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BMW Z3 - Mechanicals
Cutaway drawing of a Z3 //M Coupe.
Engines
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Four cylinder 8 valve 1.8 and 1.9 |
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Four cylinder 16 valve 1.9 |
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Six cylinder 24 valve 2.0, 2.2, 2.5, 2.8 and 3.0 |
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Six cylinder 24 valve 3.0 and 3.2 |
Early Z3s used the excellent M44 four cylinder engine and developed 140bhp. This was enough to make such a light car good fun and the revvy nature of the engine suited the Z3 perfectly. It was joined a few year later by the 2.8 M52, a classic BMW straight six. 2.2 and 2.5 M52s were added to the range as time progressed.
The M52 was eventually replaced by the more advanced M54 six in 2.2, 2.5 and 3.0 capacities. This was a more free revving engine than the M52 and the 3.0 made 231bhp compared to 193 for the outgoing 2.8, mainly due to a less restrictive intake manifold.
Later entry level cars had the unloved M43TU 8 valve engine as a stand in for the prematurely deleted M44 16 valve unit.
The Z3 has a very strong body with bolt on panels.
Body
It's worth noting that the Z3 uses bolt on body panels, including the rear arches and outer sills. This makes repairing a damaged or rusty Z3 a far simpler proposition. I've replaced a rusty rear quarter panel myself and it was easy. Used panels in the right colour can be found cheaply on ebay.
The chassis is very strong and has performed well in real world accidents. When comparing it to the MX5 and other roadsters the difference in the thickness of metal and overall build quality really stands out.
X-brace stiffens the front end.
The Z3 introduced an underbody cross brace to stiffen the front end. This is a very common upgrade for other E36s, they already have the mounting holes and just need nutserts for the bolts.
The battery lives in the boot for better weight distribution. Unusually for a BMW the space saver spare wheel lives under the boot floor in a plastic tray. The tray has an elaborate support mechanism and releasing the wheel is not obvious to the uninitiated. To save BMW technicians from the long winded task of removing the wheel to check the pressure during a service the designers fitted an extension tube from the tyre to the outside of the tray. A time saving idea but sadly not a very durable one. The tray also serves as a collector for leaves and moisture to help the spare wheel rust.
Spare wheel tray and an after market exhaust.
Suspension
Z3s used the same suspension as the E36 Compact. The front suspension was Macpherson strut with an anti-roll bar in the usual BMW configuration. However at the back the layout was taken from the previous E30 three series with semi-trailing arms in place of the more expensive Z-axle used on the Z1 Roadster.
Some say the return to the E30 rear end was purely a financial decision, others that it was done to improve packaging on such a small car. I tend to favour the former opinion. But no matter why the car used this approach the result was perfect. The Z3 drove like the really sorted E30 you'd always yearned for with better brakes and faster steering. It's just perfect and huge fun.
E30 style rear axle and suspension.
The downside of rear semi-trailing arms are that they alter the wheel's angle relative to the road under hard cornering. This decreases grip and makes the car exhibit the tail happy behavior associated with E21s and E30s. It's also good fun. The characteristic show up most in wet or wintry weather, so perhaps it can be forgiven in a roadster designed for sunnier driving.
The only real design fault was to use too soft a rubber in the lower control arm rear bushings, E46s had the same issue. Poly bushings are a cheap and easy upgrade that also improve the handling.
All Z3s of a given engine size had the same springs and dampers. There was no sports / SE option with stiffer settings as used on the three series.
Brakes
The Z3 used disc brakes all round and had ABS as standard. On the four cylinder cars BMW skimped and used non-vented front discs. They were the same 286mm diameter as the bigger cars and the only real difference was resistance to fading under hard use such as track days. An upgrade to vented discs is a simple bolt on but you'll need the wider caliper to match the disc.
The Z3 3.0 used 300mm discs from the E46 330i. These needed 17" wheels to clear them and whilst big brakes are nice an E46 was a lot heavier than a Z3 so they're not really needed. //M car brakes are described on the //M cars page.
Steering
The Z3 used similar rack and pinion steering to the E36 with standard hydraulic power assistance. The //M rack was progressive like an E36 rack, meaning it was slower in the middle of the rack than towards full lock. This was done to make the car more predictable at speed. The non-//M racks were linear so offer a sharper response in the middle at the dead ahead position, in this regard they were unlike E36 racks.
It's very common to use a Z3 rack as a much needed upgrade for the E30's slower steering. There is a legend that some M44 cars had slightly more turns lock-to-lock than others, 3.2 instead of 2.7 (E30 was 4.0) so check first if doing an upgrade.
Drivetrain
Z3's had a five speed manual gearbox including the //M cars, it's been said the six speed box wouldn't fit in the transmission tunnel but such upgrades have been done in recent years. 2.8 and above cars including the //M cars used a stronger ZF S5D gearbox.
The gear lever has a short throw and is often fitted to E30s and E36s as an upgrade part.
Automatics owners, pity be upon them, let a ZF A5S five speed unit take the strain for six cylinder cars and a ZF A4S four speed on the M44.
Roof in stowed position and early factory wind deflector.
The Roof
The fabric roof was well designed and easy to use. It was secured by simple levers at the corners of the windscreen when up. Not all cars had the electric roof but this was no hardship as it was easy to use manually. When down an optional tonneau cover could be placed over the stowed roof to tidy the car's lines.
The power roof used an electric motor to drive a hydraulic pump which in turn pushed on a piston in a long cylinder. This drove the roof frame but would not do the initial opening, once the driver undid the two levers they had to manually push the roof up a few inches at the front. The motor would only run if the driver's foot was on the brake pedal. The motor lives on the left hand side of the boot.
Fabric roof with plastic rear window.
The Z3 had a plastic rear window which was fairly durable. With age it could scratch and discolour but specialist plastic cleaners can remedy this. A new window isn't that expensive or hard to fit, it's held in by a form of zip fastener.
Various wind deflectors were offered depending on whether the car had roll over loops fitted behind the head rests. There were quite a few styles of roll hoops, some stronger than others. The Z3 is a surprisingly strong car as witnessed in accident photos. Good roll hoops anchor into the bulkhead structure and can offer real strength in a roll.
A factory hard top was available with a glass rear window and even came with it's own storage stand for the summer months. However a Z3 must have been sold with a fitting kit to accept the hard top, it's on the car's build list so do check for "hard top preparation" if you plan to buy one.
Roof hydraulic pump and piston assembly.
Technology and Systems
ASC+T
ASC+T All Season Control + Traction was an option on the Z3, sometimes standard on the larger engined cars. On the M52 they had to fit a second throttle plate under the control of the computer to implement the system as the main throttle was a cable system. The electronic throttle of the M54 did away with all that leaving a much neater and more pleasing design. ASC also speaks to the AGS control unit for automatic gearboxes.
If one wheel slips on an open differential the other will get no power. To prevent this the computer used the ABS sensors to detect if wheels were slipping and could apply the brake to ensure power went to the wheel which wasn't (using the ADB function). The computer can also reduce engine power if needed and prevent the automatic transmission from changing into an inappropriate gear.