E89 Z4 Track-ready Sleeper Build

[Asbjorn]

UPDATED overview:

OLD and now out-dated introduction:

Is this a stock Z4?

Well, almost... (click to enlarge)

TL;DR - Summary of highlights (added October, 2018, after almost finalizing the build)

Feature	Products used	Reasons	Result	Link
Semi-dry oil sump	Custom oil pan modifications (baffle, oil inlet, oil outlet), oil pump, on/off switch hidden in cabin	Avoid oil starvation on track	Seems to be working well. No problems so far (edit 9/2019: turned out I was loosing oil pressure on left hand turns with slicks, still working on this)	Installation Thread on topic
Increased power and upgraded turbo etc	VTT GC lites 2.0, @BQTuning, 7in FMIC, PR ignition, S65 injectors	Wider and increased power band, better turbo reliability (running only 18-20psi on +25psi capable turbos)	100-200km/h in 9.4s	Link
Upgraded cooling	CSF Coolant radiator, additional radiator, larger stock location oil cooler, additional oil cooler installed on drivers side. SSP DCT oil cooler.	Avoid limp mode on track. Local climate is hot and humid, with summer highs exceeding 100F	Coolant cooling still being optimized. Currently hitting 106C on track. Iats also sometimes exceed 130F. DCT and engine oil temps are OK. (Edit 9/2019: still working on this)	Oil cooler install Optimizations Testing results Update
Stiffer bushings, chassis, dampers and coilsprings	Bearing RTAB, BW solid subframe mounts, PowerFlex diff and rear lower control arm bushings, front M camber arm, front M tension strut with bearing kit, Eibach prokit (rear only), Koni FSD dampers, Ground control camber plates, H&R sway bars (front one modified to be adjustable) CIDEP chassis bars	Better steering feel, easier to place car on track, easier to control acceleration and braking	Car is more fun to drive on good roads and more predictable on track. Car is less fun to drive on bad roads as the front end bottoms out more easily.	Eibach install Track tour of China CIDEP bars
Limited slip differential	Quaife ATB	Better control-ability in dry. Ability to drift in rain.	Car is more fun to drive, and easier to control on and off limit. Differential locks faster in the dry and is now also able to lock in the wet.	Install Diff bearings went out
Lightweight DCT flywheel	M4 DCT flywheel	Faster rev changes on up and down shifts. Less strain on drive-train. Engine sounds more race-car-ish.	Car is more fun to drive fast and sounds better. D-mode is rendered unusable due to flywheel chatter in high gear, low-rpm, high load situations.	Installation
Upgraded brakes	PB brakes, custom cooling ducts, Redline brake fluid (recently swapped to endless which seems to perform better)	Reliable braking on track, slightly more front biased brake balance, OEM look.	100% satisfied, race pads are needed for track use.	PB Installation Custom brake cooling ducts
Sleeper look	Custom forged wheels in OEM design, brakes colored to match color of car.	To fool the enemy (in particular M and P cars attending track events)	Only very few people can tell this car is not a standard Z4. Most people even think the brakes are OEM. Absolutely love it.

[TBODY] [/TBODY]


Frequently asked questions

If you wanted a track-ready car, why didn't you get an M-car?
- I like 2 seat roadsters.

If you wanted a track-ready roadster, why didn't you get a Boxter
- I don't like the Boxter. Also it is not a roadster.

Where's the M-stripes, carbon bits, stubby antenna, wings, fenders, LCI parts, lowered suspension etc that other track builds feature?
- With this build, I went the sleeper-route. I want to surprise people at tracks.

Why don't you get a dedicated track car, get a racing license, and leave the Z4 stock
- At the moment, I cannot think of anything that interests me more than beating M and P cars at time attack events in a stock looking Z4.

Why is your car only slightly faster than an M4 100-200kph.
- Because it is all I should need to beat those cars on track, and I already love how fast it is. I am not interested in drag racing, and reliability was already a concern at stock power level with this car.



Intro (original text from early 2018 - now outdated)

This build thread is about a Z4 35i DCT I bought back in 2012 working as a foreigner in China. Over the years I have become more and more interested in cars, drifting and doing track days. Now it is time for the car to become similarly interested in these activities.

The main purpose of this thread is to describe the changes done from the beginning of this year as listed in the picture above. The build is expected to be finished in June, and I will try to share my experiences here as I progress.

The car has been running stock during most of its life, featuring only de-catted miltek midpipes, ESS tune and non-RFTs. Given that the roaster market is very small in China, and since I still love its design, the Z4 is still the most desirable/cost effective fun car for me to own here. I have therefore decided to see how far I can take it.

