October 7th, 2007, 06:59 PM
Supra Specialists Ireland
BPU - 1st steps in tuning the 2jzgte
With so many 2jzgte swaps taking place, i hope some ppl may find this of some use. The references will include the JDM and USDM Spec 2JZGTE's as many people can source either type quite easily these days.
In stock form, the Supra TT produces 0.76bar (11psi). Although the stock ceramic JDM turbos will handle 1.2bar (17.4psi), The USDM TT turbochargers have steel blades so have be known to run up to 1.4bar (20.3psi). The safe accepted rate with in the Supra TT community is 1.2 Bar which ensures more power but more importantly Turbo life. Above this pressure the turbos start to go outside their efficiency range, producing more heat – something the Stock side mount intercooler cant deal with reliably.
1.2Bar will raise engine power to around 400bhp. Also, the way in which this power is delivered is quite different from the stock setup, most people feel the Engine only comes alive after a BPU upgrade.
In stock form, the boost pressure the turbos produce (11psi) is controlled by back pressure in the exhaust system (I.e. highly restrictive catalytic converters and exhaust system).
To raise boost beyond the stock level the catalytic converters are removed, this allows the turbos to spin faster and hence produce more boost.. The Downside with this is the JDM turbos will in fact over boost far past their safe limit and reach over 1.6bar (23.2psi). The small size of the JDM wastegate cannot cope with the increase in exhaust gasses and is held back. At these pressures the ceramic blades in the turbo can become detached from the shaft and therefore cause failure of the turbo. On the USDM turbos this is not a problem as The wastegate size is bigger than the JDM's.
In order to add some restriction back in to the exhaust for the JDM's, a restrictor ring is added to the exhaust system. A restrictor ring is simply a metal plate that fits normally between either between the 1st and 2nd decat pipes, or the 2nd decat and cat-back. The centre of the restrictor is drilled out to a smaller diameter than the exhaust itself (normally around 2inches). A properly sized restrictor should bring the maximum boost pressure down to 1.2 bar or less. This is not needed on the USDM setup. Though the USDM spec often needs a Boost controller to get to the recommended 1.4bar (20psi) range.
The Following is the recommended upgrade path for going to BPU (basic performance upgrade) Spec. Remebering that the Decat has been done!
1) Aftermarket cat-back exhaust
The stock cat back (the pipe after the 2nd decat pipe) is extremely restrictive. In order to allow a good free flowing system this needs to be replaced with an aftermarket system. There are a huge amount of systems available, choice is usually down to style and noise/sound levels.
2) Fuel cut defender or Boost cut controller.
The stock ecu will initiate fuel cut when boost pressure reaches 1 bar for a 3 second period. In order to stop this, a device is needed in order to trick the ECU into thinking the boost pressure is lower. The Boost Cut controller or Fuel cut controller basically fools the ECU into thinking you are not running more than 1 bar of boost, though fueling by the ECU will stay the same for any level above 1 bar.
The HKS FCD is recommended for JDM as its a Map based system, and the Greddy BCC is recommended for USDM setups, which are AFM based but use a map sensor to determine Boost pressure.
3) Updated fuel pump
The stock fuel pump in the JDM is not considered suitable for BPU level power, the one in the USDM is higher specification and will be suitable.
The Walbro 255lph pump is commonly used and will be suffiecent to supply enough fuel to bpu levels above 1bar.
4) Colder grade spark plug
With an increase in boost, a ‘colder’ grade plug is required with a closer gap. There are two basic options:
- Iridium IK22 plugs
- NGK BCPR7ES -A gapping of around 0.8mm is recommended to the standard 1.1mm gap
There are extra items which should be considered and are recommended when going BPU
1) Boost gauge
Any type will do, you need to ensure at all times that your are not overboosting, a car will behave differently due to weather changes, and often during the colder times of year you will see higher pressures.
2) Wideband AFR gauge
Also known as Air/Fuel ratio gauge. This has a wideband O2 sensor mounted in the 2nd decat which measures the air/fuel mixture of the exhaust gases. This is very important to monitor, otherwise you won’t know if the air/fuel ratio runs lean under high boost, its just there to monitor but could save you rebuilding and engine!
3) Boost controller.
On USDM spec Supras, the double decat will raise the boost to around 1.2bar. To get the most to the 1.4bar Range a boost controller is used. On the JDM's, it will depend on the size of the restrictor ring. Some people Opt for a 1bar restrictor ring. This is the level of boost for normal driving, and use a boost controller for the high setting of 1.2bar.
An replacement or aftermarket intecooler isn’t required, however you need to ensure your current intercooler is in good condition and allows smooth airflow though the core. Many of the stock IC’s on older cars are now in very poor condition and suffer from correded fins, if yours is like this it should be replaced prior to going.