Bellmouth vs Divorced Flow Turbo Elbow?

[NoFlex]

Wondering which O2 housing will get better results on an sr20 with a BB t28 turbo. Bellmouth or divorced flow?

http://i.imgur.com/Cn8INot.jpg
http://i.imgur.com/UPPWfwi.jpg

[Mile High Silvia]

I run the bell mouth style, just seems like it would flow better.

I'm running s15 bb turbo with gtx28 billet compressor wheel from Pure.

[NoFlex]

I run the bell mouth style, just seems like it would flow better.

I'm running s15 bb turbo with gtx28 billet compressor wheel from Pure.


I would think so, but i see a lot of people saying dovorced flow is better

[fatduece]

I think you need divorced for internal waste gate and bell mouth for external waste gate. Hopefully somebody who has experience can chime in

[jedi03]

Yup...that is correct...I use bellmouth regardless tho due to strength of the welds and heat soaking

[Mile High Silvia]

I'd say go with the Bellmouth, because the size of the piping is much bigger and will allow better flow. Some divided designs are better than the pic you posted, that one looks like total crap in my opinion

[jr_ss]

Divorced is better. It keeps the wastegate flow from causing turbulence in the exhaust stream. In an ideal world, wastegate flow would be introduced farther down in the exhaust stream.

[5280VertDET]

Divorced is better. It keeps the wastegate flow from causing turbulence in the exhaust stream. In an ideal world, wastegate flow would be introduced farther down in the exhaust stream.

The OEM S15 turbo is divorced, if that gives you any help. Since Nissan did this, I would assume that if you are using a internal WG you should keep it as well.

[Mile High Silvia]

I noticed better top end power with my "Bellmouth" style and better spool.

[NoFlex]

The OEM S15 turbo is divorced, if that gives you any help. Since Nissan did this, I would assume that if you are using a internal WG you should keep it as well.

Yeah the s15 turbo has a little divorce plate in tge exhaust housing and yes im using the stock internal wg. Should i get a bellmouth since the turbo already has a divorce plate?

[PoorMans180SX]

Parts Shop MAX has the only proper divided wastegate donwpipe that I've seen.

http://www.partsshopmax.com/e107_files/public/1296170878_2_FT2130_dsc00977.jpg

You need to separate the flow for 10-12in to get a good result. But it WILL improve flow exiting the turbine. I'd say ideally the wastegate would never rejoin the rest of the exhaust.

If you want to buy one of those cheap, shitty, hack parts you posted, get the bell mouth one.

[fatduece]

Tomei makes a very nice bellmouth. Very cheap too!



https://www.tomeiusa.com/_2003web-catalogue/000_expreme/each-product/each-product_img/sr20_outlet/sr_outlet_hikaku02_b.jpg


https://www.tomeiusa.com/_2003web-catalogue/000_expreme/each-product/each-product_img/sr20_outlet/main_soutyaku_b.jpg

http://www.tomei-p.co.jp/_2003web-catalogue/000_expreme/each-product/each-product_img/sr20_outlet/sr_outlet_hikaku08_b.jpg






I dont mean to hijack your thread op, but doesn anyone know if these outlets are okay to use with aftermarket exhaust manifolds? Just wondering if its gonna hit anything.

[yzrider450f]

Do we even bring this up?

http://i47.photobucket.com/albums/f155/yzrider450f/s-l500.jpg

[Croustibat]

Internally gated turbo = bellmouth. The divorced design you show is crap anyway, it will leak from each side and it joins too soon. Divorced design on that kind of internally gated turbo is idiotic, it really is an item created to steal money from people.

Use a divorced design when the turbo has a divorced design only (like externally gated turbos), and dump either as a screamer or way further in the exhaust.

[Chernobyl]

Tomei makes a very nice bellmouth. Very cheap too!

Probably not everyone's definition of "cheap", but I really like the Tomei unit I have. High quality part. Recommended.

[Mile High Silvia]

Yeah the s15 turbo has a little divorce plate in tge exhaust housing and yes im using the stock internal wg. Should i get a bellmouth since the turbo already has a divorce plate?


