm gonna go with a cat. I'd just feel bad about everyone behind me on the road. I know I'd sacrifice a few ponies, but I do have somewhat of a conscious about mother earth.

I need to get a dump pipe for a silvia since I'm using a Garrett turbo with the T25 flange. I've got 15 feet of 3" stainless sittin here next to me, and I think it should be enough to take care of my exhaust.
→Dan

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Post by legacy92ej22t » Thu Jan 19, 2006 1:36 pm

Twin dump DP's will outflow a bellmouth. It's a proven fact.

Almost all twin dumps use a wastegate seperator of some kind too. Having a twin dump means smoother flow because the wastgate doesn't interfere with the turbine flow. You get way less (if any) turbalance.

And no, I mean twin dump.

I don't have any real good pics but this is my DP.

Image
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

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Post by legacy92ej22t » Thu Jan 19, 2006 1:43 pm

OK, I found some pics:

Ceramic coated twin dump. CES Racing.

Image

Image

And this is their Boost Enhancement Plate (BEP). They make specific plates for different turbos to insure a proper fit)

Image

I, as well as many others, consider the CES twin dump DP to be the best DP on the market, period.
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

legacy92ej22t
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Post by legacy92ej22t » Thu Jan 19, 2006 1:47 pm

Oh and the CES twin dump has a full 3" main dump and a 1.75" wastegate dump. That would be equivalent to a 4.75" bellmouth but with the smoother, less turbulant flow. ;)

So how is it that a bellmouth has larger overall volume?
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

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Post by Subtle » Thu Jan 19, 2006 3:34 pm

The twin dump I have has the divider as well.

The Vibrant final silencer has two out pipes that makes it look very much less of a street racer plus the shiny stainless is painted matt black

The sound is the best I've had on any car I've had 8)
Subtle (normally aspirated engines suck):
05 Legacy GT Wagon with Cobb chip.
62 Alfa Romeo Spider- had a 1.6 L with 80 hp, now 2 L with 160 torque. Curb weight 2050 lbs.
93 Leg Twgn fmic, vf34, etc. ((sold))

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Post by 93forestpearl » Thu Jan 19, 2006 5:43 pm

Pi(r^2)

A 3" main pipe with a 1.75" wastegate pipe equals about 9.5 sq inches cross sectional area. A 4.75" pipe has 17.75 sq inches cross sectional area.

I justed talked to my professor and he said its all about cross sectional area and he would put his money on the bellmouth. If you think about it, the gasses have to change directions quite abit coming out of the wastegate. The 'gate does not open completely, so exhaust slams into the wastegate, changes direction a few times before it ends up in the dump pipe on a twin dump setup.

On a bellmouth, the opening encompases the entire turbo outlet, which gives the exhaust much more room to do what it wants, therefore less restriction. So how is it a proven fact that a twin dump outflows a bellmouth? Where is the research? I put more faith in companies like Cobb and APS who have the resources and engineering staff to do the research on what works best. The APS setup is basically a twin dump, but the opening covers the whole back of the turbo. This can only be produced in any kind of numbers through casting. Cobb took a long time to come out with their downpipe because they just didn't throw something out on the market to make a buck. They have the resoruces to actually engineer their product.

I'm not saying the CES system is bad, its a great product for the money. There are better options though, and you pay for it. The cast bellmouth downpipes are much more expensive because of the R&D and capital needed to produce them.

Either way, its hard to argue with the fluid dynamics of what is going on.
→Dan

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Post by legacy92ej22t » Thu Jan 19, 2006 6:27 pm

Cobbs own website says that the twin dump is the best design. They say however that it is too costly and difficult to manufacture. BUT they say that if done properly, the twin dump is the best design.

I'm not a fluid dynamisis or whatever, so you may be right in princible but how are you taking into account the absolute chaos that happens when the wastegate gasses exit the wastegate directly into the exhaust turbines flow, thus shearing it and/or slamming into the side of the DP?

There are more variables at work here then just cross sectional area.

Another thing is as long as the flow of the wastegate is kept from interfering with the exhaust turbines outward flow, it doesn't matter how it changes directions in flow or whatever. The wastegate doesn't provide boost at all, only limits it.

The bellmouth will cause the wastegate gasses to intefere with the exhaust turbine flow.

The twin dump keeps the wastegate flow from interfering with the exhaust turbine flow at all, thus better flow of the exhuast turbine.
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

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Post by vrg3 » Thu Jan 19, 2006 6:52 pm

Dan, I mean your professor absolutely no disrespect, but his simplification reminds me of a story:

A gambler, desperate for money, asked a professor friend of his to figure out a way to ensure his horse would win the race. The professor went to his office and worked for a while, and then on the day of the race ran down to the track to meet his friend. Waving his notepad wildly, he shouted, "I have the answer!" The gambler, excited about the prospect of getting out of debt, grabbed the notepad and started reading,

"Consider a spherical horse in simple harmonic motion..."

