Hey guys, I'm gonna need some good advice here cause after seeing the posts about the boost spike with the 18G and other problems it has made me do some thinking.

Here Goes ....

1. What I plan to do (future)

In March I plan on going Hondata (I have everything, I just have to wait for school to end so I can actually get it done) I'm shooting for 7/8 psi daily driver (stock bototm end) and at times turning up the boost with my Profec B, probably 10psi MAX. But before those things happen I plan on doing the exhaust. I would like either a 2.5" or 3", here lies the problem.

Now, do I get it tunned how my setup is and not worry about all the post with the internal WG spiking and other issues

OR

Sell the mani and 18G turbo and go with a Revhard/Drag/<insert more here> and a t3/t04e turbo with an external WG?

I must say, after hearing what Joe (falcon)/ DeepSi was going through and doing all sorts of bandaids it makes me think. I really have to go over his posts, just to make sure I'm certain.

I'll add more after breakfast, HELP

[EDIT] I would like to keep all the IC piping etc, I wonder if the new mani and turbo could use the GReddy spacing of the pipes - If I went that road.


[Modified by FredoSP, 9:33 AM 1/11/2003]

 

well, if you sell it, i'll take it off your hands if the price is right

 

Ok, here's a little bit of what me and a buddy were talking about yesterday. We were trying to figure out the exact reason for the boost creep. First, the pressure before the turbo hasn't changed, the size of the wastegate hasn't changed, and only the pressure after the turbine has changed. This should increase spool up, but it still takes the same amount of exhaust pressure and shaft speed to make the same amount of boost. The conclusion that we came up with is that since the wastegate and downpipe dump into the same chamber and there is a pressure differential between the wastegate hole and the turbine hole, it must be causing turbulance with the housing. This turbulance is the cause for the boost creep, restricting the amount of air that can come out of the wastegate hole. Solution, loose the cast piece and fabricate a new one that dumps the wastegate to atmosphere. I've seen pieces like this for sr20's and i'm sure this is the reason. That's my thoughts anyways. I don't know how much room there is between the ac and turbine housing, but if someone wants to bring their car by I could look at it and see if i can fabricate something.

 

tony I can get some pics for ya....



this is the best I have, the hoses are pulled closer tho, but i guess this gives you an Idea.

 

Any pics from the bottom where i can actually see how much room there is to work between the turbine and compressor?

 

you are correct tony. i have been working on the exact part you talk about for the sr20s, and this setup definately calls for the same thing. Its also a problem on WRXs. you can either port the daylights outta the cast piece or start all over with a tubular stainless one.

 

this is the best .. I can take pics today with my digi camera



ops how'd that get there




[Modified by FredoSP, 10:04 AM 1/11/2003]

 

get a pic form the turbine side, oen that shows the internal gate and then one that shows a pic of the downpipe flange. see if u can find it on the net rather than take all ur stuff apart.

 

That's a big problem on the stock Turbo II's also. We just upgraded to external WG and brought the dumptube out the back of the car seperate of the exhaust piping.

 

<U>Stock 15G! downpipe (SOHC)</U>


<U>Proposed separate dumptube for the exhaust and the wastegate</U>


I believe tony is talking about building one of these to solve the problem. And this is what several DSM people do with the 18G turbos. Separate the dlow of the exhaust coming out of the turbine, and the exhaust from the wastegate. I was hoping that when i return to dallas i could ask you tony to make me something like this with a new downpipe


[Modified by DeepSi, 9:49 AM 1/11/2003]

 

 

ya'll, um, my "O2 housing" doesn't look like that, i think my exhuast flange is the standard 5 bolt

 

doesn't look like there is much room in there
how big are the greddy feed lines, cuz the drag one i have looks much smaller than that

 

No your o2 housing doesn't look like that, but it is somewhat similiar, i believe, as all the wastegate and the exhaust both move thorugh this.

Yeah the drag are alot smaller, greddy likes to have the oil lines well insulated. they are around 3-4an

 

Looks good...

 

thats looking at it from a flow perspective. if you look at it from the perspective of what the turbine wheel is seeing... the turbine sees a pressure differential from the enxhaust manifold to the downpipe. the greater this differential, the quicker the turbine will spool. all the internal wategate REALLY does is vent some of that exhaust manifold pressure to the downpipe side of the turbine. there is typically enough restriction such that this RAISES the amount of pressure seen on the downpipe side of the turbine, which in turn minimizes the pressure differential, which in turn prevents the thing from spooling like crazy.

remove that restriction, like we did on my car, and the wg port can be open all day and there is still damn near 0psi on the downpipe side and enough pressure on the exhaust manifold side to make the turbo spool.

venting the WG port to the atmosphere is going to help significantly. since it wont need to be dumped into that restrictive spot after the downpipe. hopefully then it can flow enough gases to behave like a tradidional external WG. the internal wastegate port is still pretty small though.


has anyone called greddy about this?

