GUIDE : HOW TO BUY A TURBO2
Here is a guide on “How to buy an 86-91 Non-Turbo RX-7”. You will find information here about both models. This guide will also contain information that relates to the Turbo model as well. Therefore, it is important to read both sections to be sure to understand all of the points. It is important to start with the non-turbo information, before moving on to the turbo models.
In general, the RX-7 Turbo is very similar to the non-turbo, with a few differences in suspension, drivetrain, brakes and engine. Here are the differences:
It is hard to give a average lifespan for a rotary turbo engine since it all depends on the maintenance it received over the years. Typically, one can expect 120-150kms.
Checking the compression on a turbo rotary is very important. The engine is stressed when it is under a signifycant amount of stress, which results in increased wear and reduced lifespan. Be careful, especially if your RX-7 is modified. The more boost, the more pressure on the engine. Look into upgrading your fuel system as the engine will need more fuel in order to prevent “deadly detonation”.
Oil consumption is slightly more elevated in Turbos, but barely noticeable.
Aside from smoke caused by used seals, which effects both N/A and Turbos, the smoke can be caused by failing turbo seals. If the compressor seal is bad, the oil bypass it to the intake , to then be burned by the engine. This will be easy to notice as the car will smoke during extended period of décélération, while the vacuum sucks oil in the seal area. An excessive amount of oil will be found in the intercooler and piping. If the turbine seal (exhaust-side) is bad, there will be a consistent quantity of smoke leaving the exhaust that will increase as the car is driven and the boost increases. If you are able to remove the pre-cat/downpipe behind the turbo, you will find oil inside. All smoke leaving the turbo will be blue.
Turbos tend to overheat more than N/A.
5th & 6th Ports
The RX-7 Turbos don’t have them
The Turbo is the best part of the TurboII! There is nothing special in the TurboII system except for the twin-scroll in the 86-88 models. So little vérifications will help determine the condition of the turbo and components. Note that the turbo is located on the passenger side of the engine between the frame-rail and the motor
-Turbocharger Heat Shields
Check that the metal heat shield is placed on top of the turbine on the exhaust-end. These head shields make a big difference for the température under the hood, as the turbo is a signifiant source of heat in the engine bay. If the shields are missing, any sensitive components, such as wiring harness, vacuum lines, collant hoses etc) can be easily burned.
-Turbocharger Oil and Water Lines
Inspect the exterior of the turbo to check for oil and water leaks. This can be difficult with the heat shield in place. Also check the connections that go to the motor. Repairing all leaks is a good initiative, but the hardest thing is finding exactly where the leak originates from (normally a gasket), depending on what line is causing the leak.
Turbos have a tendency to crack of the turbine side. Normally it happens internally so the cracks won’t be visible from the outside (specifically, the flange that connects to the manifold) this is a particularly bad sign of cracking, which typically means the turbo needs to be replaced. This can end up being very expensive. Same for the manifold. Laerge cracks in the exhaust manifold are a sign that the manifold needs to be changed, which requires the turbo to be removed.
-Turbine Shaft Play
Removing the black plastic air duct that goes to the turbo. Using your fingers, turn the compressor. It should turn smoothly and easily. There will be a little resistance since the bearing is stiff in the oil film (which is present only when the car is running), but it should be smooth during rotation. Now alternate while pushing and pulling on the shaft. It should not move. If it moves (depending on the amount of play) it will need to be rebuild or replaced (which can be very expensive). Apply some pressure on the shaft white trying to push it to the left and right. A SMALL amount of play is normal, the compressor should not be touching the housing. This play is caused by a loosening of the bearing. While you’re there, look for excel oil in the compressor housing. A small amount is normal, but if there is a lot, it may be time for a turbo rebuild.
TurboII ’86-’88 employ a system called “Twin-Scroll” which helps reduce lag at low RPM. There is a flapper door inside the manifold that closes one of the two channels of the turbo. This causes the 1st channel to direct the exhaust gasses to hit the turbine at a very precise angle, which helps the turbo spool very quickly. As engine speed increases, exhaust flow also increases, the open flapper door allows a 2nd exhaust channel to the turbo, which allows the turbo to go to it’s full potential. The Twin-Scroll was removed from 89-91 models and replaced with an improved turbo design.
-Intercooler and Piping
The intercooler (on-engine version) must not have any damage. It should not have any perforations or residue. A dirty intercooler is easy to clean, but if the fins are damaged, they will no longer be effective, and as such, will need to be replaced.
