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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 uses the EEC-IV system also 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. However, the Fiesta excels over the Escort in a number of ways which we will go into below.

The simplest and often the first upgrade to make is to help the engine's breathing with a high-flow air filter and a full stainless exhaust system. This will enable a greater flow of air into and out of the engine, giving an increase in power and making the car rev more freely. 

Filters are of two types. Panel filters are replacement elements for the standard airbox. These are fairly inexpensive and offer better airflow with little or no increase in induction noise (the sound of the car sucking in air). The second type is the cone filter or induction kit. These are cone shaped filters that replace the whole airbox and have several advantages over a panel filter. Firstly due to them replacing the airbox, the space taken up by the filter is reduced. Ideal for cramped engine bays or when fitting a different turbo (see below). Secondly they are less restrictive than panel filters, thus forcing more air into the engine and make a loud sucking induction 'roar' as it does so. A side effect of this is that if the car is run without a dump valve the turbo blades stall slightly between gear changes and the airflow is amplified through the filter producing a loud fluttering 'chatter' noise. Due to the noises cone filters make, they are very much a modification choice made by the individual. Claims have been made about the efficiency of cone filters with regards to them sucking in hot air from the engine bay. This isn't really an issue as although true when the car is at a standstill, as soon as the car picks up speed the airflow to the filter from the ram pipe will be cool. Another myth with cone filters is that they don't filter properly and grit can get into the turbocharger. So far evidence of this has been insubstantial and in most cases is likely to be down to poor installation or a manufacturing fault on one example of the filter.

Exhausts are very much down to personal preference, it's unlikely that one manufacturer's exhaust will give a noticeable increase in power over another. The big three manufacturers of RST exhausts are Magnex, Mongoose and Scorpion. Magnex are the best made systems, they fit well and produce a refined exhaust note, just a deep burble at low revs and not excessively loud. A good system to choose if the car is used a lot, especially for motorway driving. The Magnex is available with 3" and 4" tailpipe, both inwardly rolled. Scorpion systems are louder and have 3.5" or 4" tailpipes outwardly rolled only. Mongoose produce the widest range, 3.5" rolled in, 4" rolled in and 4" rolled out. The Mongoose systems are comparable in noise level with the Scorpion. Powerflow are a franchised based chain of exhaust manufacturers that specialise in tailor made systems. This enables the customer to specify the noise level, design of tailpipe and bore size of the system to their requirements or personal preference. Powerflow's prices for bespoke work tends to be very competitive to 'off the shelf' aftermarket exhaust systems.

On a standard engine, the RST's ECU will allow 9psi of boost to be run before the overboost protection cuts in and either causes the car to jerk violently or cut the ignition. This is basically the ECU shutting down to prevent damage to the engine caused by excessive boost. In order to run more than 9psi the next stage is to chip the car. On the Fiestas this involves a 'piggyback' chip module such as a Superchip, which plugs into the diagnostic port on the ECU, situated under the dashboard in the passenger footwell. The chip overrides some of the manufacturer's preset limits and on some chips also instructs adjustments to be made to the way the ECU performs certain functions.

Superchips plug-in flash module chip for the Fiesta's EEC-IV ECU.
Fiesta EEV-IV ECU in the passenger footwell under the dashboard.

An alternative method of increasing the boost is to use a bleed valve. This device 'bleeds' off boost pressure before the actuator, fooling the actuator 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 can cause the engine to detonate or 'pink', leading to premature wear and engine damage. They also remove the boost limit, rendering the ECU unable to shutdown the engine if a problem should arise.

A 'stage 1' or '165' chip, so called because of the power its claimed to give, raises the boost limit in the ECU from 9psi to 14psi. This allows the car to run around 12psi without overboosting. The exact boost pressure is set by adjusting the wastgate actuator on the turbo. The actuator has a threaded rod that enables the boost to be set by altering the preload. The spring inside is conical so the more it is compressed, the stiffer it becomes. This is how actuator preload increases the boost. A -32 or '10psi' actuator is so called because it will hold a minimum of 10psi boost. Realistically with a 165 chip and 12psi boost you could expect a power output of around 150-160bhp at the flywheel depending on engine condition and setup.

