Considering my Exhaust Options

[turboleg]

So I've been reading a LOT about our exhausts lately. I haven't spoek much on the board about the project, but I'm working on my EJ22T build. Engine is out of the car and the heads and block are nearly ready for the machine shop. In the mean time, I'm thinking about the exhaust system. I've been completely stock since I swapped out the NA engine and FWD transmission.

In all I was hoping I could through some things out there and get some members feedback on concepts, so here goes:

Manifold/headers:
I don't see very much advantage in going away from the stock manifold. It seems the cast ones work well, and if anything I would eventually go to a extrude honed/polished and ceramic coating, but I am having a hard time believing that the improvement would be worth the extra cash involved.

I though about equal length headers, but the more I read, the more it sounds as if the advantage is again not worth the cash/effort, if your not running a twin scroll - does this sound accurate? Also, I'm a little nervous that the car would sound like a Honda afterwards (I don't believe I've ever heard a equal length setup in person on a Subaru).

Up-pipe:
It sounds as if the stock up pipe is pretty efficient. I think my best option is to start out with the stock one and in the future go to a ceramic coat. In the meantime, I'll likely use header wrap.

Turbo:
Most likely a TD04 and perhaps a VF39 in the future (haven't thought through that future need yet)

Downpipe:
Ok, so here is where the fun starts for me. I've been reading a lot regarding Bellmouth vs. Divorced wastegate. I'm certainly not trying to strart any fights, but I can honestly say the Divorced Wastgate concept makes better sense from an Engineering Standpoint. So I'll likely use some extra cash to keep trubine flow and wastegate flow seperate.

I've been looking at the Invidia line-up as well as a few others. I know there is moding required no matter what WRX year DP is used, but I'm trying to figure out which is the best choice from the mod standpoint. I'd much prefer to just have to simply remove a few inches of pipe and reweld back together. What is the boards suggestion for best price vs. performance for divorced wastegate DPs? I'm considering running a Cat as I kinda like air, but it's honestly still up for debate. I think it'll be a 3" without a cat or a 4" with a cat.

Mid pipe and Axle Back:
At this point, I'm just looking for options that will fit without too much modification. I don't think there is too much advantage to anything beyond the DP as long as the cross section area is there. I'm thinking 3" diameter from this point back.

What do you guys think? Any comments are welcome.

[Legacy777]

Here are my thoughts.

I agree the stock exhaust manifold is probably the best to stick with since it retains heat better. If you can find some equal length manifolds from a JDM car or possibly even new STi, I think they will flow a little better. I don't think any extruding/honing is necessary, especially for the turbo setup you're running. As for thermal coatings, I'd highly recommend Swaintech.

Here's some info regarding the stock vs. equal length stock manifolds.
http://bbs.legacycentral.org/viewtopic.php?f=4&t=41935

Here's some info regarding the Swaintech coating.
http://bbs.legacycentral.org/viewtopic.php?f=4&t=41202


The stock up-pipe is the same up-pipe used on the STi, so it should be more than fine for what you're wanting. I would suggest also coating the up-pipe if you decide to go that route. I don't have any before & after temp comparison for header wrap. It's more difficult to work with, and I'm not sure how it compares to the Swaintech coating in terms of temp reduction, but is less costly.


What are your hp goals? A TD04 isn't much larger than the vf11. A TD05 is a pretty good all around turbo. I've been pretty happy with mine. Just a thought if you have the supporting mods/equipment.


I agree from an engineering standpoint, the divorced downpipe setup is better. I've got the CES divorced setup and have been very happy with it. I would suggest getting one that has a "separator" plate between the main turbine exhaust outlet and the wastegate outlet. This helps even more with the exhaust gasses separation.

I would suggest 3" for the size. 4" is way too big, especially if you're going back into 3". Just go 3" all the way and be done with it. Even with a cat, 3" is fine.


As for mid-pipe & exhaust, as mentioned above, just go with 3" all the way. I personally would add a resonator. It helps with the highway droning that can sometimes occur. Even with the cat & resonator, my car has a pretty "burly" and nice sound without being annoying.

[turboleg]

Hi Josh,

Thanks for the info. My HP goal is to eventually lay down 350-400 whp. In the general scheme it's a big goal in my opinion. All while maintaining a good "drivable" car thats stable. So I plan on doing this in stages. A lot of this is based on my own experimental interests.

