Mike's 128i (HPDE & DD)

[blnk-128]

First time at the Glen since doing many of the mods. The LSD with shorter gearing and stiffer suspension more than offset the switch from v730s to RS4s. I still need to add oil cooler ducting, as the day warmed up I was limited to 6500 rpm to keep temps below 280.

Notable opportunities are...

1. Brake harder and longer into 1 to get on gas earlier up the hill
2. Shifting halfway up the esses is worth about 2 tenths
3. A shallower entry into the bus stop helps carry more speed through the bus stop
4. Turn in earlier for 5 (mislabeled as 6 in the video)
5. Brake later for 6, leave in 4th to mitigate oil starvation
6. Brake later and harder for 7

[edycol]

Originally Posted by blnk-128

First time at the Glen since doing many of the mods. The LSD with shorter gearing and stiffer suspension more than offset the switch from v730s to RS4s. I still need to add oil cooler ducting, as the day warmed up I was limited to 6500 rpm to keep temps below 280.

Notable opportunities are...

1. Brake harder and longer into 1 to get on gas earlier up the hill
2. Shifting halfway up the esses is worth about 2 tenths
3. A shallower entry into the bus stop helps carry more speed through the bus stop
4. Turn in earlier for 5 (mislabeled as 6 in the video)
5. Brake later for 6, leave in 4th to mitigate oil starvation
6. Brake later and harder for 7

Ducting might be an issue here.
I track my 2011 328 xDrive at High Plains Raceway in Colorado. High altitude is a cooling nightmare. The track sits at 5,000ft and without an oil cooler, hitting 300f in summer takes 2-3 laps.
I installed a set up from N54/55. Nothing else. Regular thermostat, regular oil cooler. I have never gone over 260 in the summer at 101-102f at that altitude. At that altitude, it is harder to cool off the engine at 60 degrees than in the middle of the summer in Miami.
My setup, on the other hand, has that duct that comes on the E90, which splits between the duct for brakes and the duct for the oil cooler.
Also, I run heat during tracking, full heat and maximum fan strength. Also, coolant is only 10% concetrated for better heat dissipation.

[blnk-128]

Points well taken on the ducting, and I'm happy to say I've created a very solid inlet to my oil cooler. It fits flush with the bumper grille, and maintains a few key characteristics.

1. Inlet area smaller than the oil cooler face.
The air rushes in the inlet, then you expand the ducting gradually to the oil cooler so the volume increases. This volume slows the air down, increasing pressure at the face of the cooler. This increases the pressure delta on the face and exit of the cooler, driving air through it. My inlet area is ~33% smaller than the heat exchanger area.

2. Gradual slope.
The maximum recommended expansion rate is 15 degrees, which I set my lower plate to. This keeps the air attached to the walls and prevents it from becoming turbulent.

3. Leaving a gap to the radiator.
Because of my damaged undertray/fender liners, leaving a gap to the radiator reduces the pressure required to force air through the oil cooler. This gives the exiting air an opportunity to be sucked away to a low pressure zone, potentially one below the car. If my radiator area were fully sealed, the oil cooler should be as close to the rad as humanly possible.

4. Completely sealing the ducting.
Using a flashlight, I tested to ensure there were no air gaps between the inlet ducting and the oil cooler face. Aluminum tape is on the way to cover the seams of the inlet ducting itself.

5. Inlet faces the direction of incoming air.
Self explanatory.

I'll be shaking this down at Summit Point this weekend. If temps continue to be higher than acceptable, I'll explore getting a new undertray, fender liners, adding exhaust ducting, and potentially a hood vent. Ideally I'd like to stabilize around 250F.

[blnk-128]

The inlet ducting helped me get a few more full throttle laps, but it wasn't enough to let me run a full session at full tilt. It was 85+ ambient in the afternoon and I had the heat on full blast, but temps still climbed into the 275+ range.

My next step will be constructing exit ducting between the oil cooler and the power steering cooler + radiator. These sub 2" gaps are allowing high pressure air from the front bumper to sneak into the low pressure area behind the oil cooler, preventing maximum pressure differential for the oil cooler.

As another bandaid fix, I'm switching from Liquimoli Leichtlauf 5w-40 to Redline 10w-40 for the track season. This should give me more protection at higher temperatures and allow for two events between oil changes.

If the exit ducting isn't sufficient, the cheapest practical option would be going with a race louvers hood vent. The smartest thing to do is invest in sealing the floor with a new undertray and fender liners to maximize the vaccum effect. This would increase the efficiency of the hood vent as well. For now, I'm content to go one step at a time.

