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| Home > RX-7 > Tech/Mods > Modifications > Turbo NA Guide > Preface, Introduction |
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The question 99% of new RX-7 owners ask themselves after they have purchased a naturally aspirated (non-turbo) car is "can I turbocharge it?". The commonly accepted answer is "no". This is normally followed by advice to either buy a Turbo II, or swap in the drivetrain from the Turbo II. That advice is all well and good, as it is the easiest and cheapest thing to do. But what if you don't want a TII? Or don't have a TII parts car to swap the drivetrain from? This is the position I was in when I decided to turbocharge my '86 NA. Below details the process of my turbocharger installation. But before we get to that, there are a few key points that I need to make clear.
It is cheaper to buy a TII or swap the TII drivetrain. It's just that simple. Buying a complete TII as a car, or even the drivetrain to swap in is significantly cheaper than turbocharging the existing NA engine. Remember that there are no kits available, so every part must be bought individually. Odds are that you are looking at least $2000 US to do a minimal install, and significantly more than that once you start adding extras. When you see that the average price for a J-spec used TII engine is between $800 and $1000, then it begins to put things into perspective. The cheapest way is to put the J-spec engine on the NA transmission. All that is required after that are a few wiring harnesses, the TII ECU, and a few other misc. things.
It is easier to buy a TII, or swap in the TII engine/drivetrain. Considering that a vast majority of the parts required for this conversion will have to be fabricated from scratch, and that a significant amount of labor is involved, it is much easier to just go out and buy a TII. It is also quite a bit easier to swap in the TII engine instead of turbocharging the NA engine.
If you don't know what you are doing, don't attempt this conversion. If things like welding, cutting your car's frame, bending pipe, removing the intake, removing the oil pan or hand fabricating parts scares you, then you should not even think about attempting this conversion. In order to carry out a successful NA turbo install, you must have intimate knowledge of the rotary engine as well as turbo systems. Skills in welding are required, as well as access to all the proper tools and equipment.
You will blow your engine if you don't know what you are doing. You will be dealing with a high compression turbocharged engine, and therefore fuel and ignition timing are critical. One simple mistake and it's very easy to cause detonation (pinging). As you all know, detonation in a rotary is instant death, usually resulting in a broken apex seal. This means a rebuild at the very least, and thousands of dollars in replaced parts (rotors, housings, turbo) at the worse.
It will take a long time. This is not an afternoon project. It will take you months as most of the parts must be fabricated, scrounged, ordered online, or contracted out to others. Your car will be down for a long time while you fit everything, wait for parts to come in the mail, or sift through wrecking lots trying to find things. Be prepared.
Now, consider yourself warned. I have disclaimed all responsibility if you wish to carry out this project, and I will not be responsible for damage to your car or yourself.
With that out of the way, let's get down to business. This is not a step-by-step guide, it is simply the process I went through. Anyone competent enough to carry out this installation should have no trouble using this information in place of one.
The first part of the project simply involved a lot of thinking. I needed to decide what kind of goals I had for the car, and what kind of power I wanted to make. After a little while I decided not to have any specific goals. That way, things are left in the open with a lot more flexibility.
The choice of turbo was rather easy. The stock TII Hitachi T-18 would be just fine, since I'm sure that Mazda put a lot of thought into choosing that turbo to suite the characteristics of their engine. Good for about 14 PSI of boost, it would be more than adequate for my project. Manifolds were another issue. Because the NA lower intake sticks out from the engine so much, by itself the stock TII manifold would not work. Test fitting showed that in order to make things fit, it had to be spaced out by about 2 inches. After talking with an RX-7 Forum member who did a similar project, I found out that a spacer had to be constructed to space the turbo and manifold out from the engine 2.5". Even so, it would sit so close to the lower intake that the Air Control Valve (ACV) would need to be removed.
My original plan was to run low boost without an intercooler. This would certainly have saved a lot of trouble with piping. But the higher compression engine would not be very happy with the hotter intake charge, and limiting boost to 4 PSI sounded like no fun at all. So I decided to go with a front mounted intercooler. I had no solid plans to use any specific cooler, but when the person I bought the turbo from offered me a stock TII intercooler for $30, I couldn't refuse. It would have to be modified to function as a front mount.
Fuel, perhaps the most critical part, didn't take much thought. It was decided that the standard practice of installing larger injectors (in this case, TII injectors) would be fine, as well as a larger fuel pump. I had not decided on what pump to use, until I came across an FD fuel pump for sale. According to various information sources, this pump will support about 300 HP in an FC, so that was fine for me. An Apex'I S-AFC completed the system and allowed me to tune in the larger injectors on the stock ECU. As for the ECU, the stock '86 NA unit was retained.
Oil and water supplies for the turbo was another matter. The water supply was rather easy, as there is a coolant line that runs to the upper intake for the thermowax system. There were several ways to supply oil. Perhaps the easiest way would have been to install a T fitting at the oil pressure sender and tap off of that supply. However, since I needed to remove the oil cooler and have it repaired anyway, I chose to have the shop install a bung to allow me to install a fitting to tap oil directly from the cooler. This results in a more direct oil supply. For the oil drain, I simply drilled a hole in the oil pan and welded in a pipe.
Blow off valve (BOV) choice was not critical, and I just happened to come across an Apex'I unit that was for sale on the RX-7 Forum. Since the seller and I knew each other, it worked out rather well. Intercooler piping is standard 2" stainless, which I custom made for the car with the aid of a hydraulic pipe bender.
Most of the tools used should be standard equipment for any garage: socket set, wrenches, pliers, Vice Grips, screwdrivers, floor jack, ramps, jack stands, drills, tap and die set, jigsaw/Sawzall and a few other little things. Nothing very exotic, with a few exceptions.
Not everyone has a welder, but it is certainly required in this project unless you want to contract out all your welding. Since this is expensive and logistically difficult due to the custom work that must be done, a welder is something that must be on hand. I simply used a good old fashioned arc welder. It's a Deca 70A DC unit that I picked up from Princess Auto a few years ago for $160 Canadian. For a little more money entry level MIG units are available. For most of this work you can run flux cored wire to avoid having a gas cylinder on hand but I would definitly recommend purchasing a unit capable of running gas since you will want to use it in the future.
Since I needed to make intercooler piping, I rented a hydraulic pipe bender to make all the custom bends necessary. Most exhaust shops will bend pipe for a small fee, but because I did not know the exact nature of the bends needed, it meant that I would have to do it myself constantly testing the fit on the car.
Besides the standard wrenches, a set of stubby wrenches (in metric) and ratcheting wrenches (again, metric) were required. The tight spaces made tightening some bolts an exercise in frustration more than anything else.
It is an absolute requirement that you check out the Improvements, Changes and New Ideas page after reading through this writeup. It contains a lot more options for several steps in this process and could save you time, money or both.