How To Buy An '86-'92 Turbo RX-7
This document is the companion to How To Buy An '86-'92 Non-Turbo RX-7. The non-turbo document contains all the buying information common to both models of RX-7s. This document contains the turbo specific information. It is very important that you read both to get the full picture. It is best to read the non-turbo information first, then head back here to get the turbo specific stuff.
For the most part, the turbo RX-7 is very similar to the non-turbo, with some suspension, drivetrain, braking and of course engine changes. These differences are covered below.
It is hard to make a judgement on the "average" life of a turbo rotary since it is very dependant on the care it has received. Nevertheless, the normal guess at average life is around 100,000 miles, but I have seen engines that were still nearly prefect with over 175K on them, as well as engines that were blown at 50K.
- Checking the compression in a turbo rotary is very important. The engine is under much greater stresses when pressurized, which therefore relates to more wear and shorter engine life. Be especially careful if the car is modified, as boost increases will put even more strain on the engine. Look for an upgraded fuel system. Once the boost is increased past a few PSI, extra fuel will be required to prevent deadly detonation.
- Oil Consumption
- Oil consumption is very slightly higher on turbo cars, but it is hardly noticeable.
- Aside from smoking caused by worn seals that both the NA and turbo models can suffer from, smoking can also be caused by poor seals in the turbo. If the compressor seal is bad, oil will bypass into the intake tract and be burned by the engine. This is easy to spot since the car will smoke during long periods of deceleration as the engine vacuum draws oil past the seal. Excessive amounts of oil will also be present in the intercooler and piping. If the turbine (exhaust side) seal is bad, there will be a constant flow of smoke from the exhaust, which will increase greatly when the car is driven under boost. If you can remove the precat/downpipe from the rear of the turbo, you will most likely find oil inside.
Any smoke coming from the turbo will be blue.
- The turbo cars do run slightly hotter than the non turbo cars.
- 5th and 6th Ports
- Turbo cars don't have them.
The Turbo (and related)
The turbo is of course the fun part of the Turbo II. There is nothing spectacular about the turbo system in the TII, save for the twin scroll system employed in the '86-'88 cars. Therefore, a few simple checks will help determine the condition of the turbocharger and related components. Note that the turbo is located at passenger side of the engine between the frame rail and the engine itself.
- Turbocharger Heat Shields
- Check to make sure the metal heat shields are in place over the turbine (exhaust) section of the turbo. These shields make a large difference in underhood temperature since the turbo is a massive source of heat. If these shields are missing then many of the sensitive components around the turbocharger area (wiring harness, vacuum lines, coolant hoses, etc.) can be easily cooked.
- Turbocharger Oil and Water Lines
- Inspect the turbocharger externally and check for oil and water leaks. This may be difficult if the stock heat shields are still in place. Also check the lines where they meet the engine. Repairing any leak is normally straightforward, but it may not be so straightforward to actually get to the leaking part (normally a gasket) depending on which line is causing the leak.
- The turbos have a habit of cracking on the turbine side. Normally this happens internally and therefore the cracks are not visible on the outside. However, if you see cracking on the outside (specifically on the flange where it meets the manifold) then it is a sign of severe cracking, which will normally mean replacement of the turbine housing. This gets expensive. The same goes for the manifold. Large cracks in the exhaust manifold will mean replacement, which involves pulling the turbo. Lots of labor for someone who has not done it before.
- Turbine Shaft Play
- Remove the black plastic air duct that goes into the turbo (the turbo inlet duct, or "TID"). Now, with your fingers, give the compressor a spin. It should spin fairly freely and smoothly. There will be some dragging since the bearing will be stiff without it's oil jacket (only present with the car running), but it should be smooth throughout it's rotation. Now, alternately push and pull on the shaft. It should not move. If it does, you are looking at severe bearing and shaft wear, meaning replacement or a rebuild of the turbo. Very expensive. Apply pressure on the shaft, trying to push it left and right. Some play is normal, but it should not be excessive (compressor should not contact the housing). This play is caused by slack in the bearing, which is taken up when the oil film forms and the shaft "floats" on it's fluid bearing. While you're there, look for excessive oil in the compressor housing. Some is normal, but large amounts mean a turbo rebuild.
- Twin Scroll
- The '86-'88 TIIs employ a system called "twin scroll" to help combat turbo lag. Basically, at low RPMs, a flapper door inside the manifold closes and shuts off one of the two exhaust paths to the turbine. This causes the first path to direct exhaust gasses to hit the turbine wheel at a very sharp angle, thus quickly spooling the turbo. As the engine speed (and thus exhaust gas flow) increases, the flapper door is opened to allow the second exhaust passage to flow, thus allowing the turbo to flow to it's full potential.
This system relies on a solenoid, flapper door and actuator. Unfortunately, there is no easy way to test it. Jacking up the car and manually pressing on the actuator (front of the turbocharger, big silver can) will verify the assembly moves, but will not tell you if it works properly when the car is running. Fortunately, the twin scroll system is pretty reliable and failures are uncommon.
