The s13 200sx seems to have been designed
and marketed not as an out-and-out sports car, but as a sporty car with
suitability for the company-car market. With this in mind, the air intake
and the exhaust are quite restrictive, making the car more refined.
Removing these restrictions will unleash a good few horsepower just by
allowing the engine to do its job unfettered, and as such, may even
increase the fuel efficiency!
Air-box panel filter
The filter element from the standard
air-box can be replaced with a less restrictive version, making it
easier for the engine to suck through a bit more air. The power increase
will be relatively small with this modification, as a large part of the
restriction in the air intake comes not from the filter, but from the
design of the air-box itself. One test of various filters (albeit not on
a 200sx) found no performance gain whatsoever from a panel filter. This
modification is useful as it isn’t obvious, and some people won’t worry
about declaring its presence to their insurance company.
Complete removal of the air-box and
replacement with an induction kit will allow even better breathing, as
it eliminates both the restrictive filter and its air-box. There are
various types of induction kit available, all with different types of
filter & different filtration abilities. The ideal would be a kit with
good filtration properties (which prevents dust particles from reaching
your turbo blades) but that is not too restrictive.
One possible drawback of induction
kits is that they are more prone to sucking in hot air from the engine
bay than the standard air-box, slightly decreasing the amount of oxygen
actually taken in (as the air is less dense). It has been debated how
much of an effect this might have. This problem can be lessened by
either ducting cold air to the intake, forming a barrier between the
engine and the intake, or moving the intake further from the engine, to
an area of direct cold air feed.
Big-bore (cat-back) exhaust
For the sake of quietness, the
standard exhaust is quite narrow, which unfortunately also restricts the
flow of exhaust gases. This can be improved with a larger bore exhaust,
letting the gasses flow freely, making the engine more responsive. This
will also have the effect of making the car sound more ‘sporting’.
Stainless steel exhausts have a harsher boomier, and will last for many
years. Mild steel exhausts have a throatier subtler sound, but will last
for a shorter time.
If you’re going to de-restrict the
exhaust from the catalytic converter(s) backwards, it also makes sense
to enlarge the bore of the front pipe. This will not only improve the
power, but also the "driveability" of the car, giving it better low-rev
The catalytic converter also
significantly restrict the flow of exhaust fumes. Replacing it with a
simple de-cat pipe results in a significant increase in power and
torque, but has moral and environmental consequences. It will also make
the exhaust a lot louder, too! The cat would need to be replaced prior
to an MOT test.
The standard turbo exhaust elbow is
fairly poorly designed, being too narrow for efficiency, and creating
too much turbulence. Replacing it with an aftermarket model will
increase the power from the turbo (especially at higher revs) and make
the engine quicker to rev too. Due to the position of the turbo, this is
a time consuming modification to fit.
Increasing the boost
This is a simple idea – increasing the
level of boost will increase the amount of air the engine receives, the
Engine Control Unit (ECU) will monitor this air-flow, and add more fuel to
maintain the mixture, resulting in more power. After a point (around
300-350 bhp), all increases in power will come via more boost through a
bigger turbo; other modifications after this point are merely to allow the
engine to cope with the high boost levels.
The standard DK-spec 200sx CD18DET runs
at about 7psi. The standard ECU can only cope with a certain level of
increased boost (and correspondingly, air-flow), before it finds itself
unable to provide enough fuel to maintain the combustion mixture. If the
level of boost is too high, the risk is that the combustion mixture could
become too ‘lean’ – this would make the combustion hotter than normal,
which could damage the engine.
To guard against this, the ECU monitors
the amount of air entering with the Air-Flow Meter (AFM), which feeds the
ECU a voltage (up to 5 volts) which is proportional to the air-flow. Faced
with too high an air flow, the ECU will act to protect the engine, by
triggering the ‘fuel-cut’. This prevents combustion, presenting
potentially dangerous combustion cycles, but it also cuts the power
produced by the engine dramatically, making the car jerk violently.
There are ways of overcoming this
‘fuel-cut’, notably the HKS Fuel–Cut Defender (FCD). This works by
‘capping’ the voltage the ECU receives from the AFM, so that the ECU is
tricked into thinking the air flow is lower than it really is. However, if
you prevent the fuel cut from operating on an engine with a standard ECU,
you obviously run the risk of the engine ‘running lean’, as the ECU will
only provide fuel to match the air flow it knows about, when in reality,
the air-flow could be much higher. If you have an engine with an uprated
management system, removing the fuel-cut would be safe, assuming you are
certain the fuelling is set up well for all possible boost values, and
will not run lean. An alternative approach is to swap the 200sx AFM for
the larger model from the 300zx, which can cope with a greater air-flow;
various engine management systems have a setting to allow this change.
