Zetec Turbo Guide
The Zetec Turbo engine has increased hugely in popularity in recent years and rightly so. With twice the valves of the FRST 1600 CVH and up to a 400cc capacity increase without overbore it offers huge potential. Outputs of over 500bhp are possible and 300bhp is achievable with even a mid spec build. The Zetec is very receptive to turbocharging, if done correctly, and can be a strong engine if money is spent in the right places. For information on the differences between the Zetecs, take a look at the Zetec History article.
- Base Engines
- Block Preparation
- Reducing The Compression
- Head Gasket
- Strengthening - Basic
- Strengthening - Intermediate
- Strengthening - Advanced
- Cylinder Head
- Cams And Pulleys
- Inlet Manifold
- Injectors And Fuel Pump
- Injectors For Cosworth Management
- Exhaust Manfold And Downpipe
- Turbo Choice
- Important Note
First of all, there is little point in trying to turbocharge the restrictive 1.6 Zetec. It can be done, but as upgrading to a 1.8 or 2.0 will offer a lot more potential for only a couple of hundred pounds more it’s something of a no-brainer. The 1.8 as fitted in the XR2i and RS 1800 is a possibility, although most people opt for the 2.0, which has the obvious advantage of the extra capacity and a wider choice of pistons. The 2.0 is more expensive and sometimes harder to find than the 1.8, but having said that, locating a base engine should not be any trouble at all as it’s quite a common powerplant.
- Where? - www.findapart.co.uk
- How much? - £150 for a high mileage Series 1, to £700+ for a not even run in Series 3.
Aside from lowering the compression, which is covered below, there are a few more changes required to the block when turbocharging.
Oil feed and return
The turbo requires a high pressure supply of oil for cooling and lubrication, which then drains out of the turbo and is returned to the engine.
The feed is taken from a T-piece between the block and the oil pressure switch. The Escort RST’s braided line can be used, or an aftermarket alternative such as Moquip or Aeroquip from Think Automotive.
The return should be above oil level and normally goes into the block on OEM turbocharged engines, but as these were cast with them the only real way aftermarket is to have a boss welded to the sump, which works just fine.
Under piston oil jets
Most base engines will be fitted with these, but in the case of the 105ps 1.8 it’s advisable to fit them. The jets are mounted so as to squirt oil under the pistons to cool them.
The main internal change required for the engine is to reduce the compression ratio from 10:1 to between 7.2:1 and 9:1. This is because the cylinder pressure in a turbocharged engine is much higher than that of a NA. If we were to run a reasonable amount of boost through the standard engine it would stress the components to the point of serious damage.
The compression ratio should be chosen based on the internal strength of the engine, the grade of fuel used and how much boost will be run. Lower compression allows for more boost and lower octane fuel with minimum chance of detonation, but makes for poor throttle response off boost. A higher ratio will elicit better response but increase the cylinder pressures, putting the internals under more strain and making the engine prone to detonation.
For an engine that can run ~20psi on pump fuel, around 7.4:1 is recommended. If the engine is being built with strengthened parts and will be precisely mapped with high quality aftermarket management, or other factors such as race fuel or water injection, the same boost can be ran with a CR in the 9:1 range. This allows for no margin of error though. At this CR if the fueling were to run lean, engine damage would inevitably occur without much warning.
The Focus WRC runs a Zetec Turbo at 9:1 with a decent sized turbo, so it would appear that this is possible, especially as this car is road legal. The reason for the high CR is to recoup the power lost by the mandatory FIA 34mm restrictor. The boost curve, although strong in the midrange, tails off at high RPMs. Also bear in mind that the car is fitted with thousands of pounds worth of expensive management and engine components are renewed frequently.
High boost, high compression turbo engines are best left to those who really know what they are doing.
Reducing The Compression
There is only one real way to reduce the compression and maintain a good, strong engine and that is to replace the stock, cast pistons with forged aluminum ones. Other methods are possible but all have downsides which make them unsuitable for all but the most shoestring conversions, and as forged pistons that fit the Zetec can be obtained for relatively little expense, the savings made with other methods are not even that great.
Forged low-compression pistons
(Aftermarket pistons produced with a low CR specifically for turbocharged applications)
+ Strong, reliable
(a thin metal plate to space out the head from the block)
- Requires two head gaskets - double the chance of failure
- boost still limited due to stock cast pistons.
