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FAQ's


I have oil in the air intake piping or intercooler ducts

Boost Gauge readings at above sea level?

Where are those Pills suppose to be?

How much radial / axial play is allowed on the Turbo shafts?

What is Duty Cycle Control?

What are the part numbers for those one-way / check-valves?

Where do all those vacuum hoses go?

Turbocharger specifications

Conversions for Bars, PSI, and kg/cm2


I have oil in the air intake piping or intercooler ducts

During boost, the PCV valve closes and any engine blow-by is directed through the air intake ducts near the Primary Turbo Compressor. This results on "some" oil to deposit over time in these areas. This is normal, assuming there is not excessive oil burning coming out the exhaust.

When intake manifold pressure below atmosphere pressure, the blow-by gas flows through passage 1 and is pulled into the intake manifold.

When manifold pressure at or above atmosphere pressure, the PCV valve closes and blow-by gas flows through passage 2 and is pulled into the intake portion of the Primary Turbocharger.

Note that for newer cars, ('95 ish) the PCV valve and related hoses were removed, as the path to/from the Primary Turbocharger is OK for emissions. However, you will still get oil film buildup in the Turbocharger piping due to passage 2.


Boost Gauge readings at above sea level?

Boost Gauge will read higher when above sea level. For example at sea level, should get around 12-13psi and at 4,500 Feet, read 14-15 psi.  The Boost Gauge is referenced to the atmospheric pressure.  Less atmospheric pressure, the more measured boost on the gauge.  The ECU is compensates for the altitude by using the MAP sensor and an atmospheric sensor in the ECU, allowing for a constant amount of air volume. Yes, this means your turbos work harder at higher elevations.


Where are those Pills suppose to be?

Look at the Secondary Turbocharger Leak Diagram. Note, that on some of the newer Turbocharger castings, the restrictor pills are part of the nipples that the Wastegate and Turbo PreControl actuators get their pressurized air supply from. The restrictor pills have ~1/16" diameter hole to restrict the flow of air into these actuators. The solenoids for these actuators are pulse width modulated by the ECU to control how much the actuator moves.

More info on the pills:

Stock Wastegate Pill is about .062"

Stock Turbo Pre-Control is about .058"

As you add mods, general rule is just open up the WG pill to larger sizes. PC pill size is a very sensitive dial to turn.

Use number drills when modifying

Larger Wastegate Pill = Reduces Primary and Secondary boost and spiking

Smaller Turbo Pre-Control Pill = Reduced spike at transition, but more Primary boost and Primary spike

Typical setups:

With full intake, greddy IC, and exhaust, worked up to about .085" at the Wastegate Pill


How much radial / axial play is allowed on the Turbo shafts?

There are two directions of play to test for, first is axial, (front/back as installed in the car) there should be none. The other is radial, (left/right or up/down as installed in the car), there will be some play in the turbo shafts even in a new/re-built set, all though not much.  A way to gauge this is to see if the play is more than 1/2 to 2/3 of the nominal clearance from the compressor blades to the housing. I.E. with the compressor wheel centered in the housing measure the distance to the housing, (Figure 1: dimension "A" and "B"). Then move the compressor wheel as far as it will go to one side, then see if this is more than 1/2 to 2/3 of the original distance, (Figure 1 & 2: C > [(2/3) * A] or D < [1 - (2/3 * B)]. IMHO getting near to 2/3 is getting pretty worn but still able to be used, 1/2 is probably good for a while.  Kind of vague, but my opinion ;-). Assuming less than 2/3 play and the housings in good shape, I would not re-build at this time.

PS don't play too much with the turbos i.e. spinning and moving shaft without adding some oil to ensure a generous film for the bearings at all times, (add at the oil inlet until flows out the oil drain for a while).


What is Duty Cycle Control?

This method is used for controlling the Wastegate and the Turbo Pre-Control. Both of these actuators are required to operate between simple fully open or fully closed. The actuators need to be moved/controlled to adjust for various operating conditions, i.e. Wastegate only needs to be opened 10% at lower RPMs and 75% at higher RPMs to regulate the boost pressure.

So what is this duty-cycle control?

The Wastegate and Turbo Pre-Control actuators are supplied air pressure directly from the Primary Turbo Compressor. Between the Primary Turbo and the actuators there are air restrictors or pills, these restrict the amount of air that can flow into the actuator. With a small opening it will take longer to pressurize the actuator than with a larger opening. Now add onto this a solenoid that can vent some of the pressurized air from the actuator.  The ECU can only turn the solenoid On or Off, (no in-between analog stuff here, just digital).  However, if the solenoid is turned On/Off quick enough that only some air is vented for intervals of time that are shorter than the time it take the pressurized air to leak in through the pill you can adjust the pressure in the actuator. Thus, a change in the On time versus the Off time, (duty cycle control) will give a different pressure and move the Wastegate or Pre-Control valve some amount.

Kind of like a tank of water with an adjustable valve on top feeding water into the tank and making it fuller, and a valve at the bottom that can be only fully open or fully closed.  Someone, (the ECU) is turning the bottom valve open/closed and you don't know how long it is open or closed, but you can adjust the water level by increasing or decreasing the water flow from the adjustable valve, (pill hole diameter).


What are the part numbers for those one-way / check-valves?

The all White one: N3A1-13-1995 (note: this is a revised p/n and is a very expensive part - $40)

The Black/Green one: N390-13-995A

The Green/White one: HE41-13-995

The Aluminum one: NF01-13-890

Note that Mazda has been consolidating part numbers lately and has started using N390-13-995A for the Black/Green and White/Green.


Where do all those vacuum hoses go?

Check out a colored vacuum hose diagram.


Turbocharger Specifications:

Note this is for the 1993-1995 models.

Both Primary and Secondary Turbochargers are identical, they are:

Hitachi HT12 with a 9 blade turbine and a 10 blade compressor.


Conversions for Bars, PSI, and kg/cm2:

1 bar = 0.9869 atmosphere =  14.50 psi

1 psi = 0.06804 atmosphere.

1 kg/cm^2 = 0.9678 atmosphere = 14.22 psi