Having had my Z4 for almost 2 years now, I thought it's a good time to share some of the experiences I had with various mods people might be considering.
Limited Slip Diff - I had this mod on all my previous cars that came with an open diff so its cost was already calculated in my budget before buying the car (around £1.5k fitted). To me personally, the most enjoyable thing about driving is having that bit of opposite lock out of corners. Equally, the most disappointing thing in a RWD car - for me - is having one wheel spin up without the car going anywhere. An LSD remedies this nicely, so I got in touch with Birds UK to install a Quaife unit in the original diff housing. It's worth knowing that a helical differential like this is not really built for drifting (it never actually physically locks the two rear wheels together) but rather for maximum traction out of corners. This comes really handy when accelerating out of tight corners, especially in the wet. If you like to play around withy our Z4 and you're fan of opposite lock, this mod is imperative.
Suspension - One of my annoyances with the Z4 has always been the harsh yet wallowy suspension. Despite installing non-run-flat tyres, I've found the ride unnecessarily harsh, yet imprecise and vague when driven fast. I knew that fitting firmer suspension would only make the pain worse, so I decide to start at the dampers. I came across the Koni's Special Active kit which is supposed to mechanically differentiate low frequency (body roll) and high frequency (road imperfections) shock waves, and adjust the damping accordingly real time. On paper it sounds perfect: stiff in the corners and soft over bumps, without any electronics! I went ahead with these dampers (around £800 fitted) to see what all the fuss was about. I was surprised to find that the kit does what it says on the box. Imperfections are a little less harsh while body roll is significantly reduced despite running the original springs. While it won't make the Z4 any sharper or precise, it'll make the suspension a little easier to live with.
Air Filter - I went with the K&N replacement panel filter and have noticed no noticeable change in power or sound on the stock map. I imagine the filter becomes more of a restriction at higher power levels where airflow through the air box is higher. Unless you have a tune, I personally wouldn't bother.
Stage 1 Tune - This is where things get exciting! From factory the 35i puts out around 306 bhp, which feels plenty fast for the road. Because BMW seem to have left a healthy amount of margin on the N54 engine - later exploited in the 35IS and 1M - it'd almost seem like a waste not to unleash the extra horses with a simple tune. I have found that the easiest, cheapest and most rewarding solution here is the MHD flasher. It's an Android app which connects your phone / tablet to the DME via an USB-to-OBD2 cable. Using in-app purchases it lets you tune your car for around £200 all included. It also comes with handy features like logging, changing exhaust burble, setting boost limit by gear etc. If you do one mod to your N54, make sure it's this one! With the Stage 1+ map, you can up power to around 380 bhp, which makes night and day difference compared to the stock car. Make sure you have new spark plugs and leads just in case - they are likely to throw codes at higher power.
Stage 2 Tune - I'm not sure why I bothered pushing power beyond Stage 1, but it's not the worst decision I made in my life. To unleash more power (around 420 bhp), a couple of mods are needed first: An intercooler (to keep intake air temperatures low), a charge pipe (because the OEM plastic one likes to blow up under pressure), and catless downpipes (to enable higher flow while still passing MOT). Once these mods are purchased and fitted (budget around £1.6k), you can load MHD's Stage 2 maps which make a huge difference to how the car behaves. At this point you are pushing similar performance to an M4 or M2 Competition. Another great advantage of the bolt-on mods is the change in sound (louder burble and pops, more pronounced boost swoosh) and decreased spool times. At this point I'd highly recommend premium tyres on the rear and an LSD to put the power down.
With regards to brands, I went with a Mishimoto intercooler (relatively small, OEM fitment), VRSF downpipes and a Masata aluminium charge pipe.
Other mods - Perhaps my favourite mod was a steering wheel re-trim by Royal Steering Wheels. It brings the interior of the car back to new and you can choose from endless options in terms of materials colours, stitching etc. I went with a simple black, perforated + nappa leather combination https://www.instagram.com/p/BoBz83iH-PM/.
I also used Carly to unleash some features on the car, including roof folding in motion, side markers, digital speedo and such. More on this here: https://youtu.be/JtsxZu-m0Qc?t=569
After all this, the car still looks stock which I love:
Hope this helped anyone who is looking into modding their Z4 or considering some of the brands above. I'm curious as to what experience you guys have with mods!
