Anyone here gut out their CAT instead of putting on a midpipe or high flow CAT?

 

I have heard of people doing that, and it had no effect on the car other than opening up the exhaust. I don't see a problem with doing it other than it not passing emissions.

 

Is the highflow cat worth the money?? I heard that they don't really give you much HP. That's why I've thought about just gutting mine or putting a midpipe.

 

High-Flo cats will give you more power, but not as much as a midpipe. It really depends on what you are doing with your car which you might want.

The stock cat does flow pretty well, so it is possible to get a high-flo cat that flows less than the stock if you don't go for one that is specifically for the FD.

 

Hey Mahjik, Could I add a midpipe without upgrading my ecu? My mods are listed below (not much). I plan on keeping the stock CAT in the garage just to pass emissions every two years. Howmuch HP would I get from the Midpipe and are there any cons?

 

Yes, you can add a midpipe with the stock ECU, however I wouldn't recommend it.

As far as cons to owning a midpipe, midpipe owners probably wouldn't call them "cons" but here ya go:

* In most states they are illegal. Yes, that means you can get tickets for them. Shooting a nice big flame is a quick indication to the police that you are running one.

* Nasty heavy exhaust smell that can/will get into your clothes (I didn't want to go to work or out for dinner smelling like exhaust).

* Boost Creep. Since you are opening up the exhaust that much more, many people experience boost creep since the wastegate can be overloaded. Adding restrictor plates and/or porting the wastegate are about the only ways to control it. Boost controllers don't work in this manner which is why they alone won't stop it.

and more...

 

I think you would be better off getting a down pipe and leaving the cat alone. I believe you will see more power out of a down pipe anyway. I think you will be fine without a new ecu if you have only a midpipe or a downpipe not both.

 

Even though I have a cat back already? I don't want to upgrade the ecu just yet but I want to get rid of those hot temps from the pre-cat and of course get some HP

 

You don't need an upgraded ECU if you keep your boost around 10 PSI no matter what exhaust system you are running.

Do a search for messages from Wade. He has done probably the most testing of anyone here in the forum and the stock ECU will provide plenty of fuel for an upgraded exhaust at 10 PSI.

However, I do agree with mkoch1, don't get a High-Flo cat without a downpipe. If you can only do one now, do the downpipe first.

 

How do you like your bonez downpipe? Do you recommend it? I'm going to do exactly what you and Mkoch1 said and get just the downpipe and leave the CAT alone. Hopefully I won't run too lean. Once installed, what should I look for (other than my A/F guage) to ensure that my car is running okay?

 

You wont run lean, in fact iam in your same boat. I have DP and cat back with boost controller. I get a steady 10 psi and recently I just changed the plugs after 30k miles(OUCH!) which it runs really rich now. 2 to 3 bars on green on my autometer a/f ratio guage. You will have enough gas and you will nto run lean if you keep that boost 12 and below. You can practically do all the boltons and if you keep it at 12psi or less you will nto run lean. So make sure your not passing 12 psi and you really dont have to worry about it.

 

If your boost is staying at 10 psi after you add the down pipe you are probably fine. Keep and eye on your a/f just to make sure. If you are getting boost creep or spikes above 10 psi, that's not good. With the stock cat in place you should have enough restriction to keep the creep in check.

If you do start getting spikes or creep as a temporary fix you could had a pop-off valve and set it to 10.5 psi, or lower your boost to 8 psi, so the creep doesn't take it above 10. Not sure but I think you can change a pill of something. Best solution get and aftermarket computer.

 

I already get boost creeps!! If I'm cruising on the highway in 5th and I hammer it, I've seen it creep to 13-14. Wouldn't the creep help stabalize my AFR since I'll be running rich anyways?

God Damn it!! Why is the PFC so expensive!!!!

 

You also have to think about the air temp coming from that text book size IC you still have so you probably need all the fuel you can get. With creep like that get a boost controler. Whats funny is that everybody says that could wait. I got that as my first mod and I have never seen anything over 11 psi. When I start moddifing heavily the boost controler wont hold it. But as is right now its perfect.

