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Thread: Compressed air supercharging

  1. #31
    Administrator Daox's Avatar
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    I said I wanted to tinker with the idea of what you could do with this concept, but on a budget price and no fancy super high pressure system. So, I've been thinking about it and have come up with a rough design. I honestly think what I have come up with is completely doable and is pretty inexpensive. However, there are some draw backs (of course) that I will go over as I explain things. The setup uses the same concept of the CAS system, but drastically simplifies it, and uses primarily off the shelf components with one or two custom parts that could be 3d printed. This really would allow anyone to build the system fairly easily as 3d printing for hire is quite common these days and fairly inexpensive.

    Lets talk about this low pressure system vs the CAS high pressure system. Obviously, most of us do not have a 3000 psi capable air compressor kicking around to refill our air tank. This basically relegates us to what a standard air compressor can kick out. Mine happens to go to 150 psi, so that is what I will be using for my calculations. That is a pretty huge draw back right off the bat. That means our air tank has to be 20x larger to hold the same capacity! The upside is our engine is tiny compared to most, so we don't need as massive of a tank compared to most engines.

    As previously mentioned, at wide open throttle (WOT) AND peak rpm, our engine is inhaling about 140 CFM of air. If I was going to setup a system like this, I'd like to get about a 30% boost in power so I could say my monster Mirage has three digit power output! (This means I'd like 100hp). So, to get a 30% boost in power, we need 30% more air. 140 * 1.3 = ~180 CFM. This is where we start. We need 180 CFM of airflow for as long as possible from our air tank. Looking at standard air tanks, 10 gallon tanks seem pretty common and cheap. Amazon has them for about $50 shipped to your door. You can probably find them cheaper locally. This tank would easily fit in the trunk of your Mirage, heck two would even fit pretty easily back there I think. Of course, that begs the question, how long does a 10 gallon tank last at 180 CFM? The answer is a whopping 4.5 seconds. I made a simple excel calculator to mess around with this.

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    If we add that second tank in, we get 9.1 seconds. Woohoo! Now you can live your life 9.1 seconds at a time.

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    Now, this number is actually conservative. It will be longer as 180 CFM will be the absolute max flow you'll see at peak rpm. But, we aren't at peak rpm the entire time we're accelerating (unless you have a CVT). It will likely last another second, maybe two with a manual. So, two 10 gallon tank setup will get you one 'pull' on boost. That doesn't sound too great does it? Well, lets continue on and see this to the end. After all, we just took two cheap air tanks and slapped them in the back of the Mirage, we're not in this real deep yet, right?

    Next, we'll look at how to regulate the compressed air and get it into the engine in a controlled manner.


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


  2. #32
    Moderator inuvik's Avatar
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    Mount one of these for a quick shot!

    https://www.ebay.com/itm/5-GAL-AIR-T...-/331710676768

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 automatic: 40.5 mpg (US) ... 17.2 km/L ... 5.8 L/100 km ... 48.6 mpg (Imp)


  3. #33
    Administrator Daox's Avatar
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    Alright, lets continue this wild goose chase!

    So far we have two 10 gallon tanks in the back of our Mirage at this point. This will hold ~9 seconds of boost and is refillable at home with a regular air compressor. The next step is to figure out how to get the air from the tanks into the engine. Thus, we need a fat hose capable of carrying 180 CFM to the engine. Based off some airflow charts, I'd want to go with a 3/4" ID hose. This creates a fairly small pressure drop and will allow us to get the most from our tanks of air. 3/4" air hose is actually not expensive at around $2 per foot. Figure you need 15 feet at most, and you're at $30 for air hose.

    Next up, we need a way to control the flow of this air. We need a way to turn it on and off and more importantly a way to regulate the air flow to the engine. We're starting off with 150 psi. We do not want to just stuff the engine with all of that or bad things will happen. So, I think this can all be done with a $5 part. Yep, $5. Okay, so not really just $5, but we will start there. The device I'm talking about is a ball valve. The ball valve can open and close depending on how much airflow we need. A 3/4" ball valve is around $5 at your local hardware store.

    We have a nice valve that will allow us to regulate air flow to the engine, but we can't possibly manually throw a ball valve and control this thing anywhere near accurately. So, we bring in the electrons to help. It wouldn't be too hard to slap a stepper motor on a ball valve and you have very accurate and fast control of that valve. Stepper motors are also pretty darn cheap. I imagine you'd be able to get away with a one that costs less than $15.

    Now, we need to control that stepper motor in some way. I'm a big fan of the arduino. There is code all over the internet that could help you do this project right quick. They also make stepper motor control boards that simply plug into the arduino that make things even easier. The arduino costs about $15, and a stepper motor control board is another $10. That takes care of powering and controlling the stepper motor, but we need a way to sense the boost pressure. That one is pretty easy too, we just need a MAP (manifold air pressure) sensor that we can feed to the arduino. This will allow the arduino to use a continuous feedback loop to monitor the boost pressure and regulate the ball valve accordingly. With the right programming, it will automatically compensate for the tank pressure as it slowly drains. A map sensor is pretty cheap too. Lets say $20.

