What vehicle do you drive?

What is it?
BPU stands for “Basic Performance Upgrade”, a term coined by US firm Suprastore for a basic upgrade package for the TT Supra. BPU is essentially what other marques refer to as "Stage 1” engine modification.

The BPU upgrades allow the engine to produce more power by raising the boost pressure the turbos produce.

In stock form, the TT produces 0.76bar (11psi), however this can be raised; it's generally accepted that the stock ceramic Jspec turbos will handle 1.2bar (17.4psi). The Export spec (UK/Euro/US) has steel blades so will, in general, survive at higher boost pressures. 1.4bar (20.3psi) is not unheard of.

1.2bar is the "accepted" safe limit with regards to a) detonation, b) actually getting more power, and c) some level of longevity. It's also accepted that you're taking an allbeit very small risk each time you use full boost. 1.2 bar is generally safe, but at 1.4 you're pushing your luck.

There are limitations with pressures above 1.2bar, the turbos are already outside of their efficiency range and the additional heat generated will raise the intake air temperature considerably – thus negating the effect of increased boost pressure.

In both Jspec and export spec, BPU will raise engine power to around 400bhp. Not only will it release more power but it allows much quicker turbo spool-up, which vastly increases drivability.

How it works
In stock form, the boost pressure the turbos produce is controlled by back pressure in the exhaust system (I.e. highly restrictive catalytic converters and exhaust system). There are two approaches to BPU dependant on the model of car; as such the next section is split between Jspec and Export spec:


Fundamentals of BPU

Jspec:
To raise boost beyond the stock level the restrictive catalytic converters are removed, thus allowing the turbos to spin faster and produce more boost pressure.

There is a down side to this. With both cats removed the turbos will in fact over speed far past their safe limit and reach over 1.6bar (23.2psi). This is due to the small size of the jspec wastegate which cannot cope with the increase in exhaust gasses.
At these pressures the ceramic blades in the turbo can become detached from the shaft and therefore cause catastrophic failure of the turbo.

In order to add some restriction back in to the exhaust 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.

UK/Euro/US (Export) spec:
To raise boost beyond the stock level the restrictive catalytic converters are removed, thus allowing the turbos to spin faster and produce more boost pressure. Different to the jspec, the export spec has a larger wastegate which can handle the increase in exhaust gasses.
Therefore boost pressure will be maintained at only slightly above stock levels, typically 0.85bar (12.3psi). In order to raise this further it is necessary to install a Boost controller to change the way in which the wastegate opens.
A restrictor ring is not required on the export spec

Note: On both models it’s possible to raise the boost with simply adding a Boost controller or Bleed valve; however this is not recommended since the huge resistance of the cats is still in place. This will result in significant extra heat being generated in the manifold and could cause serious engine damage due to raised exhaust gas temperatures.


Parts required:

Obviously all that’s needed to raise the boost pressure is a double decat & restrictor ring (Jspec) or double decat & boost controller (export spec). However, it will not work without further modifications. The following will be required in both models:

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, but any good quality aftermarket system will be suitable for a BPU level of modification.

2) Fuel cut defender
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.
(See quick link for further details)

3) Updated fuel pump
The stock fuel pump in the jspecs is not considered suitable for BPU level power, the one in the export spec is higher specification and will be suitable. However as many of these cars are approaching 13 years old it should be standard practice to replace the fuel pump.
The Walbro pump is commonly used, however the standard pump that comes with the export spec is a better specification and has quieter operation (though considerably more costly).

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
The iridium’s will last longer (most people get >10k miles) but typically cost £60 a set
The NGK’s need replacing around 3k miles, but cost £14 a set


Recommended, but non-essential parts:

That’s it for the required parts, though there are two items which are highly recommended to ensure you can monitor the health of your engine:

1) Boost gauge
A simple electronic or mechanical boost gauge can be mounted in the dash to view the boost pressure. An electronic boost gauge is recommend as most will come with a peak hold or even playback function, thus allowing easier monitoring of maximum pressures

2) AFR gauge
Also known as Air/Fuel ratio. 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 (and therefore result in piston meltdown). Though it won’t allow adjustment, it will warn you that something is not right if it does go lean.

3) EGT gauge (optional to AFR gauge)
Also known as Exhaust Gas Temperature. This has a temperature probe fitted into one of the exhaust runners (as close to the cylinder as possible). It performs basically the same function as the AFR gauge by monitoring the condition of the exhaust gases. High temps (sensor mounted post turbo 950degrees is dodgy, >1000degrees is a very bad thing!) will likely result in engine damage due to lean mixture. However there are some cons when comparing this to the afr gauge:

- It is much slower to react
- Failure of the temp probe (i.e disintegration) will result in the particles entering the turbos potentially causing failure
- The exhaust runner requires drilling and tapping which can result in swarf entering the manifold before the turbo. This could result in damage to the turbo blades.

A safer place to tap the probe is in the exhaust or downpipe after the turbo. It will stop the risk of swarf ending up in the turbo and turbo damage in the event of probe failure. There is a downside - Installing it post-turbo introduces such a big and variable heatsink into the equation it's pretty much useless. People take anything from 100 to 250degC off the aforementioned maximum, meaning that your gauge could read 800degC and mean anything from imminent meltdown to running nicely. No-one has put an EGT sensor before and after the turbo and datalogged the variance so it's 100% guesswork, and that's the last thing you want on the ragged edge.

4) Intercooler
A replacement or aftermarket intercooler 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 corroded fins, if yours is like this it should be replaced prior to going bpu.