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Thread: Deleting rear cats

  1. #1

    Deleting rear cats

    I found someone to delete my rear cats, my question is this ok on a stock car with no tune, will this cause driveability problems, do the front and rear cats correspond with each other on a stock car, I also plan on doing resonator delete tips, I was thinking of replacing the mufflers but wondered if it would be to loud, I noticed that the o2 sensors are in front of the first set of cats but behind the second set of cats, should i get the cats gutted out or put in a straight piece of pipe, when i was at safford on june 16th for the show one guy had his rear converters removed but i think he had a tune, i go for emissions testing in august but i heard all they do is plug into your computer to see if there are any codes, again i dont plan on doing a tune that is why i am wondering if deleting the rear cats is ok or am i going to have driveability problems, any advice would be gratly appreciated.

  2. #2
    That would be me. Didn't have any problems with it at all. Did notice a slight mpg increase, exhaust tone was a little louder and felt a little more power.

    I do have a Xcal2 tune, flowmaster 40 series mufflers and res-delete tips extended out 1.5" past the bumper to help cut down on the interior drone noise.

    Just do one thing at a time, take the rear cats off and see how it sounds to you. If it's just right then leave the rest of the exhaust alone, if you still want some more rumble then get some res-delete tips and if that still doesn't do it for you aftermarket mufflers. You have a wide range of mufflers to go with so that will just be personal preference on what you will like.

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

  3. #3
    Join Date
    Dec 2004
    Location
    Yuma, Az
    Age
    53
    Posts
    271
    I also have the rear cat delete. I went with a simple chop'em out and put in a straight pipe. For me, that is ok because there is no emissions inspection. If there were...I surely would not chop them out. Even if your emissions test is only a code check and not an actual exhaust gas sampling they may still do a visual inspection.

    I have the flowmaster 40's with the rear cat delete, normal megs tips...it is about twice as loud as the other marauder I own that has only the 40's. It is an aggressive sound that can at times be annoying...like when you had that third beer and want to get home quietly.

    as far as the tuning part, i think that you can get along just fine with the stock tune. the 02 sensors are located after the first set (closest to the engine).

    My exhaust shop guy was all for this mod when i went in for the stock muffler to flowmaster 40 change out. when he got under the car and saw the four cats, he jumped all over it and offered to do it for 10 bucks a side (added 20 bucks to the job...not bad). His standpoint was that it is (according to him) legal in arizona and it would add sound and release some of the back pressure on the engine.

    be good!
    Curt

  4. #4
    Join Date
    Apr 2006
    Location
    Hills of Eastern Kentucky
    Age
    34
    Posts
    203
    I too am considering deleting my second set of cats, the only thing that I wonder about, is how much louder will it make my exhaust? I currently have the Flowmaster Super 40's, and they made the car quite louder than stock, so how much louder should I expect the car to be if I deleted the cats? I do suppose though if it I did it, and it wasn't loud enough, I could try to get some non-res tips.

    P.S. There are no emissions testing here in Kentucky, so I don't have that to worry about.
    2003 300B
    Flowmaster Super 40s
    JLT CAI
    Avital Remote Start
    SS Inserts

    More to come

  5. #5
    Here is exactly what it will sound like with rear cats delete, flowmaster 40's and res-delete tips. Yes it will make your car louder, the exhaust will be more free flowing and you will feel a little bit of increase in power in the mid-rpm range.

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

  6. #6
    They dont do a visual inspection in my state, it sounds like it will be okay to do, I will probably do the rear cats first and see how it sounds, if it is not loud enough then maybe the resonator delete tips, as i said before they just plug into the computer to see if there are codes, I know on the reinhart exhaust with the cobra manifolds they have 2 converters, wondering if i should wait until after emissions, are the rear cats more restrictive than the front ones, at safford on the 16th of june one guy stated he can go 50 miles more on a tank of gas, if anyone else has deleted the rear cats and gone through emissions, please chime in.

  7. #7
    If you have them removed, just make sure the piece of pipe is put on good and their are no leaks. You will be fine. The front and rear cats are the same exact units, the only reason why their is a 2nd set is to help catch and clean whatever the 1st set misses.

