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Thread: Scorpion Exhaust

  1. #11
    Senior Member Mitz's Avatar
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    Minihaha .. Thanks for this..

    you beat me in opening the muffler first .. Nobody has done this in our local forum yet .. when I posted about exhaust rattles in my exhaust system there, somebody advised that the rattle was coming from the muffler. I was planning then to rip it in some future time when I will have a replacement muffler. Looking at the pictures, I can deduce that the rattle is coming somewhere else, i,e, from the secondary CAT. (I will have that 2nd CAT ripped to see what's inside).

    I have a Headers made by STIVO (similar to Speedlab's); selective rattling is observed around 1k and 3K RPM's that developed slowly in due time. After more than 1 year & a half, it developed into an irritating one.

    This is my planned mod for 2Q/2016.
    Name:  JdDv3rW.jpg
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    1. Headers already in place as replacement of the exhaust manifold/primary CAT
    2. Secondary CAT to be replaced w/ High-Flow Type (ECO III Universal)
    3. Stock Muffler for replacement with the ff. choices:
    • Flowmaster Super HP-2 Series muffler
    • Walker Pro Fit muffler
    • Flo~Pro Heavy Duty muffler

    4. Resonator may or may not delete



  2. #12
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    that pressure chamber creates the backpressure doesn't it?

    that's why on speedlab's dynos, they claim that the original muffler design is necessary to retain power. any modifications to the mid muffler would lose some power.

    though for me it's negligible. and all my past full tank fillups i did after replacing my mid muffler with a cherrybomb, it gave me better FC. I used to average 9-10km/L. now it's a consistent 14km/L. and that's with spirited driving with upshifts at 6k at highways. i don't know if that matters but the figures doesn't lie.

  3. #13
    ミラージュ Minihaha's Avatar
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    backpressure

    Exhaust flow is actually really complicated to do "right."

    I will try to be brief.

    Backpressure is not advantageous (I'm sure some here will disagree*).
    However it's essentially unavoidable in some form.
    The goal is to utilize the 'backpressure' wave to enhance exhaust flow out of the head.
    Any orifice or opening creates a pressure wave that travels 'back' up the pipe.
    Ideally the pipe is engineered to use this reverberation to positive effect.
    It is a very difficult task.

    *look at a dragster. They are open pipes for maximum power, and the pipe lengths are tuned to achieve the 'back' pressure wave (that develops as the exhaust spills out from the pipe's constraints into the open atmosphere) at exactly the right RPM range to achieve maximum gains.

    The problem often encountered is: an exhaust is engineered from the factory, as soon as you change it you are more probably making it questionably more effective (for power).
    Unless you engineer the system to the level that the manufacturer did. Which takes a lot of effort (engineering, tools, test equipment (lots of equipment), trial and error, etc.).
    Now eliminating as much backpressure as possible is a good goal but if in the process you 'detune' the pressure wave that was previously improving head flow (at the 'correct' engineered engine speed) you haven't gained anything but noise, and have likely negatively impacted the torque curve in an RPM region encountered regularly (i.e., mid-range); you've gone and created the dreaded "flat spot."

    Also - put a turbo in your exhaust stream and little matters after it, all 'tuning' discussed in the paragraph above is of considerably lesser value, except that you definitely want the minimum backpressure for the turbo, having backpressure after a turbo is not advantageous (for performance).

    FWIW: No engineering was involved in my exhaust modification and I make no claims to enhanced performance in terms of higher power output. I cobbled that thing together, lol. The minuscule size of the OEM exhaust pipe makes adapters necessary, but I did my 'best.' Do I hope it helped, sure, but I didn't measure it to verify, so I cannot say it did.
    That's where dynos come in. Proof is in the pudding, as they say.
    Last edited by Minihaha; 01-03-2016 at 05:04 PM.
    ゼロ

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 33.4 mpg (US) ... 14.2 km/L ... 7.0 L/100 km ... 40.1 mpg (Imp)


  4. #14
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    Quote Originally Posted by Mitz View Post
    Minihaha .. Thanks for this..

    you beat me in opening the muffler first .. Nobody has done this in our local forum yet .. when I posted about exhaust rattles in my exhaust system there, somebody advised that the rattle was coming from the muffler. I was planning then to rip it in some future time when I will have a replacement muffler. Looking at the pictures, I can deduce that the rattle is coming somewhere else, i,e, from the secondary CAT. (I will have that 2nd CAT ripped to see what's inside).

