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Thread: Custom QUIET Performance Exhaust

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    Still Plays With Cars Loren's Avatar
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    Custom QUIET Performance Exhaust

    I'm gonna try to make this as brief as possible. It won't work. But, I'll try. Do me a favor, if you're NOT interested in performance mods, stay out of this thread. I'm not trying to generate more MPG here, I'm trying to make faster autocross runs. But, I hate loud cars. Both because I have significant tinnitus already, and because I don't like to attract attention to myself or disturb other people when I'm driving. So, the goal is good flow with more power and torque... but, minimal increase in volume.

    I ordered the SuperCircuit header for my Mirage. It's on the way from Malaysia. I'm cheap, I'm not going to dyno this thing. But, I do plan to take some measurements. I'll get 3rd gear pull power and torque numbers from the Torque app, and 0-30/0-60 times from the same app. I can read throttle position, so I may even play with something like hand-timing 20-50 at 50% throttle in 3rd or something like that. If I can come up with something repeatable that's not "full-throttle acceleration", I'll include it. The numbers won't be gospel, but they WILL quantify improvements. And if I remember, I'll even do some exhaust sound videos... maybe take some dB measurements (my autocross club has a sound meter).

    I'll take baseline readings before I start, readings with just the header, and whenever I get the exhaust done, I'll get readings with the full system.

    So, stay tuned. I'll try to provide as much data as I can as things progress!

    As it stands, the drivetrain is completely stock. I've done LOTS of suspension work, and I've changed the engine oil. No mods to the intake or exhaust at all.


    Simplify and add lightness.

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    Still Plays With Cars Loren's Avatar
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    As mentioned, the cute little 3-pipe header is on its way from SuperCircuit.

    Some background on what we "know" about Mirage exhausts and the benefits of the header:
    1) SpeedLabs (not the one I bought, but very similar in design) claims a 10.3 hp gain with their header + intake + Unichip tune. Not extremely useful information if you're not buying the full package, but it points to there being 10+ hp on the table.
    2) SpeedLabs also claims that there is little to be gained by changing the exhaust after the header. Of course, they haven't developed a proper exhaust, nor do they sell it. I bet if they had it for sale, they'd find a way to make it show some power!
    3) SuperCircuit has a dyno chart showing JUST the improvement of their header at about 3-4 hp. (4-5%, that's believable) And also the improvement of removing the second cat and running larger pipe at a total increase of 9-10 hp. (also believable)

    My goal is to first get that 3-4 "easy" hp. And then get as much of the rest of it as I can without making the car loud. I'm really more about the torque. 10% improvement in torque would make me very happy. And that would only be 7 ft/lbs. Pretty sure I can get there.

    I've had a pretty slack schedule this week, so I spent some time researching exhaust design and came up with a good exhaust plan. Initially, I thought I'd do a 2.0" exhaust, but I've changed that to 1.75". Why? Because those who know will tell you that it's all about keeping the exhaust velocity up, and if you go TOO large on the pipe, velocity goes down. That's great if you have a turbocharger, or if your goal is maximum high-rpm horsepower. But, I'm autocrossing in a low-powered car... the last thing I need to sacrifice is mid-range torque! Getting off the starting line and digging out of turns, that's what an autocross car needs to do.

    The OE pipe is 1.5" OD, about 1.45" ID. I found a reference that states a 1.5" ID pipe is good for max 78 hp. Go figure. 1.75" is good for a little over 100, which is about 10 more than I ever expect to see with this engine. 2" would be overkill, and I think it would hurt the usable torque. Plus, it would add a few pounds of unnecessary weight.

    Florida is a no-inspection state, so I could get away with doing whatever I want with this exhaust. But, growing up in the 70's and 80's, I know what a non-catalyst exhaust smells like. And my wife wouldn't ride in it. And I do sort of like trees. So, a catalytic converter is a must.

    Unfortunately, the smallest high-flow cat available is 2" ID. So, I'll make the first part off of the header 2" into the oversize cat. That should almost guarantee that the cat isn't a significant restriction to exhaust flow. Then I'll neck down to 1.75" for the rest of the system.

    Fortunately, small pipes and components are CHEAP. Magnaflow cat, Walker muffler, Jones resonator, and a few J-bends add up to just under $150! I'll probably pull the trigger on that later this month.