(machining the crowns of the standard cast pistons)
- Further weakens pistons that are already unsuitable for turbocharging, boost levels are severely limited.
With forged pistons there are a number of options for the Zetec. The cheapest is to use those originally designated for another type of turbocharged car. In this case the most common source for 2.0 pistons is the Vauxhall C20LET from the Cavalier and Calibra Turbo. Fitted to a Zetec these will give a CR of 7.4:1
The C20LET bore is 86mm, compared to the 2.0 Zetec’s 84.8mm, so a slight overbore of the block is required. This presents no problem as the block is likely to have some wear on it and there is enough material to maintain the wall thickness. This will take the original 1998cc to 2045cc. Also required is modification to the rods to accept the 21mm wrist pin.
Despite being badged “Duratec RS” on the cam cover, the Focus RS engine is in fact a modified Series 3 Zetec, with the same cast iron block (unlike a Duratec HE, which uses an alloy block). Focus RS pistons may be used, however these are sized for the standard 84.8mm bore and therefore only suitable for brand new and not seasoned (used) blocks as they won’t sit tight after a bore / hone. Also be aware that the Focus RS uses a fully floating pin arrangement, so the pistons must be mated with the Focus RS or aftermarket rods. They won’t fit with the standard Zetec rods.
There is a reasonably large range of aftermarket pistons available. Mostly due to the ability of the manufacturers to produce pistons to custom specification.
|JE||85mm||Series 3 only||9.0:1|
|JE||84.8mm||Series 3 only||8.0:1|
|Focus Central||84.8mm||Series 3 only||8.2:1|
|Focus Central||85.3mm||Series 3 only||8.2:1|
|Arias||any||Custom made to order||any|
The metal Series 3 (Focus) Zetec head gasket is fine for turbocharged use and has been used without problems a up to 2 bar boost. As far as I have been able to determine. The turbocharged Focus RS uses the same gasket as the NA engines.
Strengthening - Basic
Due to the increased stress on the engine from turbocharging, key areas need to be strengthened. Fortunately the Zetec is a fairly strong unit, and not much needs to be done in order for an engine producing a fair amount of power to be reliable. The weakest link is the connecting rod bolts. These should be changed for ARP items (around £80). The rods themselves will handle around 250bhp and it’s advisable to have them shot peened, a metal treatment method that increases the fatigue performance.
Strengthening - Intermediate
For engine with higher target outputs, or as a degree of future proving, the rods should be replaced with aftermarket forged steel items. Expensive yes, at around £700, but a lot cheaper than rebuilding or replacing a wrecked engine due to a rod bending or snapping.
Strengthening - Advanced
Head and main studs
A stud and nut will always provide a superior clamping force than the standard head or main bolts. It is beyond the scope of this article to explain the physics involved but suffice to say that it is common practice with high performance engine to use this set-up.
- Where? - ARP Bolts
- How much? - £160 head, £120 main
Steel main caps
The main caps are what hold the crank to the block. High power outputs can cause the stock cast caps to fracture, the antidote to this is stronger billet steel ones. At present no company seems to offer these. Esslinger used to have them listed but they now appear to be discontinued.
As the standard crank is good for over 400bhp a billet steel crank is only really needed for the most extreme engines, or those that are using a custom stroke. Typical cost is around £1400 from Raceline or Dunnell.
WRC CGI Block
As it sounds, this is the actual block used in the Focus WRC. Although the casting must be identical to a production vehicle (The Focus 2.0) the material may be different. The Use of Compacted Graphite Iron (CGI) results in a block 20% stronger yet still lighter than the standard iron unit. Limited numbers of these blocks have surfaced onto the public market. Exercise caution when buying as some are reputed to be rejected castings. Cost is around £1000 from private ads / eBay
Nothing needs to be done here, bar any modifications to fit the inlet or exhaust manifolds. The head flows relatively well and 270-300bhp should be achievable without any work so long as the rest of the engine is correctly specified and built
Releasing more power is done via the usual method of enlarging the ports and fitting bigger valves. Plenty of places are able to do this including Area Six / Fiesta Frenzy, Ric Wood and Puma Race Engines.
Cams And Pulleys
The standard Zetec cams are fine although for maximum power Area Six / Fiesta Frenzy produce a pair of Zetec Turbo cams which have turbo specific profiles honed after years of development.
It has been discussed that the using a mix of the 105ps and 130ps cams may yield good results although no-one appears to have a definitive word on this yet.