Limited Slip Diff - I had this mod on all my previous cars that came with an open diff so its cost was already calculated in my budget before buying the car (around £1.5k fitted). To me personally, the most enjoyable thing about driving is having that bit of opposite lock out of corners. Equally, the most disappointing thing in a RWD car - for me - is having one wheel spin up without the car going anywhere. An LSD remedies this nicely, so I got in touch with Birds UK to install a Quaife unit in the original diff housing. It's worth knowing that a helical differential like this is not really built for drifting (it never actually physically locks the two rear wheels together) but rather for maximum traction out of corners. This comes really handy when accelerating out of tight corners, especially in the wet. If you like to play around withy our Z4 and you're fan of opposite lock, this mod is imperative.
Suspension - One of my annoyances with the Z4 has always been the harsh yet wallowy suspension. Despite installing non-run-flat tyres, I've found the ride unnecessarily harsh, yet imprecise and vague when driven fast. I knew that fitting firmer suspension would only make the pain worse, so I decide to start at the dampers. I came across the Koni's Special Active kit which is supposed to mechanically differentiate low frequency (body roll) and high frequency (road imperfections) shock waves, and adjust the damping accordingly real time. On paper it sounds perfect: stiff in the corners and soft over bumps, without any electronics! I went ahead with these dampers (around £800 fitted) to see what all the fuss was about. I was surprised to find that the kit does what it says on the box. Imperfections are a little less harsh while body roll is significantly reduced despite running the original springs. While it won't make the Z4 any sharper or precise, it'll make the suspension a little easier to live with.
Air Filter - I went with the K&N replacement panel filter and have noticed no noticeable change in power or sound on the stock map. I imagine the filter becomes more of a restriction at higher power levels where airflow through the air box is higher. Unless you have a tune, I personally wouldn't bother.
Stage 1 Tune - This is where things get exciting! From factory the 35i puts out around 306 bhp, which feels plenty fast for the road. Because BMW seem to have left a healthy amount of margin on the N54 engine - later exploited in the 35IS and 1M - it'd almost seem like a waste not to unleash the extra horses with a simple tune. I have found that the easiest, cheapest and most rewarding solution here is the MHD flasher. It's an Android app which connects your phone / tablet to the DME via an USB-to-OBD2 cable. Using in-app purchases it lets you tune your car for around £200 all included. It also comes with handy features like logging, changing exhaust burble, setting boost limit by gear etc. If you do one mod to your N54, make sure it's this one! With the Stage 1+ map, you can up power to around 380 bhp, which makes night and day difference compared to the stock car. Make sure you have new spark plugs and leads just in case - they are likely to throw codes at higher power.
Stage 2 Tune - I'm not sure why I bothered pushing power beyond Stage 1, but it's not the worst decision I made in my life. To unleash more power (around 420 bhp), a couple of mods are needed first: An intercooler (to keep intake air temperatures low), a charge pipe (because the OEM plastic one likes to blow up under pressure), and catless downpipes (to enable higher flow while still passing MOT). Once these mods are purchased and fitted (budget around £1.6k), you can load MHD's Stage 2 maps which make a huge difference to how the car behaves. At this point you are pushing similar performance to an M4 or M2 Competition. Another great advantage of the bolt-on mods is the change in sound (louder burble and pops, more pronounced boost swoosh) and decreased spool times. At this point I'd highly recommend premium tyres on the rear and an LSD to put the power down.
With regards to brands, I went with a Mishimoto intercooler (relatively small, OEM fitment), VRSF downpipes and a Masata aluminium charge pipe.
Other mods - Perhaps my favourite mod was a steering wheel re-trim by Royal Steering Wheels. It brings the interior of the car back to new and you can choose from endless options in terms of materials colours, stitching etc. I went with a simple black, perforated + nappa leather combination https://www.instagram.com/p/BoBz83iH-PM/.
I also used Carly to unleash some features on the car, including roof folding in motion, side markers, digital speedo and such. More on this here: https://youtu.be/JtsxZu-m0Qc?t=569
After all this, the car still looks stock which I love:
Hope this helped anyone who is looking into modding their Z4 or considering some of the brands above. I'm curious as to what experience you guys have with mods!