    For ease of fitment and serviceability, I'll be making the front part with the cat a separate flanged piece, and the rest will be an actual "cat-back".

    Using components that are very similar to stock except slightly larger diameter, I don't expect it to be a great deal louder than stock. Being larger pipe, and replacing two 1.5" cats with a single high-flow 2" cat will surely make it a LITTLE louder. But, that's okay. Maybe you'll hear it coming. And it will intimidate you. Or not.

    If you're wondering, this is my "shopping list" so far:
    • Jones A3012S Resonator (1.75 x 17” : 3 x 12“ can)
    • Walker 18135 Muffler (1.75 x 22” : 6 x 17” can)
    • Flowmaster 2220120 Cat (2.00 x 12.75” : 4.25 x 8” can)
    • Three 2.00” 2-bolt flanges
    • Two 1.75” J-bends
    • One 2.0” J-bend


    Everything except maybe the cat is mild steel. I'm not building this for bling. I live in Florida. And I know me... if I still have this car in 3 years, I'll be surprised. So, I don't need to double or triple the cost of this exhaust by paying for stainless steel.

    I'm equipped to cut and fit the pipes together, and maybe tack them in place. I have a friend who is a much better welder than I, I'll probably have him do the final welding on it. All said and done, I shouldn't have much more than $200 in the whole exhaust, not counting the header.
    Last edited by Loren; 05-18-2018 at 06:09 AM.
    Simplify and add lightness.

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    In for the info for sure...

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 44.4 mpg (US) ... 18.9 km/L ... 5.3 L/100 km ... 53.3 mpg (Imp)


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    Finally, some measurable data. This ought to be good.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 50.2 mpg (US) ... 21.4 km/L ... 4.7 L/100 km ... 60.3 mpg (Imp)


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    Quote Originally Posted by Loren View Post
    ...
    If you're wondering, this is my "shopping list" so far:
    • Jones A3012S Resonator (1.75 x 17 : 3 x 12 can)
    • Walker 18135 Muffler (1.75 x 22 : 6 x 17 can)
    • Flowmaster 2220120 Cat (2.00 x 12.75 : 4.25 x 8 can)
    • Three 2.00 2-bolt flanges
    • Two 1.75 J-bends
    • One 2.0 J-bend

    ...
    Instead of the Flowmaster 2220120 you may consider
    92363 Eastern Universal Catalytic Converter
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    Very cool thread. I look forward to seeing your progress, and especially your before and after testing.

    That being said, personally I would not go with 1.75". I think you will loose torque over the vast majority of the rpm band. You may gain it up really high, but low for sure and mid to even mid-high will likely suffer. Personally, I would stay with 1.5 as it'll keep a bit more midrange. However, if you want to upsize, I would only go to 1-5/8". That is good for 92hp, and that is still more than what you'll hit with a few bolt on mods. You can even buy mandrel bends in that size here:

    http://www.mandrelbends.com/mandrel-...gauge.html?p=2

    I do believe SpeedLab did a good job developing their mods, and they know what they're talking about. I believe they were hired directly by Mitsubishi to make up those parts for some rally car / race thing when the Mirage first came out.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.6 mpg (US) ... 19.4 km/L ... 5.2 L/100 km ... 54.8 mpg (Imp)


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    Moderator Eggman's Avatar
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    And for audio level testing you can use an app on your smartphone to measure before and after.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 50.2 mpg (US) ... 21.4 km/L ... 4.7 L/100 km ... 60.3 mpg (Imp)


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    Still Plays With Cars Loren's Avatar
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    Good resources on the cat and mandrel bends!

    I'll have to research Eastern Catalytic. One of the biggest reasons that I opted to go with Magnaflow is their name and reputation. Lots of people use them with good results. Contrast to a lot of negative reviews from no-name generic cats. But, I also know that a modern OE cat of the right size isn't going to restrict the flow that it is designed to handle, I don't really "need" a super high-flow cat. It's just that ours is designed to handle 74-78 hp. (and in reality, it's probably designed to be as small and cheap as possible while still meeting the emissions requirements... very likely sacrificing some power in the name of cost and weight) One of the factors I was going to look at before making the final decision on the cat is what the diameter of the collector on the header is. If it's 2", then it might make sense to go with the 2" cat. If it's smaller than that, then it would be better to keep the smaller diameter for flow velocity.