As the OEM cams are not doweled, it is possible (but fiddly) to make finite adjustments to the timing. For ease of setting though a pair of vernier pulleys are recommended.
A turbocharged engine will nearly always require more fuel than a NA counterpart of the same displacement. This is exactly the case here and the standard Zetec injectors are not able to flow enough for much more than a couple of pounds of boost.
The first problem faced is that a NA 1.8 or transplanted 2.0 in a Fiesta will 90% of the time use the Fiesta Zetec EFi inlet. This uses unusual side-fed injectors which are difficult to obtain in higher flow rates. There are a number of solutions which, as ever, depend on budgets and targeted power outputs.
Zetec EFi manifold with new fuel rail
The Zetec manifold is retained, but the fuel rail is replaced with one that uses end-fed injectors such as the FRST or XR2i item. The complication here is that there is no simple and obvious way to mount the rail. Some fabrication will be necessary.
+ Ports well matched
- Requires adaptation / replacement of the fuel rail
FRST / XR2i EFi manifold and adaptor plates
This avoids needing to adapt the fuel rail by using it with the manifold it was intended with. Two spacer plates are required. One to address the mismatched mounting holes on the manifold and head, and another to “sandwich” the upper and lower portions of the manifold to clear the rocker cover, which sits higher than the CVH. The failing point here is that the ports differ in shape between the two engines, so the airflow is disturbed somewhat, inhibiting power.
+ Direct bolt on fit.
- Ports not matched.
Compatible OEM manifold and adaptor plate
At the time of writing, the only OEM manifold that has seen use with the Zetec is the Rover 820 unit. this has medium length runners, a 1.8-2.0 sized plenum and the port shape is almost identical to the Zetec. The bolt patten unsurprisingly doesn’t like up, so an adaptor plate is used. Tests have shown this manifold is capable of flowing enough for 360bhp.
+ Good port match and flow ability.
- Limited availability.
Fiesta Frenzy Manifold
If the power of the engine is intended to exceed 300bhp, then the flow abilities of the standard Zetec or CVH EFi manifolds become restrictive. There are a couple of options for those looking for the ultimate setup, the first being the Fiesta Frenzy “Zero-Loss” unit. This is a short-runner sheet-metal manifold with a plenum sized for a 2 litre displacement. It’s not cheap at around £600, but has been proven to flow enough for over 500bhp and should not present any restriction for a good deal more than that.
+ Direct fit, virtually no restriction.
The final option is a completely bespoke design. This may also be required due to unusual plumbing from say a single pass intercooler or longitudinal engine fitment. It’s important to note that inlet manifold design is something of an exact science and should be left to someone who understands the principals involved.
+ Perfectly tailored solution.
- Cost, difficulty in commissioning.
Port lengths are a very important consideration, not because they affect power levels as such, but more because they affect at what point in the rev range peak power is produced. Longer runners promote a build up of air leading to low down torque, whereas shorter runners shift power up the rpm range at the expense of low down torque.
A note on the air inlet pipe running across the cam cover
Some people have expressed a preference for an end fed manifold, explaining that it is devoid from any increase in air inlet temperatures due to the inlet pipe running across a hot engine. In reality the velocity of the air passing through the pipe is sufficient enough for it’s temperature not to be affected to any measurable amount.
Central or side entry?
The symmetrical layout provided by a central entry manifold is a desirable characteristic for equal flow, but not one that is vital. Plenty of high flow manifolds, both those designed for the Zetec and those for other cars are side entry.
Injectors And Fuel Pump
As mentioned above, the standard Zetec injectors will be insufficient. Once again, intended power outputs govern the choices here. Running any component at the limit of it’s ability is never wise and this is especially true with injectors. Failure to keep up with fueling requirements can lead to extensive, not to mention expensive, engine damage. Always size generously.
The standard fuel pump will need upgrading too. The T25 EEC-IV Escort Cosworth’s item will fit for a mild upgrade (up to 250bhp) or there are up-rated items designed for the Cosworth with flow abilities up to 500bhp.
Flow rate is not the only governing factor concerning injector choice. Impedance will need to be selected based on the engine management system used. Aftermarket systems such as Autronic, Pectel, DTA and Gems are adaptable to work with a wide impedance range, but standard Ford systems are more fussy. The FRST EEC-IV requires high impedance of ~ 16ohms and the Escort Cosworth Webber Marrelli require much lower, around 4ohms.
