BIC Divorced Downpipe

[stolensupra]

First of all thanks to everyone so far that has been so helpful so far in my top end rebuild especially IJ, Shaeff, and Dylan Wiggins (sorry I forgot your forum name)

A 3 inch BIC divorced downpipe was on my supra when I bought it. I had contemplated cutting out the recirculation on several occasions so I could have that spool and roar at full boost. Now during my rebuild with the turbo out I've noticed the separating piece on the dp flange is not a perfect seal to separate the wg and compressor flow streams. I'm glad I didn't vent to atmosphere yet as I'd have a huge turbulent exhaust leak. My question to all the experts in this one is what do you think of eliminating the divider on the dp flange and mig welding a divider directly into the hot side turbo housing between wastegate and compressor wheel and making sure the top of the divider is perfectly flush with the flat sealing surface. It seems that at least in theory this would be a solution to the problem of turbulent exhaust flow and non sealing ddp's. Let the debate begin.

 

[americanjebus]

Well for one thing the size of the gap is really small, to make any kind of argument you would first have to come up with a value for the peak volumetric flow of air and peak temperatures associated with that value through both the turbine and wastegate. Air which is already turbulent to begin with. Using the density of air for that temperature, the volumetric flow, and the length traveled over this small plate you will have to calculate the Reynolds number associated with air flow over this plate.

http://en.wikipedia.org/wiki/Reynolds_number

http://www.ecourses.ou.edu/cgi-bin/eBook.cgi?doc=&topic=fl&chap_sec=08.1&page=theory
This air is already turbulent so the added turbulence of this plate will have to be calculated to see if it even makes a difference. From there you would have to calculate the difference in pressures associated with the air above and below this separator to determine if there is a significant change. Now i know that with most NON straight pipe exhausts the pressure is higher in the upper exhaust portion due to back pressure which creates a low pressure effect in the wastegate pipe which in turn pulls more air leading to the phenomenon of boost creep associated with these downpipes.

Its not a matter of discussion, just do the math and you'll know.

 

[theKnifeArtist]

I wasn't happy with the lack of a perfect seal either. Read my thread here.

http://www.supramania.com/forums/showthread.php?114441-DDP-Leak-Solution-Ideas-(PICS)

I ended up recirculating the DDP. I should of updated the thread. You can see it on my build thread.

 

[stolensupra]

Well for one thing the size of the gap is really small, to make any kind of argument you would first have to come up with a value for the peak volumetric flow of air and peak temperatures associated with that value through both the turbine and wastegate. Air which is already turbulent to begin with. Using the density of air for that temperature, the volumetric flow, and the length traveled over this small plate you will have to calculate the Reynolds number associated with air flow over this plate.

http://en.wikipedia.org/wiki/Reynolds_number

http://www.ecourses.ou.edu/cgi-bin/eBook.cgi?doc=&topic=fl&chap_sec=08.1&page=theory
This air is already turbulent so the added turbulence of this plate will have to be calculated to see if it even makes a difference. From there you would have to calculate the difference in pressures associated with the air above and below this separator to determine if there is a significant change. Now i know that with most NON straight pipe exhausts the pressure is higher in the upper exhaust portion due to back pressure which creates a low pressure effect in the wastegate pipe which in turn pulls more air leading to the phenomenon of boost creep associated with these downpipes.

Its not a matter of discussion, just do the math and you'll know.

Wow that is a wealth of info. What I am saying is that If there are air gaps around that plate and my wg dump tube has been made non recirculated alot of exhaust will take the path of least resistance free of traveling through a muffler one cat and 6 feet or so of exhaust pipe and go to atmosphere through what is supposed to be wg only exhaust. I am trying to find out the simplest and most effective way of doing this. If I close these gaps common sense will say there is no way it will be MORE turbulent than the current situation.

 

[stolensupra]

Has anyone else had any exhaust leak issues through an atmospheric wastegate dump tube on a divorced downpipe? I'll try to get a picture of my flange up here soon to better explain my point.

 

[shaeff]

When I was running a BIC DDP mine sealed up perfectly. No leaks at all.

 

[radiod]

I've got a BIC on my car and it seals up nicely as well.

 

[becauseican]

There is no way to get a 100% seal on the DDP divider due to the casting differences of the turbine housings, each one has slight imperfections which make it impossible to make it 100%. Also the shape is really odd where it meets the trurbo at the gasket. There also has to be some clearence so it can be installed easily and leave room for expansion. Now taking out the divider and trying to weld onto the turbo housing is going to take alot of time and effort, assuming you know how to correctly weld to cast iron, and then you will still have a slight gap between it and the DP because of the gasket thickness.

Now this is all assuming that you have a genuine BIC DDP not some cheap china made knock off, as I cant say much for those.

 

[stolensupra]

That is the exact information that I was trying to find. I do have the receipt from the original owner buying and installing the BIC so it is real. Is there any true way to have a DDP that vents the wastegate to atmosphere without an exhaust leak?

 

[MKIIISupraGuy]

I have one as well. Mine does have very slight leak around the seal, reduced it somewhat with a new gasket. Now its only an afterthought. I know it leaks, but nobody else does.

