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.
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.
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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)