 

I though the issue with boost creep was that the wastegate wasn't large enough. If a boost controller worked for Street King, its worth a try. Spending 300 on a boost controller is better than a 1000 on a pfc. You need a boost controller some day anyway.

I am suprised you are not getting fuel cut at 14 psi.

 

yeah mkoch1, sounds a little weird.

 

So in other words, I should shut the hell up and save my money until I can get a PFC.

I've never had the fuel cut out on me. It creeps up to 14 slowly and then comes down slowly. It doesn't hold there very long. Thanks for your input guys

PS Howmuch did adding the downpipe change the sound of your exhaust? Louder Ricier?

 

My DP made mine sound louder w/a deeper tone, not ricier. I also have my cat gutted, only because i don't have enough cash right at the moment to get a MP. My setup is a M2 DP > Gutted cat > RB catback. Flows fine.

 

Are those the only mods you have? How does the car run? Do you even have a boost gauge?

 

Yeah so far i'm running a dp and cb set up.. and its workin fine for me now..

It made my car sound a bit louder, but after putting in the dp u can hear your turbos spool up now..

 

No, those are not my only mods and I rely on the unreliable boost gauge on the S-AFC. I have a stage 3 race port, the exhaust you know about, s-afc, profec-a, that's about it for performance.

 

I feel I'm pretty qualified to respond on this subject.

midpipe pros: more high (above 4500) rpm power, maybe 20rwhp on stock twins, if that. shooting flames. loud as hell. seemed to me to puller harder on the highway especially.

midpipe cons: much less power (but alot of noise) below 4k rpms, shooting flames, loud as hell, your back bumper gets incredibly filthy from the fuel, smells kinda nasty, yet appealing at the same time. Most importantly, boost creep, and easier chance of leaning out.

After blowing 2 motors within 2 months (long story--first was inadequate self-tuning and second was a bad ******* tank of gas [thanks exxon]) Dave at KD Rotary (who knows a thing about these crazy Wankels we love so much) was of the very strong opinion that I install a high flow cat. He told me tuning was more difficult with a midpipe, and that *it was more difficult to keep residual fuel in the motor with no backpressure.* He basically told me that for a street car with stock twins a midpipe wasn't worth the risk.

Re: Boost creep. I boost controller will help control spike at transition, but won't (won't) affect creep. Only a ported (enlarged) wastegate can help alleviate boost creep by diverting more exhaust flow away from the turbine, thus (hopefully) keeping boost in check.

Now, Dave had advised against a midpipe all along, back to when I bought the car at the beginning of '99. For the first and only time, I disregarded his advice. I was sick of blowing motors so I finally listened to him.

I'm very happy with the high flow (bought from rx7.com btw): nicer exhaust tone, more low end, I don't **** off the neighbors anymore with the noise. No flames, which I kinda miss.

In closing, I'll direct you to my sig to demonstrate that good power can be made with a high flow cat

Hope this helps--

 

And I feel pretty qualified to actually answer the question regarding a gutted cat. I noticed a performance gain, period. It may not be as much as a down pipe, but that's fine with me since I used the DP money elsewhere. The only cost for me was a six pack of beer to my neighbor for helping me cut it open and weld it shut..

I have been told that you don't need to cut it open, but after having not been able to beat it out, and having been already commited with denting the core, I had to perform the operation.

I do like the fact that I will pass visual in this area. (Don't need to hear it from you non smog states)

 

I was responding to some of his dpasseto's subsequent posts

Also, do you have a gutted precat, but the stock cat? That's the first time I've heard of someone gutting their precat. Works for me, I suppose.

And Dpasseto, if I understand you correctly, you're getting boost creep (not spike) to 14 psi with the stock cat? Spike happens at the turbo transition (~4500 rpms) for an instant, while creep happens at higher rpms and increases with rpm. Creep is much worse than spike.

Rich

 

ha! i haven't been around in a while and it's good to see i'm still a trendsetter.....mahjik, nice avatar