How did our BMW 435i’s new oil-control measures work at Daytona?

Of course, you have questions, so here are the answers, to the best of our ability to address them this early.

Since we had the bottom of the engine apart, we threw in new rod bearings. BMW Sixes have a bit of a reputation for rod bearing wear, and with the known oiling problems of the N55 engine, we figured it was good preventative maintenance on our 73,000-mile engine.

We did find some scoring on a few bearings–most marks were superficial, but one had some texture to it–but overall the bearings looked … okay. Not great, but not dire.

Anyway, new bearings were the order of the day, since, repeat the BMW owner’s mantra with us: “while we were in there … .”

And since we had the opportunity for a track day lined up immediately after replacement of those bearings, of course we were concerned about break in.

“With bearings, we throw them right on the dyno or right on the track. No worries,” was the assessment of BimmerWorld’s Phil Wurz. “With something like rings, you need some break-in miles for them to properly seat, but bearings are good to go right away in our experience.”

You don’t need to tell us twice. Homeward to Daytona (both our house and the track).

Of course, the first session on track was a bit nerve-wracking, with one eye constantly on the iPad showing the oil pressure and temperatures through the MHD tuning app.

To recap, after logging dangerously low oil pressure readings under braking at previous track tests, we opted for BimmerWorld’s N55 oil control kit, which leverages the hardware that was factory-installed in the N55-powered M235i Racing model.

This track-only model–still seeing action in the SRO TCX class–uses the baffled oil pan from the M-spec S55 engine along with a secondary oil scavenge pump driven by a shaft off of the main oil pump. The scavenge pump grabs oil from the front corners of the pan, as well as from the turbo drain, and deposits it in the main sump well in the rear.

BimmerWorld’s James Clay described their own experiences with the pair of N55-powered M235iR racers they owned: “Absolutely bulletproof. We had motors with 60,000-plus race kilometers on them with zero issues.”

Clay also praised the similar arrangement in their current GT4 race cars: “The GT4 cars aren’t dry sumped. They use basically the same arrangement as this.”

So, our setup had the pedigree, but one eye was still fixed on the gauges. And … it was all fine. No indication of pressure drops, oil temps around 265 even after several back-to-back hot laps, and coolant temps kept in check during continuous lapping as well.

A review of the data log confirmed our real-time monitoring. Where oil pressure was previously dropping to below 30psi under braking, then showing signs of cavitation upon returning to throttle, with our new bits in place, the pressure never dropped below about 50psi under any circumstance.

With Daytona essentially being a huge, extended dyno with interspersed hard-braking areas, we feel like this was a good test of the ability of the oil system to keep up with demand, and it seems to have passed with flying colors.

Since the system effectively adds no horsepower, classing is unchanged for NASA TT, which is still based mostly on weight, power and tire size.

These reliability mods will bump us from the Sport division to the Tuner division, which allows alternate oil control. The good(?) news here is that the bump in prep levels also opens us up to a few more opportunities to solve other problems.

Tuner also allows urethane suspension bushings, which came in handy when we noticed our front trailing arm bushings were absolutely smoked. (While at BimmerWorld, we had to drop the front subframe to access the bottom of the engine.)

Luckily, they had the proper set of Powerflex bushings on the shelf, ready to slap in. Well, more than a slap, more like a move involving a 15-ton press, but you get the idea.

Anyway, solving a problem like that with a performance part is doable in Tuner, while in Sport, we would have had to replace our worn OEM bushings with identical–and costly–OEM bushings.

Tuner also opens us up to the possibility of a true limited-slip differential, although this is a bit more complicated matter as the stock ring gear is welded to the carrier and requires machining to remove.

But, look, now scope creep has entered this story. We’ll talk more about all that stuff as the project progresses. For now, we’re happy with our new oil and new front bushings.

The car is a real joy to drive, especially now that we don’t have to worry about the engine lunching itself unexpectedly. It just turns lap after lap with the gauges in the green so we can just focus on driving.

Our VBox data for one of our faster clean laps looked pretty good, and the car felt stable and predictable in the high-speed braking areas of DIS where you’re hauling down from near terminal velocity–particularly in Turn 1, where braking will occur on various surfaces and slopes as you exit the tri-oval onto flat ground and have to brake through the transition between the two. The car stays stable and solid here.

But the real thing to notice in that Circuit Tools screen capture is just how chill everything looks inside the car. Part of this is the nature of Daytona itself.

Although it’s big, Daytona is very much a momentum track. The key to going fast is doing the absolute minimum amount of work possible because every time you make friction, you slow yourself down. So, you won’t see a lot of sawing at the wheel or toss-and-catch or making dramatic control inputs to force weight transfer.

And the BMW 435i is a companion particularly well-suited to this approach. It loves a calm hand, and overdriving this rather heavy, relatively underpowered car just slows you down.

Best of all, it’s still a true street car. We run the a/c with the windows up on grid until the very last second, and as soon as we get back home, we pop in the stock seat and street brake pads and cruise down to the Tastee Freeze for a frozen banana in complete comfort.

The only downside at Daytona was a LOT of fuel consumption. Our typical session consisted of an out lap, six hot laps (admittedly with a lot of traffic at the well-attended TNiA event) and a cool-down lap. This used around five gallons of gas, which seems like a lot for a 300-horsepower car.

Then again, Daytona is negotiated at full throttle for the better part of two minutes of the two-and-a-quarter-minute lap, so maybe it’s not entirely surprising.