The Focus ST has been the mainstay of the performance Ford vehicle line-up for more than 20-years, with the final mark boasting the most performance, tech and refinement of the bunch.
There's an awful lot to like about the Mk4 Focus ST, but with a few choice upgrades you can get near RS levels of performance and fun - here's our five favourite mods.
One of the best value performance upgrades you can make to the Focus ST is without doubt, a stage 01 performance calibration.
As with all (ICE) Internal Combustion Engine-powered vehicles, the OE calibration is typically restricted by both emissions regulation and what the base engine team determine is the maximum safe power and torque output - based on their own internal sign-off limits.
The reality, is these limits were often put in place years, or even decades before and don't always test an engine, or the calibration performance in a true 'real world' scenario, as used by you (their tests are often much harsher than reality).
Whether the limiting factor is in-cylinder pressures, turbo speed, or something else, what you get from the forecourt is often a restricted form of what's reliably possible to extract - and this is true of the 4-cylinder 2.3-litre EcoBoost engine found in the Focus ST.
It's always sensible to help your engine breathe more easily, but even without any other hardware changes, stage 01 software offers a genuine peak gain of circa 70bhp+ and 110Ftlb+ which is enough to completely transform your ST.
A premium calibration will offer a more responsive vehicle that allows for safer overtaking, is generally more drivable day-to-day and of course, is a lot more fun when properly using the extra performance on road, or track.
Extra functionality can also be included into the base strategy (the governing structure of what can and can't be done within the software running on your ECU), to allow for things like more (or less) pops and bangs, sharper pedal maps, higher rpm limits and with devices like our HP Tuners FLASHlink (which uses a Bluetooth OBD adaptor and an app running your smartphone to make changes on-the-fly), you can also install anti-theft and specific fuel-based performance calibrations, plus a whole lot more besides.
The extra performance, character and ultimately overall enjoyment that can be instantly unlocked to the base vehicle makes a stage 01 calibration our #1 essential upgrade.
Note: The ST was available with both a manual and auto transmission option and 09Design support all ECU models up to April 2024 where a revised ECU strategy was deployed. We're close to being able to offer a solution for the latest build dates, so keep an eye on our social channels for more info.
One of the best value performance upgrades you can make to the Focus ST is without doubt, a stage 01 performance calibration.
As with all (ICE) Internal Combustion Engine-powered vehicles, the OE calibration is typically restricted by both emissions regulation and what the base engine team determine is the maximum safe power and torque output - based on their own internal sign-off limits.
The reality, is these limits were often put in place years, or even decades before and don't always test an engine, or the calibration performance in a true 'real world' scenario, as used by you (their tests are often much harsher than reality).
Whether the limiting factor is in-cylinder pressures, turbo speed, or something else, what you get from the forecourt is often a restricted form of what's reliably possible to extract - and this is true of the 4-cylinder 2.3-litre EcoBoost engine found in the Focus ST.
It's always sensible to help your engine breathe more easily, but even without any other hardware changes, stage 01 software offers a genuine peak gain of circa 70bhp+ and 110Ftlb+ which is enough to completely transform your ST.
A premium calibration will offer a more responsive vehicle that allows for safer overtaking, is generally more drivable day-to-day and of course, is a lot more fun when properly using the extra performance on road, or track.
Extra functionality can also be included into the base strategy (the governing structure of what can and can't be done within the software running on your ECU), to allow for things like more (or less) pops and bangs, sharper pedal maps, higher rpm limits and with devices like our HP Tuners FLASHlink (which uses a Bluetooth OBD adaptor and an app running your smartphone to make changes on-the-fly), you can also install anti-theft and specific fuel-based performance calibrations, plus a whole lot more besides.
The extra performance, character and ultimately overall enjoyment that can be instantly unlocked to the base vehicle makes a stage 01 calibration our #1 essential upgrade.
Note: The ST was available with both a manual and auto transmission option and 09Design support all ECU models up to April 2024 where a revised ECU strategy was deployed. We're close to being able to offer a solution for the latest build dates, so keep an eye on our social channels for more info.
