Turbo replacement: access, studs, gaskets and wastegate preload

There is no factory procedure for the turbo alone in the pages we have, so this is what owners said. It is advice from a handful of posts, not a step-by-step. The studs and torque in particular come from single posts, so treat them as a starting point.

Does the engine have to come out?

• No. In 2020 two owners confirmed you can take the turbo off from underneath with the clam on and the engine in place. One of them warned that access is tight, as it is with everything on these cars, and the asker was going to look again at the exhaust, which has to come off to reach it.
• In 2015 one owner said he would cut an access hatch in the bulkhead, as another owner had, to make the area much easier to work in. We haven't seen the hatch.
• One owner described the whole job as a few hours.

If you do want the engine out for something else, see Engine removal and installation (Turbo).

Parts to have ready

One owner changing from a standard turbo to the Astra VXR unit asked what he needed beyond the turbo and a manifold gasket. The answers in 2013:

• Studs and nuts. They are all the same and can mostly be reused. The parts catalogue lists ten M8 x 25 studs and ten nuts.
• The clamp from the turbo to the downpipe. An owner who had done the swap said you can reuse the old one.
• The pipes. You will already have what you need on the old assembly. You will probably want new gaskets for the oil and water pipes.
• Gaskets and washers. The list is in the parts above. It looks like a lot of small items, but they are cheap compared with doing the job twice.

Studs and fasteners

• The stud head is a small torx, so a suitably small socket removes the stud. Many come out with the nuts as you take them off. One owner reused any stud that stayed put and replaced only those that snapped.
• Torque. One owner thought "something like 16 Nm" for the studs and pointed to a supplier's guide. This is a recollection, not a figure we have seen in a manual.
• No thread lock. The same owner advised against it, as even high-temperature grades are only rated to about 200°C and a turbo gets much hotter. That is his reasoning, not a manufacturer's instruction.
• Seized and snapped studs. One owner doused all the nuts in WD40 for ten minutes and the rest came out without a fuss. He got a snapped stud out by tapping a 7 mm socket over the end. Another owner had two studs that wouldn't move, and both sheared. A specialist got them out without removing the head, but had to drill out the bolts on the exhaust just below the pre-cat. A snapped stud doesn't necessarily mean the head has to come off: one owner thought it can be done in situ unless it breaks too deep and has to be drilled and re-tapped.
• The heat shields tend to fall apart as you work them out.
• An owner recalled the oil banjo bolt as 22 mm, so you may need that socket.

The wastegate actuator and preload

• The preload is set by how far the lock nut on the actuator arm is turned along the shaft. If you move the actuator from your old turbo to the new one, set it to give the same preload, which isn't necessarily the same number of threads showing on the shaft.
• A turbo supplied as a complete assembly (for example the Astra VXR unit) comes with the actuator fitted, so there is nothing to move. One owner said that actuator is set to the Astra VXR pressure. If your car runs a similar boost it should be fine, and if not it needs to be raised or lowered to suit.

Do you need a remap?

The owners disagreed:

• One said a straight swap wouldn't need a remap to keep the fuelling acceptable, as the ECU will adapt, and that a remap just squeezes out the last couple of horsepower.
• Another said that swapping the turbo makes no difference to power unless it is mapped, and even then other limits (inlet cooling, clutch and injectors) get in the way before the standard turbo is the problem.
• A third said you need the map adjusted to get more power or torque from a bigger turbo.
• In 2015 an owner who fitted a K06 had to take the car home on a safe map, because the standard fuel pump couldn't keep up. He fitted an uprated pump and then needed a remap to use the extra power. That is one owner's experience, and it is worth knowing before you go bigger.
• One owner suggested that if you are having the turbo overhauled, with a stage 4 car in mind, uprated bearings and seals are worth asking about. We haven't seen the details.

For power and fuel limits see Turbo stage 2.5, exhaust and power limits, and for one workshop's account of the swap itself, Turbo swap: standard turbo to the VXR (Z20LEH).