Tuning the RS Turbo
The RST is by far the easiest and cheapest Fiesta to tune, and has been around long enough for the majority of Ford tuners to
offer upgrade packages and conversions. The engine is almost identical to the 1596cc Compound Valve
Hemispherical (CVH) unit found in it's bigger brother, the Escort RST. The main differences are the engine management system, which user the
EEC-IV system used in the Zetec engine, and the utilization of the smaller Garrett T2 turbocharger. Both of these differences
restrict the tuning potential in comparison with the Escort, so it's always the case that any company offering chip conversions
will charge more for extract the same power out of the Fiesta, compared with the Escort.
The simplest upgrade to make is to help the engine's breathing with a high-flow air filter
such as a K&N 57i Induction Kit and a full stainless exhaust system. The next stage is to chip the car. On the Fiestas this involves a "piggyback" chip which plugs into
the diagnostic port on the ECU, situated under the dashboard in the passenger footwell. A "stage 1" or "165" chip, so called
because of the power it will give, raises the boost pressure from the factory set 6psi standard to 11 or 12psi. The chip also
instructs the ECU to increase the airflow and fuelling, this prevents the engine "pinking"
which will cause premature wear and engine damage. Also included in the package should be an uprated actuator, so that the wastgate opens when the boost
pressure reach 12psi, whereas the standard actuator will release the wastgate at 6psi. Devices like bleed valves "bleed" off
boost pressure before the actuator, "fooling" the ECU into thinking it is running lower boost than it really is. The main problem
with bleed valves is that although cheap, they raise the boost pressure without allowing the ECU to make adjustments to the
fuelling, which will cause the pinking problems mentioned above. power increases from the 165 conversion are dependant on
the mapping of the chip and the condition of the engine, as well as other modifications to the car. Realistically you could expect
around 150-170bhp at the flywheel. Expect to pay in the region of £250. The next stage of chip, often referred to as "stage 2"
or "195" is supplied with higher flow 701 "beige" injectors. These are necessary
to supply enough fuel to cope with the boost set at 16psi. The cost of the 195 conversion is usually around the £800 mark, because of the injectors.
In order to run high boost without the engine "detonating" and destroying itself, it is necessary to lower the compression. Turbocharged engines run lower compression that standard cars for this reason. This is why they feel sluggish when off boost. As a general rule, the more boost a car runs, the worse it will feel off-boost. Many of the Zetec turbo conversions run small turbos at 6-8psi, the low boost pressure negates the need for lowered compression.
Anyone you ask will give you a different opinion on what the next step should be. Some will advise moving up to a Hybrid or T3
turbo, and some will suggest a cam and head work. Cam kits like the Piper T2, will give more power at the top end of the rev
range, at the expense of less low end and mid range power and lumpy idling. The T2 is specifically listed as a "high boost" kit
designed for cars running 15psi or above, and is claimed to give an power increase of 25bhp. Compare this with the 15bhp
increase that a cam would give on a CVH XR2i, and the paltry 10bhp on the Zetec engines, and you begin to see why the CVH Turbo
engine is so popular. Head work, such as gas flowing and porting involves machining the engines cylinder head to create a
smoother path for the air and fuel. This smoother path allows the air and fuel to flow more rapidly, thus increasing power. A
common trick on the I4 engined Mk5 and 6 Escort RS2000's is to re weld the exhaust manifold. When the manifold is produced
at the factory it is welded on the inside, which restricts the flow of the exhaust gasses,
increasing back pressure. The modification is to weld the manifold on the outside, then file of the welds inside.
The stumbling block of the Fiesta is the T2 turbo, which is simply too small to reliably boost more than around the 16psi set by
the 195 chip. Any owners seeking power outputs of over 200bhp will need to change the turbo to a larger model. The hybrid
T2 and T25 turbos will fit straight onto the Fiesta's engine as a direct replacement, however, modifications will be required in
order to use the Escort's T3. The Escort's exhaust manifold will be required, as this fits straight on to the CVH engine. The
radiator will need to be mounted further forward to fit the larger turbo, and an Escort air filter or aftermarket filter is also
necessary. It is also possible to use hybrid turbos intended for the Escort, such as the T35 and T3.5. Even Cosworth units can
be made to fit, though this will necessitate a custom manufactured manifold.
Engine mechanics dictate that the lower the temperature of the inlet charge, the denser the air and the more power the engine
will produce. There are a number of ways to decrease the inlet temperature. Increasing the size of the intercooler and / or
radiator helps, but is difficult due to lack of space in the Fiesta engine bay. The most
efficient device is a chargecooler. The chargecooler system is water cooled, rather than air, and has it's own reservoir tank. It is not reliant on airflow and can be
positioned anywhere in the engine bay. Pace
Products are generally regarded as the leaders in this field.
The next step up, after you have squeezed every bit of power out of your 1600, is to increase the capacity. It is possible to increase the 1597 to just over 1600 by skimming the pistons. Some Ford tuners, such as Power Engineering, produce large capacity CVH engines. PEs "System 2" is a 1900cc CVH unit as seen in Matt Booth's RST. Matt's engine is still running the standard T2 with head work a chip and PE cams, and set to 8psi boost, produces 180bhp. With 16psi the power output rises to over 210bhp. This spec engine with a T3, chargecooler and other tweaks can easily make nearly 300bhp.
Many tuners are now offering "ZVH" engine conversions. These are a hybrid engine, utilising the best parts of each unit. The Zetec bottom end is mated to the CVH head, with the capacity increased to 1.8, 2.0, 2.1 or even 2.4. forged pistons are used, as the original CVH items are now too small for the new capacity. This created a very stong engine, capable of running much higher boost than an equivalant size CVH, and power figures of well over 300bhp are not uncommon. Fiesta Frenzy (01522 778787) are regarded as the leaders in the ZVH field, having completed many conversions in the last few years.
The next evolution of the ZVH is a full blown 16 valve unit. This engine is essentially a turbocharged 2.0 Mondeo unit, totally rebuilt to cope with turbocharging. The unit is strengthened in key areas and a highly tuned example, running a chargecooler and T35 turbo, can produce over 280bhp at only 16psi boost. At 35psi the power output rises to over 400bhp.