Goal for acceleration/braking: Street, drift and track-readiness. Responsiveness, predictability and reliability trumps power. Power goal is somewhere just above a stock M4. I don't drag, and track-reliability is important to this build.
Suspension goal: Street, drift and track-readiness. Lowering not an option because the car needs to work on Chinese roads. I also think M sport suspension is too harsh for street use here. (I later decided against this and installed Eibach pro-kit in order to improve stability above 150km/h)
Interior/exterior design goal: Sleeper / OEM. I do not want the car to look modded at all.




Complete list of mods, and timeline

Here is the complete list of mods as well as some stuff I am not changing that may surprise


Engine N54
Stock silencer - because it is silent. Have yet to see proof that it significantly limits power below 500hp.
VTT inlets - installed in May
VTT GC lites 2.0 - installed in May (rear WG stuck open on OEM turbos).
VTT Alu hot-side charge pipe - installed in May (these were later found to be leaking due to over-heated hoses, and additional alu shielding was added)
Custom-made race-catted downpipes and new O2 sensors - installed in May (These were later replaced with OEM catted downpipes in order to be able to pass annual inspection)
Miltek de-catted midpipes - installed
VRSF race FMIC - installed in May (This was later replaced with 7in nonHD FMIC)
ER charge pipe (DV, Z4 type) installed in May
Turbosmart Kompact DVs w/ Z4 kit - installed in May
CSF coolant radiator - installed in May
High speed oil cooler fans - installed in April, then removed again in July.
NGK 95770 spark plugs - installed in June
S63 injectors - installed in May
Precision Raceworks ignition - installed in July
VTT PCV valve and BMS oil catch can - installed in July.
"Semi-dry oil sump" with additional oil cooler and oil pump connected directly to baffled oil pan - installed in May
n20 tmap sensor - installed in October to avoid occasional 2ABC codes

Transmission DCT
M4 flywheel - installed in April. Adds a form of chatter in certain driving situations, and is not recommended for daily driven Z4s.
SSP DCT oil cooler and oil pump connected directly to the SSP DCT oil pan (turned on at track only) - installed in June

Differential/sub frame
New OEM rubber giubo - installed in May (I wanted the OEM alu version, but wrong part was shipped by ECStuning. Currently waiting for better options to hit the market)
Powerflex subframe rear inserts - installed in May, then later replaced with bimmerworld solid mounts in October
Powerflex diff front and rear poly bushings - installed in May.
Quaife ATB differential - installed in May.

Suspension front
Koni FSD - installed
Eibach pro kit - installed
M front tension struts - installed, later added bearing kit in october
M front wishbones - installed
Ground control camber plates - installed in August
H&R 28mm sway bar - installed in April

Suspension rear
Koni FSD - installed
Eibach pro kit - installed
M RTAB + RTAB limiters - installed in May
Powerflex lower wishbone outer bushing - installed
Powerflex sway bar bushings - installed
H&R 21mm adjustable sway bar - installed in April

Chassis strengthening
CIDEP front strut tower bar
CIDEP lower bar kit (see picture below)



Brakes (changed brake bias from 67/33 OEM to 69/31)
Front PB big 6 pot, 356mm floating, no PB logo, OEM colors - to be installed in March
Rear PB small 6 pot, 330mm floating, no PB logo, OEM colors, E-brake - to be installed in March
EBC yellowstuff - installed in March. Switched to PB race pads for better track readiness.
Redline RL 600 brake fluid - installed

Wheels OEM (car was delivered with cast 293 wheels from factory)
Rear 18inch custom made 293 replicas, forged aluminum, 18x9.5 ET40 (stronger, wider, yet lighter than OEM)
Front 18inch custom made 293 replicas, forged aluminum, 18x8.5 ET35 (ET changed compared to OEM in order to reduce kingpin offset)
Rear tires 265/35
Front tires 235/40

Exterior
None

Interior
Custom made sport seats in OEM color prepared for 4 point racing harness. (These were later removed again, please jump to page 4 to read why)

 

[Asbjorn]

Brakes (changing brake bias from 67/33 OEM to 69/31)
Front PB big 6 pot, 356mm floating, no PB logo, OEM colors - to be installed in March
Rear PB small 6 pot, 330mm floating, no PB logo, OEM colors, E-brake - to be installed in March
EBC yellowstuff - to be installed in March
Redline RL 600 brake fluid - installed

Today the PB brakes finally went in. Unfortunately my first attempt failed last week. The EBC yellowstuff DP4005R I sourced myself, turned out to be too thick (18.5mm) and the disc wouldn't fit. I have now ordered DP4032R instead. DP4032R is basically the same pad type but 16mm instead of 18mm. However, as lead-time turned out to be 3-4 weeks, I decided to grind down the DP4005R pads as a temporary solution to finish the installation now.

