Tweaking and tuning an MG is nothing new; it’s what created the company. But tuning a diesel MG? That’s something all together different, says Adam Sloman. The MGB owners won’t be happy…
When the MG ZS was launched back in 2001 it was joined by a diesel, the L-series Turbo diesel. First seeing use way back in 1995, the L-series was already six years old when it made its debut in the MG Zed range. However, the mix of impressive handling and diesel economy broadened the appeal of MG’s mid-liner and it’s gone on to become popular with tuning enthusiasts. Enthusiasts like Pete Cowlishaw, 29, from Bristol.
“I got the car as a 22nd birthday present,” recalls Pete, in 2004 when the ZS was less than a year old. “I had to wait a while for the insurance to become a bit more reasonable before I could start to modify it.” Initially, Pete upgraded the air filter, fitted a decat pipe to the exhaust system and increased the turbo’s boost to 19psi, improving drivability no end.
In 2007 the gearbox was rebuilt, “The ZS gearbox cannot cope with much more torque than about 250lb ft. To extend the life of the box, I fitted steel caged bearings, a Quaife ATB differential, together with an uprated clutch. The L-series is a heavy engine and it’s got rid of the understeer. I can now keep my foot more planted as I corner or change direction.”
The turbo was then reworked with new, larger turbines. “The compressor is from a Land Rover Td5 while the exhaust is from a Saab.” MG tuning specialist Matt Stevens fitted the turbo, gearbox and injectors. “The car was really smokey – you had to be gentle pulling off before the turbo spooled up, if you put your foot flat to the floor, you couldn’t see cars in the rear view mirror!” The high levels of smoke were traced to faulty fuel injectors, so the ZS returned to the workshop, where its fuel levels were reduced. “I then replaced the injectors. I combined the original ones from the ZS with older Rover 200 ones.” adds Pete. “The result was 50lb ft extra torque at 2,500rpm not 3,000 as before, and another 10bhp. More significantly, there was next to no smoke when on the road.”
The car then developed head-gasket failure. “It suffered from head lift – the cylinder pressures got so high it forced the head up and the exhaust gases got into the coolant galleries.” adds Pete. The head gasket problem saw Pete consider further modifications. “I spoke to Matt at length; one area we talked about was the intercooler. Matt believed the car could do with something more substantial, since the original MG Rover one isn’t all that great.” The exhaust manifold was showing temperatures of 850 degrees Celsius and Pete felt things were getting a little out of hand, though he was pleased with the projects progress. “It was developing 160bhp and around 220ft lb of torque”. A boost leak from the intercooler caused him to think his custom turbo had failed, which led to a further chat with Matt. He then worked out the most efficient way to route the pipe work to the intercooler and Pete ordered the necessary parts.
A new MAF (mass airflow meter) gave an extra 10ft lb of torque and another 5bhp, and the voltage to the fuel pump was then increased to improve the fuel’s flow rate. The ZS was now developing 170bhp and an impressive 269ft lb of torque, compared to the original 111bhp and 192lb ft. Annoyingly, another head gasket failure was just around the corner. “I got a bit over-enthusiastic and blew it again!” The water loss was soon traced to a broken thermostat and a water pump that was past its best and Pete and Matt worked out that the turbo’s housing was too small and restricted gas flow. “The waste gate wasn’t coping with the volume of gas passing through it.”
After spending almost £11,000 on improvements, including significant investment in his hybrid turbo, Pete is keen to retain it and look at other ways to continue the car’s development. “I need to lower the pressure on the exhaust manifold, so I’m considering an external waste gate.” But, as with any project car, it’s never finished. “For now I am happy with it getting me from A to B quickly!” says Pete.
Pete would like to thank: Matt Stevens for all the dirty work, Matt Reidy for the remapping and Steve Cleenz Car Detailing.