A 'stage 2' or '195' chip raises the boost limit to 16psi and also makes adjustments to the timing and fueling to cope with the higher boost. In order to supply enough fuel for this, 701 or 'beige' injectors are required. These have a higher flow rate than the standard blue injectors and the map on the 195 chip is programmed for these. An advantage of the EEC-IV over the Escort RST's KE Jetronic, is the ability to change the injectors like this, rather than having to fit a 5th injector system which is hard to ensure even distribution of the fuel to each of the four cylinders. A 195 chip will give around 170-180bhp, again dependant on the car that it is fitted to.

The next stage in tuning is an uprated intercooler or chargecooler. Engine mechanics dictate that the lower the temperature of the inlet charge, the denser the air and the more power the engine will produce. 

The first method to decrease inlet temperatures is by increasing the size of the intercooler. The function of the intercooler is to cool the air passing from the turbocharger to the inlet manifold (known as the inlet charge). It does this by passing the charge through a core similar to a radiator. The greater the surface area of the intercooler core, the greater the cooling effect on the charge. Pace Products are the most well known aftermarket intercooler manufacturer and their Fiesta RST alloy intercooler has a 50% greater surface area than the standard item and provided a 12 degree C reduction in inlet temperature at 70mph.

A more effective method of cooling the inlet charge is a chargcooler. A chargecooler works differently to an intercooler in that it uses water rather than air for cooling. An electric pump flows water from an alloy reservoir known as a header tank, through a pre-rad at the front of the car where it is cooled, before entering a jacketed core where it cools the inlet down to 30 degrees C. The pre-rad is very small in dimension compared to an intercooler so is easy to locate in the Fiesta's engine bay. The core itself is not reliant on airflow so it can be placed anywhere in the engine bay. Under the battery tray in the case of the Pace system.

The stumbling block of the Fiesta is the T2 turbo, which is simply too small to reliably boost more than around the 16psi. In order to produce more boost it is necessary 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. These units are basically uprated versions of the Fiesta's standard turbo and due to the size have very little lag. There are a number of problems associated with such a small turbo however, the cost of a T2, even a reconditioned standard unit is quite high, and due to it's size it struggles to maintain pressure at higher rpms and runs out of steam at the top end.

A common solution to both of these problems is to use the standard or hybrid T3 turbo from the Escort RST. One of the main reasons for Ford fitting the T2 to the Fiesta was lack of space under the bonnet. In order to fit a T3 it is necessary to move the radiator and intercooler forward by an inch or so to make space for the larger turbo housing. The Escort's exhaust manifold and filter are also required along with a few other bits of piping and tubing.

High lift 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 10bhp on the Zetec engines, and you begin to see why the CVH Turbo engine is so popular. A vernier pulley will enable fine timing adjustments to be made for an optimum torque curve. 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.

In order to run high boost (much over 18psi) 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. To extract the maximum power from a 1600 CVH the compression ratio needs to be lowered from the standard 8.2:1 to 7.5:1.

The next step up, after every bit of power has been squeezed out of the 1600, is to increase the displacement. It is possible to increase the 1597 to just over 1600 by boring the block, commonly known as a 1mm overbore. Some Ford tuners, such as Power Engineering, produce large capacity CVH engines. PEs 'System 2' is a 1900cc CVH unit based on a bored out 1600 block with larger pistons and a longer stroke crank.

A more modern high-capacity engine is the 'ZE-VH' or 'ZVH' 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 or 2.1. This bottom end has a fully counterbalanced crank, oil jet sprays for under piston cooling and a larger capacity oil pump. The 1.8 and 2.0 can use the original Zetec pistons machined to lower the compression or for higher boost application, forged pistons such as Mahle, Arias or Accralite. The forged pistons coupled with the stronger Zetec block make for a very strong engine, capable of running much higher boost than an equivalent size CVH, and power figures of well over 300bhp are not uncommon.

The next evolution of the ZVH is a full blown 16 valve unit. This engine is essentially a turbocharged 2.0 Zetec 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 250bhp at only 16psi boost. At 25psi the power output rises to over 300bhp.

 [resources] relevant links >>
Superchips http://www.superchips.co.uk
Accralite http://www.accralite.com
Arias Pistons http://www.ariaspistons.com
Pace Products http://www.paceproducts.co.uk
Magnex http://www.magnexexhausts.com