How to build an M car beating Z4 in three easy steps...

[Asbjorn]

Step 1
Buy a low mileage N54 equipped Z4, preferably with EUR/is brakes. Step one is done.

Step 2
Realize that on most tracks, the stock M car with the most potential is the M4 GTS. It beats M5s, most 911s and even some Audi R8s in terms of lap times. How does it do this then? I would say the main advantages of the GTS are the tires, power-to-weight ratio, stamina and balance.

So lets establish the benchmark - what do we need to match or improve upon?
GTS tires: 265/35R19 front, 285/30R20 rear, Michelin Pilot Sport Cup 2. Note the larger diameter rear. This changes the tire patch area relative to the front, improving traction out of turns. Note also that these tires are a bit wider than the stock 225/255 RFTs of the Z4...
Power: 492hp with WI. So almost 200hp more than the Z4 depending on N54 map...
Weight: About same as a Z4 DCT, but with worse front-to-rear weight balance, finally some tailwind then!
Stamina: Track-ready cooling system from factory which is only limited in terms of DCT and differential cooling. The oiling and fueling systems can also handle prolonged G forces on track. Finally the brakes are ceramic... A stock Z4? Well, everything starts to overheat after a lap or so... It also suffers from oil and fuel starvation to some extend, although not as bad as, say, an Audi S3.
Balance: The GTS comes with 3-way adjustable KW coilovers. However the sway bars are not adjustable, and camber is less than -2 degrees up front. Some room for improvement there, but of course the stock Z4 was set up for understeer and comfort from factory.

So what do we do?
Tires: With stock sized struts, camber plates and M control arms, it is possible to dial in around -2.5 degrees camber up front. More can be added with coilovers, but -2.5 is already more than what the GTS offers, and is almost never too much at any track. -2.5degrees should allow us to run a square setup with 275/35R18 tires on 10J ET40 wheels adding a small spacer up front. Full steering lock will come with some rubbing, but this is not a problem on track. The tires selected must of course outperform the cup2s of the GTS. Examples of such tires include Hankook RS4 in the dry or Michelin PS4 in the wet. Done.
Power: Well there's the 600whp VTT guide here for inspiration. I would go for less power and just match the GTS to improve longevity of everything on track. I would also make sure to run a bit more octane than needed for the power chosen. Perhaps add a simple WMI system and only run it on track. Keep the stock Z4 airfilter and snorkel in combination with silicone inlets and a free flowing exhaust to keep temps down. Finally try and get a slightly oversized turbo that works with the stock outlet to avoid a ton of hassles in the future. Stock double-walled manifolds are also recommended to keep under the hood temps down.
Finally the N54 better be in good condition with new injectors, vacuum lines, coils, plugs, o2 sensors, N55 camshaft seals, vanos solenoids, lpfp, hpfp etc as documented here (post #2). I also recommend running one green revshift mount on the passenger's side with idle set at 900. Alternatively just go for the 35is mount. Don't choose 60A or 80A mounts as they will melt. Oh and pick your tuner carefully. Done.
Weight: Already on pair with the M4 GTS, and with better weight distribution for lap times. Done really. You can choose forged wheels, remove the rtab vibration dampers, get lighter adjustable suspension arms, aluminum brake calipers, lighter wheel carriers, M4 flywheel, exhaust, carbon trunk etc if you have money to spare (trust me, you don't).
Stamina: For the cooling system you will need to triple the size of the oil cooler, increase the total radiator area by at least 50%, increase intercooler area by at least 100% and you will also need to add a huge DCT oil cooler. I already mentioned WMI and it will help cooling iats and egts as well. Try not to waste money on increasing the thickness of the main radiator or FMIC. Area and flow is what is important here. Feeling overwhelmed? Then get a 6MT Z4 and just add a large auxiliary radiator and fmic to get started, and remember to do some cooling laps here and there. You will also need an accusump or semi-dry oil sump for tracks with left hand hairpins, and at least 40% fuel in tank for tracks with very long right hand turns. As for brakes you need a good set of racing pads and racing brake fluid. Optionally you can add brake cooling to prolong pad life. Done!
Balance: Get 3-way coilovers or better to match the KW setup of the GTS in terms of adjust-ability. Then add camber plates and adjustable sway-bars to outperform the GTS. I would also mount the rear sub frame directly to the chassis, stiffen the differential mounts and replace all suspension bushings with bearings just for longevity and predictability. Step two is done.
Adding a wing and front spoiler will look cool, but in reality upgrading tires from cup2s will probably make more of a difference. However I do recommend adding a locking differential, hardwiring an AiM solo 2 dl + smartycam system into the cabin, and hire an experienced racing driver to help find the optimum setup for each track that you want to go to. But if you are already an excellent driver, none of this will be needed.