    I have a Headers made by STIVO (similar to Speedlab's); selective rattling is observed around 1k and 3K RPM's that developed slowly in due time. After more than 1 year & a half, it developed into an irritating one.

    This is my planned mod for 2Q/2016.
    Name:  JdDv3rW.jpg
Views: 2158
Size:  11.5 KB
    1. Headers already in place as replacement of the exhaust manifold/primary CAT
    2. Secondary CAT to be replaced w/ High-Flow Type (ECO III Universal)
    3. Stock Muffler for replacement with the ff. choices:
    • Flowmaster Super HP-2 Series muffler
    • Walker Pro Fit muffler
    • Flo~Pro Heavy Duty muffler

    4. Resonator may or may not delete
    I looked through the repair manual and couldn't find reference to a secondary cat. It looks like a cat but could it be a second resonator?

  5. #15
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    yeah i agree with you minihaha. we're not building purpose built racecars after all. we're just after the nice exhaust note these aftermarket mufflers produce.

    Quote Originally Posted by ahausheer View Post
    I looked through the repair manual and couldn't find reference to a secondary cat. It looks like a cat but could it be a second resonator?
    i doubt coz it has its own heatshield like the first one.

  6. #16
    Senior Member Mitz's Avatar
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    CATS normally do have a heat shield while resonators do not..

    Name:  2nd cat converter.jpg
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  7. #17
    Moderator Eggman's Avatar
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    I read somewhere that original catalytic converter designs with one converter took a while to warm up to operating temperature in order to do their job.

    Manufacturers then put a smaller cat closer to the exhaust manifold to warm up quicker. This would reduce emissions sooner after a cold start. Also, the heat from the first converter would help get the second converter up to temperature sooner, and also further reduce emissions.

    Someone here please correct me if I am wrong on this. Thanks.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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  9. #18
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    I agree its probably a cat. Just amazed it is not mentioned in the repair manual or listed on any part diagram.

  10. #19
    ミラージュ Minihaha's Avatar
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    It is a catalytic converter

    Quote Originally Posted by ahausheer View Post
    I agree its probably a cat. Just amazed it is not mentioned in the repair manual or listed on any part diagram.
    Without a doubt, no question about it, it is a cat.
    I removed mine and can verify. There are other threads around that mention it; it is (what I call) a 'passive' cat., the O2 sensors that work with the fuel injection to achieve the right Air:Fuel ratio are "on" the first cat. This 'passive' one doesn't create much restriction, both cats are a honeycomb pattern of say: 'straws,' arranged longitudinally to the flow.

    I agree that it is rather odd it is not mentioned.
    ゼロ

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 33.4 mpg (US) ... 14.2 km/L ... 7.0 L/100 km ... 40.1 mpg (Imp)


  11. #20
    ミラージュ Minihaha's Avatar
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    the install

    Current 'cobbled' (& permanent/long term) exhaust set-up:
    I ended up with this because I wanted to install the MagnaFlow myself, not bring it back to the shop that put in the straight pipe.

    In 'designing' it I was able to get every connection to male into a female except for what the shop had already installed at the 'end' (left side of picture). The dashes represent a pipe inside a pipe (i.e., if the pipe is on the outside its a solid line, if its on the inside its a dashed line).

    Not particularly proud of this cluster but it is solid, removable, and works well.

    Biggest down side (that I neglected to consider): the MF actually protrudes about 1.5/2" below the bottom of the car. See the bottom picture.

    Name:  oem pipe_1.jpg
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    Name:  IMG_20160103_144540_edit.jpg
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    ゼロ

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 33.4 mpg (US) ... 14.2 km/L ... 7.0 L/100 km ... 40.1 mpg (Imp)


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