Simple and Effective Boost Control for Toyota 1G-GTE Twin Turbo 6


Written by Jonathan Walker supragt@ihug.co.nz


[ Turbo control | Stage 1 | Stage 2 | Tuning ]



Many thanks to Stuart Woolford, stuartw@kcbbs.gen.nz whose knowledge and experience made this project possible!!


Disclaimer: Only experienced and competent personnel should perform this operation. I take no responsibility whatsoever for any damage or injury either indirect, or consequential, caused by modifying your turbo system. The procedure described below allows the driver to operate the turbocharger system at pressures well beyond the intended factory boost. This can, and will, shorten the life of the turbochargers, in some cases significantly. If you wind up the boost, keep a keener eye on your rear view mirror for clouds of white or blue smoke! Also, be prepared for the power gains associated with this procedure. If you ran 7PSI and wind the boost up to 17PSI, you will have a lot more trouble keeping control of the car (especially on corners…). Be aware that the boost will shoot up quicker than it did before. Traditionally the 1G will not hurt you unless you bury the throttle, but BE CAREFUL!!


This operation was performed on a 1G-GTE with Air to Air intercooler. The Water to Air intercooler model procedure is a tad more complicated with having to remove the heat exchanger assembly in the intake path to get a hose tail tapped in, but the principle is the same.


Before attempting to pull off this modification, you will need to understand the turbo system, and how the pressure is controlled.


Blow off Valve: Before running the engine at high boost levels, ensure you have a blow off valve fitted. As a rule anything over standard boost should have a BOV. This releases the boost pressure when the throttle is closed to prevent compressor stall (loss of power) and associated stress on the compressor and throttle plate. For information on fitting a Bosch plumb back blow off valve to your 1G GTE see Phil Strong’s note in the technical section of this site. I have fitted and am currently using a Blitz blow off valve, however will be removing this and fitting a Bosch instead within a couple of weeks. If you fit an externally venting (atmospheric) blow off valve, (the ones with the trumpets – usually), expect the car to misbehave. Do not waste your money on one of these if your car has an airflow meter (read ALL 1G-GTE’s). Buy and install a Bosch blow off valve.

Turbo Control 101


In order to control the wastegate system more effectively, we must take boost pressure for the wastegates from the intake pipe, just before the throttle body. By doing this we ‘delete’ the restrictive intercooler and piping from the boost pressure vs. turbo pressure equation.

When you open the throttle on a turbo (or twin turbo) engine (generally under load), the exhaust gas volume increases significantly. This exhaust gas is routed through the turbocharger’s turbine side, and increases the turbocharger RPM. As the turbo RPM increases, as does the pressure on the compressor side of the turbo. At full throttle, and any reasonable amount of RPM, the engine will be making a lot more exhaust gas than the turbocharger needs to provide the set boost pressure, so we need the excess exhaust to bypass the turbine. This is what the wastegate system is for. Each turbo has a valve on the turbine side, connected to an actuator (pneumatic piston) on the outside of the unit. A hose to the compressor side of the turbo connects the actuator to a source of boost pressure. Once the boost pressure reaches a certain level, the wastegate actuator, via a connecting rod, pushes the wastegate open, allowing exhaust to bypass the turbine, preventing the turbo from over speeding. When the pressure is reduced, a spring forces the wastegate closed again.


To control the boost, we need to fool the wastegate system into thinking that there is a lower amount of boost, so the system allows more exhaust through the turbine than normal, causing the turbo to spin faster, and produce more pressure. This is an over boost condition. To do this we take direct control of the wastegate actuators. By preventing the entire produced boost from reaching the wastegate system, we fool it into ‘thinking’ there is not enough boost. Effectively, we are impeding the full operation of the wastegates.


We will no longer be taking the pressure to operate the wastegates from the compressor side of the turbos, we will be taking it from the intake pipe after the intercooler. This causes the wastegates to open slower than normal, thereby causing the boost to rise quicker at low RPM, and also, due to the 1-3PSI pressure drop across the intercooler, the simple act of rerouting the pressure feed will increase the boost by 1-3PSI.


The pressure regulator valve will govern how much pressure is fed to the wastegate actuators from the intake pipe. The lower the pressure to the wastegates, the higher the final boost pressure. The pressure regulator requires air to be flowing through it in order to effectively regulate pressure. It ensures that the pressure on its outlet side remains constant once the pressure rises past the set limit on the inlet side.

 As the wastegate actuator diaphragm is a dead end, we need to bleed air out of the system. The needle valve, routing air from our pressure feed system back into the air pipe, provides the necessary airflow through the regulator. The needle valve is NOT there to control boost, and a lot of cheap junk aftermarket boost control systems, use only a needle valve, this is ineffective at accurately and satisfactorily controlling boost. The reason for bleeding the air back into the intake, between the pressure regulator and the wastegate actuators, is that once the air has been metered and accounted for, we cannot let it leave the intake system.


The result of the below described operation:

  1. The turbo boost will rise quickly at low RPM compared to standard set up, as the pressure to the wastegates it now taken just before the throttle body, as opposed to just after the turbo compressor. Therefore the pressure to the wastegates is lower than it normally would be at any given time.
  2. We have control of the level of extra turbo boost (with the pressure regulator).
  3. We have limited control of the speed of the reaction of the boost control system (with the needle valve).


With that, I will now describe the procedure for customizing the boost control system, using pneumatic engineering products.


Engine view - Turbo collector, and the intake pipe, where we will start with the modifications. This photo is pre-modification.

You will need:



*1 x Norgren pressure regulator valve (inline, self relieving) with 1 Bar replacement spring, and 2 x ¼” hose tails to fit

*1 x Shako (or other suitable) inline needle valve, and 2 x ¼” hose tails to suit

2 x 1/8” BSP, ¼” Hose tails, with 2 locking nuts

14 x 6-16mm Hose Clamps

2m ¼” I.D. Fuel Hose, or similar high temp hose

2 x ¼” Tee Joins (or 1/8 Female tee with 3 x 1/8” BSP hose tails – available through Norgren/Enzed)

Thin Gasket material. I used S-207 0.8mm thickness gasket material; a 330 x 330 sheet is about $7

PTFE Thread tape or other thread sealant


* - These valves were supplied courtesy of Stuart Woolford, who can be contacted for more information here.




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