7. INCREASE BOOST PRESSURE.
Many of the worlds turbo vehicles are set by the manufacturer at a very conservative level
of usually around .5 -.7 Bar or 7-9 Psi, as well as building the motor with a low static
compression of around 6-7:1.
This obviously does not put any great stress on the operating parameters of the motor
under normal day to day use across a wide range of driver styles. The manufacturer
obviously wants the vehicle to perform well but does not want any problems or claims under
the terms of the warranty period.
Lucky for us the general trend of most manufacturers who build high performance vehicles
is to enhance the engine and drive train to withstand far higher levels of horsepower than
is usually developed by the standard level of factory tuning. This fact is borne out by
the sport of motor racing where many types of virtually standard cars compete with
success, after some basic preparation.
I have found that from my own experience that my Mitsubishi STARION has had no mechanical
problems that I can relate to being caused by extracting more horsepower.
This also seems to apply to my Nissan
HR32 Skyline as well.
Apparently the STARIONS at Bathurst were developing more than 400 HP with the standard
drive train holding up.
When first released in Australia, they cleaned up Group 'E' for three years or so with good reliability,
and this probably holds true for most other Japanese built vehicles . Anyway what I am
trying to say is that you can extract a lot more power with reliability if you do what is
required to keep the fuel air mixture correct and maintain the engine as well.
The compression ratio on some of the more modern turbo's is in fact quite high now and the
boost is also higher at around 1 BAR(14.7 PSI) The main reason that the factories are able to
generate the higher power with reliability, is that the electronics controlling the fuel
air mixture are much more developed along with the other components.
The secret seems to making more power is to ensure that the correct fuel air ratios are
always kept in check and detonation the big killer is kept at bay.
With this in mind the the
first thing that you probably want to do is increase the boost level a few PSI.
8. INCREASING BOOST
Most factory turbocharged cars have at least some aftermarket support that
includes upgraded turbo kits. However, these can be quite pricey and if
you are a bit of a
parts geek or junkyard warrior you can often put together a pretty
good upgraded turbo setup from parts found in other factory turbocharged
For example, turbo Saabs are
excellent sources of parts as they have Garrett
turbochargers with a very common bolt pattern and good quality intercoolers.
Subaru and Volvo turbo cars are also great sources for turbo parts.
If you're looking to up the PSI
of your stock turbocharged car without doing a lot of parts swapping though, you
can do this fairly easily just by making slight modifications to the wastegate.
The computer control software on most vehicles can adequately cope with increased fuel to
compensate for the extra air volume of a few PSI. Some computers have a fuel cut off PSI
level just below 1 BAR (14.7 PSI @ sea level) that will turn off the
can come as a bit of a shock at the time, so care is in order. The method to achieve the
boost increase is varied with make and model of vehicles but most are similar to the
concept explained as following on the Mitsubishi STARION or CORDIA.
Basic boost control is maintained by the WASTE GATE Canister actuating arm holding closed
a valve that can allow exhaust gas to bypass the turbo exhaust wheel. See the diagram for
As the throttle is opened by your lead weighted foot, the
engine RPM's increase along with
the amount of boost and exhaust gas pressure. The exhaust gas flows through the manifold
into the snail scroll of the turbo and exerts pressure on the wheel vanes causing it to
turn at a speed approaching 100,000 RPM at full power.
This exhaust pressure can be decreased by routing a varied amount bypassing around the
wheel by the actuation of the valve attached to the WASTE GATE control arm.
The waste gate canister is a sealed chamber that has boost pressure from the turbo intake
compressor snail routed to it. Internally it has a diaphragm with an arm attached to it
that moves in and out dependent on the level of boost pressure applied to the diaphragm
overcoming a built in spring that returns the arm to the central position when not under
boost. This spring is normally set by adjustment of the arm to keep constant pressure on
the bypass control valve to not allow it to open until overcome by a preset level of boost
that is dependent on the adjustment of the arm tension. If you are lucky you can see an
adjusting screw on the end of the arm that allows a small movement that can control the
boost by a few PSI.
Adjustment of the boost level by unscrupulous operators in the past has been done by just
bending this arm to increase pressure on the spring so more boost is needed to open the
This obviously is not the best way to go about controlling the level as ideally you need
to be able to have at least two levels of boost to compensate for wet weather driving or
those times that someone else drives your car.
I was not keen on this idea at first, thinking that I would want the power all the time,
but after driving in the wet I soon changed my mind.