Improving the efficiency of your air intake gives multiple improvements; from an enhanced intake sound, to a reduced pressure drop across the intake system - which means your engine (and turbo) doesn’t have to work so hard to make the same level of power and torque than it would otherwise.
A high-flow panel filter offers a cheap way of providing a small airflow improvement, induction noise boost and performance gain. The airbox doesn’t even require tools to access the filter on the Focus ST, so this truly is a DIY swap that anyone can do themselves.
With substantial torque gains available with Stage 01, Stage 02 and hybrid / big turbo options, that means a LOT of air being moved and the potential for restrictions in the intake system.
The ultimate low-pressure-drop setup involves replacing the OE airbox for a more open cone-style intake, although with engine bay heat comes the concern of a loss of power due to the increase in intake temps.
That's why rather than a simple filter fitted to an aluminium pipe, our induction kit solution offers a semi-enclosed airbox setup, complete with a carbon fibre filter housing and carbon fibre air-feed.
Although more difficult to design and manufacture, the carbon fibre material also boasts an inherent thermal benefit, that stops unwanted heat transfer, helping to maintain peak power for longer - and offering an unrivalled induction noise.
Whichever induction kit you opt for, make sure it’s properly designed to provide optimal airflow, whilst preventing as much heatsoak as possible - avoid an open filter simply fitted to a pipe, unless you're purely after a noise increase and a reduction in power output!
Improving the efficiency of your air intake gives multiple improvements; from an enhanced intake sound, to a reduced pressure drop across the intake system - which means your engine (and turbo) doesn’t have to work so hard to make the same level of power and torque than it would otherwise.
A high-flow panel filter offers a cheap way of providing a small airflow improvement, induction noise boost and performance gain. The airbox doesn’t even require tools to access the filter on the Focus ST, so this truly is a DIY swap that anyone can do themselves.
With substantial torque gains available with Stage 01, Stage 02 and hybrid / big turbo options, that means a LOT of air being moved and the potential for restrictions in the intake system.
The ultimate low-pressure-drop setup involves replacing the OE airbox for a more open cone-style intake, although with engine bay heat comes the concern of a loss of power due to the increase in intake temps.
That's why rather than a simple filter fitted to an aluminium pipe, our induction kit solution offers a semi-enclosed airbox setup, complete with a carbon fibre filter housing and carbon fibre air-feed.
Although more difficult to design and manufacture, the carbon fibre material also boasts an inherent thermal benefit, that stops unwanted heat transfer, helping to maintain peak power for longer - and offering an unrivalled induction noise.
Whichever induction kit you opt for, make sure it’s properly designed to provide optimal airflow, whilst preventing as much heatsoak as possible - avoid an open filter simply fitted to a pipe, unless you're purely after a noise increase and a reduction in power output!
Despite its size and weight, the Mk4/4.5 Focus ST feels relatively nimble and has a great chassis that can be exploited in everyday use - and even the odd track day.
As always though, the OE rulebook means that the optimal setup for the performance enthusiast has to be balanced with the mass-market requirement and that's where a set of performance lowering springs, albeit with the right poundage allow you to lower the vehicle's centre of gravity, enhance turn-in and provide a more responsive overall chassis, without compromising on ride quality - critical, for the numerous owners that use their cars on a daily basis.
Go too low with the OE damper and you'll not only risk front bumper scuffs, you'll also promote 'crashing' and poor dynamic control where there's minimal damper travel left under compression - you'll also have eyes on stalks trying to dodge the potholes that litter the roads - in the UK, anyway.
Our performance spring reduces the ride-height by 20mm on the front axle and 25mm on the rear, giving an optimal aesthetic drop, combined with a significant handling boost - all whilst still being compliant enough for daily duties.
Despite its size and weight, the Mk4/4.5 Focus ST feels relatively nimble and has a great chassis that can be exploited in everyday use - and even the odd track day.