The twin scroll flapper door system was removed on '89+ cars due to better turbo design. '89+ turbos still have two scrolls but use a divided manifold instead.
- Intercooler and Piping
- The intercooler (located on top of the engine) should be free of large dents. There should be no holes, and the fins should be straight and not filled with crud. A dirty intercooler is easy to clean, but one that has most of it's fins bent will be very ineffective and will need to be repaired or replaced.
The piping to and from the intercooler should be in good shape, with no holes or large dents. Carefully inspect the rubber hoses and check for cracks. It is common to find large cracks which will show up as a boost leak (low boost when driving, loud hissing noise). They are fairly inexpensive to replace.
- Boost Pressure
- If you have an aftermarket boost gauge available, check the boost pressure. The boost on a stock car should read about 5.5 PSI for an '86-'88 and 7.5 PSI for an '89+. If the car modified, expect more boost. The pressure you see will depend on the modifications. Low boost can have many causes, from a clogged air filter to a dead turbo. Keep this in mind.
There could be many pages written about modified turbo cars as there are so many options from mild to wild. From stock turbochargers to hybrids to huge aftermarket units there is a wide variety. The key is to know that any modifications have been performed properly and safely.
- Boost Gauge
- Any modified turbo car should have an aftermarket boost gauge installed as the stock gauge has a limited range and will be effected by an FCD (see below).
- Raised Boost
- Probably the most popular turbo modification is to raise the boost. The stock Hitachi HT-18 turbo is good for about 12-14 PSI before it starts pumping more heat then air and it's life expectancy drops dramatically. If the stock turbo has been running at these levels for extended periods then it is probably already at the end of it's life. With any boost increase, fuel modifications to support the increased airflow are absolutely necessary.
- Fuel Cut, FCD and Fuel System Modifications
- The stock fuel system is programmed to prevent overboosting the car by cutting fuel past about 8.5 PSI. This system is designed to protect the engine and must be defeated if higher then stock boost is run. Fuel cut feels a bit like the car hitting a wall just after 8 PSI. The Fuel Cut Defender (or FCD) is available from most of the vendors (there is also a DIY version) to trick the ECU into thinking that the car is running less then 8.5 PSI of boost, thus avoiding fuel cut. However, the FCD does not add more fuel to the engine in response to higher boost. Because of this, just running around with high boost levels and an FCD is a very bad thing and virtually guarantees short engine life. One would hope that there is a special place in hell for those that sell a car with cranked up boost, an FCD and no other supporting fuel mods.
For cars running the stock turbo at less then 10 PSI, a fuel pump is generally all that is required. Cars running more boost and upgraded turbochargers will require larger injectors, an upgraded pump and some way to control all of this. The exact configuration will depend on how the car is setup and there are many, many options. It is most important to verify that at least something has been done to supply the engine with the proper amount of fuel.
More radical modifications will require a complete fuel system upgrade, known as generically as a "standalone" or "standalone EMS". There are many options but most popular are the systems by Haltech, Microtech, Wolf and the Megasquirt. Each of these systems is set up differently and it is beyond the scope of this document to cover them all. However you will want to examine the wiring harness and quality of installation carefully. Is wiring neat and tidy? What is the condition of the connectors? Is everything fused? Beyond that, there is the quality of the tune. Does the car start easily cold or hot? Drive smoothly? Any smoke? It is definitely recommend that if you are not familiar with standalone systems that you seek out someone who is.
- Turbocharger Upgrades
- There are countless turbochargers available in countless combinations and specs. However most of the techniques for checking the stock turbo also apply to an aftermarket unit. In addition to checking the turbocharger you will want to check out the manifold. Poor quality aftermarket manifolds have a tendency to crack, and have thin flanges that leak easily. Generally the more massive a manifold, the better.
- Boost Controllers
- Boost controllers allow you to raise the boost, program your own boost curve, etc. A boost controller cannot lower boost past what the turbocharger would naturally achieve so adding a boost controller is not a fix for an overboost situation. Electronic boost controllers are always better then manual. Be careful with boost controllers installed in 89+ cars because this can cause boost spikes if done improperly.
- Modified cars should have ported wastegates to avoid boost spikes. This is vitally important for '86-'88 cars but not that great a concern for '89+ as they already have a decent wastegate from the factory.
- The stock intercooler is only good for the stock turbo or mild hybrids, and only then to about 12 PSI. An aftermarket cooler that mounts at the front of the should be installed for any turbo upgrades and higher boost stock setups. Check the quality and fitment of the piping, quality of the connectors and just general cleanliness of the installation. These intercoolers can cause cooling problems so make sure to drive the car under a variety of situations (stop and go, highway, low speed city) to make sure the car's temperature is under control.
- Blow Off Valves
- The TII is equipped with a stock bypass valve which vents back into the turbo inlet duct. These can leak after about 10 PSI or so meaning that cars with upgraded turbos are generally running aftermarket blow off valves.
Some owners will open vent their stock valves for the "pssst" noise on shifts. Since the valve naturally leaks a little at idle, this requires the addition of a check valve at the BOVs output to prevent vacuum leaks. This is essentially a pointless modification that is basically a noise maker.
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