Liam's Z4C race car project
- Thread starter Liam22
- Start date
It has helped me alot Liam with my own build! thanks to yourself 
I'm back for a quick review of 2025 before getting into 2026 plans.
Pre-season prep was all about the diff. Purchased a 3.73 crownwheel and pinion and had it fitted into my existing LSD. I considered doing this myself but it was quite a learning curve the first time and I have less time than ever. Removed the diff from the car and delivered it to a local specialist with all my spare shims. Turned into a lengthy (and expensive) install. One of the Kazz clutch plates had sheared its teeth so I needed to order a full rebuild kit with new 6 new plates. Then apparantly I have a 188L pinion (not 188K) and now I have a custom pinion spacer so I can use 188K pinions.
Shakedown test of the new diff was good and bad. The diff really helped on acceleration and top speed. Since 2020, top speed on the back straight at Snetterton has increased from 121mph to 130mph!!! I also gave @Max Crilly his first track experience for his 18th birthday and was blown away by his speed. Within 1s of my lap time on his first track day and first time in the car.
At the end of the day I bolted a fresh set of AO52s on the car to scrub them in and do a single flying lap. At the apex of Bombhole the OSF control arm sheared its inboard balljoint (at 90mph). An unrestrained wheel does a lot of damage at that speed.
The repair job was extensive:
Needless to say, this took quite a while and forced me to miss the first race of the season. I didn't get out until July.
Race results
Disappointingly short season, made up for with the 1hr40min race at Oulton Park. Including an exciting refuelling pit stop.
Plans for 2026 coming up…
Pre-season prep was all about the diff. Purchased a 3.73 crownwheel and pinion and had it fitted into my existing LSD. I considered doing this myself but it was quite a learning curve the first time and I have less time than ever. Removed the diff from the car and delivered it to a local specialist with all my spare shims. Turned into a lengthy (and expensive) install. One of the Kazz clutch plates had sheared its teeth so I needed to order a full rebuild kit with new 6 new plates. Then apparantly I have a 188L pinion (not 188K) and now I have a custom pinion spacer so I can use 188K pinions.
Shakedown test of the new diff was good and bad. The diff really helped on acceleration and top speed. Since 2020, top speed on the back straight at Snetterton has increased from 121mph to 130mph!!! I also gave @Max Crilly his first track experience for his 18th birthday and was blown away by his speed. Within 1s of my lap time on his first track day and first time in the car.
At the end of the day I bolted a fresh set of AO52s on the car to scrub them in and do a single flying lap. At the apex of Bombhole the OSF control arm sheared its inboard balljoint (at 90mph). An unrestrained wheel does a lot of damage at that speed.
The repair job was extensive:
- Replace wheel
- Replace tyre
- Replace wing
- Replace wheelarch liner
- Replace sill
- Replace bent damper piston (didn't spot this until end of season)
- Replace track rod end (both sides)
- Replace anti roll bar drop link (both sides)
- Replace control arm (both sides)
- Replace rear control arm bush
- Remove and paint front subframe (could not remove the sheared ball joint with it in place)
- Repair undertray stiffening plate
- Repair inner wheelarch seam
- Repair custom exhaust downpipe (got smacked by the control arm)
- Wheel alignment
Needless to say, this took quite a while and forced me to miss the first race of the season. I didn't get out until July.
Race results
- 05-Jul-2025 Anglesey [2nd]
- 02-Aug-2025 Snetterton [1st]
- 20-Sep-2025 Oulton Park [2nd]
- 11-Oct-2025 Donington Park [2nd]
Disappointingly short season, made up for with the 1hr40min race at Oulton Park. Including an exciting refuelling pit stop.
Plans for 2026 coming up…
Last edited:
Attleborough, Norfolk
I'm back for a quick review of 2025 before getting into 2026 plans.
Pre-season prep was all about the diff. Purchased a 3.73 crownwheel and pinion and had it fitted into my existing LSD. I considered doing this myself but it was quite a learning curve the first time and I have less time than ever. Removed the diff from the car and delivered it to a local specialist with all my spare shims. Turned into a lengthy (and expensive) install. One of the Kazz clutch plates had sheared its teeth so I needed to order a full rebuild kit with new 6 new plates. Then apparantly I have a 188L pinion (not 188K) and now I have a custom pinion spacer so I can use 188K pinions.
View attachment 288724
Shakedown test of the new diff was good and bad. The diff really helped on acceleration and top speed. Since 2020, top speed on the back straight at Snetterton has increased from 121mph to 130mph!!! I also gave @Max Crilly his first track experience for his 18th birthday and was blown away by his speed. Within 1s of my lap time on his first track day and first time in the car.
At the end of the day I bolted a fresh set of AO52s on the car to scrub them in and do a single flying lap. At the apex of Bombhole the OSF control arm sheared its inboard balljoint (at 90mph). An unrestrained wheel does a lot of damage at that speed.
View attachment 288725
The repair job was extensive:
View attachment 288721
- Replace wheel
- Replace tyre
- Replace wing
- Replace wheelarch liner
- Replace sill
- Replace bent damper piston (didn't spot this until end of season)
- Replace track rod end (both sides)
- Replace anti roll bar drop link (both sides)
- Replace control arm (both sides)
- Replace rear control arm bush
- Remove and paint front subframe (could not remove the sheared ball joint with it in place)
- Repair undertray stiffening plate
- Repair inner wheelarch seam
- Repair custom exhaust downpipe (got smacked by the control arm)
- Wheel alignment
View attachment 288722
View attachment 288723
Needless to say, this took quite a while and forced me to miss the first race of the season. I didn't get out until July.
Race results
- 05-Jul-2025 Anglesey [2nd]
- 02-Aug-2025 Snetterton [1st]
- 20-Sep-2025 Oulton Park [2nd]
- 11-Oct-2025 Donington Park [2nd]
Disappointingly short season, made up for with the 1hr40min race at Oulton Park. Including an exciting refuelling pit stop.
Plans for 2026 coming up…
Looking forward to seeing Team Crilly sharing the car.
Let me know when you’re at Snetterton and I’ll see if we can get an East Anglian fb group gathering to cheer you on.
They are Meyle HD items.
Peak loads on brand new Yokohama AO52 tyres are very high - like slicks. I must have fatigued them after 5 seasons and 29 races.
I replaced them with the same type and will limit them to 15 races going forward. Another unexpected consumable!
Someone told me the Meyle HD wishbones had replaceable ball joints?
Or did I imagine that?
Oh man, I really miss the RX8. It was the best handling car I've ever driven. Just a delight.
Double wishbones all round, big brakes, lightweight details everywhere, and an engine that sits behind the front axle line. The Mazda engineers did some overtime!
Engine was pretty reliable for me. Did 28 races before it blew a side seal. But needs lots of preventative maintenance and is a PITA to look after. One of the reasons I selected the N52 to replace it. No pull out of the corners made it difficult to race with. But the noise at 10,500rpm was sublime!
Noise and handling evident in this video. Sorry for non BMW content!!!
They do indeed. Decided not to do that on this occasion as the failed arm had taken quite a beating.
But I did press out the old ball joints out of curiosity. Notice how the ball joint areas have more material around them compared with the OE items that were on the car when I bought it.
Replacement ball joints are just under half the price of a whole arm.
Thanks for confirming. So if you swapped them out every 15 races, it would effectively cost the same as you now having to replace the whole thing after 29, but with added peace of mind that they aren't getting so stressed.