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  1. #1
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    Member No: 26535 PeteK is an unknown quantity at this point PeteK's Avatar
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    Remove the cat or not?

    Starting Sept. 1st, Missouri will no longer require emissions inspections on cars older than 1995, so I have a quick question for you guys.

    Has anyone removed the catalytic converter without any other engine mods? I'm sure that the US version of the S38 was designed to work with one and I'm just curious as to what would happen if I just ran straight pipes from the header to the muffler. Would that freak out the ECU?

    Thanks in advance!
    Pete

  2. #2
    Andy
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    Search...

    I posted some dyno charts of my before and after. The result was chunky loss of torque below 4000 rpm and maybe around 15hp more above 4000rpm.

  3. #3
    M5zealot
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    hp torque loss possible

    I agree you could loose hp and torque by removing cat. But can it really be that significant? I have had chip and cam gear installed since 1989 when Dinan came out with them. All my experience w/ exhaust mods (all 5 ) were with these two items installed. I will definitely post dyno results soon. I was just waiting to break in my new engine. I will do runs w/ and w/out track pipes and other cold air intake system my buddy has given me to to try out. Also have a MAF conversion to try out. I'm not removing the headers though! Should be interesting.

  4. #4
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    Re: hp torque loss possible

    Thanks for the info guys, I look forward to seeing the dyno charts!

    One important thing that I failed to mention is that it has the European exhaust headers already on it... I'm sure that changes things a little.

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    Re: Remove the cat or not?

    I think the problem you'll have is fuel metering for the new setup. The AFM is setup to run a cat and 02 sensor. Make sure your new pipe has a bung for the 02. What I'd do, if you really want to run without a cat, is find someone who can do some dyno testing and burn a custom chip for a flow through setup.

    You can also call Frank Fahey in San Diego.., he sell a track pipe and will probably have some great info on maximizing output when running a straight pipe. Although I'll bet ya $20 that he says to just install his cam gear.

    Good luck.

    P.
    ---------

  6. #6
    M5zealot
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    Re: track pipe

    I have Fahey Track pipes and had custom made straight pipes prior and ECU did not freak out. I don't have dyno results but I'm sure hp increase was at least 10HP. The best thing was the raw and crisp rasp the stock US exhaust became. Pulling to redline is sheer joy. Just installed Racing Dynamic headers this week and the engine pulls even stronger! Waiting for dyno time this month. Engine just passed 2,450 miles. I think its ready to see what she throws down at the rear wheels. I ran a straight 3 " exhaust years ago with a magnaflow muffler and definitely decreased needed back pressure and showed significant torgue lose. Ditched that system right away. Euro set up is more obstuctive because it was designed for cat free operation. US system flow more to make up for cat. Carl Nelson, of La Jolla Independant (my engine rebuilder) gave me these words of wisdom years ago. I'm selling my non fahey track pipes if you are interested. Randym5z at coxdotnet

  7. #7
    M5zealot
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    Re oh forgot

    I have a DINAN chip and cam gear too.

  8. #8
    M5zealot
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    track pipe pic

    As Philo stated, important to have o2 sensor installed. fahey pipe is on left pipe just past cross flow tube

  9. #9
    LouHM5
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    Re: Remove the cat or not?

    Has anyone considered product #781302 from Supersprint? Drill down from website in link. Looks like you get the O2 bung, and it will probably give more backpressure than straight pipes. Quieter too.

  10. #10
    LouHM5
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    repaired link


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