The install itself went fairly smoothly, and I would say most shops should be capable of doing the job. Unfortunately I got a parking brake fault (yellow light) while testing the e-brake (not at first, but after testing it several times in a row). I believe this is because my cars electronic parking brake module is faulty. I have had problems with it before and basically never use it anyway. I just need it for annual inspections. More time is needed to find a permanent solution, and I do not blame the brake kit or installation process for this.

The purpose of this upgrade is to achieve a track-ready brake setup that looks completely stock to the untrained eye. My hope is that if anyone ever notices it, they'll think: "Wow, Z4s really come with nice brakes". This is why I picked the "no logo" option for the calipers, and had the hats colored silver to match the wheels. I picked bronze as the caliper color, because I think it matches the color of this Z4. I admit dark silver would have looked even more stock.

The setup I have chosen should be track-ready (in terms of 30min sessions), because it can handle more heat than the stock setup. Main reasons are:

1) The brake discs are completely floating, larger and features directional inner cooling vents.
2) The pads are larger, and the compound can handle much higher temperatures compared to OEM.
3) The brake fluid can also handle higher temperatures, which delays pedal fade.

Although both front and rear calipers use 6 pistons, only the front piston area was increased compared to OEM. This basically gears down the brake pedal, leading to a pedal that travels a bit longer compared to stock. My initial impression is that this is absolutely fine, and even makes left foot braking a bit easier. I picked 6 pistons over 8 due to better reliability and responsiveness on the track. 8 pots look better of course, and you can also get larger looking 6 pistons, but I think these are perfect "sleeper" calipers.

With this setup I also changed the brake bias from 67/33 to 69/31. I will try to evaluate at a later point if this was beneficial or not.

I would like to thank Dan from PB brakes for offering exceptional support and advice during the entire buying process.

 

[NoQuarter]

Those seats turned out great!

 

[Asbjorn]

Those seats turned out great!

Thank you! What is great about these seats, is that people think they are stock. They also feel great for spirited driving and in corners. They are stiffer and offer better car and road feel.

However I do not recommend this particular seat design for the Z4 - as it turns out, the shoulders are a bit too wide. Also I would say racing seats in general are not recommended for daily driven Z4s. They take away a lot of practicality and comfort.

 

[fmorelli]

Asbjørn, your car is coming along nicely. I'm amazed at what you are doing while retaining such a seemingly stock look. Definitely the most understated sleeper Z4 I've seen. Wait until all the other bits go in. Please keep the posts up!

Are you planning to swap out the electronic brake module? What problems did you have with it before? I'm curious as I don't recall seeing anyone post issues with that part on a Z4 ...

Filippo

 

[Asbjorn]

Asbjørn, your car is coming along nicely. I'm amazed at what you are doing while retaining such a seemingly stock look. Definitely the most understated sleeper Z4 I've seen. Wait until all the other bits go in. Please keep the posts up!

Are you planning to swap out the electronic brake module? What problems did you have with it before? I'm curious as I don't recall seeing anyone post issues with that part on a Z4 ...

Filippo

Thanks Filippo

We swapped out the electronic brake module yesterday, and that solved the parking brake problem. The part was updated several times according to realoem, so this may tell us something. We never learned what went wrong with it. It came out of the car looking brand new...

We also did some coding yesterday and managed to remove the seat and airbag warnings caused by the sport seat installation. Unfortunately I was not able to record what was changed, but I can report that the changes required are specific to each BMW series and model trim. I did not succeed just by copying what 3-series owners did, and had to arrange remote coding.

Anyhow, am very happy that all warning lights are now gone.

 

[Asbjorn]

Transmission DCT
M4 flywheel - to be installed in April (others should consider MFactory instead)
ESS tune (no change, works well)
Considering an oil cooler upgrade, but never had problems with the DCT.

The installation of the M4 flywheel has now finished. I also tried installing UUC black line transmission mounts with cups. However these went out again after only one day of testing. They simply cause too much NVH, even without the cups installed (we tried). The problem here is that the M4 flywheel itself already causes additional vibrations, and with the stiffer mounts, the car simply sounds broken during city speeds. During spirited driving, or when just revving in neutral, the NVH is awesome and makes the car sound and feel very aggressive and racecar-ish. But it just wasn't worth the trade off in comfort for me. I wish I could turn it on and off with a button, but since I cant, I am leaving it off. (Edit it later turned out one of the engine mounts had failed, and I did not check if the transmission mounts were torqued correctly, so I might give them another go another day)

Now I am just running OEM mounts combined with the M4 flywheel. As documented elsewhere on Spoolstreet, the M4 flywheel is a much lighter design, and it offers faster rev changes. This is pretty awesome!