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

  8. #8
    Have not heard anyone say that I will be throwing codes, I am going to make the appointment tomorrow, I hope to see you guys in Hagerstown, MD. in early August.

  9. #9
    You won't throw any codes, sorry for not saying exactly that. I had included that when I said "Didn't have any problems at all".

    The rear cats sit behind the rear O2 sensor anyways.

    You can always just go get your vehicle emissions done early and then go to get the rear cats removed. That way the emissions are done and out of the way for 2 years.

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

  10. #10
    Thanks for the reply, I am having it done on friday the guy is charging me $150.00 , i am sure i could find it cheaper but he is close by and has done work on my cars before, i talked to a buddy of mine at chevrolet and he said the same thing that as long as the o2 sensors are in front of the rear converters i will be fine, you have to let me know if you are going to be in Hagerstown the first week in August, otherwise we should meet because I would like to see your car, I dont think Gaithersburg is that far from Jessup, hope you dont live next to the jail in Jessup if it is still there.

  11. #11
    Join Date
    Jan 2004
    Location
    Somewhere in the N.C. Triangle
    Age
    68
    Posts
    26,250
    Deleting the rear cats is fine, you won't throw any codes and you'll have less back pressure. You can delete the rear O2 sensors also, although you may need a tune to make sure they aren't read by the OBDII. Whay not go all the way and get some hi-flow cats to replace the remaing 2 stock cats? I'd go with Magnaflows for the mufflers.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  12. #12
    Join Date
    Aug 2006
    Location
    MA
    Age
    36
    Posts
    5,893
    I'd give you a video clip of mine, but I have full exhaust, ctrlraven's is the best you'll hear close to stock since he has only muffler's and rear cat's gone. Sounds good too!
    '03 A #1801 - Tuned By Outlaw Dyno
    445rwhp/408rwtq - 12.6/110mph
    DR Vortech NOIC #5
    Sold
    '88 Mustang LX - Built 306ci, built AOD, built 8.8"
    '11 F250 Powerstroke - 476hp/1208tq

  13. #13
    I thought there were only 2 o2 sensors, when I got underneath the car I saw 2 sensors after the first set of cats, I dont think there are any sensors after the second set of cats, I will check tonite, I am going for my test in august, they just plug into the spot underneath my dash to see if there any codes, I have to wait till then because i missed my last date, they are supposed to mail me something soon, whats the point of deleting the two rear sensors, where are they, if they are behind the first set of cats I should be fine, I have listened to cars with the magnaflows, a little to loud for me, cats first, maybe resonator delete tips if I want more sound then maybe mufflers.

  14. #14
    Quote Originally Posted by Raudermaster View Post
    I'd give you a video clip of mine, but I have full exhaust, ctrlraven's is the best you'll hear close to stock since he has only muffler's and rear cat's gone. Sounds good too!
    Thanks, yeah hopefully I can get some long tubes before MVV.

    Marylandmarauder, just an fyi. If you go rear cats delete, flowmaster 40 series and res delete tips this is what the inside will sound like, Drone FTL

    http://youtube.com/watch?v=vuh4WH1jVDU

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

  15. #15
    Quote Originally Posted by Marylandrauder View Post
    I thought there were only 2 o2 sensors, when I got underneath the car I saw 2 sensors after the first set of cats, I dont think there are any sensors after the second set of cats, I will check tonite, I am going for my test in august, they just plug into the spot underneath my dash to see if there any codes, I have to wait till then because i missed my last date, they are supposed to mail me something soon, whats the point of deleting the two rear sensors, where are they, if they are behind the first set of cats I should be fine, I have listened to cars with the magnaflows, a little to loud for me, cats first, maybe resonator delete tips if I want more sound then maybe mufflers.
    Their is a set of O2 sensors in the first pair of cats, then the second set is what you saw which is in between the 1st and 2nd cat.

    2004 Silver Birch
    300B
    Build date:9/29/2003, Adopted on 12/02/05
    Exhaust by Greg
    13.630 @ 100.49 mph (11/21/10)

    2015 Ford Focus SE Sport FWD
    2013 Lincoln MKS EcoBoost AWD (377whp/423tq).
    2010 Ford Fusion Sport FWD
    1989.5 Ford Mustang 5.0 LXsport

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