 

::: Please read all, Twice! :::
AHA! I gotch yo ***! If you cross reference and research all the recent posts on the internal wastegate subject you will inevitably come across my originally bringing this idea up. My brother and I have been researching this topic extensively and have a few points to make.
First off, the greddy turbine flanges are unique to the Greddy kit. At least on the SOHC, it is a wacky 4 bolt unit that has absolutely no relation to a mitsu discharge.
Any attempt at making a turbine flange will be a custom machine shop job, but not impossible. We will be getting a gasket from Greddy to have the flange made.

Secondly, I had posted the DSM 02 bypass (shitgate) previously, only to get the idea out there. DO NOT go out and buy a DSM unit as it will not even come close to working. There are 2 reasons for this. One is that it will not bolt up.
The second reason is this: http://www.turbochargers.com/accesso...dwastegate.htm
Did you notice anything? Mitsu turbine housings use a seperate discharge for the wastegate and for the turbine. The open atmosphere,or external gate, dump for the wastegate works because of this fact. The wastegate/turbine will not bleed into eachother. After some brainstorming, here is the solution. Take your turbine discharge flange, be it custom or in my case a Garrett T-25, and firstly, make a hole where the internal gate would be. The next thing is to have a divider welded to the turbine side of the flange to seperate the 2 paths. This would have to be snug, but allow for thermal expansion, I believe. After this is completed, you are free to port your internal gate and have either an open atmosphere, or closed loop dump... OR, remove internal gate, remove flapper, and port opening significantly. You would then plumb an external wastegate off of this. Like so:
http://www.gnttype.org/techarea/pict...es/ATRDP2.html
Keep in kind, this is from a GN-T type, internally gated T-3, with divided discharge (refer to earlier in post). My brother, BigD+Itsuki, and I will be proceeding down this path come spring. He will be having a custom flange made, and I will use a standard Garrett T-25 flange, modified as stated. Since I am putting my kit together, I will be going the external wastegate route, and I think he will too. This is just some food for thought. If anyone, after reading this, has any questions, would like to donate us money, or is a machinist who is interested, please IM me or BigD+Itsuki. Thanks for reading.
P.S. DO NOT give up on the Greddy kit.
P.P.S. Nowhere does it say weld onto turbine housing.
P.P.P.S. Re-read 2 more times.


[Modified by JalopySiR, 7:15 AM 1/12/2003]

 

Jalopy,
I read your post three times, and i agree. And that is what i was trying to say, but I could not. Yeah i knew that we could not use the same one that DSM people use, but what i was trying to say is that we can get somebody with mad welding skills, like tony to build me one.

 

but what is my bolt pattern?? i swear it looks axactly like the standard 5 bolt pattern.... i could be wrong though, but yeah, the wastegate and exhause are vented into the same housing..... i think i am going to do that falnge thing where i have a divider welded, and then run a dumptube in somewhere farther down into the downpipe with an upgraded internal wastegate ans use one of the GReddy pressure releif valves to prevent boost spike and boost creep

 

i am not sure what your bolt pattern is, i am assuming you have a Greddy Prelude kit. The Greddy Si Kit has a 5-bolt pattern.

 

If you can get me a pic of the 5 bolt discharge, I assume this is the 18G turbo, I can possibly get a bunch of these units (divided outlet flanges) when I find a machine shop that can do what I ask. This would be assuming it is a standard T-25 5 bolt discharge. If I get alot of interest....

 

i think i could get some of that stuff done locally, like having a divider welded to the turbine housing, and portin it, BUT, where can i get my hands on one of those enlarged flapper doors?

 

NOT TO THE TURBINE HOUSING!!!!!!!!!!!!
Do I have to edit the post? Weld the divider onto the turbine side of the FLANGE. The divider will insert into the turbine housing to seperate the housing, but will not be attached. Snug, but allow for thermal expansion. No welding onto cast iron. There will be no modifications to the turbine housing other than porting the wastgate, and possibly removing/enlarging flapper. Only remove if going external gate. If anyone has any questions, or wants to give me money because I'm a genius, please IM me.

 

elaborate please.

 

Welding to cast iron isn't know for working too well. The particular weld job you've suggested would have to stand up to the extreme heat of the turbine discharge area. I would rather have you weld steel to steel, as on the flange. Even then, it'd have to be a really good welding job...