Modified MG ZS diesel - Adam Sloman

DIESEL ZS
Boy from
the black
pump
Once upon a time the phrase
‘performance diesel’ was something
of an oxymoron, but the diesel engine
has seen intense development in
recent years and now powers
motorsport winners at Le Mans and
in the WTCC. But what if you
wanted modern oil-burner
performance in your ZS?
Words and pictures: Adam Sloman
30 MGE November 2011
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hen the ZS launched in 2001, the range
W
included a diesel, the 115bhp L-series
Turbo diesel. This made perfect sense
because while MG and diesel power may
not have an extensive history together,
diesel engines have seen increasing use in
cars with a sporting intent, especially
since the dawn of the new millennium.
And it worked – a mix of sporty driving characteristics and
diesel frugality gave the ZS diesel a broad appeal, and it has
even become popular with enthusiasts thanks to its tunability.
29 year old Pete Cowlishaw is one of those enthusiasts. He
got his first taste of MG during a Racing Experience day at
Thruxton Circuit and, having driven a V6 ZS180, he was
hooked. ‘It was great,’ he says of that memory. ‘I loved the way
it drove and I wanted one straight away. I’d considered a diesel
SEAT Leon and a petrol Toyota Celica, but the MG was what I
wanted. I very nearly bought a V6 180, but at the time there
was no way I could insure it. Plus, I cover a lot of miles for
work and I wasn’t keen on the petrols.’
Pete’s age, combined with that high-mileage career
developing and installing software for pharmaceutical
companies, meant he had to look at a more economical ZS,
and the diesel fitted the bill perfectly. And while some younger
motorists are content to simply swap a set of wheels or perhaps
add a body kit, Pete has forgone the styling tweaks in order to
concentrate only on improving the performance and
driveability of his MG. ‘I got the car as a 22nd birthday
present,’ he recalls. ‘That was in 2004, and the ZS was just nine
months old. I had to wait a while for the insurance to become a
bit more reasonable before I could start to modify it.’
Pete’s first changes saw him swap the air filter, fit a de-cat
pipe to the exhaust system and up the turbo’s boost to 19psi. (If
that sounds unreasonably high to those more accustomed to
Below: Pete
Cowlishaw
wanted an MG
that was fast and
fun, but it also
had to be long
legged and frugal.
www.mgenthusiast.com
November 2011 MGE
31