    Mandrelbends.com! I forgot about them. And I didn't know they made intermediate diameter bends. Interesting. Will need to research my pipe diameter some more. This was the initial reference that led me to 1.75" pipe... but, I didn't consider that 1-5/8" might actually be readily available!

    Good thing about making plans... they can change. I'm in no hurry, I can look into it some more. 1-5/8" may actually be better.

    Quote Originally Posted by Eggman View Post
    And for audio level testing you can use an app on your smartphone to measure before and after.
    Tried that. Wasn't impressed with the results. That's why our club ended up buying a proper meter. It's a $20 meter we picked up on Amazon. But, it seems accurate enough, and repeatable. Also very easy to use. It has a peak-hold feature, so I can set it 20 feet behind the car, 50 feet behind the car, 100 feet behind the car... do a drive-by, whatever. And I can get some good reference numbers.

    One of the many things I've learned over the years is that exhaust sound levels are very subjective. One person's "it's not that loud" is another person's "OMG, how can you stand to drive that???" That's why I want to get some actual dB measurements.
    Simplify and add lightness.

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    Still Plays With Cars Loren's Avatar
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    Really quick search (while I should be doing other things) indicates that there aren't a lot of 1.625" mufflers available. I'll probably stick with my 1.75" perfectly-sized Walker muffler.

    And, while I could neck the 1.75 outlet of that muffler back down to 1.625, there's little reason to at that point. That voluminous muffler is going to slow down the exhaust flow. And slower is quieter, which is our secondary goal. So, nothing wrong with the larger tube after the muffler.

    Really, I think I'm looking at the 1.625" pipe up to the muffler. Mount the muffler as far back as possible so that there's a nice long column of high-velocity air that's going to want to keep moving. The replacement muffler is a few inches shorter than stock, so it can easily be mounted probably 6-8" further back.

    With the cat and an extra flange in there, we're only talking about maybe 8" of pipe ahead of the cat, and 10" behind it. Dr. Jeckyl wants to put the cat as close to the header as possible so that it reaches proper operating temperature and scrubs the exhaust as efficiently as it can. Mr. Hyde wants to put the cat as far back as possible so that it doesn't interrupe the high-velocity exhaust flow coming out of the header! Fortunately, packaging dictates that it sort of needs to go in the middle in the stock location.
    Simplify and add lightness.

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    Still Plays With Cars Loren's Avatar
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    Ugh... still waaaaaaiting on this header to show up.

    Talked to my friend who will be doing the welding on the exhaust. I was tossing around the idea of using 18ga tubing to save a little more weight in spite of it being a little more fragile. He said it's quite a bit harder to weld 18ga vs. 16ga. So, I'll stick with the 16ga.

    I'm still waiting until I have the header in-hand to measure the collector output pipe diameter before making final plans and ordering parts for the exhaust.

    Did a little more research on exhaust tubing size. On most small-displacement cars that I've seen dyno sheets for, going a little "larger than you'd think" doesn't have as much of a negative effect on the low end as you might expect, but ALWAYS yields more high end HP.

    The header itself should have larger primary tubes, which will raise the peak torque RPM a bit. But, it also has much, much LONGER primary tubes, which should improve torque BELOW peak. And that's just from the header. I'm not sure the exhaust after the cat is going to make all that much difference. The tube from the collector to the cat can all be considered "collector length". Increasing the collector length is also going to move the torque curve down. Hard to say exactly what the net result will be, but I *think* it should be a torque curve that is fatter both above and below peak. The only way to know for sure would be to experiment with different configurations and do a BUNCH of dyno testing, none of which I'm going to do. I'll just make my best guesses based on the research and calculations that I come up with, and be happy that even if the torque curve doesn't end up exactly where I want it, there WILL be more "area under the curve" and provide an overall net gain. (and I will be testing the effects of the header with both the stock exhaust and the new one... so I'll at least have some overall acceleration numbers that will hopefully show a net improvement)

    And lastly, I just can't get excited enough to go out and do baseline measurements. I did start taking some baseline sound measurements from inside the car, but I didn't have a pen handy to take notes, so I'll have to do it again. Suffice it to say that the stock exhaust is unbelievably quiet from inside the car. But, you already knew that.


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