Diesel ST Surprises

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Alex Paull had one aim with this Focus: to make a Diesel ST as fast and powerful as a standard petrol version. With the help of Pumaspeed, MaxD Out and many long hours in the workshop he has achieved it – just! – and he’s not finished yet!

Words & Phototgraphy: Simon Hastelow

Alex Paull is a sensible guy. His A previous company car was a VolksWagen CC (poncey Passat to you and me), the brown-suede-shoes of the motoring world that even real VAG enthusiasts could only describe as ‘reliable’.

When it came to replacing the CC we should be thankful that Alex’s sensible hat slipped slightly and allowed him to consider the Focus ST and Golf GTi. But, they would have to be in diesel form due to his work and the very high mileage he covers each year.

He tried both cars and, although the Golf was ‘OK’, it was just about as thrilling as the CC (ie not very). All he could think about was the ST225 he owned a few years ago, in bright orange. He recalled: “It was a great car, so I wondered if the Diesel ST could give me the same performance.”

The decision was made: ST Diesel it was, with the added desire to tune the diesel lump, but no idea how it could be done.

We are not short of tuning companies in the UK but almost without exception the Ford specialists are only interested in petrol power. The ones that do mention diesel seem to restrict the options to better air filters and induction (as they are mostly common to both fuels).

So, let’s look at the benchmark that the petrol Mk3 ST sets.

£27,650 gets you onto the ST ladder. For this, you’ll get a car that Ford reckons will get you 39 miles down the road for every gallon of premium unleaded. In most real-world tests, driven by humans rather than robots, that gallon will have depleted after just 25 miles at the very most. You do get a top end power figure of 247bhp and a zero-to-sixty target of 6.5 seconds. The ST is a very, very good car and trounces all over the competition.

The Diesel ST in fresh-off-the- forecourt condition is almost five-grand cheaper. Gives 182bhp, 0-60 of 8 seconds and fuel consumption of 60+mpg and CO2 of just 110g/km. It is obviously not as quick as the petrol but all the figures make it the almost perfect company car: good fuel economy, low tax bracket, low road tax, lower insurance. It is the sensible choice.

The lines are now clearly drawn. For the diesel to compete, Alex has to eek out an extra 65bhp and a 1.5 seconds off the 0-60. Let the head-scratching commence.

Alex quickly became quite disillusioned by the response from some of the big names in Ford tuning circles, almost without exception he was told to go elsewhere, no-one was interested in heavy-oil burners so he resorted to trying a plugin box. These are widely available and promoted on t’interweb. They promise you massive gains in power and better fuel economy. The one that Alex tried offered a ‘massive’ 39bhp increase in power, only half what he was aiming for but a big first step. As most of us already know, these miracle black boxes are largely useless as most do little other than over-fuel the intake by fooling the ECU into thinking the engine is cold.

It was a chance visit to Pumaspeed that saved Alex from this folly but also set him on the right track. Initially he only went along to speak to them about lowered springs for his ST. They recommended and supplied a full set of H&R springs but, after talking to Alex about what other things he was planning to do, a light-bulb must have appeared over someone’s head at Pumaspeed HQ.


They had been considering work with a Diesel Ford for some time but the imminent arrival of the Mk3 RS had put plans on hold while they concentrated efforts on the new Focus, which, quite rightly, everyone suspected was going to be a massive hit. But after a bit of discussion, Alex agreed to let Pumaspeed use his ST as a development vehicle for diesel tuning.

Alex’s Focus was driven into the workshops with just 44 miles on the clock and a two-week timeframe to do whatever the geniuses could come up with. He still had use of his old VW CC for that amount of time but it was going back after that so there was a finite deadline to deliver the ST with the required boost in performance.

This would be OK for most petrol cars, there’s already a hell of a lot of kit to choose from and even a DIYer could select stuff almost at random and get that much extra power. However, there was no such option with the diesel.

First off was a Dyno run. This confirmed suspicions that the plug-in magic box was doing nothing at all so was removed and returned to the seller.

The main issue for Pumaspeed and the guys from MaxD Out was that the diesel ECU was locked down and no-one had cracked it yet. The computer wizards were sent away to do their stuff while the rest of the team got on with the physical aspects like looking at better induction, intercooler and exhaust.

They experimented with quite a variety of air filters and induction systems, eventually finding that an off-the-shelf K&N filter offered the best results while also being the correct form and size to fit without any modifications.

They also selected the R-Sport Stage 3 intercooler as used in the ST250 but mounted it as far forward as possible to give it the maximum amount of airflow and removing any unwanted obstructions. They had to alter the air conditioning pipework to accommodate it all but the result is very neat. And very effective! Both aesthetically and in performance terms.

MaxD Out took exactly a week to crack the mapping and develop a completely new Stage 1+ remap. A dyno run confirmed that this was capable of giving Alex’s ST 220bhp with huge amount of torque right across the rev-range.

The next part of the equation was the exhaust. The Diesel Focus obviously comes with a DPF to help with emissions and clean-air regulations. The challenge was to be able to create a full exhaust system that included a DPF delete. Previous forays into DPF deletes had thrown up all kinds of issues with throwing up errors as the Delphi-ECU looks for feedback from the DPF.

MaxD Out hit the jackpot again and the last Dyno run confirmed a figure of 240bhp. This was the target everyone was looking for and they’d done it in almost record time. Big smiles all round!

Other options for even more power are under consideration – like a hybrid turbo for instance – but everyone seems to be happy with what they’ve achieved so far so that will come at a later date.

Not that Alex has been focussing entirely on the power, the looks of the car are very important too. And in this respect we think he has pulled of the masterstroke of tweaking the external look of the car while also remaining fairly restrained and given it a fantastic stealthy appeal.

The Maxton front splitter, RS rear spoiler, grilles, light surrounds and RS bonnet vents are all colour coded the same gloss-black to match the rest of the car and act as subtle highlights to the grey exterior. Even the headlights and rear light clusters are ‘blacked’ as much as is allowed. To round it all off Alex has fitted a full set of Pumaspeed Turismo 18×9 Alloys in black.

What started off as a quest for a sensible company car has turned into a very sprightly car indeed. It ticks all the sensible boxes whilst also packing a punch when required. We can’t wait to see what Alex and Pumaspeed come up with next. Can an ST hit 300bhp while rolling coal?
R-Sport Stage 3 Front Mount Intercooler, R-Sport Prototype 3” DPF Delete Exhaust, K&N Air FilterMaxd Stage 2 Diesel Map, Pumaspeed Low Vibration Mount
H&R Springs
Mahogany Dipped Engine Plastics
Maxton Front Splitter, MK2 RS Bonnet Vents, Heko Wind Deflectors, Pumaspeed Tourismo 18×9 Alloys, MK2 RS Spoiler in MK3 RS Colour Scheme, Tinted Rear Lights & Reflectors, Custom Badges, Gloss Black Front and Rear Plastics, Uprated Bulbs all round