Some engine management systems will remove the fuel-cut altogether.
Another factor to consider is the ambient
air temperature – colder air is more dense, so will provide a greater
amount of oxygen at a given boost level. You might find that a car well
set up for the summer will trigger the fuel cut in the winter.
Some methods of increasing the boost can
be susceptible to ‘boost spikes’ – short-term increases in boost above the
expected level. Brief spikes rarely cause problems with ‘running lean’,
but can lead to uneven power delivery and hitting the fuel cut. These
spikes are unpredictable, and thus it is sensible to always install a
boost gauge to monitor the boost pressure, before you embark on any of
A variety of these are available. At
their simplest, they are just a mechanical pressure gauge that is
plumbed into the boost circuit via a long pipe. More complicated
versions may run electronically, orhave features such as ‘peak boost
hold’, which lets you know the highest level of boost achieved without
staring constantly at the gauge whilst driving. They are usually mounted
either in the driver’s eye-line (such as on the A-pillar) or on the
central console, near the stereo. They display the current boost
pressure (either in bar or psi).
Gated boost valve
This modification involves inserting a
valve into the pipe controlling the turbo’s actuator. The valve involves
a variably-spring-loaded ball-bearing in a tube; when the level of boost
pressure reaches the level set by the spring pressure, the ball-bearing
moves, allowing excess pressure to leak out, maintaining a steady boost
pressure. This allows the boost pressure to run higher than that set by
This is a development of a similar
valve, called the Bleed Valve, which was renowned for boostspikes.
This replaces the standard turbo
actuator, and allows a different peak boost pressure to be set. These
are more difficult to integrate with an electronic boost controller,
should you later wish to fit one.
An in-car module, combined with a
replacement boost solenoid under the bonnet, allows different boost
levels to be set, and also changed from the cockpit whilst driving. Can
also feature extra functions, such as an incorporated boost gauge, and
look good too!
As the power produced by the engine
increases, you’ll need to exchange the spark plugs for ‘colder’ rated
equivalents. This is because a more powerful engine will run hotter, and
this can cause the tips of the standard plugs to become hot enough to
ignite premature detonation of the fuel, before they actually provide a
spark. Colder plugs are formulated to resist this. The ‘coldness’ of the
plug needs to be suitable for your level of power; if you choose a plug
that’s too cold for your engine, it won’t reach its optimum temperature,
and will become ‘coked up’.
The intercooler comes after the turbo,
before the engine. It cools the air from the turbo prior to it reaching
the engine, making it denser, therefore allowing a greater amount of
oxygen to reach the combustion chamber for a given volume or air. This
increases the power and efficiency of the turbo system, compared to
non-intercooled turbocharged engines. Cooling the charge air also lessens
the liklihood of detonation. The standard 200sx intercooler is mounted in
the left front wing, and is reasonable for everyday driving. However, it
is insufficient for more powerful engines, and can suffer from ‘heat-soak’
upon hard driving with standard engines – it becomes too hot to function
usefully as a heat exchanger.
Uprated wing-mounted IC
These intercoolers are improved by
virtue of providing a much larger surface area for cooling, and by being
better positioned for access to cool air, in the middle of the front
spoiler, below the bumper. They can require cutting of the front bumper
to be fitted, and some will require the installation of a smaller
battery, or relocation of the battery to the boot.
The standard turbo on the CA18DET is a
Garrett T25. This can be exchanged for a large range of turbos, each of
which will alter the engine’s characteristics in various ways.
Larger turbos can provide a greater
volume of air for a given boost pressure, meaning that lower boost
levels are required for the same level of performance.
Larger turbos are less restrictive to
the engine at the exhaust manifold, so provide greater performance for a
Larger turbos heat the air less for a
given pressure, resulting in cooler and denser charge air.
Larger turbos can provide more boost
in the higher reaches of the rev range, where smaller turbos start to
run out of puff and drop the boost they produce.
Larger turbos generally require a
longer time to ‘spin up’ and start making boost – they have a greater
‘lag’. This can make them less convenient for every-day driving, but is
less of a problem for power/speed applications. This can be minimised by
specifying a ball-bearing turbo.
Ball-bearing turbos suffer from less
friction, so spin up faster (and therefore have less lag) than their
non-ball-bearing equivalents. Thus you could have a significantly larger
turbo than standard, without sacrificing driveability. Also,
ball-bearing turbos such as the Garrett GT series are stronger and not
prone to fail at high boost like conventional 270 degree bearing turbos.
Unfortunately, they are also much more expensive.