    That is almost our entire system. We finally need a way to block off atmospheric air when we hit the boost. I think an old drive by wire throttle body would do just the trick. The arduino could be used to flip it shut when you mash the go button. Lets say you can pick one of these up for another $20.

    And with that, I think we pretty much have an entire system minus some clamps and miscellaneous hardware. Here is a little diagram that lays things out.

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    If we add up all our costs, we're looking at about $200. While I realize its only ~9 seconds of boost (at max go), that is pretty darn cheap, and I think this thing would be a blast. Yeah, it would be work to piece this thing all together, but its really not that complicated. I know two big air tanks in the trunk seems ridiculous, but you could just add quick disconnects and remove them anytime you didn't want them in there.

    One thing that may be an issue would be the OE MAP sensor on the Mirage. I'm not sure what will happen when it sees positive pressure. You may have to clamp the voltage to stop fuel or ignition cut. I know some cars do this.

    In any case, I think this is totally doable. If I had more time and spare cash to throw away on a fun project, I would probably consider it since it sounds so fun.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


  4. #34
    Moderator Eggman's Avatar
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    Quote Originally Posted by Daox View Post
    In any case, I think this is totally doable. If I had more time and spare cash to throw away on a fun project, I would probably consider it since it sounds so fun.
    And pretty harmless, too.

    I mean, what could go wrong?

        __________________________________________

        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)


  5. #35
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    Quote Originally Posted by Daox View Post
    One thing that may be an issue would be the OE MAP sensor on the Mirage. I'm not sure what will happen when it sees positive pressure. You may have to clamp the voltage to stop fuel or ignition cut. I know some cars do this.
    Any risk of running lean and blowing the engine up? Did we establish that the injectors can cram in enough fuel, quick enough to maintain a safe AFR?

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        click to view fuel log View my fuel log 2014 Mirage ES 1.2 automatic: 36.9 mpg (US) ... 15.7 km/L ... 6.4 L/100 km ... 44.3 mpg (Imp)


  6. #36
    Administrator Daox's Avatar
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    Quote Originally Posted by Eggman View Post
    And pretty harmless, too.

    I mean, what could go wrong?
    Nothing a new engine couldn't fix.



    Quote Originally Posted by Tyrelirwin View Post
    Any risk of running lean and blowing the engine up? Did we establish that the injectors can cram in enough fuel, quick enough to maintain a safe AFR?
    I'm sure there is, and that is something else that would need to be looked into. As far as I know, we do not know the flow rate of the injectors, or the flow rate of the OE fuel pump. Its possible that both may need to be upgraded to run a decent amount more power. For smaller power bumps, I'm sure they'd be fine.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


  7. #37
    The Gearhead Project TGPDR1665's Avatar
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    Hi there. Before I run my mouth in response to an admin's idea on a forum where I'm nobody at all, I'd like to say, as a former admin/mod on multiple DSM boards back in the day—who genuinely loves the Mirage and wants to see the next generation of Mitsubishi enthusiasts succeed—I think the only merit in attempting such a project would be for novelty.

    If this sort of thing worked, it would be commonplace. It is not. (There's a reason why there aren't any dealers listed on their "where to buy" page. It's hokey.)

    The quickest way to (dis)prove the concept would be getting the tank and regulator/valving (you'd want a way to measure/confirm actual CFM from the tank, and maybe a spare intake elbow with a fitting for the air line) and taking a Mirage to the local dyno. Tip: Tell them you're trying something "for the lulz" so they don't hang up on you.

    Strap the car to the rollers. Do a baseline. Then do a run where you trigger the air into the throttle body to see what—if anything—actually happens. That's going to give you the least expensive way of testing what's been long established as a waste of time.

    Quote Originally Posted by Daox View Post
    If we add up all our costs, we're looking at about $200.
    Worth mentioning, used OEM turbos are on ebay for under $80 these days. Including basic fabrication of a manifold and plumbing, it's likely you could build a scrappy, DIY turbosystem for under $500.

    Much love and respect, one Mitsubishi guy to another. I mean no disrespect. Just been down this road a few times. It's never ended well. Novel curiosity? A Mythbusters approach, maybe? Sure. Go for it.

    #ichimaiiwa

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    Daox (01-18-2019)

  9. #38
    Administrator Daox's Avatar
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    Quote Originally Posted by TGPDR1665 View Post
    I think the only merit in attempting such a project would be for novelty.
    I concur!



    Worth mentioning, used OEM turbos are on ebay for under $80 these days. Including basic fabrication of a manifold and plumbing, it's likely you could build a scrappy, DIY turbosystem for under $500.
    If we had a usable tuning solution, that would definitely be on the table.


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


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