I did alot of research when I fitted mine. Most people suggest 12-14 maximum. As the stock injectors max out at 16 I think. But do it right, don't go max, get it tuned and make it safe, over boosting is the number one killer for engines!!
I call 12~14 psi 14 being the sharp edge of safe boost levels - when injectors start running out of flow capability. Yes some have been able to go to higher levels and I ran mine at 14 with no signs of detonation on the pistons for a couple of years. I run my new engine on 12 to be safe and will only go higher once I have bigger injectors and a tune. I believe the turbos start to run out of puff at around 16-18 again people have pushed higher and had varying levels of success
I ran 18psi.....however it had plenty of fuel and the timing was really safe. Going for 22 - 24psi on e85 soon. On a pretty stock zed I'd keep it at 12psi.
I plan to go 15psi on stock turbos but with research i found that 16.7psi is the absolute peak efficiency for stock turbos before they make more heat.
The tune depends what you are using your car for. I use mine as a daily drive I have a Microtech ECU with a Greddy boost controller and few years back I set my ECU and boost to suit long drives of an hour in length at 100kph going to work with using added boost for overtaking in 4th gear. Now I am living close to work and doing more frequent drives of about 10-15kms, so have retuned my ECU and boost accordingly as it is more stop start driving at much lower speeds and in 2nd and 3rd gears, adjust my boost accordingly. I like a bit of boost in lower gears. Running 12-14 PSI should be ok if its a daily drive.