This is about the limit for the standard FRST injectors. A very low boost engine may only require this amount of fuel, but it would be fairly pointless to go to the expense and trouble of building a Zetec Turbo engine to only produce this level of power, when the CVH alternative is both cheaper and easier.
The practical limit for “Beige” 701 injectors, commonly sold as part of the 195 “Stage 2” chip upgrade for the FRST. Maybe suitable for low boost conversions.
At this level there are no injectors sold specifically as FRST upgrades. There are however units which exist with the correct impedance and a suitable flow rate for this power. Bosch 0 280 150 737 from the Audi 2.2 turbo with a flow rate of 305cc/min being one example.
Injectors For Cosworth Management
There is plenty of choice at this impedance, from the OEM yellows for ~220bhp to greys for over 500bhp.
4 or 8 injectors?
For a time, many high performance turbocharged engines used two injectors per cylinder rather than just the one. The most well known example possibly being the Sierra RS 500 Cosworth’s Pectel Super 8 setup. Logic might suggest that where one injector cannot flow enough, two are required. In fact it is the contrary; how little the injectors can flow. Due to limitations of the engine management. Large injectors were not able to open and close quickly enough to supply small amounts of fuel at idle. Consequently 4 standard injectors were used between idle and the boost threshold, with the other 4 kicking in for extra fuel when on boost.
Recent progression has made it possible to use large injectors and still maintain reasonable emissions and a smooth running at idle.
A reliability bonus of a 4 injector setup is that should an injector fail, combustion in that cylinder would cease, rather than run lean.
The standard Zetec management is missing a number of vital capabilities for controlling a turbocharged engine. The most important being able to sense boost and adjust fueling to suit.
A Zetec turbo will run fine on FRST management, although this needs to be the 0FAB (OFAB) type as the 0FAC (OFAC) can only measure 1.5 bar (21psi) of positive boost due to it’s 2.5 bar map sensor. This can be overcome by an experienced mapper though. Fitting wise, nothing much needs to be done bar changing the injectors and possibly the map sensor. The main expense is mapping, due to it’s specialist nature and a reputation for being more difficult to map than aftermarket systems.
It is possible to run a Zetec on the Cosworth’s Webber Marelli system but this requires the relocation of several sensors and the conversion of the distributor based ignition system to fire the Zetec’s twin-coil pack. More information is available at www.zetec-turbo.co.uk
The more complex an engine, the more complex the management needed to control it must be. For high spec engines a motorsport spec system provide advanced features such as data logging, anti-lag and individual cylinder trims. Another advantage of this type of ECU is that they are often easier to map than OEM systems like EEC-IV.
The plugs will need to be changed for colder running ones. The Focus RS ones are a good choice for 200-250bhp builds but it’s probably a good idea to have the head machined to accept Cosworth plugs as these run colder still and offer a wider range of choice.
The standard Zetec coil pack is fine, as are the plug leads. Stick to genuine Ford items though as aftermarket ones tend to cost more yet offer inferior performance.
Exhaust Manifold And Downpipe
The downpipe will need to be replaced or modified to join the centre section of the exhaust to the turbo. As for the manifold, there are three choices here, either the Escort RST manifold, an aftermarket one such as FFM, or a bespoke fabricated one from an exhaust manufacturers.
The standard, cast ERST option is the cheapest, although it does present a problem in that the bolt pattern does not align with the Zetec head. This can be rectified in two ways:
- Drilling and tapping new holes
All but one of the holes can be re-tapped, the final one breaks out of the casting. A blob of weld can be used to fill the gap before tapping, or it can be left as-is, only a third or so of the thread is missing.
- Adaptor plate
Quicker and easier than tapping, but more expensive and also moves the turbo forward around 1cm, which is less than ideal on the Fiesta, where space between the engine and radiator is crowded enough as it is.
Fiesta Frenzy / Area Six Tubular Manifold
This gets around the space issue by relocating the turbo to one side, over the gearbox. It is constructed with a Zetec flange, so is a direct fit to the head, and is of a tubular stainless steel design (although not with equal length headers). Tested to over 500bhp.
The main advantage of repositioning the turbo is to give more clearance between the engine and radiator. This allows for rear mounted fans, so a full sized intercooler can be fitted. It also keeps heat away from the alternator and starter motor.
Fitting requires several alterations:
- Battery tray removed and battery relocated to boot.
