Zcar Turbo Information


This page has been compiled from internet sources, especially from  posts on zcar.com thanks to all! It is presently a work in progress and at this point, it simply is a lot of cut and pasted info. I am in the process of streamlining the presentation.

Newbie Turbo Info is here. It is highly recommended that you read it first before continuing





Block Diagrams:

Stock 280zxt airflow diagram
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L28ET Air Flow (click to expand)

Modified 280zxt airflow diagram

Typically modified 280zxt turbo flow/part diagram (click to expand)

Overview of air flow in the above diagram

  1. Exhaust air spins the turbine
  2.  Air is sucked into intake (due to spinning compressor and piston suction on down stroke).
  3. Air flows through the AFM and its flap moves proportionally. The AFM sends a signal to the "computer" to tell how much air is entering the engine and the "computer" tries to add enough fuel via the injectors to maintain an approximate 15:1 air to fuel mixture.
  4. Air passes through the turbo's compressor section where it is compressed. The process of compressing heats the air (talk to Sadi Carnot). The amount of compression is called "boost" and is usually measured in PSI however a BAR is often used. 1Bar = 14.7PSI which is the average atmospheric pressure at sea level.
  5. The hot compressed air flows internally through the intercooler. Wind from the car's motion passes externally over the intercooler and carries away heat. Thus the internal pressurized air is cooled.
  6. The cool pressurized air passes over the throttle body, through the manifold and into the combustion chamber via the intake port.
  7. The cool pressurized air is mixed with injected gas upon entering, compressed by the piston, then ignited by the sparkplug.
  8. The expanding gas from the explosion pushes the piston down then exits via the exhaust port.
  9. The exhaust gas passes through the turbo's turbine, spins it and starts the cycle again.

Overview of feedback and protection devices/functions in the above diagram

  1. The waste gate is a door to allow exhaust air to bypass the turbine. It is opened and closed to modulate how much exhaust gas flows over the turbine and in turn modulates how fast the turbine spins the compressor which, in turn, controls how much pressure is built up in the manifold in area "A". Too much pressurized air entering the combustion chamber can cause premature detonation as the piston compresses the hot high pressurized air. So-called "detonation" can push the piston backwards against the engine's momentum and destroy it. The waste gate is mechanically opened and closed by the waste gate actuator.

  2. The boost controller modulates the waste gate actuator. The input line (lime green colour) to the boost controller can be connected to monitor the pressure at "A" in the manifold (as shown) or alternately to monitor the pressure at "B" at the outlet of the compressor. The boost controller is set to limit the maximum boost pressure. For a stock ZXT the boost controller's set point is fixed at ~6psi but for an intercooled zxt it is typically set to between 10 and 16psi.(more boost means more power from the engine but also increases the risk of detonation).

  3. The pop-off valve is simply an emergency pressure release device to prevent over-boosted air from entering the combustion chamber. It functions by venting the air to the engine compartment when the pressure rises above the maximum boost threshold. For a stock zxt with boost set at 6psi, the pop-off vents at ~9psi. For an intercooled zxt with the boost controller's maximum boost set to 12psi, the pop-off valve would be set to ~ 14psi. The pop-off valve can protect the engine in the instance when the waste gate or waset gate actuator fails. If this were to happen, boost levels could go well beyond 25psi without a pop-off valve present.

  4. The blow-off valve is opened when the throttle valve is abruptly shut to prevent back-pressure on the compressor.
    In normal operation, air flows though the compressor then freely into the engine, thus the pressure on each side of the open throttle valve in "A" and "B" is nearly identical. However, immediately after the TB valve is abruptly closed (foot off the gas pedal), the air flow through the engine is nearly brought to a complete halt at the TB. Exhaust air and self-momentum of the turbo wheels continues to spin the compressor. The compressor then continues to pack air into the now sealed area "B". The packing of air rapidly increases the pressure in "B". This high pressure air in "B" causes backpressure on the compressor and slows it down. (a bad thing for performance and it also causes an unusual strain on the compressor). Since the blow-off valve is monitoring the pressure in "A" (lime green colour), it can tell when the pressure in "B" is different from that in "A". If this pressure differential is too high, the blow-off valve will open and allow the high pressure air in "B" to vent back in "C". This equalizes the pressure on each side of the compressor thus it spins freely and does not suffer the back pressure problems.
    A common mistake is to vent the blow-off valve into the engine compartment rather than re-circulating to the front of the compressor. By venting the air that was "metered" by the AFM, the air to fuel mixture changes and the engine runs rich.