Get the Bellmouth, look around and find one that has the biggest piping because turbos need room to breath!


The tomei unit pictured on the left is one of the best in my opinion! I have the same one on my coupe, with a Megan down pipe since it has the flex section. The greddy unit I had before was a Bitch to fit with the solid piping

[Croustibat]

find one that has the biggest piping because turbos need room to breath!


It is a T28, have you seen how small the wheels are ?

[PoorMans180SX]

It is a T28, have you seen how small the wheels are ?


The best exhaust for a turbo (regardless of turbo size) is the shortest or biggest one. This has been proven like 5 billion times.

Smaller turbine = bigger restriction = even more of a reason to run the biggest exhaust you can.

[Mile High Silvia]

What he ^ said!

[Croustibat]

The best exhaust for a turbo (regardless of turbo size) is the shortest or biggest one. This has been proven like 5 billion times.

Smaller turbine = bigger restriction = even more of a reason to run the biggest exhaust you can.

hmmmm no. We have seen numerous iterations of "bigger is better". But proof ? You can't prove that with a demonstration. A demonstration can be admissible to show something is wrong.


The flange on that turbo has like a 1.6" exhaust wheel diameter. The wastegate flapper is like 1" in diameter. That is 2.8 square inches.

A 2.5" downpipe is 4.9 square inches. Please, explain to me (with numbers) how a 3, 4, or 5" is going to be better, because i am so downright stupid i don't get it.

[KAT-PWR]

hmmmm no. We have seen numerous iterations of "bigger is better". But proof ? You can't prove that with a demonstration. A demonstration can be admissible to show something is wrong.


The flange on that turbo has like a 1.6" exhaust wheel diameter. The wastegate flapper is like 1" in diameter. That is 2.8 square inches.

A 2.5" downpipe is 4.9 square inches. Please, explain to me (with numbers) how a 3, 4, or 5" is going to be better, because i am so downright stupid i don't get it.

I am in for this info.
The only reasoning I see to support bigger is better is that less pressure behind the turbine and naturally a greater pressure in front of the turbine, the least amount of resistance behind the turbine wheel would lead to faster spool.
In King talon terms,
From the existence of expanding gasses due to the internal combustion process exhaust gas ideally maintains velocity with appropriate sized exhaust runners before the turbo. As the gas is violently trying to escape the exhaust ports it generates a lot of heat and pressure which must be controlled with the proper air fuel ratio and header pipe diameter. On a stock SR I prefer 12.5:1 under full boost of 12psi. There becomes a pressure differential between pre turbine (high pressure) and after the turbine (lower pressure). The pressure pre turbine must be greater than post turbine otherwise the turbine wheel would not spin and it must always be greater pre turbine. The greater the pressure post turbine the less effect the expanding exhaust gasses have in imparting energy on the turbine wheel. Theoretically as you would increase the exhaust diameter to infinity the pressure is decreased towards 14.7 (atmospheric pressure) . This means the pre turbine pressure would impart all of its energy (none being lost to back pressure) to the turbine wheel, spooling it faster

[Mile High Silvia]

There ya go crustybat! Some people's children.....

[dorkidori_s13]

That divorced outlet shown in the original photo is shit anyways just looking at how it is designed to dump exhaust gasses into the piping itself. The wastegate side enters at a hard angle and would divert wastegate pressure to where it actually creates MORE turbulence due to the outlet being pointed directly at the opposing wall of the piping (causing a direct flow interference).

The Parts Shop Max design keeps the exhaust gasses flowing evenly at the same angle and same direction (basically a proper 2:1 design).

But if you're worried about getting the most out of your T2 series turbo, you're better off upgrading to a smaller T3x series turbo... Pushing 300+whp out of a larger turbo is much easier than pushing it out of a T2x series turbo... Better CFM at lower boost pressure with less wear to the turbo yada yada yada

[PoorMans180SX]

I am in for this info.
The only reasoning I see to support bigger is better is that less pressure behind the turbine and naturally a greater pressure in front of the turbine, the least amount of resistance behind the turbine wheel would lead to faster spool.



