Midpipe w/stock ECU but ported wastegate
 

I want to replace my main catalytic converter because I think it's clogged and it's an upgrade I'd do in the future anyways. Instead replacing the cat, I wanted to just use a midpipe.
Already have a down pipe and cat back installed. I know usually you would like to get a standalone before using a midpipe, however I am wondering would a midepipe be safe to drive around with (avoiding WOT) seeing that I had my stock turboes rebuilt and wastegates ported by BNR? Also wondering because I want to delete my airpump while I replace all the vacuum lines.
Like I said, I'm going to be avoiding WOT until I can get a PFC and tune.

I would not advise it unless you can stay out of boost with 100% certainty. You have already increased your volumetric efficiency with the downpipe and exhaust beyond what the stock factory calibration was setup to handle and thus are already running leaner than what Mazda intended you to run at. Thats the weakness of a speed density fueling system it can not account for additional airflow at the same manifold pressure.
Also your factory ecu will freak out without your airpump. It injects air not only into the cat but also pre oxygen sensor. Wirhout the airpump the ecu will think you are running rich and will try to pull fuel thus most likely resulting in crappy idle and off idle acceleration and tipin performance.

With a working boost controller you could do it. Just limit the boost to 10 psi.

My suggestion would be to remove the cat, and try to shake all of the loose crap so it falls out the ends. If you can shake all the loose stuff out, your cat will flow really well.

Disconnect your ic pipe, buy a used pfc, find a basemap

Boost control can't decrease boost below WG spring.

Ah, didn't think of it that way, I forgot that it would probably lean out the AFR a bit. I guess both will have to stay in for the time being. Thanks for teaching me something new.

As it seems I can't delete the airpump or the cat, I will just follow this recommendation and try to get all the loose stuff out. Thanks!

I've read the same thing somewhere else too, thanks for confirming.

A BC won't prevent creep, which is what he'd normally be risking with an open exhaust. However if the WG is ported, I doubt he'd have a issue.
Maybe a bigger unknown is how will the car run without an airpump on the stock ECU. Seems like reported consequences on that run the spectrum from nothing at all, to idles like crap and hesitates.

If it does creep, you could always fit a restrictor plate between the flanges of the midpipe.

Is it safe to drive with highflow cat instead stock catalytic? I also have stock ECU and don't have BC.

^Yes. You'll be fine.

Great, thnx

Trying to save your motor here.

If you baby it you will be fine. In the early days of the FD plenty of people pushed the stock ecu with bolt on's. We're well past that necessity now, and so this is not recommended. But, the truth is you're probably OK if you take it easy and plan on getting a PFC very soon.

Beware, though. Getting a PFC in and tuned can be a longer road than some expect. Depending on how you go about it.

Slow2K, I will relate my experience with a similar set up.

I ran with stock mount intercooler, Infini Y pipe, downpipe, stock cat, cat back and boost controllers to keep the boost at 10psi and a Supra fuel pump. My Innovate wideband showed air fuel ratios in the high 11s. I would consider this a safe set up for anyone.

I put in a resonated mid pipe and had boost creep on the secondary turbo (not able to lower with boost controller as wastegate and pre control are both fully open already). I made several undersized gaskets for between the midpipe and catback and found the 2" one worked to eliminate boost creep. My air fuel ratios were in the low 12s with this set up (pretty lean)

I removed the midpipe and 2" restriction and put in a 3" SMB resonated "high flow" cat. This also eliminated boost creep and air fuel ratios were in the low 12s.

Summary-
One can eliminate boost creep with wastegate porting and boost controllers, but you are changing the volumetric efficiency of the system enough you are running lean on the stock ECU.

remove the restrictor pills and have the turbos run off waste gate spring pressure

:icon_tup: Somebody who gets it. I have ran 50+ rx7s over the years this way. Full exhaust, and all the bolt ons for that matter with the restrictor pills removed from the lines going to the wastegates. You will see a consistent 8lbs of boost with some slight creep at high rpm to 9-10 lbs which is completely safe on stock ecu.

Enjoy.

I've thrown the air pump delete out the window for the time being as it is always something I can do later without much hassle. So, boost creep with the ported wastegate seems to be a possible hit or miss based on all the replies, but what I've also become concerned about is "volumetric efficiency" everyone is talking about now, and the fact that less restriction and more air will mean running more lean constantly.

That's true, thank you for the idea although I'd probably go about removing the restrictor pills as it's less of a hassle.

I definitely plan to take it easy, just still debating because of the fact that I'd be running quite a bit leaner now. Can you explain a bit more what you mean about getting a PFC being a longer road than expected? Thanks.

Thank you for sharing your experience and making me more aware of the fact that it's not only boost creep that needs to be watched for, but leaning out the AFR because of less restriction. This is likely to have changed my mind about the midpipe for now.

Restrictor pill removal actually sounds like a pretty smart idea to lower the boost level, however what I've become concerned about is the leaning of the AFR, which I don't think is controllable without an AFC or some type of stand alone.

The stock ECU actually has some provisions for boost spikes already in it, so it supports more boost than most people give it credit for... To DJ's point, it's been done many times before but that is the most effective way to run a midpipe on the stock ECU. In most cases, people usually creep around 2-3 PSI so using the wastegate level of 7 allows for creep to around 9-10 PSI which is fine (if it happens). As also mentioned, restrictor places can also be used to help control creep as well if needed.

you go lean when your PSI goes higher then your ecu allows if you remove the resrictor pills you wont go higher then the Stock ecu allows and you wont risk blowing you motor untiil you get a new ECU ,

if you dont , you may be perfectly fine , and maybe spike to 11-12 psi and be just fine .

or it may spike to 16 psi and lean out and blow your motor .

the BNR twins move more air then the stock twins do. remember that

I definitely learned quite a bit today, hah. Looks like I'll be keeping the restrictor pills on the side as I replace the vacuum lines.

Thanks for the advice, I don't actually have BNR stage turboes, I just have stock twins that were rebuilt by them, and when they rebuild the stock twins, they port the wastegate.

Hey gents, apologies for bringing up this old thread but this applies to me based on where I am at with my FD so didn't want to start a new thread....cheers to searching the forums :nod:

@djseven - I am planning to run a 3" downpipe, mid pipe and cat back. All on the stock twins, with stock ECU. I have read what people are saying about porting the WG etc.... however, I was wondering, if I remove the restrictor pills do I still need to port the WG??
I am not that experienced with the porting bit but I can always get someone to do it for me if necessary.

Any other suggestions/advice much appreciated.
Cheers

Removing the boost pills SHOULD get you in a safe zone, but every car is different. You won't know until you try it out.

And, you really need to save up for a PowerFC.

Dale

Thanks Dale, PowerFC is definitely in the works...I wanted to "learn" / "feel out" the car in its stock mode (minus the exhaust), since its my first FD, and then when I go single I can appreciate the significant difference :blush:

Cheers

You may want to note the significantly different smell too.

LOL! will do Sgtblue :icon_tup: