Ive just written this quickly as a guide to fitting a zlet into a mk4. If there is anything I have missed tell me and I will add it in.
Why do this mod?
It is a great way to increase the power of your car without spending huge sums of money on tuning your current engine and also gives a great base for further performance modifications once completed
It is reccomended that BEFORE undertaking the zlet conversion that you fit at least turbo spec brakes (308mm front disks, 264mm rear disks) and also fit uprated suspension to help handle the extra weight of the new engine. Without these modifications stopping and cornering may become problematic
The parts required vary for different specs/models but the parts needed for most are;
Z20LET engine and engine bay loom
Z20LET dash loom
F23 gear box and selector cable setup
All Z20LET engine mounts
All boost pipes and sensors
Drive shafts (ideally from a zlet but vectra diesel shafts can also be used)
A full socket set
32mm deep socket to remove hub nuts
Various size screw drivers both posi and flat head
Male and female torx bits set ranging from very small for trim to very large for mounts
An engine hoist
Set away at least 3 days to do this, more if possible
Start by jacking the front of the car up and securing on axel stands and also chock the back wheels. Once jacked up remove the front wheels, front bumper and if possible the front arch liners
Begin to disconnect the old engine bay loom. Start by removing the battery and disconnecting the brown swivel plug infront of the relay plate and engine fuse box. When disconnecting the loom it is easiest to begin with the sensors next to the brake fluid reservoir and work your way down the driver's side wing, along the front of the car and up the passenger wing to the large blue plug that passes through the bulkhead. To remove the plug a thin walled 10mm socket is required. These arent branded as thin sockets but can be found in very cheap socket sets that come with 1/4 ratchets (as sold in halfords for around £10). Also unplug the connector from the coolant control module (located behind the front bumper) that goes across to the radiator. The power steering loom doesnt need removed. If you unplug the 80a fuse from the fuse box you can slide the connector for the loom out of the way
Once the loom is disconnected begin to remove the old coolant lines. Start by draining the radiator and then disconnect the hoses going to the radiator and also the header tank. The header tank can then be removed by releasing the securing pin and pulling it forwards. Next disconnect the lines down the back of the engine that run to the heater matrix and also the 2 main radiator hoses as well as the smaller top hose. The radiator is held in by 2 small torx screws on either side. Once removed the radiator assembly can be lifted out of the car. If the car is fitted with aircon the aircon pipes will also need to be disconnected. The refrigerant is toxic so have the system professionally de-gassed before removal.
You are now almost ready to remove the old engine. First remove the battery tray and remove the metal brackets which hold the relay box and fuse box. Disconnect the hydraulic line that runs to the clutch and carefully move it out of the way. Remove any remaining inlet pipe work and at this stage also remove the exhaust. If possible take the whole mainfold off as this will make removal much easier.
Now the drive shafts need removed. Start by cracking off the hub nuts on each side. These will be very tight. Once the hub nut has been loosened remove the whole hub (unbold caliper, suspension and track rod end then remove the hub from the wishbone). The driveshaft is removed from the gearbox by pulling. As the hub is still attached to the other end you can use for extra leverage to pull the shaft from the box. Ensure a container is in place to catch any lost gearbox fluid as the driveshaft is removed.
The final step before the engine comes out is to remove the old gear selector mechanism. All mk4s (apart from the 2.2) use a selector rod. From inside the car remove the bottom of the centre console and unbolt the torx bits holding the selector rod in place. From inside the engine bay then unbolt the mechanism from the selector rod and remove the split pins holding the selector mechanism to the gearbox. If these pins wont come out unbolt the whole selector housing from the gearbox.
The engine is now ready to come out. The mounts are located at the top on the driver's side and passenger side, one down at the front on the subframe and the other at the bottom at the back of the engine. Support the engine with a hoist and begin to loosen off the mounting bolts. Once all mounts are slackend remove the bolts. The best to start with is the rear mount and front mount as the top mounts are still connected so will reduce the risk of the engine slipping. Once all mounts are disconnected the engine can be lifted out complete with the gearbox. It is easiest to bring the driver's side up slightly to help the gearbox clear the chassis leg
Once the engine is out it gives you a chance to clean/paint the engine bay if you want. Also remove the remains of the gear selector mechanism. It is held in place by 4 bolts on the subframe at the rear of the engine. The front 2 can be accessed with a torx socket but the rear 2 can only be accessed fom behind with a flexible head 10mm ratchet.
The new engine is now ready to go in. To fit the engine from the top the oil filter needs to be removed or it will hit the chassis leg. Once removed hoist the engine up using the crane and get it so that the gearbox side sits lower than the engine side. Move the engine to above the engine bay and begin to lower it down. If you have left the ZLET aircon pump connected the engine will need pushed back on the crane to allow it to clear the slam pannel. Carefully lower the engine down until the gearbox touches the subframe. Connect the drivers side top engine mount and the top gearbox mount. Once this is done use a jack under the engine to alter its position so that the gearbox mount and front engine mount can be connected up
Now the engine is fitted you can begin to refit the coolant system. Start by refitting the radiator and hoses to the heater matrix. Also connect the coolant hose from the turbo to the top of the radiator. At this stage leave the header tank off as it will obstruct the refitting of the loom
Re-fit the holders for the relay plates and fuse box. The ZLET engine loom can now be fitted. As with the removal begin with the brake fluid reservoir and work your way around the engine up to the large blue plug at the bulkhead. If you are fitting an ABS pum now is the time to do it. If not it has no detremental effects upon the running of the car. The ECU for the ZLET sits down next to the battery. There is an earth that connects onto the ECU - ensure this is connected or the car will not run. Check the loom to make sure all earths are reconnected. The other commonly missed earth is behind the coolant control module.
The clutch lines can now be re-connected. The old clutch line will mate up with the f23 one so bolt the 2 together. Bleed the clutch using an easi-bleeder and pump the clutch pedal. It uses the same fluid reservoir as the brakes so make sure you keep an eye on the level to stop it dropping below minimum.
Now is also a good time to fit the new gear linkage. The f23 cables clip onto the mounts on the box and then run through the bulkhead into the car. Fit the new gear selector and put the cables into the correct holes. To align the gears simply push in the metal pin to lock the gearstick in neutral. Check to make sure that the gearbox is in neutral and clamp down the cables.
Now is time to begin the interior. On some electric throttle models tha dash loom doesnt need changed. However, on the 1.6 cable throttle I used it did so I will show this. Begin by removing the centre console and disconnecting the plugs from the stereo etc. Next unbolt the steering wheel by removing the airbag and removing the large torx bolt. Once that is done unbolt the dashboard (2 bolts either end, 3 bolts across the top under the window de-mister pannel and 2 bolts by the base of the centre console).
Remove the dash board. It is difficult to remove the dash as it is tight over the steering column but it will come out with patience. Once removed begin disconnecting the dash loom noting the positions of all components. The best way to do this is to start at the fuse box end and onec one sction of dash loom is removed replace it with the new. Dont touch the heater loom as this is the same regerdless of model and will only create extra work
Remove the cable throttle pedal. It is held in by 3 torx bolts, remove these and the cable and it will come out. Fit the electric throttle pedal and plug it in. The next thing to do is to fit the transponder ring. This is located around where the key goes and needs swapped over to the one that matches the new engine. The chip in the key also needs swapped over for the new one. You can now refit the whole dash. There will be spare plugs left over unless you have fitted all optional extras fitted to the turbo models
Now it is time to refit the drive shafts. The zlet ones have a bracket which bolts onto the back of the engine to support them. Shafts sorced from other models dont have this. Push the shafts into the box until you hear them clunk into place then refit the hubs, suspension and brakes. Once this is done you can fill the box oil up
Now is time to finish off the last couple of jobs. The battery tray and battery needs fitted, the coolant header tank and its hoses can now be connected and all of the turbo pipe-work can be connected up. Follow the loom to make sure all sensors are connected and re-check all bolts to make sure they are correctly torqued. Also re-connect the air-con hoses to the radiator. As the oil filter was removed for fitting this can be replaced (use a new one) and the engine oil topped up. Also fill the coolant up to the required level. At this point the exhaust should also be fitted
Once everything is connected up its the fun part. Get in the car and turn the ignition on. Begin by checking everything works - indicators, lights etc etc. Turn the key and with a bit of luck this will happen;
With the engine running check everything over. Make sure there are no fluid leaks, nothing rattling etc and once you are satisfied take move the car. Start very slowly and move forwards and stop to check the brakes are working properly. If all is well take it for a careful short drive. Once this is done check everything again - bolts, fluid etc and if all is well go and drive it properly and enjoy your 200bhp
If there is anything I have missed tell me and I will add it