The venerable S5x and M5x motors that have powered so many club-racing BMWs aren’t as numerous as they were 15 years ago. With so many of those straight sixes put out to pasture, the diehards had to find a replacement.
One Sacramento-based builder stumbled upon another widely available inline-six that once powered so many members of the BMW fleet. Justin Ross of Magic Developed had to consider the successor to the M5x engines, the N52, when his reserves started to run dry.
“The M54s had all been bought up by the Spec E46 runners,” said Ross, who had been feeling the squeeze. At the time, he had a motorless E46 racecar collecting cobwebs in a corner of his shop and no plan for it – until he thought of something his non-racing work had introduced him to.
A Convenient Discovery
With so many E90-generation BMWs coming to him for basic maintenance, he had gotten acquainted with the N52 which powers so many of them. “The starter on the N52 is bound to fail, and in order to access the starter, you have to take off the intake manifold. Looking at the port sizes, I figured it would make a lot more power that the 225 horsepower it’s advertised with,” he said.
“I’d seen many Nurburgring endurance cars successfully running the N52, they had their own spec class for years,” he continued. Maybe this aluminum block six had potential to be a reliable race engine with respectable power.
Price is still in its favor. Between $1,200 and $1,700 will fetch a low-mile example, and plenty are still in circulation. Bonus: they come with a new batch of transmissions which fit in the E46 chassis. “With the correct Z4 mounts, it’s a direct drop-in, and it will mate to the GS6-37 from an E90 330i or Z4 3.0si,” Smith said.
It’s almost totally modular.
“We use almost all the ancillaries in the E46 chassis. Though the N52 power steering pump is there which we fit with our own hoses to mate to the E46 rack. We also made our own upper radiator hose to fit to the radiator and lower hose to fit to the N52 electric water pump,” Ross added.
Though the motor itself is cost-effective, some of the parts used are not. The water pump is one part of this powerplant which is a definite wear item. At almost $400, it’s not cheap, and “it wears out at 60,000 miles without any exception,” Ross said.
There are other little idiosyncrasies to consider. The block is made from a magnesium-aluminum alloy which needs a special touch. “You have to be careful cleaning it; no acid, only solvent. Don’t let any water pool, either,” he warned.
It also requires torque-to-yield aluminum bolts—one-time usage—and they’re not cheap, either. “The hardware and gaskets required for the swap will run you about $400,” Ross added.
“The alusil cylinder liner on the earlier blocks can corrode – you need to watch that,” Ross added.
“The motor evacuates oil through the PCV—some motors more than others. I installed a pipe that moves the PCV to the rear of the car. Prior to that, I had to add a quart of oil every three hours since so much of it was being sprayed all over the engine bay and even in the cabin,” Smith said.
Thankfully, the list of shortcomings is short, and so is the list of necessary power-adders. Only a few bolt-ons are needed to make a proven 250-to-260 wheel horsepower: a single-stage intake from the turbocharged N54, the N54’s throttle body, and aftermarket exhaust manifold.
“Since we already had a MaxxECU in the car, we used that. It makes life easier since we’re blending different motors and chassis, but it’s still a pretty straightforward swap. The MaxxECU is lightyears ahead of its rivals in CANBUS control, and if you’re nerdy, the sky’s the limit with most protocols.”
The safety measures installed in the MaxxECU have helped the motor and given it a protected life, but that hasn’t stopped Ross from pushing the motor to points “which would’ve caused an S54 to blow,” he said.
“After we took a rock in the radiator at Circuit of the Americas, we went three hours with the water above 240°F – no problem. We also drove the 6 Hour at Utah where the oil was hovering around 305°F most of the race, and we finished in first place. We even over-revved it to 8,900 once, and it kept going for another six months!” Ross said.
“The stock radiator and integrated oil cooler work well enough,” Smith added.
“BMW moved the coolant temperature sensor to the coolant outlet, so I was a little alarmed when I first read the temperature—the sensors on the M/S motors are mounted on the cold side. There’s some variance due to the electric water pump, but I try to run it at about 210 to 220 degrees. I see oil running at 270 degress with the factory oil cooler, but Motul has confirmed this is well within the oil’s range of capabilities,” Ross explained.
It’s also quite economical—one of the biggest draws for Smith, whose venture into turbocharging had resulted in middling finishes and a hefty gas bill. “I’d been inspired by Brett Strom to swap a turbocharged four-cylinder into my car. His Audi TCR car showed me that the DI turbo motors were efficient, and would probably reduce the number of stops needed,” Smith said.
This was before Strom’s B46 project – but Smith tried the first of the DI turbo four-cylinder motors in his E46: the aluminum, open-deck N20, mated to the GS6-17 six-speed, later to be replaced by the GS6-37. At the time, the N20 was the lightest motor fitting that criteria, and Smith’s emphasis was on making a lightweight machine that was nice to its tires.
It turned out that the N20 was not so efficient without a sequential gearbox to keep it in its narrow powerband. Plus, he blew up a couple motors on 93 octane, and though 100 octane kept the N20 humming, it was pricey. “Fuel was getting expensive, and I needed better efficiency,” he said.
Smith joined Ross and Magic Developed one weekend for an enduro in their newly swapped E46. After that weekend, Smith was sold.
Following a Fellow Trailblazer
Even adding a couple of cylinders to the front of his car didn’t influence the handling much. Having a magnesium-aluminum block sheds about 45 pounds compared to the M54, and about 110 pounds under an S54—a noticeable weight difference—people coming from E46s M3s note that it ‘turns in well. I figure without the N20’s turbo ancillaries, the two engines weigh about the same,’ Smith added.
Smith, always concerned with weight, figured that the N52 would weigh about the same without the Accusump he’d had on his M20 and the turbo-related bits. He believed lubrication could rely entirely on an (F8x M) S55 oil pump.
Not only was it a poor fit, the pressure was still dropping too much under braking and around left-hand turns. He turned to Ross for a solution. Ross built a baffled pan for Smith, who decided to mount an Accusump in the footwell and run an extra quart of oil.
Oiling issues addressed, he started seeking out easy power adders. One interesting feature with the N motors is its Valvetronic system, which is infinitely variable. Adding Modified Intake Lift Valvetronic (MILV), alters a piece of the valvetronic hardware which results in additional lift on the intake side and has been shown to increase top-end horsepower.
Like Justin, he tried the N54 single-stage manifold at the top of the rev range and the expense of the bottom end, but he eventually switched to the triple-stage from the 330i, which gives more midrange. “I didn’t need high-rpm power for ST4 on Maxxis or other +1.6 tires. Instead, I targeted 230 to 240 horsepower with a broad powerband,” he elaborated. Again, it was low weight and fuel economy—he was happy short-shifting with the extra grunt—which took precedence.
At that power level, it’s been fairly economical. As he learned at last year’s Sunchaser 6 Hour, he was able to get away with consuming as little as 10 gallons an hour when aided by yellow flags.
The swap left Smith satisfied, successful, and solvent. No big-ticket items looming on the horizon, the N52 has simplified his race weekends and given him a chance to refine the ST4 car he’s done so well with. There’s always been an assumed risk running some of BMW’s punchier S5x and M5x motors, but the last stab Munich made at the atmospheric inline-six proved that most of the high-dollar performance they offered doesn’t need to cost so much.