The car sounds and behaves in a more sporty way, and also feels faster and more responsive. The downsides are added vibrations under load at the lowest RPMs. Worst case is driving uphill in 7th at 68kph. The solution is to drive one gear lower than usual in such situations. Honestly it makes D in normal mode annoying to use, because it up-shifts very early to 7th. Everything is fine in S + normal or above. I usually drive in DSC_off + M as it provides the most communicative steering feel, without the sports throttle and sports gearshifts. But this basically means I cannot drive the car casually anymore, and can't lend the car to others.

So this upgrade is not recommended for daily driven Z4s with DCTs.

 

[Asbjorn]

Suspension front
Koni FSD - installed
OEM non-M-sport springs - probably the only option that is not too harsh on Chinese roads
E9x M3 front tension strut - installed
E9x M3 front wishbones - installed
Tower spindle removed to increase camber - done
H&R 28mm sway bar - to be installed in April

Suspension rear
Koni FSD - installed
E46 M3 RTAB + RTAB limiters - to be installed in April
Powerflex lower wishbone outer bushing - installed
Powerflex sway bar bushings - installed
Powerflex sway bar end-link bushings - to be installed in April
H&R 21mm adjustable sway bar - to be installed in April

Chassis strengthening
CIDEP front strut tower bar
CIDEP lower bar kit (see picture below)

Today the H&R sway bars went in, both front and rear. The supplied H&R rear bushings were oversized, so we modified the PowerFlex bushings and used them instead. We kept the end links stock as we did not experience any clearance issues using the middle position. The stiffest (inner) position might be a problem, but I do not plan to use this setting on normal roads. I run OEM springs, so no link height adjustments were necessary.

As for the CIDEP bars they bolted right in. Some of the bolts had to be exchanged for longer ones, but that was to be expected. In my case, the strut tower bar also had to be painted black in order to adhere to the stealth/OEM+ design philosophy of this build.

The car now corners flatter at higher speeds. The steering also feels a little bit heavier and the ride comfort was slightly reduced. I will report back with final conclusions when I have tried the setup on the track. Unfortunately the front sway bar is not adjustable, so I am keeping the OEM one in case I need to soften it down again.

 

[fmorelli]

Very nice, Asbjørn. Do you have a link to the CIDEP stiffening bars?

Thanks,

Filippo

 

[Asbjorn]

Very nice, Asbjørn. Do you have a link to the CIDEP stiffening bars?

Thanks,

Filippo

I'm afraid its a very Chinese brand:

Link

You may also consider this

Ultra Racing

 

[NoQuarter]

I have had UR bracing on my 535 for a few years now. Front on top and bottom struts, and on the rear.

Along with M5 pull bars and the chassis became very stiff. I could feel the difference just backing out of the driveway.

They don't stay pretty for very long. The bottom bars of course but even the strut tower bar in the engine bay needs a repaint.

 

[Asbjorn]

Today we installed brake cooling ducts and oil cooler fans.

The main reason I installed brake cooling ducts is to prolong the life of rotors and pads during track use. Below is the result, seen from the front of the car.

A very interesting find is that if you do not want to install ducts, you can improve front rotor cooling just by removing the bottom covers on each side. There is an air duct built into the wheel arch trim that may direct some air towards the inside of the wheel. They are normally unused, as they are hidden by a cover on each side.

When I am done with the most important upcoming track events, I plan to change the duct design, by cutting it as below. This will lower the chance of scraping and make it easier to live with day to day.

Here's what we did at the rear:

Here is the rear rotor

We used the factory rotor shields, and just welded rings to them like below.

As for the oil cooler fans, we used a push-pull configuration using high powered water resistant fans. The idea here is to see if it is possible to improve the efficiency of the standard oil cooler, as no easy-to-install aftermarket oil coolers are available for the Z4. I have never experienced limp mode on the track, but the oil temperature does climb, which I would like to avoid.

The next track event will show if the fans are an improvement or not. They stay off entirely on public roads, as they are not needed for daily or spirited driving.

 

[NoQuarter]

Will your ESS tune alter the water pump to help keep oil temps lower?

 

[Asbjorn]

Will your ESS tune alter the water pump to help keep oil temps lower?

