To get it down to where the stock turbo is would require a 2.4mm headgasket and I'm sure you could have one made. It will hurt quench though having the piston that far from the head. Not a deal killer but I bet you loose a little power and it may hurt the longevity of your engine. Not by much, you wouldn't even notice the power loss with the turbo on there.str8upclownen said:not really wouldn't a custom 3.2mm headgasket do the job? and with the thicker headgasket means you could safely turn up the boost
Here's the point though, the stock 5sfe can already be taken up to ~15-16psi without race fuel depending on the turbo you use. When you drop the compression as you suggest that probably makes it good to ~16-17psi. So really it would only be worth it if you already had the fuel management to run that much boost and wanted that extra little bit. The mechanical limitations are only part of the equation. You have to get the right amount of fuel and timing to be able to use what you have. If you don't do that first then no matter how low your compression is your engine isn't likely to survive long.