NA (Z22SE): what you can fit
One owner in 2017 put it bluntly: there aren't many options for the Z22SE, and the two he listed were a Tullet 4-1 or the Dbilas cast iron manifold. Others added more.
| Option | What owners say |
|---|---|
| Standard cast manifold | Prone to cracking, but cheap to replace. See NA exhaust manifold replacement. A cracked-looking manifold may just be a broken stud. |
| Tullet 4-1 | The usual choice, described as "big bucks". There are two versions: one for a standard or 2.5" exhaust, and a larger one for a Stage 3 supercharger that needs the full 3" system. Needs the coolant hoses off to fit. |
| TMS 4-1 | Needs the rear clam off to fit. |
| Dbilas cast | A cast manifold for the Z22SE. One owner who had one "years ago" asked in 2017 whether it was still sold; nobody answered. |
| Borbotta (Italy) tubular 4-1 | An owner quoted 2017 prices: manifold 650 euro, full de-cat system 400 euro, racing cat 650 euro, end box 480 euro, 64 mm diameter. Nobody reported fitting one. |
| US imported 4-2-1 (Tsudo, a Weapon R copy) | An owner uses one to form a 4-2-1 system; he says it is far from optimal but works much better than standard. Another warns that an eBay copy won't simply bolt on: the 2-1 downpipe is set up for a front-engined car, so it needs re-orienting and welding, and it may need a boot cut-out. The outcome of the 2020 purchase isn't posted. |
What you get: one owner who got hold of a second-hand 4-1 and had the car re-learn (re-mapped) said it helped the mid-range noticeably, but also made the car louder. His rule of thumb: a manifold is a really good way to unlock torque. Another NA owner who asked what power gain to expect in 2013 didn't get a figure.
The standard casting, modified
In 2020 one owner modified a second-hand standard NA manifold, mainly to get rid of the EGR take-off on cylinder 4. He is clear that equal-length manifolds are an improvement and that this was making the best of things.
- He removed the casting flash and the thick boss for the heat shield lower bolt, taking the weight from 4.649 kg to 4.498 kg. Smoothing the ports and bores took it to 4.415 kg.
- He welded a plate into the EGR channel and added metal to the cylinder 4 port, then reshaped it. He also shaved the bumps in the ports that give clearance for the studs.
- On port matching, he explains two schools of thought: match the manifold port to the head port, or leave a small step as an anti-reversion lip. He chose the step, reasoning that you can grind more out but can't grind it back in.
- His verdict was that it felt better in the mid-range, but that is a seat-of-the-pants judgement, and he had also removed the EGR in software.
He ordered the imported 4-2-1 header in the end, and had thought about designing his own that keeps the catalytic converter. With the cat in place he reasoned the primaries could only be about twice the original length without cutting into the clam. That design remained an idea in the thread.
Turbo manifold
- On the Turbo the exhaust manifold is cast as one with the turbine housing, so one owner says a cracked one means a new turbo, as no one reconditions the standard unit (his understanding in 2007).
- The Astra VXR turbo was said to be cheaper than the standard Turbo part and gives more power. Another owner says the VXR turbo has a more efficient compressor with lower intake temperatures, and a different owner reports his VXR manifold cracked in under 18 months.
- One owner explained why he thinks they crack: a hot spot where the gases diverge at cylinder 3, in the join of the third and fourth arms. That is his opinion.
- Dbilas Turbo manifold (2007): a recent fitter praised its thicker casting and more even gas loading, saying the supplier had never seen one crack. Another owner who fitted one said mechanically it was a nightmare: the oil pipes have to be bent severely, the exhaust pipe and intake pipe need modifying, a torque wrench can't be used on two of the fixings, and it weighs 1.8 kg more than standard. Owners differ. The second owner adds that it moves the turbo's inlet and outlet positions.
- TMS tubular (about £700, 2007): said to be a tubular manifold with a flange that lets you fit a Garrett turbo.
- One owner fitting a Dbilas found the original "bolts" wouldn't go into the lower holes. Another explained they are studs and nuts that have corroded together, and the studs should already be tightened into the head before the manifold goes on. For the studs, one owner used a standard socket; the size wasn't recorded.