Stage 1 - Shift some bottom end torque and increase the driving experience in the mid-high range RPM. I think the Delta Cams and a bit "slower" spooling turbo will be beneficial:
-Build bottom end to reliably hold 400 whp
-Port, polish, and flow match the EJ22T heads - I know EJ25D heads flow better, but it's kind of a personal choice and it has peeked my Engineering interest to see how far I can take the EJ22T heads.
-Install my Delta 230-220 grinds, at the same time have a valve grind completed
-TMIC (I also have to locate an SS hood for the 91 to make this happen)
-Exhaust work as we are currently discussing
-Grimmspeed 8mm Intake Manifold spacers
-Bigger injectors - TBD - I'm thinking 440's to start
-Install my wideband, electonic boost, and EGT (I'm keeping in mind that me EGT needs to be mounted so my Divorced downpipe choice will likely be centered around the idea of having an extra bung prewelded in)
-Standalone or piggy back and perhaps an FCD depending on the route taken (I'm going to talk to my local Subaru Tuner to see what they feel has worked the best for a stable and reliable system - and also what they have the ability to tune with today)
-and lastly, I'm thinking of doing an Electronic Boost Controller to utilize the turbo a little more efficiently
I think with the above mods I can probably lay down a 240 hp - This may be overstated?


Now the reason for the TD04 choice; my transmission is by FAR the oldest part of the car, I pulled it out of an old NA wagon that lacked shift bushings (to put it nicely). The transmission has around 320k miles on it at this point and has been dead reliable with the stock EJ22T. But I'm 1000% sure that if I try pushing 300+ horse through it it's going to last around one upshift/downshift sequence and then give up. So this is really the constraint. After I either build this 4.11 or drop in a built 3.90 I'll be more anxious to swap to a larger turbo. What I think to be true is that the TD04 spools later than the VF11 and I figured it would be a better combo for my delta cams - tell me if I'm dead wrong here.

Stage 2:
I believe at this point most of the supporting mods will be built into the engine.
-After transmission build I will likely upgrade to a VF39 (again I haven't researched much on this topic, I'm more or less basing the turbo choice on what others have done and said).


Up pipe: I'll take a look at the Swaintech, but alternatively I may have located an STI up pipe for sale that has been sent to Grimspeed for coating. I don't know what the boards opinion of this option would be. I was for some reason onder the impression that the STI had a different flange on the up pipe.

Down Pipe:
I guess one of my biggest concerns is th moding required, since I will most likely buy a DP for a WRX or STI, which model year would I be looking for for the least moding. I would be much more comforatble hacking up some pipe after the DP rather than to take a new DP and start cutting pipe length out or adding it in.
I think I am pretty much set on a 3" DP divorce, I was actually concerned that leading into too big of a chamber woudl actually effect the flow of hot gas, for some reason I have an idea of something similar to an Eddy current occuring, whereby I would not be moving gas at the same speed through the pipe. Just a thought, I have no idea if it's true.

From the Down Pipe back I am in agreement that 3" is the way to go, I don't feel there is any advantage to anything larger at this point. I will indeed us a resonator, I have a bit of a howel at certain times with the VF11. It sounds pretty mean, but it is slightly annoying after a 200 mile drive. On the other hand I currently have my competition stereo installed...it's one hell of a 3500 Watt exhaust noise canceler.

Again thanks for the help!

[Legacy777]

For that HP goal, I'd suggest a stand alone. You might be able to do it with a piggy back, but I just don't think it's the best route to go, unless you can get a tweaked Rob tuned ECU to support that HP.

From my experience, the staged approach ends up being more money in the long run and more downtime vs. saving up and doing it all at once. However, the staged approach usually means less down time at one particular time.

These engines were never meant to be "screamer"/ high revving engines. The head design is more suited for low to mid range power. The Delta cams are supposed to help the heads breath better at high rpms. Personally, I don't think you want to take power away from your lower end. That's what makes these motors more unique and perform the way they do.

The TD04 will spool a little later, but I wouldn't expect a huge difference between it and the vf11.

I think you'll need a FMIC for the kind of power you're wanting to put down....that or a good AWIC setup.

Regarding the injectors, to give you an idea, Dan (93forestpearl) is running 1,600 cc/min top feeds and he's around 400 whp. You may not need that much, but you will likely need 600 - 800 cc/min injectors to meet those power goals.

The EGT needs to go in the up pipe or manifolds, and won't affect what you do with the down pipe.

I understand your concern on the transmission. I have (had) the same concern, and is why I decided to go with a 6spd.

The twin scroll turbos have a different up pipe setup. The regular turbo STi's have the same up pipe as we do.

[James614]

You keep mentioning modding your DP to fit, but WRX downpipes don't need any modifications to fit, at least not for '02-'07. You just need to modify/extend the mid pipe to fit the longer wheelbase of our cars vs the Impreza.

[turboleg]

Hi James,

That's what I've been wondering. I have not issue modding the mid pipe. I didn't want to buy a DP and have to modify it. Thanks for the confirmation.

Direction has changed slightly. I want to get this thing back on the road this summer. So I am actually going to have the block and heads worked on at a local shop, add a TMIC, VF39, Meth kit, along with a stand alone. Next phase after the drivetrain build will likely be a set of EJ20 or EJ25 heads, modding of the bottom end to enhance CR for the head choice, and a FMIC.

Thanks for all your help guys.