DIESEL ZS
Above: Pete’s ZS
manages to look
surprisingly edgy
without the
benefit of trick
paint or lairy
body kits.
Right: Diesels are
built to take
heady pressures,
and 19psi of
boost equates to
a shade over 1.3
bar on the gauge.
Right: Scangauge
connects to the
OBDII port and
shows info such
as coolant and air
intake temps and
fuel consumption.
petrol engines, bear in mind that the L-series in standard trim
should run at 16psi.) After some research amongst the owners’
community, Pete found 19psi was as high as the boost could go
safely. While it didn’t make the MG massively quicker, Pete
says the cars driveability improved no end. ‘A friend had taken
me out in his modified L-series Rover 400. It was a cracking
car, dyno’d at around 165bhp with 240lb.ft of torque, while
still giving decent economy if it was sensibly driven. Seeing
what could be done really inspired me. He said he’d spent
around £2000 on parts, and the return for that looked good. I
budgeted up to £4000, but soon passed that.’
A promotion in 2007 meant Pete was able to put a bit more
money into the project, and it began in earnest. Initially he had
the ZS gearbox rebuilt and a Quaife ATB differential together
with an uprated clutch fitted. ‘The PG1 gearbox cannot cope
with much more torque than about 250lb.ft,’ he explained. ‘A
popular modification across the forums is to pop some steel
caged bearings in there when they start changing clutches, and
after speaking to a few people in the Rover tuning scene, I
decided it was a sensible thing to do to extend the life of my
gearbox. The modified Rover I had ridden in had a Torsen diff,
and I really felt the torque steer pulling at the wheels until the
diff kicked in and straightened it out. Putting the Quaife diff in
mine meant I could keep the power down – this has transformed
the handling to the point where I can keep my foot firmly
planted as I corner or change direction.’
Pete then sourced a Stage 2 hybrid turbo, which uses a
standard ZS diesel housing, but is machined out to take the
biggest turbines possible – the compressor side from a Land
Rover TD5 and the exhaust side from a SAAB. The car was
then sent to Matt Stevens (aka Rally Matt) who fitted the
turbo, gearbox and injectors. ‘The car was really smokey,’ says
Pete. ‘The car was driveable, but you had to be gentle pulling
off before the turbo spooled up, and if you put your foot flat to
the floor, you would obscure cars in the rear view mirror.’
The reason for the ZS’ smoking habit was eventually traced
to faulty fuel injectors. ‘They were made up by a chap on the
32 MGE November 2011
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MGRover.org forum, and no-one really knows what
specification they are. They should not have produced the
levels of smoke that I saw.’ The ZS returned to Matt Reidy’s
workshop, who reduced the fuel levels, but to little effect. ‘We
still had exhaust gas temperatures in excess of 850°C at full
throttle! I decided to get rid of those injectors and fit the current
ones. The result was 50lb.ft of extra torque at 2500rpm instead
of 3000rpm, and 10bhp up top. More significantly, there was
next to no smoke when on the road.’
With things far from ideal in terms of emissions, the car then
suffered a head-gasket failure. ‘There was no mayo like you see
on a K-series when oil and water mix,’ Pete says. Instead it
suffered from head lift, which is when the cylinder pressures get
so high that they force the head up a touch and allow the
exhaust gases to get into the coolant galleries.’ While he was
repairing this, Pete had the head ported and sourced a set of
head bolts used on the American NASCAR racers, while the
fasteners come from a Subaru Impreza WRX.
The head gasket failure meant Pete was now considering
other modifications too. ‘I spoke to Matt at length; one area we
talked about was the intercooler. Matt felt the car could do
with something more substantial, since the original MG Rover
one isn’t all that great.’ With the exhaust manifold showing
temperatures of 850°C, Pete was inclined to agree. Matters
came to a head when a boost leak from the intercooler caused
him to think his custom turbo had failed, which led to a further
chat with Matt. ‘Most people use older injectors from the
Rover SD1, but I combined the original ones from the ZS with
older Rover 200 ones,’ he explained. Matt then worked out the
most efficient way to route the pipework to the intercooler
before I sat down with a Demon Tweeks catalogue and started
ordering the necessary parts.’
By early 2010 the car was ready for a remap, which showed
that it was peaking at only 130bhp. A new MAF (mass airflow
meter) meant an additional 10lb.ft of torque and another
5bhp, but as Pete says: ‘It wasn’t much of an improvement, to
be honest. The problem is the ECU restricts everything. Matt
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then suggested upping the voltage to the fuel pump in order to
improve the fuel’s flow rate.’ It worked. The next time the ZS
hit the rollers it was showing a healthy 170bhp and an
impressive 269lb.ft of torque. ‘I wanted a nice, flat torque curve
and I got it!’ Pete says with a grin.
Things didn’t last quite as long as Pete had hoped though, as
another head gasket failure was just around the corner. ‘I got a
bit over-enthusiastic with it and blew it again. Thankfully I was
able to replace the lost coolant and nurse it back home, driving
with a five litre bottle of water on the seat next to me.’ After a
bit of investigation, Pete found that any time the ZS was driven
with any vigour, it lost coolant. The water loss was soon traced
to a broken thermostat and a water pump that was past its
best. ‘The water pump was replaced, and I worked with Matt
to develop a pressure reader on the exhaust manifold, which
we thought might be causing the head gasket problems.’
Working on a process of elimination, Pete and Matt worked
out that the turbo’s housing was too small and restricted gas
flow. ‘The wastegate wasn’t up to dealing with the volume of
gas passing through it; we hooked up a standard boost gauge
to read the pressure and it was off the scale.’ After such
significant investment in his hybrid turbo, Pete is keen to retain
it and to look at other ways to lower pressure on the wastegate.
Deciding to try out an external waste gate, a prototype was
built up from copper piping, but proved unsuccessful. ‘It was
melted by the exhaust after 500 miles and was un-silenced, so it
was extremely noisy.’ So the next step will be for Matt to
fabricate a stainless steel version, with an external wastegate
Above: Diesels
don’t feature in
MGE often, but in
this millennium
they have rock
solid sporting
credentials.
“The cylinder pressures got so
high that the head lifted and
exhaust gas got into the coolant”
November 2011 MGE 33

DIESEL ZS
Above: Pete
started his ZS
project with track
days in mind, and
it may yet veer in
that direction. But
for now...
running off a pressure sensor in the tubing and with a restrictor
plate to reduce the surge in case too much gas goes astray.
When they get the external waste gate working, it’ll need to be
plumbed into the exhaust system or it will be way too loud.
So after an investment of over £10,000 and plenty of blood,
sweat and tears, is Pete’s ZS finished? ‘When I get the car to the
point where I can drive it flat out without it breaking, then it
will be done. I could get a larger turbo, but that would mean
more development work. Once I have got reliability, I may
consider that route, but I am not going to pursue it just yet. I
don’t think I will change the car much anyway – it would take it
over 200bhp and give even more torque than it is currently
running, but I don’t exactly need that level of performance.’
Pete’s project focus has changed as the car has developed and
although the goal posts have shifted, he’s still very happy with
the results of his efforts. ‘I originally started this to make it a
track car,’ he confides, ‘so maybe in time it will get stripped and
lowered and made more track focused, but for now I am happy
with it getting me from A to B quickly. Mind you, the day I use
“A wastegate was made
out of copper pipe, but it
was melted by the
exhaust after 500 miles”
full throttle again will be the day I grin like a kid. It will really
live up to the description that Matt gave it when he likened
driving it to a Windsor chair with an ASBO!’
Pete wishes to thank Matt Stephens (TopStar Sport &
Racing, 0844 822 7012) for all his work, Matt Reidy (Reidy
Remaps, www.reidyremaps.co.uk) and Steve Dobson
(www.stevescleenz.co.uk) for his cleaning wizardry.
Right: ...after all
the changes that
have gone under
the skin, it is time
to take stock and
let the ZS prove
its reliability.
34 MGE November 2011
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