This is exactly the reason.

You can see this everywhere on turbo cars. Stock turbo evo's gain 30whp from externally dumping the wastegate, and 50whp on big turbo bolt on cars.

Take off your exhaust after the downpipe. The turbo will react faster.

Switch to a hood exit and it will be even faster.

The turbine wheel is always the restriction in the system, so any reduction in restriction after the turbine helps the turbo make boost faster and restricts the entire system less.

Now of course there are diminishing returns. A 3.5" exhaust on a gt2560r car probably adds more weight than it makes in more power. A bigger bellmouth can't hurt though, especially if you feel like porting the outlet.

[Kingtal0n]

I am in for this info.
The only reasoning I see to support bigger is better is that less pressure behind the turbine and naturally a greater pressure in front of the turbine, the least amount of resistance behind the turbine wheel would lead to faster spool.
In King talon terms,
From the existence of expanding gasses due to the internal combustion process exhaust gas ideally maintains velocity with appropriate sized exhaust runners before the turbo. As the gas is violently trying to escape the exhaust ports it generates a lot of heat and pressure which must be controlled with the proper air fuel ratio and header pipe diameter. On a stock SR I prefer 12.5:1 under full boost of 12psi. There becomes a pressure differential between pre turbine (high pressure) and after the turbine (lower pressure). The pressure pre turbine must be greater than post turbine otherwise the turbine wheel would not spin and it must always be greater pre turbine. The greater the pressure post turbine the less effect the expanding exhaust gasses have in imparting energy on the turbine wheel. Theoretically as you would increase the exhaust diameter to infinity the pressure is decreased towards 14.7 (atmospheric pressure) . This means the pre turbine pressure would impart all of its energy (none being lost to back pressure) to the turbine wheel, spooling it faster

I didnt say any of that. I cant even read it.

There is more to it than just having an open dump after a turbine. If you remove the downpipe completely so the turbine wheel can directly "see" the atmosphere you will lose performance, despite that simulating the largest exhaust possible (none). There is some gain to be had with the coordination of exhaust gas flow as it exits the turbine. An elegant design would change shape (of both turbine wheel and exhaust system) as the turbine and engine requires more flow, but it would never "disappear"



But if you're worried about getting the most out of your T2 series turbo, you're better off upgrading to a smaller T3x series turbo... Pushing 300+whp out of a larger turbo is much easier than pushing it out of a T2x series turbo... Better CFM at lower boost pressure with less wear to the turbo yada yada yada

This is where you all need to be these days. It is 2016 guys, top mount manifolds are affordable and reliable. We all know brake boosters are the number one cause of 240sx engine bay fires. Buy a blanket and a heat shield, and Get With The Program.

[Croustibat]

This is exactly the reason.

You can see this everywhere on turbo cars. Stock turbo evo's gain 30whp from externally dumping the wastegate, and 50whp on big turbo bolt on cars.

Take off your exhaust after the downpipe. The turbo will react faster.

Switch to a hood exit and it will be even faster.

The turbine wheel is always the restriction in the system, so any reduction in restriction after the turbine helps the turbo make boost faster and restricts the entire system less.

Now of course there are diminishing returns. A 3.5" exhaust on a gt2560r car probably adds more weight than it makes in more power. A bigger bellmouth can't hurt though, especially if you feel like porting the outlet.


I am genuinely interested in understanding how anything that could flow more than what can flow through the turbo is going to be less restricting.

The elbow and downpipe have bends, so this limits the flow, but in what proportions ? I can't see it creating a restriction when the surface is already twice the turbo exhaust surface, but i may be wrong. I'd just like to understand why, not just "because you say so" or "because everyone else is doing it".

Why would anyone use anything bigger than a 2.5" elbow with a gt2560r? Isn't twice the area the turbo has already overkill ?

[KAT-PWR]

I didnt say any of that. I cant even read it.

