Wallace Performance have this upgrade advertised on there web site
V-Max Power Upgrades for Z20LET
EVO 235 - (235 BHP/425NM)
"Our new Z20LET kit is designed to give a faster, more aggressive response from very low down in the rev range. Unlike other manufacturers beliefs, the standard Z20LET is only good for a power figure of 235BHP. This is given by manufacturers spec and the turbo is working at 100% it's maximum load capabilites. If more power is desired the turbo charger has to be changed"
"The standard intercooler is a very good design and gives a low pressure drop with a good decrease in temperature. Changing this intercooler for a larger one with smaller end tanks will result in a higher pressure drop, defeating the purpose of changing the intercooler"
But they are they advertising this, else where on their web site,
Vauxhall Z20LET Phase II conversion
"Building on performance increases of the Phase I upgrade, Phase II increases power to 247 bhp and 290 ftlb torque. This is achieved by adding a 9 litre intercooler placed in the original fitting area.
The Intercooler enhances power by reducing the overall intake temperature thus creating cooler air into the intake"
Which is almost exactly the same performance figures and intercooler set up that Courtenay and EDS/Regal offer and completely contradicts what they say in their EVO 235 upgrade advertisment.
See for your selves