Step 3
Bed in the racing brake pads and sign up for a track day. All set!

So there you go, a complete summary of my experience working with the Z4 on track during the last two years!

Bonus Q&A
Q: What if I want to beat a slightly modded M4 GTS? Like say one with camber plates, a stage 2 flash and 285 soft slicks?
A: Well, good luck with that...

Q: The length of this three step plan is exactly why I bought an M4 GTS!
A: That was not a question...

Q: Wouldn't it be easier to start out with an M2C instead of the Z4?
A: Yes, and less expensive...

Q: Could such a build be made to match the +500hp Z4 GT3 on track?
A: The GT3 has down-force, double wishbones motorsport suspension, 13J wheels and weighs 1,190 kg / 2,624 lb. The answer is no...

 

[Asbjorn]

Although a bit old, here is a well written article from Bimmerworld on how they build their 335i track car

N54 Project Car | BimmerWorld

BimmerWorld built an N54 powered street and track focused E90 335i Project Car. This page chronicles the build of our N54 project car.

www.bimmerworld.com

To my surprise the wrote the following about rod bearings:

"Contrary to perceptions, bearings do wear on non-M cars as well. It’s not just S54 and S65 engines that see bearing wear. Our N54 had 83,000 miles when we decided to pull the oil pan and check the bearings. We didn’t have any indication or hint of the wear so we were shocked to find significant wear on three out of six cylinders. And it makes sense when you think about the stresses and forces being applied to bearings of a high-output turbo engine. We hadn’t heard of “early” bearing wear on N54 engine previously but now we were looking at it first hand. A new set of factory bearings with WPC treatment were installed. "

 

[Bnks334]

N5x cars offer a pretty big bang for the $.

Although a bit old, here is a well written article from Bimmerworld on how they build their 335i track car

N54 Project Car | BimmerWorld

BimmerWorld built an N54 powered street and track focused E90 335i Project Car. This page chronicles the build of our N54 project car.

www.bimmerworld.com

To my surprise the wrote the following about rod bearings:

"Contrary to perceptions, bearings do wear on non-M cars as well. It’s not just S54 and S65 engines that see bearing wear. Our N54 had 83,000 miles when we decided to pull the oil pan and check the bearings. We didn’t have any indication or hint of the wear so we were shocked to find significant wear on three out of six cylinders. And it makes sense when you think about the stresses and forces being applied to bearings of a high-output turbo engine. We hadn’t heard of “early” bearing wear on N54 engine previously but now we were looking at it first hand. A new set of factory bearings with WPC treatment were installed. "

Yeah I've pointed people to this many times. N54 owners constantly try to point out the 1 or 2 N55 failures that pop up but ignore the daily posts about blown up N54's lol Blame whatever you want but it happens and a recurring "rod bearing replacement" should probably be considered as a maintenance item like on other engines. Every 80K wouldn't hurt or every few "race" seasons. No engine lasts forever in these conditions. Metal fatigues and wears.

 

[NoQuarter]

I saw something recently here I think that listed a parts list for N54 rod bearing replacement.

Anyone recall if there is decent DIY post anywhere with parts, etc? Does newtis.info include proper info on getting it done?

 

[etropic]

@Asbjorn In case you're still around...

I'm half way through your other main thread about your car and looks awesome.

I'm curious in all the racing and track time if you ever felt like the DSC was a hinderance. Either in Sport+ with traction on or DSC fully off. And if you ever coded anything different for it... or even coded anything (or felt the need to) code the DCT itself.