As always though, the OE rulebook means that the optimal setup for the performance enthusiast has to be balanced with the mass-market requirement and that's where a set of performance lowering springs, albeit with the right poundage allow you to lower the vehicle's centre of gravity, enhance turn-in and provide a more responsive overall chassis, without compromising on ride quality - critical, for the numerous owners that use their cars on a daily basis.
Go too low with the OE damper and you'll not only risk front bumper scuffs, you'll also promote 'crashing' and poor dynamic control where there's minimal damper travel left under compression - you'll also have eyes on stalks trying to dodge the potholes that litter the roads - in the UK, anyway.
Our performance spring reduces the ride-height by 20mm on the front axle and 25mm on the rear, giving an optimal aesthetic drop, combined with a significant handling boost - all whilst still being compliant enough for daily duties.
The brakes are adequate as standard and are actually very good if you've ended up with a car running the larger discs / caliper on the 'Track Pack'.
As the brakes are used to assist with the eDiff setup (brake based torque vectoring), even with a Stage 01 power upgrade you'll be needing more durable stopping performance than before and whether you're looking to simply enhance your outright stopping power regardless, or just when the OE discs and pads have called time, a set of uprated grooved discs and matching performance pads are a relatively cheap and easy way of enhancing initial bite and resistance to fade - the grooved face of the disc helping to deglaze the pad and promote even pad wear.
Combine this setup with a set of braided brake lines and you'll have a great fast road setup with better stopping performance on tap... but if you're particularly punishing on your brakes, or you're venturing out on track, a big brake kit really is the ultimate way forward (and with two 6-pot forged caliper options and a 355mm disc/bell setup available, we more than cater for owners that want the best stopping performance and pedal feel for this ST)
The brakes are adequate as standard and are actually very good if you've ended up with a car running the larger discs / caliper on the 'Track Pack'.
As the brakes are used to assist with the eDiff setup (brake based torque vectoring), even with a Stage 01 power upgrade you'll be needing more durable stopping performance than before and whether you're looking to simply enhance your outright stopping power regardless, or just when the OE discs and pads have called time, a set of uprated grooved discs and matching performance pads are a relatively cheap and easy way of enhancing initial bite and resistance to fade - the grooved face of the disc helping to deglaze the pad and promote even pad wear.
Combine this setup with a set of braided brake lines and you'll have a great fast road setup with better stopping performance on tap... but if you're particularly punishing on your brakes, or you're venturing out on track, a big brake kit really is the ultimate way forward (and with two 6-pot forged caliper options and a 355mm disc/bell setup available, we more than cater for owners that want the best stopping performance and pedal feel for this ST)
The back-pressure drop in a GPF-back system helps exhaust gasses escape more easily, but as the OE setup has been well optimised for flow, power gains are minimal.
However, the audible boost available is substantial and with a carefully designed rear muffler, the 2.3-litre EcoBoost found in the ST can be tuned to sound arguably better than the similar engine / exhaust setup in the Focus RS, with a better tone, more authentic crackle and generally nicer sounding output available.
As the OE in-car sound is synthesised via the speakers, upgrading your exhaust with the right soundtrack adds a much needed dose of authentic character to the car - and certainly the 09D system in Sport / Track mode is sure to put a smile on your face!
The back-pressure drop in a GPF-back system helps exhaust gasses escape more easily, but as the OE setup has been well optimised for flow, power gains are minimal.
However, the audible boost available is substantial and with a carefully designed rear muffler, the 2.3-litre EcoBoost found in the ST can be tuned to sound arguably better than the similar engine / exhaust setup in the Focus RS, with a better tone, more authentic crackle and generally nicer sounding output available.
As the OE in-car sound is synthesised via the speakers, upgrading your exhaust with the right soundtrack adds a much needed dose of authentic character to the car - and certainly the 09D system in Sport / Track mode is sure to put a smile on your face!
Our five favourite mods for the Mk4/4.5 Focus ST for owners wanting near RS levels of performance and fun!
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