Twin Turbo vs. Single on L28 engine:

L28 with twin turbo

280zxtt02.jpg (88835 bytes) 280zxtt.jpg (75543 bytes)
L28 with twin turbo

L28 with twin turbo (Twin Mitsubishi TDO5 16G's w/ 7cm housings) click here for more info

twinturbo260z.JPG (120291 bytes)
L26 260z with twin turbo (click on picture to expand). click here for more info


Block diagram for a Dodge Stealth Twin Turbo Set-up



Protection Devices:

The primary purpose of protection devices in the turbo system is to prevent detonation. Detonation is caused by too much heat or too much pressure (which causes heat) when the piston is compressing the intake air during the engine's compression stroke. The combined heat from the turbocharged air AND the heat from the compression stroke can ignite the gas in the cylinder prematurely. The resulting early explosion pushes the piston in the reverse direction (against the rest of the engine) which causes extremely high pressures on the piston, rod, crank arm, rings, head gasket, valves. It is easy to understand the principal of pressure causing detonation if you think of how a diesel engine works: The diesel has no spark plug to ignite the fuel, the heat from the pressure does it!

red hot exhaust side of turbo charger

Typical example of power gain from an intercooler is sometimes an added bonus (~10% to 30%) 



How to: (The basic mods and tips)

Electronic Boost Controller 
For a stock ZXT, the boost is controlled by the waste gate actuator. It has a ~7psi  spring in it holding the waste gate shut.....its also has a diaphragm in it that's hooked to the intake manifold. So when you get to 7psi+ of pressure (boost) inside the intake the pressure behind the diaphragm is greater than the 7lb spring holding the waste gate shut so it starts to open up the waste gate...
An electronic boost controller it performs the same task, the same way; but instead of just letting the intake manifold pressure do the actuator. it has a valve between the intake and the actuator and it computes how much pressure gets to the actuator after it has computed what would be best ......it monitors a bunch of things going on in the engine and figures the best way to do it (optimally). ...and costs you a lot of money.


VW Turbo Block Diagram

BOV and POV Info

Stock 280zxt airflow diagram with special items highlighted
similarparts.jpg (146516 bytes)
L28ET Air Flow (click to expand)

Emergency relief valve = Pop-Off Valve
Vacuum Control Valve + Auxillary Air Control Valve = "Pseudo" Blow Off Valve


What other Zcar drivers have:


Applied L28ET Air Flow, Calculations, and Turbo Maps

Walk through of calculating Air Flow under boost and translating this to Compressor maps



DIY Links with Great Pics!

Mechanical Turbo Boost Increase

Adjustable Pop Off Valve

Intercooler Installation

Turbo Upgrade


Typical Costs

ECU $50 on Ebay
Harness $50 on Ebay
Fuel Pump $50 on Ebay
Intercooler & Intake mandrel bends from JCwhitney $150
Exhaust $150 - $300 depending on what you want?
Silicon connectors +/- $100
Tune-up stuff - plugs, wires, cap, rotor, fuel filter, hoses, $150
K&N intake filter, since the stock one will be hard to fit $50.
Do you plan on turning up the boost? I assume you do since you asked about the intercooler.
Boost & A/F gauges, boost controller: $150
Does your 240Z have a decent cooling system? If not, spend $200-$400 on new radiator, clutch fan and/or aftermarket electric fans.

280zxt microfiche drawings

L28turboexploded_.gif (40262 bytes)
L28ET Turbo (Click to expand)

oil cooler exploded.gif (16566 bytes)
Oil Cooler (Click to expand)

turbointake explosion.gif (19222 bytes)
Intake Manifold (Click to expand)

egr exploded.gif (9185 bytes)
EGR Area (Click to expand)

Garrett Air Research T3 Turbo

A stock 82 ZXT has Garrett Air Research T3 Turbo installed.

T3 Turbocharger
The T3 turbocharger is designed for today's wide speed range medium displacement engines requiring good low speed torque for responsive drivability and tailored control of boost pressures from idle to rated speed. The T3 is engineered to provide an economic performance boost for diesel and gasoline engines. The T3 will effectively cover most engine ratings from 175 to 250 hp, in gasoline/petrol applications. Over 2,000,000 T3 turbochargers have been produced.

T3 Specs
Weight 5.3 Kg
Compressor Diameter 51.4 mm
Turbine Diameter 53 mm
Bearing Span 31.9 mm
Moment of Inertia 2.1*10-5 Kg/m²
Oil Flow 1.2 l/m SAE 30 - 90ºC - 2.75 Bar

T3 Flow Maps

Garrett Air Research T3/T4 Hybrid Turbo

A T3/4 Hybrid Turbo has the Exhaust Side from a Garrett T3 and the intake side from a T4

It is easy to see that the T4 is designed to flow more air. (Opening has 1.48X bigger cross sectional area)

Recommended upgrade for a stock L28ET engine (280zxt) is T3/TO4B  cost ~ $500

T3/T4 Turbo Install (great pics)



Z32 Turbo Page

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