The block itself was machined to accept 12mm head stud inserts. This is after evosport discovered the stock 10mm studs could allow the head to lift slightly and cause gaskets to blow under pressure. Fortunately, the bigger studs allow a greater clamping force and are less prone to blow gaskets.

Before it's clamped down the head received a mild porting to clean the airways.

The stock 3.2 cams were then refitted because Gary found they work well in turbo applications, where most aftermarket profiles sacrifice boost with too much overlap and exhaust timing.

The turbo

As we mentioned, the turbo is a Garrett GT40R. It was chosen because its size gave the best combination of manifold pressure, volumetric efficiency, compression ratio and airflow. It was mounted on an Active Autowerke cast exhaust manifold and fitted with a Tial wastegate. The engineers at evosport then fabricated a custom exhaust using their own downpipe and a Remus muffler. The 3" pipe uses V-bend flanges so there are no gaskets to leak. It also has two performance cats and all the stock emissions gear. And because the car was originally an OBD1 325i it was thought it could pass the visual and tailpipe emissions tests.

One reason the car had running problems was it arrived at evosport still using the OBD1 computer. This was always going to be discarded, especially when the tuner works closely with AEM to develop Euro applications for its standalone EMS computer. They would also fit AEM's four-channel CDI ignition system, plus a 3.5bar map sensor and intake air temp sensor.

Having worked with AEM for a while, evo has a wiring harness that allows the EMS to plug into the factory wiring. Then they wire the CDI directly to the six ignition packs and it's ready to go. The company even has a "plug-n-play" EMS for OBD1 and OBD2 cars that doesn't require the CDI system. It's sold with a base program to get the car running and you can email your log files to Gary, who will check and correct if necessary.

The bigger turbo would require more fuel, and Gary calculated that 650cc injectors from RC Engineering would do the job. At this size the injectors would be working at 60% efficiency, rather than smaller injectors where the duty cycles are strained to maximum capacity. However, they required a 250 lph high pressure fuel pump and larger fuel lines in a modified fuel rail.

To keep the turbo efficient, it would also get a GReddy Type-S blow-off valve and an air-to-water intercooler (chargecooler) with a custom heat exchanger at the front of the car.

The final mods before the car could be road tested were a custom Clutchmaster clutch in the stock M3 five-speed and a Quaife diff to distribute all that power. "The stock tranny is holding up well despite us not taking it easy. In fact, I've driven the piss out of this car and it's doing fine," Gary admitted.

So with a basic program in the AEM EMS, Gary could start road testing. He aimed for a 15:1 air/fuel ratio and gave the ignition lots of advance to make it smooth. He reckons the car will return about 20mpg on the freeway, but you can forget that if you get on it. That's because on boost, Gary was more concerned with detonation and spooling the turbo.

Tuning

With the car running cleanly on the road, it goes on the dyno to be tuned. Gary looks at the increase in volumetric efficiency at different boost levels and starts plotting curves up to 18psi, although the engine will only run to a maximum of 12psi. It's possible to plot up to 35psi with the EMS, but he prefers to concentrate its processing power on the area he wants.

With the curves plotted, the car goes back on the road for verification and is finally handed over to the customer. It's then his job to drive it in traffic with the a/c on and report back any bugs that will be ironed out. Fortunately, these are rare since Gary claims, "The AEM EMS is well suited to daily driving thanks to its continuous Lambda feedback, sophisticated idle control, as well as air temp correction, coolant temp enrichment and knock sensor feedback. You can program it to adjust both ignition and fuel under these conditions. This means the standalone won't remove the pleasure of daily driving your car."

The EMS also allows Gary to plot the boost curve against road speed. This has enabled him to increase boost as the car's speed increases. So the faster you go, the faster you go. However, he admits that even at 12psi the car is almost too powerful, but it's a very exciting car to drive as a result.

So how much power does it have? Well evosport claims 451hp at 6400rpm and 410 lb/ft at 5600rpm at the wheels.

These are very respectable numbers but they're going to cost you. An engine to this spec could be in the region of 20 grand - that's about $6500 for the motor, $6000 for the turbo conversion, another $3200 for the AEM EMS, plus labor. "The same results could be achieved for less," Gary explained, "but we build in safety margins to provide durability and daily drivability. Our engines won't throw a rod and leave you stranded."

With so much work done to his car, Ivan has no intention of selling the old girl yet. In many ways he's still getting used to the power and intends to spend the next 12 years enjoying it.

Guinea pig I had reservations about this BMW Convertible turbo. I know convertibles are heavier and the car looked close to factory. However, I'd heard stories about it annihilating other Evosport cars on the freeway, including their E60 M5, so I should have known what to expect.

Anyway, Gary took me for a spin on the way to our photo location. During normal driving the car was surprisingly smooth and unflustered. Admittedly, it possessed a deep groan that would intimidate a small child. I also noticed the suspension was firm, but not too tight. However, the interior was absolutely mint, and the re-upholstered Sparcos were astoundingly supportive.

And then it happened. We encountered a clear straightaway near Huntington Beach and Gary opened the throttle. I both felt and heard the rear tires lose traction and spin for half a second. Once we gained traction, we disappeared into what had once been the distance, leaving traffic behind us.

When Gary shifted, the noise of the blow-off valve boomed into the open ****pit, making itself heard across the city. Sadly we weren't able to do any high-speed freeway runs but the car was quick when launched off the line. Very quick. It definitely needed more traction to get away fast, but wheel spin can be entertaining in its own right. Sam

Euro Tuner Mag