 

[Asbjorn]

@Asbjorn In case you're still around...

I'm half way through your other main thread about your car and looks awesome.

I'm curious in all the racing and track time if you ever felt like the DSC was a hinderance. Either in Sport+ with traction on or DSC fully off. And if you ever coded anything different for it... or even coded anything (or felt the need to) code the DCT itself.

Please be aware that there is some misinformation in that thread, ie things I did at the time, thinking it would work, only to learn later it didn't. Hope you are able to navigate through all of that.

I never used sport+ on the track. I might have used traction in the rain which is similar to sport+ but without the hard shifts upsetting the chassis (not to mention the throttle map). Otherwise I just used DSC=off.

DSC=off worked fine for me, both with and without the quaife LSD. I never touched the coding of it. I know it can theoretically overheat the rear brakes, but it wasn't a concern I had. Overheating started much earlier in other parts of the car anyway. I also didn't feel the need to code the DCT itself for track use - the shifts are perfect in DSC=off + Manual mode. I mainly coded the DCT for better feel on the street running automatic modes M4 flywheel etc.

What you might need to consider more is the throttle map as well as your engine tune. Lots of street maps provide full power when the pedal is only 70% pressed. This makes the car feel faster, but actually you loose some resolution in the pedal. You dont want this on/off behaviour when coming out of corners. Larger turbos and more power in general only magnifies the problem. At the very end, we intentionally we reduced the mid-rpm power in my tune, making the car slower overall, but more exciting to rev out. I still have it like this on the road today. During the tuning I would also make logs with 50-60-70% throttle, holding the pedal still to track if the input would vary artificially with rpm.

I did want to make a dedicated wet track throttle map and put it under sport, but the other stuff took so much time that I never got around to it. And you don't really want such a map in sport for street driving anyway, but where else to put it.

So in conclusion, dont worry too much about the DSC. It turns off pretty nicely. I would look into runing an adjustable racing ABS way before touching the DSC. But then again, there are some other basic limitations with this car that are of much bigger concern, and that just cant be solved no matter what (oil starvation, high center of gravity, engine cooling etc). Hence why I have reverted to street/GT use only.

 

[etropic]

Please be aware that there is some misinformation in that thread, ie things I did at the time, thinking it would work, only to learn later it didn't. Hope you are able to navigate through all of that.

I never used sport+ on the track. I might have used traction in the rain which is similar to sport+ but without the hard shifts upsetting the chassis (not to mention the throttle map). Otherwise I just used DSC=off.

DSC=off worked fine for me, both with and without the quaife LSD. I never touched the coding of it. I know it can theoretically overheat the rear brakes, but it wasn't a concern I had. Overheating started much earlier in other parts of the car anyway. I also didn't feel the need to code the DCT itself for track use - the shifts are perfect in DSC=off + Manual mode. I mainly coded the DCT for better feel on the street running automatic modes M4 flywheel etc.

What you might need to consider more is the throttle map as well as your engine tune. Lots of street maps provide full power when the pedal is only 70% pressed. This makes the car feel faster, but actually you loose some resolution in the pedal. You dont want this on/off behaviour when coming out of corners. Larger turbos and more power in general only magnifies the problem. At the very end, we intentionally we reduced the mid-rpm power in my tune, making the car slower overall, but more exciting to rev out. I still have it like this on the road today. During the tuning I would also make logs with 50-60-70% throttle, holding the pedal still to track if the input would vary artificially with rpm.

I did want to make a dedicated wet track throttle map and put it under sport, but the other stuff took so much time that I never got around to it. And you don't really want such a map in sport for street driving anyway, but where else to put it.

So in conclusion, dont worry too much about the DSC. It turns off pretty nicely. I would look into runing an adjustable racing ABS way before touching the DSC. But then again, there are some other basic limitations with this car that are of much bigger concern, and that just cant be solved no matter what (oil starvation, high center of gravity, engine cooling etc). Hence why I have reverted to street/GT use only

Great stuff man. Thanks for your time!