 

[Bruno Molly]

Whats the deal with the Head you said you had??? contact me man? We've been waiting for Month's for you to contact us...
Darren

 

[gsxr141]

hate to bump an old thread. i have the bic ddp, and have a slight leak as well. you can hear that some of the exhaust is coming out of the dump tube all the time.
as long as it isn't causing a loss of power, i'm ok with it. besides, you can hear the turbo spooling up now so that's cool.. lol

 

[pipelinewill]

I honestly don't get the point of the BIC ddp, since you can flow more horsepower thru a normal 3" down pipe than the stock turbo is good For, what's the point? and the Wastegate passage isn't even big enough, so you boost creep and hit fuel cut or blow the motor if you install one. someone please explain to me a why anyone would ever install one unless all they care about is noise.

 

[OfnaRcR4]

I honestly don't get the point of the BIC ddp, since you can flow more horsepower thru a normal 3" down pipe than the stock turbo is good For, what's the point? and the Wastegate passage isn't even big enough, so you boost creep and hit fuel cut or blow the motor if you install one. someone please explain to me a why anyone would ever install one unless all they care about is noise.

Read up on them more.


Sent from my Htcclay's SuperCM7 G2 using Tapatalk 2

 

[suprarx7nut]

I honestly don't get the point of the BIC ddp, since you can flow more horsepower thru a normal 3" down pipe than the stock turbo is good For, what's the point? and the Wastegate passage isn't even big enough, so you boost creep and hit fuel cut or blow the motor if you install one. someone please explain to me a why anyone would ever install one unless all they care about is noise.

A divorced downpipe should lessen the amount of boost creep. Boost creep occurs when the wastegate flow is restricted more than the exhaust. More gas flows through the turbo instead of the wastegate and you have a rising boost pressure. This can happen with many aftermarket downpipes/exhausts which allow the exhaust path to flow freely. A divorced downpipe provides a less restrictive path for the wastegate gases. Of course, it also benefits the regular exhaust stream by separating the wastegate flow so both paths flow more easily.

I've got a Raptor Racing 3" divorced recirc'd and with a 54 trim ct-26 I get boost creep only in the very top of 3rd, 4th and 5th. It takes some time to actually see the needle move up on the boost gauge and I don't find myself in a situation where I can go WOT in the top of 4th for more than a few seconds very often at all.

I set the boost controller to 11-11.5 and I have my warning on the gauge and high limit on the controller set to 12.5 psi and it's only triggered once during a long 5th gear pull.

*edit, oh yeah... and then there's the fact that Toyota used them in their Group A racecar. If Toyota deemed it useful that's worth way more than virtually anyone's opinion on here, lol.

 

[OfnaRcR4]

*edit, oh yeah... and then there's the fact that Toyota used them in their Group A racecar. If Toyota deemed it useful that's worth way more than virtually anyone's opinion on here, lol.

Thanks for the pics, awesome.

 

[Nick M]

Is there any true way to have a DDP that vents the wastegate to atmosphere without an exhaust leak?

Since the old thread is bumped.....Yes. You can also have a shroud on the turbine.

I honestly don't get the point of the BIC ddp, since you can flow more horsepower thru a normal 3" down pipe than the stock turbo is good For, what's the point? and the Wastegate passage isn't even big enough, so you boost creep and hit fuel cut or blow the motor if you install one. someone please explain to me a why anyone would ever install one unless all they care about is noise.

At full throttel acceleration, such as bragging rights on a dyno, you will reach the wastegate setting. And it will open to hold the boost at....where ever you set it. And that air will create turbulent air in the exhaust, limiting scavenging and maximum power.

 

[pipelinewill]

I appreciate your replies however it is my understanding that A)a 3" exhaust with internal wastegate only becomes restrictive well above 400HP, at wich point the stock turbo isn't enough anyways and B) suprarx7nut sick photos but racecars are a different game and it looks like that ddp has a bigger pipe for The wastegate gas to flow thru. if you can't do a full pull in 3rd without overboosting thank you for proving my point. ddps are cool, and i understand their point, but on my car i get more problems (fuel cut, popped a motor) than benefits (none).

"Boost creep occurs when the wastegate flow is restricted more than the exhaust"

If exhaust and wastegate go thru the same pipe the restriction is the same, but when the pipe coming out of the wastegate is different and of an insufficient diameter boost creep can occur. You can't stand up for ddps on mk3s if you have boost creep issues.

 

[Insidious Surmiser]

sorry but I've seen dyno charts showing ~30whp gain over a standard 3" DP... gain comes from elimination of turbulence. The turbulence was a factor taken into consideration when the engineers designed the turbo/wastegate as the wastegate clearly creates turbulence, restricting flow which helps regulate turbine speed. my ct26 on a DDP wanted to just keep spinning past 15psi, when I had it set @ ~half that amount of boost. (keep in mind I'm talking about creep, mainly in 4th and 5th gears) With the exhaust split the wastegate does not flow enough, and turbine flows too much. It would be highly recommended to have some fuel system upgrades (IE 550's + lexus afm) if you're intending to run this downpipe. either that or have your wastegate ported out some... I'm sure that would've helped.


just so you know... the 1.75" dump tube is not the restriction... it's the actual wastegate

all in all it's a great mod, and it's a fact that it will make more power than any other downpipe setup... BUT just like anything else, you have to have the right supporting parts/modifications

 

[Nick M]

You don't need to be anywhere near 400 hp to have turbulence. And just so you know, I don't run a divorced down pipe.