Conventional turbos have 270 degree
thrust bearings – the bearings go three quarters of the way around the
shaft. This is fine until you start running much higher boost than
standard, which puts much higher thrust loading on the bearing, causing
the turbo bearing to wear rapidly and eventually fail. Turbos with 360
degree thrust bearings are designed to be much stronger, and are
necessary if you want to run above (approximately) 17 psi.
Some turbos will be direct ‘bolt-on’
replacements for the standard T25, other turbos will require
modifications to be made to the turbo manifold or the oil/water feed
As the engine becomes more powerful,
it will require more and more fuel, and at higher pressures, especially
at times of peak power output. The standard fuel pump can only safely
provide fuel to around 240bhp (or more accurately, about 14-15psi), at
which time it is prudent to replace it with an uprated model, to guard
against underfuelling and running a lean mixture.
Fuel Pressure Regulator
The fuel pressure regulator (FPR)
regulates the pressure in the fuel rail. Typically a fuel pump will pump
much more fuel than is actually used by the injectors. The excess is
returned to the fuel tank. The regulator maintains a constant fuel
pressure by controlling how much is returned to the tank (it operated by
a simple diaphragm and spring). At atmospheric pressure (i.e. vacuum
hose disconnected) standard fuel pressure is 43 psi. An uprated FPR will
allow a degree of control over the eventual fuel pressure, which can
help wring more performance out of hard-pushed injectors. This can be
slightly risky long-term, however, and larger injectors should be
considered. Another factor operating on the FPR is intake manifold
pressure: fuel pressure is then varied according to manifold pressure in
a 1:1 additive ratio. So if running 15 psi of boost, the regulator
supplies fuel to the injectors at a pressure of 58 psi (that is 43 psi +
Fuel injector modifications
Put simply, larger injectors can provide
more fuel per single injection, so can maintain the correct air:fuel
mixture at a higher boost level, in a more powerful engine. One pitfall is
that the standard ECU cannot cope with controlling larger injectors; they
must be accompanied by some form of improved engine management system. 80%
is generally the industry’s maximum desired duty cycle for continuous
operation of fuel injectors.
370cc injectors - standard injectors.
It may surprise you to learn, that the
standard are only suitable for up to approximately 235 bhp at 80% duty
cycle at normal fuel pressure. For shorter periods of time they can be
run at 90%, usually without any problems, but under no circumstances
should they go above 95%. At 90% duty cycle, assuming fuel line pressure
of 58 psi, they can support around 270 bhp. At 95% they can support
around 280 bhp at the same fuel pressure. At 68 psi fuel pressure (this
is an estimate of the pressure you might see at 15 psi boost, with a
1.7:1 fuel regulator) they can support just over 300 bhp at a 95% duty
cycle. Remember, the fuel pump will be working hard to supply fuel at
this fuel pressure, so a decent upgraded fuel pump is essential. So
370cc injectors CAN support 300 bhp, but it is not recommended, and only
for short periods.
Standard ECU modified by daughterboard
(e.g. “Jez Chip”, Norris, Blitz Access, Mines VX). A modification is made
to the car’s standard ECU allowing a modified set of maps to be run (these
are burned permanently into an EPROM).
Might be tricky to re-map (usually has
to be sent back to its maker). In seriously modified vehicles the need
to retain an Air Flow Meter may cause a problem (as explained above).
Unless mapped actually on the vehicle, you may still need a piggyback
computer to get it “perfect” due to differences in particular
modifications, and variances between individual vehicles.
These are wired into the car’s ECU loom
and work by modifying the signals that the ECU sends and receives.
Apexi S-AFC/S-AFC II - This nice
looking unit with a blue screen acts on the cars MAFS signal allowing
you to trim fuelling +/- 50% at a number of RPM and throttle points. Can
be used to install larger MAFS and/or injectors. It has no ability to
alter ignition timing, nor any “fuel cut defencer” function. It is
however quite cheap and is very popular worldwide.
Greddy E-manage – this is a relatively
new system. Out of the box, it is a very basic Air Flow “trimming”
device similar in capability to the old model S-AFC, with 5 screws on
the front to adjust fuelling at 5 RPM points. With the optional software
and harnesses it becomes a fully mappable piggyback capable of
controlling ignition timing as well as fuelling. It also has built in
drivers for 2 extra injectors, “fuel cut defencer” function, and an idle
stabiliser. An optional pressure sensor allows it to operate when the
cars AFM’s capacity has been exceeded. Unfortunately, few tuning
companies in the UK are currently familiar with the product, although it
is quite straightforward to use the software.