I have decided to keep the factory set points and maps for both oil and water, even if they are more efficiency than race oriented by default. My focus is on upgrading the cooling capacities instead. I bought a CSF water cooler, and plan to use water wetter as well. I will install more aux coolers if I have to.

My main concern is actually the DCT, because I don't know how well it is cooled by the heat exchanger, and the M cars have separate oil coolers for it. The M4 GT4 even uses the M6 transmission oil cooler, although all other coolers are standard M4. But so far I have never had problems with the DCT.

Anyhow, my general thinking is, if the cooling capacity is too low, it does not matter what you do in the software, you will hit the roof sooner or later anyway. You are at best just delaying the problem. If the cooling capacity is right or slightly oversized, then everything just works, and more reliably also.

 

[Plisken]

Interesting thread! PB Brakes are great.

 

[Asbjorn]

Just a quick update on the build. All remaining parts are confirmed to arrive second week of May, and I expect to have the car up and running shortly after. These parts have already arrived:

In the last minute I also decided to add an oil pan baffle to the build - I needed to replace the oil pan gasket anyhow due to a very slow leak.


And on another topic, last weekend I participated in one of the largest BMW events in southern China at Guangdong International Circuit. Unfortunately I could not participate myself, due to the turbo problem that started this build (sticky wg). But it was a great event nonetheless, and I got some lap times to compare my own performance against.

Here a video from the event (hosted on a Chinese site)

Link

And some pictures

When comparing these times to my previous personal best (1:33.57), I would have finished third in the class A, which I am quite happy with. I set this time around four months ago before the wastegate crapped out.

The winning M2 ran Cup 2 tires and a ton of mods. Same was true for the winning M4, and I would say top 3 in both classes all ran either Cup 2 or P zero tires.

 

[Plisken]

What a great thread to follow. I can't wait to read your impressions on QUAIFE LSD ! Congrats for the timing lap, it looks like you have great driving skills!

Unfortunately I got a parking brake fault (yellow light) while testing the e-brake (not at first, but after testing it several times in a row). I believe this is because my cars electronic parking brake module is faulty. I have had problems with it before and basically never use it anyway. I just need it for annual inspections. More time is needed to find a permanent solution, and I do not blame the brake kit or installation process for this.

Would be great if you could tell us how you will solve the problem, many Z4 owners have trouble with this e-brake and it will interest many people.

 

[Asbjorn]

What a great thread to follow. I can't wait to read your impressions on QUAIFE LSD ! Congrats for the timing lap, it looks like you have great driving skills! Would be great if you could tell us how you will solve the problem, many Z4 owners have trouble with this e-brake and it will interest many people.

Thanks mate! As for track driving, I'm definitely still learning!

I selected the Quaife product mainly to make it easier to drift, especially in the rain. The advantage should be that it locks more rapidly than the factory brake-based system. However, I am quite impressed by the factory system, so I do not expect radical improvements in good road/weather conditions, certainly not in terms of lap times.

As for the e-brake, the conclusion was that I needed to replace the EMF module, which is expensive but easy. Now everything is fine.
According to realoem, the part has been updated several times, so there may have been a problem with it from the supplier.

When the e-brake first started malfunctioning two years back, my local dealership removed some software functions (to have the fault ignored) and it started working again. At that time the dealership said they had seen the problem many times before, and that the actuators would typically be working fine, which turned out to be true and still is. However, if others experience problems with the e-brake, I recommend just DIY swapping the EMF module instead of having BMW mess with the software. I lost a few iDrive functions due to this, and the solution didn't last anyway.

 

[Asbjorn]

Last weekend I attended another track day event, this time in Ningbo China. The Ningbo circuit is probably the most exciting circuit in China, as long as we exclude the Shanghai F1 circuit. A few BMWs attended the event together with a couple of supercars as well as track cars. Once again, the Z4 could not participate as planned due to parts coming in late.

Here are some pictures from the event.

This week we are working more or less full-time on the car. Starting from the rear, the differential is now out to have the Quaife core installed. Today we also installed PowerFlex bushings/inserts for the differential and sub frame, as well as the M RTAB + RTAB limiters.

We also replaced the rear wheel bearings - just because now was a good time to get it done anyway.

Hopefully we can continue at the front tomorrow or the day after, depending on when the turbo parts finally arrive. Unfortunately the oil pan baffle is delayed and wont be installed in this go.

 

[fmorelli]

Very nice. So how did you decide to go with the urethane bushings for the rear subframe and diff? Any concerns about squeaking or higher NVH?

Filippo