There is more to it than just having an open dump after a turbine. If you remove the downpipe completely so the turbine wheel can directly "see" the atmosphere you will lose performance, despite that simulating the largest exhaust possible (none). There is some gain to be had with the coordination of exhaust gas flow as it exits the turbine. An elegant design would change shape (of both turbine wheel and exhaust system) as the turbine and engine requires more flow, but it would never "disappear"




This is where you all need to be these days. It is 2016 guys, top mount manifolds are affordable and reliable. We all know brake boosters are the number one cause of 240sx engine bay fires. Buy a blanket and a heat shield, and Get With The Program.

It was satire talon.:tardrim:

[Mile High Silvia]

Why would anyone use anything bigger than a 2.5" elbow with a gt2560r? Isn't twice the area the turbo has already overkill ?


You can't have too big of an exhaust with a turbo, especially with a big turbo. Bunch of vr6 guys run 4" systems to breath upwards of 700hp. Back in my vw days I ran 6766's with the largest t4 housing they had which was .94 and I still hit full boost at 4K. I switched my style tho and now I love
Fast spool and small turbo efficiency.

I run the s15bb t25 with pure billet wheel, tomei outlet, Megan downpipe(bcuz flex section), and apex'i N1 exhaust. I love my setup, it performs

[Croustibat]

Yeah, big turbos, losts of boost, i get it. gt2560r ? Nope. I run one, i also have a free flowing 3" exhaust, a shiney elbow and a 3" flex downpipe, but it just is overkill. And it takes room; i bet a 2.5" one would flow better as the bends could be smoother...

[Mile High Silvia]

Yeah, big turbos, losts of boost, i get it. gt2560r ? Nope. I run one, i also have a free flowing 3" exhaust, a shiney elbow and a 3" flex downpipe, but it just is overkill. And it takes room; i bet a 2.5" one would flow better as the bends could be smoother...



My system is super smooth, not too many bends after the downpipe and there's no way 2.5" is better than 3". Just not even a question in my mind. I've owned a few turbo cars that I built myself and I can assure you that the larger piping is the way to go. I'm sure I can find some dyno videos on YouTube somewhere comparing down pipes or exhaust systems. I don't have any dyno comparisons myself but it's just a matter of efficiency. The easier a turbo can breath The better it will perform with less stress from back pressure

[codyace]

In the grand scheme of things, neither setup is going to affect power *that much* to make me go out of my way for one design or the other. Either way you're using a crappy internal wastegate.

IMO the bigger thing, and MOST important thing, is to get the best quality option, as changing that thing is the single biggest PITA in the world. The PBM setup looks nice, but that big ass single piece downpipe/j pipe would annoy me. I'd go as far as to put a v band midway on it on it just to make install easier.


I'm still personally a fan of the OG Greddy J pipes, with divorced housing for guys wanting to stay internal. Never had an issue with them cracking ever, and we've proven to have made some of the better performing setups utilizing them too (at least on the gt28rs/gt2871r/gtx28 setups)

However the 'best' setup IMO would be one of the newer Tomei bellmouths, and then putting an external wastegate atop the factory manifold. This way you eliminate the biggest issue, and that is controlling the stupid internal gate.

[kyle1a2]

I run the bell mouth style, just seems like it would flow better.

I'm running s15 bb turbo with gtx28 billet compressor wheel from Pure.

What kind of set up are you running with that turbo and what kind of power is it making? I've been thinking about having mine upgraded.

[PoorMans180SX]

In the grand scheme of things, neither setup is going to affect power *that much* to make me go out of my way for one design or the other. Either way you're using a crappy internal wastegate.

However the 'best' setup IMO would be one of the newer Tomei bellmouths, and then putting an external wastegate atop the factory manifold. This way you eliminate the biggest issue, and that is controlling the stupid internal gate.

Or just buy an EFR and have an awesome internal gate and a V-band downpipe.
:2f2f:

[Mile High Silvia]

What kind of set up are you running with that turbo and what kind of power is it making? I've been thinking about having mine upgraded.

