The (Almost) Complete Guide To Turbocharging The Naturally Aspirated Second Generation RX-7

The (Almost) Complete Guide To Turbocharging The Naturally Aspirated Second Generation RX-7 - Improvements, Changes and New Ideas

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Since the original project took place in 2001/2002, there has been much discussion on different ways things could have been done. Some of these ways are improvements over what was done originally, some are just different and some may be easier in certain situations. These alternatives are covered here.

The Exhaust Spacer

The 2.5" exhaust spacer was used originally because it was the easiet thing to do at the time. While certainly not elegant it does work well. A much better solution is to build a custom manifold to space the turbo out and up to allow it to clear the lower intake. The manifolds flow is far superior to the spacer, it eliminates the need for multiple gaskets and perhaps most importantly removes the need to notch the frame. Anyone making a spacer will also be equipped to build a manifold as the process is the same (the spacer is basically a manifold in itself anyway). The flanges are available from Racing Beat or Mazdatrix for both 13B and 12A engines. Suitable pipe is available at most industrial plumbing stores very cheaply. You will want "SCH 40 weld els". They come in several radii, the most common being 45 degrees and 90 degrees. The turbo flange you will need to fabricate yourself as none of the RX-7 stock turbos used standard flanges. If you are interested in making a manifold and need some guidance, SDS EFI has a great article on turbo manifold fabrication on their website. With a little work you can have a very nice manifold for well under $100 using easily available parts.

Oil Sources

If tapping the oil cooler isn't practical for your particular installation, they are many other oil sources. Since the rotary exposes so much of it's oiling system externally, finding an appropriate oil source is easy.

1. Tapping The Oil Cooler Lines: If you are willing to make stainless braided oil cooler lines using AN fittings (or already have them) then it is easy and convenient to tap them for oil. Using a fuel pressure take off fitting (such as Russell part number 670360) will give you a -10 female connection on one side, a -10 male connection on the other side an a 1/8" NPT port in the middle. This fitting simply connects in series with an oil cooler line at either the front cover or the cooler (there's not really a lot of space at the back of the engine). You can then continue using an 1/8" to -4 adapter and build your turbo feed line out of -4 braided stainless and AN fittings, or go cheap (not recommended) and use high pressure rubber hose and a standard 1/8" pipe nipple.
2. Aftermarket Oil Filter Pedestal: Most of the vendors sell oil filter pedestals that are tapped for gauges. Mazdatrix and Speed Machine Performance each have their own version. These provide either 1/8" or 3/8" tapped ports to which you can attach an appropriate pipe nipple or NPT to AN adapter. The benefit of this configuration is that it is very easy, it gives you an extra port for a gauge and it's likely that the stock o-rings under your existing pedestal are leaking anyway. The disadvantage of course is that you will be spending $50 or more on the pedestal and you have to plug the unused hole if you do not plan on installing a gauge.
3. Tap The Stock Pressure Sender Feed: The oil pressure sender is another good source of oil. By removing the sender, installing a "T" fitting and then reinstalling the sender you can tap filtered oil directly from the engine's oil gallery. The threads at the engine are 1/8" BSPT not NPT. So you will need a 1/8" male BSPT to 1/8" female NPT adapter, the appropriate T fitting, and then a 1/8" NPT male to 1/8" BSPT female adapter (to allow you to mount the pressure sender). The unused branch of the T fitting can then be used with NPT to AN adapters, a hose barb for rubber hose or compression fittings for hard line. All of this should be cheap and available at your local hydraulic store. The only real disadvantage is that the oil pressure sender sticks out quite a bit after all the fittings are added which can cause clearance issues and looks a bit weird.
4. Tap The Front Iron: All 12A and 13B engines have an oil passage in the front iron that leads to a flat spot on the top of the spark plug side. From the factory, non-turbo engines have a plug pressed in, while turbo engines are tapped for the banjo bolt to supply the turbo with oil. You can drill and tap this area and then use the stock feed tube (it will have to be cut free from the vacuum spider and lengthened) or use an adapter to convert to AN sizes so you can make your own lines. Of course this is complicated and if you end up getting drilling/tapping chips into the oil gallery they will be very difficult to extract (try a magnet on a stick) and will cause serious bearing damage as they go through the engine. This approach isn't really recommended unless the engine is already disassembled.

Oil Drain Options

There are also several oil drain options if you don't plan on welding a piece of pipe to the oil pan.

1. Use A Flange: Russell makes an adapter flange that bolts to the flat spot on an oil pan and then provides a male -10 AN flare for direct connection to the matching -10 AN fitting. All you need to do is drill a few holes in the oil pan. However since none of the rotary oil pans are very flat (except for the front of the 1st gen 12A and 13B pans) you will have a hard time finding an are to mount such a flange.
2. Tap The Oil Pan
: The oil pan is just thick enough to be tapped for 1/2" NPT. You can tap the pan and then use a 1/2" to -10 or -12 AN adapter. Or simply use a 1/2" NPT hose nipple and connect to the turbo with rubber hose (yuck). Lots of sealant will be needed on the threads to prevent leaks, and since the threads are thin they will not stand up to much abuse.
3. Install an AN Fitting Directly: Earls sells steel -10 AN male flare weld bungs which you can weld directly to the oil pan after drilling a hole. This makes for a compact and neat installation but does require removal of the pan. And if you damage the flare, then you're basically stuck until the pan can be removed and the bung replaced.
4. Tap The Front Cover: If you look just under the metering oil pump, you will find a flat spot on the front cover. This provides ample area to tap for the fitting of your choice. However the metering pump may get in the way depending on the fitting you choose. Again there is the risk of getting metal chips in the engine but since they will fall into the flange a simple oil change will usually flush them out.
5. Install The TII Front Cover: Of course the stock TII front cover already provides an oil drain connection. ATP Turbo sells a billet T4 style drain flange that will bolt directly to the front cover. It has a 1/2" NPT female thread to which you can either attach female plumbing fittings or use an NPT to AN adapter. The stock drain tube can also be modified to fit as well. Of course, swapping the TII front cover in place is a bit of an operation requiring removal of the front hub (it's nut is tightened to 90 ft-LBS and there is a risk of upsetting the torrington bearings during the procedure) so it is probably the last choice with so many other options already available.

Avoiding The Frame Notch

If you do use a spacer and would like to avoid the frame notch, there is a fairly easy way of preventing the wastegate actuator from interfering. Simply remove the wastegate actuator from the turbo, mount it to either the frame or inner fender and connect it to the wastegate arm with bicycle gear cable. The wastegate actuator arm will need to be trimmed and brackets fabricated but it is a simple job.

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