Dastek Unichip - Commonly offered by
tuners in the UK. This operates in a similar manner and offers similar
capabilities to the E-manage. Some reports suggest it may be less able
than other systems when it comes to dealing with larger injectors due to
a limited range of adjustment.
HKS Fcon Pro V - This takes the
concept further in that it is actually a complete management system
installed in the manner of a piggyback. It is actually capable of
running the car without the original ECU according to HKS. This system
is used in many “big power” cars in Japan. Custom fit looms for many
applications. Specialist (expensive!) set up required.
Full management systems are available,
such as those from Motec, Omex, DTA, GEMS, etc. These completely replace
the cars standard management system. They generally require a large amount
of custom re-wiring and may require other changes, such as to the ignition
system. They are getting more competitively priced now, and it may be
possible to get one installed for less than £1000.
ALS - Anti Lag
The reason for Anti-lag is, as it's name
suggests, to decrease or eliminate the lag induced by a turbocharger. It
is mainly used in rally where all Group A or WRC cars are turbocharged.
When you want big power out of a 1.8 / 2.0 litre engine you need a
turbocharger, and the more power you want the bigger the turbocharger has
to be. But a big turbocharger takes a long time to spin up and create
boost pressure and that's where the ALS (Anti Lag System) comes in.
Because every second a car is off boost a lot of time is lost on a
rallystage. To get rid of the lag the needs to keep spinning at full speed
at all times. This includes when the throttle is closed for a gearchange,
when braking for a turn and when you're a the start line ready to take
off. To keep the turbo spinning while the throttle is closed you need
exhaust (lots of hot air basically) to keep turning the turbine wheel.
What you need for ALS:
ECU capable of ALS.
Anti-lag valve - Replaces the original idle speed control valve.
Turbo with minimum 360thrust bearing.
EGT gauge - So you know when your turbo and manifold is going to melt.
Wiring to "arm" the anti-lag and switch it off - This simply involves
wiring in a switchable earth to one of the ECU pins.
This goes for so-called "mild" anti-lag (see further down for info), for
the real WRC stuff you need another (very expensive) turbo, exhaust
manifold and a few other bits.
With the ALS installed - when you let go of the throttle, the valve that
replaces the standard idle valve in a modified throttle body opens to let
the air continue through. The amount of air this valve can flow is the
only thing that affects anti-lag, the less the airflow, the less effect
the anti-lag has. Then the ECU retards the ignition timing by 30 degrees
so the fuel is ignited when the exhaust valves are open and most of the
fuel is already in the exhaust manifold and turbo. That makes lots of nice
and hot exhaust to spin the turbo and create boost pressure.
A small "mild" ALS valve can flow enough air to make 0psi boost pressure
at idle/off throttle (rather than -25psi of vacuum), sometimes up to 7psi
of boost, which makes the turbo hit full boost almost straight away when
you press the throttle. The big WRC anti-lag valve can flow enough air to
produce 22psi at idle (or off throttle), which makes the car have no lag
at all. That will increase the driveability of the car a lot.
Unfortunately the WRC ALS puts a big strain on the turbo and exhaust,
whereas with the 'mild' anti-lag setup is practically as reliable as not
using an ALS at all. It will gradually burn out your silencer baffles, but
all that does is make your exhaust louder.
Some people say that the fuel will cause "borewash" making the need for a
rebuild all the time. But that is not the case. The amount of fuel used in
anti-lag is not enough to cause any significant bore wash (unless you use
£5 budget oil), most performance cars fuel on overrun, unless they have
been mapped for good emissions, not mapped like that because of
The only real thing you have to be wary of with anti-lag is that Exhaust
Gas Temperatures (EGT) go sky high but there's no real worry as you could
be on the overrun for well over 30 seconds on 'mild' anti-lag before the
EGT will get dangerously high. If EGT gets too high it could melt the
exhaust and/or turbo. The engine internals will not have any problems.
For full-on WRC anti-lag the specs is as with 'mild' anti-lag but with a
bigger WRC ALS valve, and a anti-lag turbo with Maram 247 shaft and
turbine wheel with 7° cut-back blades, Nimonic wastegate spindle and
everything nicely put together by a reputable company. You will need that
as the extra stop/start shocks and extra heat would eat a standard shaft
in minutes. A stainless steel exhaust manifold may be handy too as it
could stand more heat than standard one.
For road use you will not need more than 'mild' anti-lag, and for track
use it might be best too as you're on track at sustained periods of time
and the WRC anti-lag may be too severe for those long sessions.
The ALS system won't increase the outright power of your car but it will
significantly increase the power delivery - much much more low down torque
since the car gets on boost a lot earlier than without the ALS.