Eliminate pre-cat sections. Bad idea?
 

My down pipes leak where they bolt up to the main cat, and are so bad and weak that they are not repairable. My mechanic says that he can bend pipes to replace these sections, mounting the O2 sensors in their original location and eliminating the 2 pre-cats all together. Are there ANY issues with eliminating the pre-cats, performance or bad exhaust note wise? He said he could do it out of 1 7/8" or 2" vs. the 1 3/4" stock. Any recommendations? Thanks!

Re: Eliminate pre-cat sections. Bad idea?
 

some members here has done it before
not sure if it changes anything though ~

Re: Eliminate pre-cat sections. Bad idea?
 

If you are replacing the front pipes, it is strongly suggested to use small cats or pre cats in the new section, otherwise you may have an issue with emissions. If you eliminate the resonator/precat assemblies on the front pipes, you will have an annoying buzz between 2500 and 3000 RPMs. Been there, done that. :o

Re: Eliminate pre-cat sections. Bad idea?
 

This is on my off-road SVX, not my daily driver. I'm not worried about emissions here, more any negative side effects to eliminating them. Thanks!

Re: Eliminate pre-cat sections. Bad idea?
 

Serious resonance FTL! Replace them with small SS resonators.
(been there, done that)
-Bill

Re: Eliminate pre-cat sections. Bad idea?
 

Could you give me an example of these SS resonators? You say you have taken the pre-cat sections out and replaced with SS resonators? How did it affect the sound of the car? Thanks! Jordan

Re: Eliminate pre-cat sections. Bad idea?
 

Usae the Areo Turbine AR20 resonators from Verocious motorsports. About $52.00 each plus shipping.



1992 Subaru SVX LS-L (OBDI)
Harry Newman "newsvx" has them installed on his 92 pearlie in place of the pre-cats. He has 2" headpipes onto the resonator and 2" pipes out of the resonator into a Magnaflow 94007 high-flow main cat (dual 2" in and single 2.5" out). His use is mainly off-road (autocross) as well.

It does not change the sound or affect the emissions on the 92 (OBDI) cars. Here is a photo of them on Harry's car:





1996 Subaru SVX LSi (OBDII)
I did the exact same setup on my 96 LSi. The OBDII cars are a little more sensitive to not having the front pre-cats in place. About a month after the install, I started getting a CE light about my converter being inefficient (Code 420-- Catalyst System Efficiency Below Threshold - Bank 1).

I removed them and replaced them with Magnaflow universal pre-cats #53104 from Performance Peddler and everything has been operating flawlessly ever since. Their best price is 49.00 each with shipping.

Here are photos of my 96 OBDII with the Aeroturbine AR20 resonators



As I said earlier, the resonators do not change the sound to any degree over the OEM units, they just give the exhaust pulses a place to expand, similar to the pre-cat.

Since they are cheaper, I would go with the Magnaflow pre-cats. That way it is totally emissions compliant, should you ever want to sell the car and need an inspection.

.

Re: Eliminate pre-cat sections. Bad idea?
 

THank you SVXCESS! This is exactly the information I needed!

Re: Eliminate pre-cat sections. Bad idea?
 

I will plan to do 2" off the headers, including the O2 sensors. Then into AeroTurbine AR20 resonators, with more 2" into the main cat. What diameter pipe comes off the main cat headed towards the resonator before the muffler? I would need a Main Cat with that diameter single outlet, and the 2" inlets. Any model suggestions? Is there an O2 sensor on the Main Cat, giving our cars 3 of them? Thanks!

Re: Eliminate pre-cat sections. Bad idea?
 

The pipe that comes out of the rear of main cat, into athe resonator and all the way back to the rear muffler is 2.5"

The main cat you would need is the Magnaflow 94007, It has dual 2" inlets and a single 2.5" outlet. The 1992 SVX only has the 2 O2 sensors in the headpipes.

The third O2 sensor in the main cat did not show up until OBDII in 1996. That cat would be the 94037 (with the O2 bung)


The stock resonator has been known to fail quite oftenand have broken baffles with age, causing a buzzing or rattling under acceleration about 2500-3000rpm.

The option I used was to replace it with the Aero Turbine AR25 resonator, which is the same inlet/outlet diameter (2.5") as the stock resonator. Welded into the same position as the stock one.


You can see my third O2 sensor mounted in the pipe behind the main cat. Gives a cleaner reading there and is much easier to change than at the top of the cat.

.

Re: Eliminate pre-cat sections. Bad idea?
 

I believe you have the model numbers mixed up for which has the O2 sensor. I am considering having my exhaust guy make the cat back, or else get AWD's cat back system. Is it diffacult to have someone unfamiliar with the SVX bend the pipes correctly to clear the differential etc, so that nothing touches and nothing is so low to the ground that it drags?, I have drop springs.

Re: Eliminate pre-cat sections. Bad idea?
 

You are correct and I have since fixed my post.

The 94007 is the OBDI cat for the 1992-1995 SVX, Dual 2" inlet, single 2.5" outlet.



The 94037 is the OBDII cat for the 1996-97 cars. Same configuration, but with the O2 boss at the front of the cat.