- Support brace between manifold and gearbox.
- Bespoke downpipe.
- Longer oil feed and return pipes.
- Heat wrap on downpipe to protect brake servo.
One minor, but notable advantage is that as the downpipe is now routed over the gearbox and behind the engine, the Mondeo sump can be used rather than the more sought-after Fiesta item.
Only really required for very serious applications, such as those with an external wastegate or unusual fitments. As with inlets, design should be left to an expert who is well versed with exhaust flow characteristics.
A complete guide on intercooling will be published at a later date, but the best option for a Zetec Turbo is a large front mount air-to-air intercooler from Pace, GRS Motorsport, or Pro Alloy. It will require some cutting of the front bumper but this is a small price to pay for the increase in airflow.
Turbocharger sizing theory is complex enough that it could easily merit an entire article for itself. To simplify it somewhat the size of the turbo dictates what power will be made and also the power curve. A smaller turbo will spin up faster and feel more responsive, but won’t produce as much power as a larger one. The larger turbo will produce more power but exhibit more lag. How big a turbo to use depends on the target power output of your engine and how it will be driven.
The FRST T2 is far too inadequate and even the ERST T3 is on the small side for a 1.8 or 2.0 Zetec Turbo. The T3 and T34 from the Sierra end Escort Cosworth are more suited to the ZT, as they are sized for a 2.0 engine. Be aware that although the Cosworth turbo will mount to the ERST exhaust manifold, they don’t have the necessary exhaust elbow to connect to the Escort’s downpipe.
For a very drivable engine producing 200-250bhp the Focus RS’s GT 2560LS turbo is a good choice although likely to be somewhat expensive due to limited availability. It will also require the Focus’ exhaust manifold.
Your engine builder will be able to specify a suitable turbo to use. For a self-build a combination of reading up on turbo sizing theory and speaking to a supplier / manufacturer should see you right.
Turbo - Water cooled or not?
The water cooling system on a turbo has little or no effect once the turbo reaches operating temperature and is certainly not required for correct operation. The reason for it’s existence is to enhance both the warming up and cooling down times. When the engine is shut off, the turbo continues to retain heat, which can cause the oil inside it to become carbonised, damaging the turbo. With the water cooling, the turbo has a supply of cold water which drains into the turbo and evaporates, dissipating heat. It continues to draw in this water until the turbo’s core has reached such a temperature that the water no longer evaporates and the flow stops.
Car manufacturers fit the water cooling so that it’s not necessary to wait for the turbo to cool down after use. It would be quite an inconvenience to have to sit for 5 minutes or more at a standstill before you could switch off the engine. As a general rule, if letting the turbo cool down by either idling at a standstill or driving low / off boost for up to 20 minutes is not going to be an issue, then the cooling may be discarded. However on a day-to-day car it’s probably best left on.
One exception to this rule is certain turbos within the Garrett GT series. Garrett advise the use of water cooling for some models.
Proper intercooling is vitally important for a Zetec Turbo engine. There is quite a wide choice of intercoolers and chargecoolers available, the Zetec Turbo Cooling Guide covers these in detail.
The type of radiator used is normally governed by the intercooler setup. An intercooler designed for a FRST will normally be intended to fit with the standard FRST radiator, which is narrower than the NA cars. Fortunately it’s no less effective due to the thicker core.
If the turbo is going to be water cooled then the radiator will require the appropriate connections for the water pipes. This prevents the use of an XR2i item or suchlike so the choice falls between the FRST item or an aftermarket alternative.
Due to the increased power and torque outputs of the engine, the standard gearbox and clutch will not be up to the job. A full guide to up-rated transmission will be published at a later date, but as a minimum a paddle clutch and strengthened gearbox with LSD should be fitted.
An Important Note About Build Budgets
Building a Zetec Turbo, or having one built for you is never a cheap project. The biggest “hidden” expense is that of all the ancillary parts - gaskets, bolts, piping and hoses etc. All the little things mount up to a fair amount of your budget so it’s advisable to have 50% more funds available than you think it will cost.
Having said that, in terms of cost for performance the Zetec Turbo represents exceptional value for money. This is mostly due to the inter-compatibility between Ford models and the low cost of donor engines. As an example, for an engine build cost of around £5000, Paul R’s Zetec Turbo FRST recorded a quicker 0-60 time (4.89) than a Ferrari 512 TR (4.9).