I'm running a Isis manifold, tomei outlet pipe, and apex'i exhaust. Aem standalone, map conversion, 18ish psi. Not sure what power I'm making but I'd say atleast 350 with really fast spool. I'm also running water meth injection with a pre turbo nozzle.

http://i1213.photobucket.com/albums/cc476/DubSacAssassin/GC/IMAG0340.jpg (http://s1213.photobucket.com/user/DubSacAssassin/media/GC/IMAG0340.jpg.html)

[Mile High Silvia]

http://i1213.photobucket.com/albums/cc476/DubSacAssassin/GC/IMAG0355.jpg (http://s1213.photobucket.com/user/DubSacAssassin/media/GC/IMAG0355.jpg.html)

http://i1213.photobucket.com/albums/cc476/DubSacAssassin/GC/IMG_20140307_100058.jpg (http://s1213.photobucket.com/user/DubSacAssassin/media/GC/IMG_20140307_100058.jpg.html)

http://i1213.photobucket.com/albums/cc476/DubSacAssassin/GC/IMG_20140307_095705.jpg (http://s1213.photobucket.com/user/DubSacAssassin/media/GC/IMG_20140307_095705.jpg.html)

http://i1213.photobucket.com/albums/cc476/DubSacAssassin/GC/IMAG0342.jpg (http://s1213.photobucket.com/user/DubSacAssassin/media/GC/IMAG0342.jpg.html)

[PoorMans180SX]

Just an FYI, pre-turbo meth injection doesn't do anything different than post intercooler meth injection, besides corrode everything.

[kyle1a2]

Nice, I might give them a call. Ive got injectors, poncams, tomei manifold and elbow, Power FC and before the car runs, head studs and gaskets. Id like to hit around 325.

[Mile High Silvia]

Just an FYI, pre-turbo meth injection doesn't do anything different than post intercooler meth injection, besides corrode everything.

It actually cools the intake air,making it more dense, and thus working the turbo less. It's working great for me and a ton of other people on YouTube.


Check this video out! These guys are like the pioneers of pre turbo water injection!
https://youtu.be/VaKpzgL4b9o

[PoorMans180SX]

That is my friend Paul's video, and it did nothing more for IAT's than post intercooler did...

[Mile High Silvia]

Cool, I also have a small s15 turbo with billet wheel so it's being pushed to near its limits. Pure said I could run probably 25psi but that's more than I need. Only running 18psi right now. I drive my sr pretty hard so long pulls and drifting the meth is great. Cold mornings here in Colorado are the best because the tank is super cold and there's zero traction

[dorkidori_s13]

Cool, I also have a small s15 turbo with billet wheel so it's being pushed to near its limits. Pure said I could run probably 25psi but that's more than I need. Only running 18psi right now. I drive my sr pretty hard so long pulls and drifting the meth is great. Cold mornings here in Colorado are the best because the tank is super cold and there's zero traction


S15 T28 is only good to about 18psi... anything over 18psi is WAY past its efficiency range. even at 18psi, it dips back to 14-15psi in higher RPMs simply because the turbo is too small. if you want 20-25psi, youre gonna have to go with a larger GT28 or smaller GT30.

[Mile High Silvia]

S15 T28 is only good to about 18psi... anything over 18psi is WAY past its efficiency range. even at 18psi, it dips back to 14-15psi in higher RPMs simply because the turbo is too small. if you want 20-25psi, youre gonna have to go with a larger GT28 or smaller GT30.

I have a billet compressor wheel from pure. It does drop off but I'll be swapping in a stock manifold with external wastegate sometime in the future (codyace mod). I have the manifold and mvr wastegate laying around

[dorkidori_s13]

billet compressor wheel or not, youre trying to push the turbo well beyond its efficiency range. basically what youre trying to do is force a ton of air thru a cocktail straw, where if you went and got yourself a boba straw to do the same thing, it would have a much easier time! just saying...

[Crazyced]

Also take into consideration the fact that the divorced outlet might have fitment issues with the steering rack on 240sx.

[Mile High Silvia]

Edit: drunk post!

Haha

[Mile High Silvia]

I'm usually trying to stuff something into a hole that "it" doesn't technically fit in. It's all good brotha! I love my setup and that's all that matters! If I cared about other people's opinions, I wouldnt be on this forum.... Haha