The piping to and from the intercooler should be in good shape, no holes or bumps/lumps/ Inspect all rubber hoses thoroughly and check for cracks. It is common to find large cracks that result in boost leaks (low boost while driving will have a loud buzzing sound) Hoses aren’t expensive, so don’t be afraid to change them.
If you have an aftermarket boost gauge, check the boost pressure. Stock boost should be 5.5PSI for 86-88 and 7.5PSI for the 89-91. If the vehicle is modified expect more boost, as the pressure will depend on the modifications. Low boost problems can originate from many places, from a dirty air filter to a dead turbo. Keep all options in mind.
A lot can be written about turn vehicles since the options vary greatly from mild to wild! From stock turbos to hybrids to large aftermarket turbos, the options are endless. It is important to know that no matter the modification, be sure that it was done in a clean and safe manner.
All turbo vehicles should be equipped with an afterwork boost gauge (ex: HKS, APEXi, DEFI, Greddy) as the stock gauges have a smaller ranger in values and are blocked by the FCD (see below for more info on FCD)
Probably the most popular modification on RX-7 Turbos is to increase boost. The stock Hitachi HT-18 turbo is good up to 12-14PSI before it will start to pump more heat than air, thereby reducing the lifespan by a notch. It is runs like this for an extended perçois of time, it will soon approach its last breath. With all increases in boost, upgrades to the fuel system are necessary to support a larger quantity of air.
-Fuel Cut, FCD and Fuel System Modifications
The original fuel system is programmed to prevent overboosting of the motor, by cutting the gas at around 8.5PSI. This was designed to protect the engine and must be removed in order run at a higher boost. The Fuel Cut Defender (FCD) tricks the ECU into thinking it is running at a PSI lower than 8.5, which avoids the Fuel Cut. However, the FCD doesn’t add more fuel to the engine in response to the higher boost rate. Because of this running an FCD with a high boost level is not good and will guarantee a reduced lifespan for your engine.
For vehicles with a stock turno running less than 10PSI, a fuel pump is generally the only thing needed. Cars running more boost and an upgraded turbo will need bigger injectors (500cc, 2000cc), fuel pump, and something to control it all (ex: HKS PFC F-CON). The exact configuration will depend on your vehicle’s setup, and there are A LOT of options. It is important to check that at least something was done to provide the engine with all the fuel it needs.. More radical modifications are needed for a complete fuel system upgrade. Which also goes by the name “standalone” or “standalone EMS”. There are several options, but the most popular are Haltech, Microtech, AEM and Adaptronic Power FC. All of these systems have their own particular way of functioning.. Be sure to examine the wiring harness and be sure it was properly installed with quality and attention. The tuning quality is VERY IMPORTANT. The recommended solution is to deal with a professional shop like Derwin Performance.
There are countless options for turbos as well as many combinations and specs. The same precautions should be used for both stock and afterwork turbos. Be sure to check the manifold. A poor quality manifold tend to crack, are very thin and leak easily. Thicker manifolds are generally the better ones.
Boost controllers allow increased boost and the ability to program a boost-curve (and more).A boost controller can’t drop the boost more than the stock product. Also, a boost controller will not fix an “overboost” problem. Electronic boost controllers are always better than manual ones. Be careful when installing a boost controller on a 89-91 RX-7 as this can cause a “boost-spike” if not properly installed.
Modified vehicles should have a wastegate in order to avoid boost spikes. This is vital for 86-88 models but not as big of an issue for 89+ due to the fact that the original waste gate can do the job..
The stock intercooler is only good enough for the stock turbo or small hybrids, and only up to 12PSI. A front mount aftermarket intercooler for all turbo upgrades as well as boost increases. Check the quality of the piping and its installation, everything should be nice and tight. These intercoolers can also cause cooling problems, be sure to test the car in many different situations (stop and go traffic, highway, low-speed city driving etc) to be sure the temperature is always under control.
-Blow Off Valves
The TII is equipped with a stock bypass valve that goes back into the turbo’s inlet duct. The activate after 10PSI, which means that vehicles equipped with a turbo changer or boost augmenter have an aftermarket BOV.
Some owners will open their stock blow-off valve for the PSST noise during shifts. Since the valve leaks slightly by design on idle, this requires a verification of the output check valve of the BOV to prevent vacuum leaks. This is a totally useless modification that only makes a a noise. The BOV should be recurculated before the turbo of the (stock) MAF is still being used.