Summit Point Main

Annoyingly, my Mac virtual machine setup stopped connecting with AiM data while at the track this weekend. I wanted to test an extra half quart overfill on top of the 1.5 qt overfill on Sunday afternoon, but I realized I needed to start from a fresh baseline to actually have meaningfull results. I'll need to plan a track weekend where I drive on Saturday with a 1qt overfill, then do an oil change Saturday night to test a 1.5qt overfill on Sunday.

As for the driving, I PR'd by 2.6s despite not putting together a quality lap. As the RS4s have heat cycled out, they've introduced a tremendous amount of understeer due to reduced weight transfer. If I stay on them, I either need to add rear brake bias, add a rear sway bar, or reduce load transfer up front through weight management (i.e. sunroof delete, carbon hood, A/C delete, etc...).

[blnk-128]

Let's set some context, what is brake bias?

Brake bias is how a car splits its stopping power between the front and rear wheels.

There are two ways that you can mess up splitting the cars stopping power.

1. Too Much Front Bias (e.g., 70% Front / 30% Rear)
   The front tires do all the heavy lifting.The car becomes very stable and safe in a straight line.It will refuse to turn easily into a corner (understeer). Hard braking will lock up the front wheels.
2. Too Much Rear Bias (e.g., 50% Front / 50% Rear)
   The rear tires are doing the heavy lifting. The car becomes very unstable, and the back wants to come around to the front (oversteer). Hard braking will lock the rear wheels, similar to pulling the handbrake.

From the factory, BMW wants its cars to understeer as it's easier for drivers to intuitively control. This is not desirable on track. As such, many builders/racers look to shift their bias rearward. This promotes corner entry oversteer, which is faster, and allows for slightly shorter braking distances, also faster. Go to far however, and the results can be disastrous if you're not expecting the rears to lock up.

Here is a summary of what causes a need for bias to move in one direction or the other.

Mechanical Changes That Shift Optimal Bias Forward (and vice versa)

• Grippier tires
• Increasing COG
• Shortening the wheelbase
• Moving weight forward in the car (i.e. battery relocation)
• Increasing front downforce relative to rear downforce

Now here's a summary of how we can control brake bias on one axle.

Mechanical Changes That Increase Bias on an Axle (and vice versa)

• Higher friction brake pads
• Larger brake rotor diameter
• Larger caliper piston area
• Master Cylinder proportioning valve changes (won't be covered here)

On the BMW 1 series cars, both the 128i and 135i use stepped-bore tandem master cylinders. This means both the front and rear circuits always see the same brake pressure. The brake pedal acts on the first (larger) piston, which transfers a fixed amount of brake pressure (i.e. 80 bar) to the front brake circuit and 80 bar to the secondary (smaller) diameter rear circuit. I've attached a visual that made this clear to me. As such, changing between these master cylinders will not adjust brake bias.


This research brings me to my reason for going down this rabbit hole. After switching to my current braking setup, I've experienced a tremendous amount of understeer and it's obvious why after looking at it. I introduced a massive increase in front brake piston area and rotor size, with only a small piston area increase in the rear plus additional pad friction to counteract it. These changes moved my bias 1.2% more forward than BMW shipped from the factory, so my rear tires are underworked on track. Using a brake force calculator, I've identified complimenting the F3x front brakes with the F3x 44mm rear brakes is a way to shift my bias significantly rearward. I can achieve this while running a lower friction pad, which gives me the opportunity to move bias even more rearward if desired. It's almost like BMW designed these two to work together from the start. This ultimately arrives at a 62% front bias, which is 2.5% less than factory and 3.7% less than my current setup. This is right in line with the M235i race car which runs on slicks, so i expect to be in a safe range.



I considered the 135i rear setup as well, however it didn't provide enough flexibility to shift my forward bias lower than 63.8%. 335i brakes would've been a good option as well however Hawk doesn't make DTC60/70 pads for them.

The main downside to this setup is the weight. In total I've added ~13lbs in unsprung weight to the front and rear axles, which comes with significant performance losses.

I'm using the adapters from VYS garage to mount the calipers, DTC60 pads, rotors from an e60 that allow me to keep the handbrake, and junkyard calipers. All in cost will be ~$1000.

[jelenp]

Have you upgraded the fan shroud and fan on your car? One of our local buddies runs a M5/M6 1000 watt fan in his 135is with the 1m shroud and fan relays. That might help a little with your temps, haven’t done it yet myself but your thread is so useful might as well drop this in