Independent research and development has generally shown that two completely independent exhausts -- one for the wastegate and one for the turbine -- works best for big power. It seems to make sense to me -- even in terms of cross-sectional area, a bellmouth doesn't really provide more than two pipes that fit properly over each outlet, right?

So the idea with a twin-dump pipe is to approximate the above ideal without creating disruption at the point where the two flows are recombined. That's a little hard to do, like Matt said, but CES put a huge amount of testing resources into figuring out all the dimensions involved in their design.
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Post by Legacy777 » Thu Jan 19, 2006 8:18 pm

Cross sectional area is NOT all that it's about.

Simple fluids. You take the same mass flow of a fluid through identical pipes. One is fully turbulent flow, one is fully developed laminar flow (meaning that the flow profile looks like a U as it travels down the pipe). If had the pipes going into buckets for a specified time. The bucket that has the laminar flow going into will have more fluid in it.

The above scenario is an "ideal" case. exhaust flow is more then likely not fully laminar. Also, you typically don't have fully turbulant flow through an entire pipe. It will eventually become more laminar unless you have radical changes in fluid direction, etc.

Other thing to note, turbulant flow is slower because of friction. The fluid impinging upon itself as well as the pipe wall. All this friction will create heat. So if you really wanted to do some testing....take a similar twin dump & bell mouth down pipe, measure the exhaust temp after the wastegate enters back into the main pipe for the twin dump. Also measure the temp at a similar location downstream for the bell mouth and see which is higher.

More then likely the bell mouth will be higher.

Again this is an over simplified example, and there's a lot of variables and differences....but it kind of help explains the theory behind it.
Josh

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Post by 92whitelegacy » Thu Jan 19, 2006 10:11 pm

matt? how much did the ces twin dump cost you? i see u have an engine stand your gunna be my friend come these next few months :twisted:
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by legacy92ej22t » Thu Jan 19, 2006 10:55 pm

They usually only sell TBE systems and they run in the $1600 range. The DP all by itself would probably run around $550-$600 but they'll only ship them in a group buy or if you pay all the freight (expensive, from Brisbane Australia).

I think every one of us that are running CES DP's got them in the whole TBE system.

That engine stand is actually down in my basement right now, holding my other engine. ;)
-Matt

'92 SS 5mt. All go and no show. Sold :(
'94 Audi UrS4 Modded (new project)
'96 Outback 5mt.
'07 Legacy 2.5i SE

[quote="Redlined"]
Oh... and I hope the fucker get bunked with Gunter, arrested for raping Gorillas.[/quote]

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Post by 92whitelegacy » Thu Jan 19, 2006 11:25 pm

well for lack of money ill be goin 3" bellmouth :( cause im gunna need a new clutch soon, and im gunna need alot of money to do that( i dont think i can do it with the tools, or space i have here) cottman trannys wants like $460 bux for labor. but yea im just gunna go wit a 3" bellmouth from ebay, and custom piping an a sweet muffler let u guys know how it sound/looks
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by Subtle » Fri Jan 20, 2006 1:36 am

See my above post regarding a divorced DP

for $450 cdn in Vancouver
Last edited by Subtle on Thu Mar 16, 2006 6:37 am, edited 1 time in total.
Subtle (normally aspirated engines suck):
05 Legacy GT Wagon with Cobb chip.
62 Alfa Romeo Spider- had a 1.6 L with 80 hp, now 2 L with 160 torque. Curb weight 2050 lbs.
93 Leg Twgn fmic, vf34, etc. ((sold))

92whitelegacy
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Post by 92whitelegacy » Fri Jan 20, 2006 2:07 am

yea, but i can get a bellmouth off ebay for alil under 160$ shipped :)
92 ss 275k+mi, kartboy shifter/bushings, gauges. VRG3 FCD II, NGK I'4s, TDO5-16G 4" dp CAT-less 3"tbe 4.11 gears.

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Post by 93forestpearl » Fri Jan 20, 2006 6:31 am

Good point about the wastegate flow interfering with the turbine outlet. I forgot about that. Thats why I like APS's downpipe the best, as it combines the best of both worlds. It has separate paths for the turbine and wastegate, but also starts as the same size and shape as the turbo outlet. Its cast iron to boot. I wish they sold it serparately.

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Post by Legacy777 » Fri Jan 20, 2006 7:20 pm

That APS unit is pretty nice. I don't understand....what's not sold separately? Just the cast part? You have to buy all the hardware and stuff. I can't see the hardware being that much....but who knows.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

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