Alright, so here’s some of the basics. To add a turbo to a naturally aspirated car you need to complement it with a variety of other goodies to make sure your car’s engine doesn’t explode. A basic turbo system should include the turbocharger, oil feed and drain lines for the turbo, coolant feed and drain lines for the turbo (if your turbo happens to be watercooled as well), a turbo manifold, some kinda of exhaust piping to get all those lovely chemicals out from your car, intake piping for the turbo, piping for the compressed air between the turbo and intake manifold, a rising rate (auxilliary) fuel pressure regulator to increase the fuel pressure when you’re in boost so you don’t run lean, and some sort of timing control. Other cool little doodads are a boost gauge so you can see how much PSI you’re running then go brag to your friends, and a blowoff or recirculation valve. Since the idea here is to retain the stock ECU, we will be using a AFPR to mechanically raise the fuel pressure across the fuel rail (shhh, the ECU won’t know a thing). Then the Bipes timing controller will intercept and alter the CAS signal to the ECU to control your engine timing based on RPMs, intake air temp, and airflow. A Bosch recirculating bypass valve was also purchased because the engine likes to stall when meter air is just vented to the atmosphere. However, the Bosch recirc. valve will not be needed because the turbocharge has an integrated recirculation valve. Nearly all of my parts were purchased second hand off of eBay because it’s ultra cheap.
There’s nothing better to compliment your turbo than a free flow, mandrel bent exhaust (well, maybe an intercooler, but I already got one :P). A free flowing exhaust reduces back pressure and lets your turbo spool up a couple hundred RPMs sooner. Depending on how you make it, you can also cut some weight off of your car because factory exhaust systems are usually god-aweful heavy. I jacked up the front of the car and put it on jackstands to get some clearance so I could go under and measure. Because of the way the driveway is laid out, I didn’t need to put the rear end up on jackstands because the slight slope gave me ample space to work with. The entire system was made from one and a half 2.5” mandrel bends bought online (the other half was used in the downpipe) and part of a 10′ long 2.5” straight pipe I picked up at a local muffler shop.
Here’s the downpipe tacked together with some small sections from the mandrel bends to make the gentle curves so it snakes between the car’s steering shaft and the transmission. The top part is from the factory downpipe portion that came with the “kit” I purchased. I was told it was 2.25” but it’s just about the exact same size as the 2.5” piping, so no complaints there. This was done by cutting and tacking small sections of piping until the bends fit nicely so the downpipe wouldn’t hit any of the surroundings. This was pretty tough because I had to keep mounting and unmounting the turbo and manifold to take the downpipe off so I could weld it up (bad design, I know) and this along doubled the time it took to make the dp. I didn’t want to weld underneath the car, there’s something about laying on my back and welding about a foot above me that just doesn’t seem too appealing. However, once the bends were done, the rest was fairly easy. I left the stock cat-back exhaust on so I could see how far I had to extend the straightpipe so that it’ll reach the cat. I welded a 2.5” 3-bolt flange (purchased online along with the mandrel bends) onto the end of the straightpipe so I could continue the rest of the exhaust from there. A note on the flanges – they are really large and clearance between the driveshaft and the body of the car will be pretty tight. What I did was grind down the corners of the flange down to the holes for the bolts.
Now we don’t want to be feeding our engine some really hot air do we? One of the most effective mods that can be done to a turbocharger setup is the addition of an intercooler. There are two types of intercoolers, air-air and air-water. Air-air intercoolers rely on the ambient air to decrease the temperature of the pressurized air from the turbo, much like how your radiator cools the engine coolant. On the other hand, an air-water intercooler uses water to cool the intake air. A simple air-water intercooler could be an air-air intercooler with a jacket welded over the fins. What happens is a high-flow pump pumps water over the fins of the intercooler, thus cooling the air, then moves the water out to an external radiator, which then cools the water and it gets pumped back into the intercooler. An air-water setup isn’t hard to make if you can weld aluminum, but I can’t, so I went with an air-air setup. Some of the advantages of an air-air intercooler is that it requires much less maintenance than the air-water setup because you don’t have to worry about coolant leaks out of the system or into the intake pipe, or pump or coolant line failures. My setup consists of an aluminum Saab 900 intercooler, some aluminum piping that came with my Volvo turbo kit, some piping that came with the Saab intercooler, and 2 2” mandrel U bends from JC Whitney. My Miata has both power steering and air conditioning, so running the intercooler piping ain’t gonna be easy, and the pipe lengths are going to be fairly long. I ended up going with an under-the-radiator piping setup as it seemed to be the most effective with my conditions with the least amount of bends. The couplers you see are 2” ID flexible exhaust hose from my local boating supply store. At about 5$/ft, and each foot makes 3-4 couplers, this is a steal, and much better than those fancy, expensive silicone couplers. I’m not sure what the exact material is, but it’s mildly flexible and reinforced with a twine mesh, so there should be any problems with these not withstanding the heat and elements. Being a huge fan of the DIY nature, I came across this article in the tech section of the DSMTuners.com website on making your own fiberglass reinforced silicone couplers. All of the credit goes to their forum member wret for this idea. I decided to try it out and make the reducer couplers on my own since they are expensive and would take about a week to order and get in the mail. The throttle body inlet is 2.5” while the intercooler piping is 2”, so I needed a custom coupler there. The Mass Airflow Meter is 2.75” and needed to mate up with my 2” piping, so I also need a custom coupler there. I also needed a sharp 90 degree elbow coupler coming off of the 2.25” intercooler inlet so that the pipes didn’t hang too low. All in all, these couplers were not too hard to make, they don’t look necessarily all that pretty, but beauty is in the eye of the beholder, and these things work great!
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