Turbo Exhaust Back Pressure

Hey all, I'm running a built 3.5L VQ35DE block (Wiseco pistons, rods, ARP hardware, etc.), stock cams and heads, a ProEFI ECU, a single GT35R turbo w/1.06 T3 exhaust housing and E70 for fuel in my street car. Right now, it's making about 525whp on approximately 12 psi of boost.

On 12 psi of boost it's seeing about 26 psi of exhaust back pressure (measured at the exhaust housing), so that's roughly a ratio of 2.2:1. Now, on 18-19 psi my car should make just over 600whp. My question is if I turn up the boost to 18 or 19 psi what potential issues may I encounter as my exhaust back pressure rises?

When I originally had my car tuned on 91 octane the car stopped making power at a little over 500whp, beyond that any more boost I added didn't yield anymore HP, just a sharp increase in torque. That's when I decided to setup a flex fuel sensor and run the car on ethanol. So, can I just increase the boost till the car stops making HP with additional psi, or will there be other issues I need to consider?

Thanks all!

Can you do anything to reduce the pressure after the turbo?

What size down pipe and exhaust are you running?

That back pressure is suspiciously high for a GT35R on a 3.5 litre engine at a modest boost level. I'd be suspicious of something down stream of the turbo being a restriction. It may even be worth checking post-turbo to see what the back pressure is. As a general rule of thumb I like to see a ratio of less than 2:1 EMAP:MAP. That's not set in stone though but as the EMAP rises you're going to see less gain in power. Ultimately the dyno will show you where the turbo starts to fall flat though.

"26 psi of exhaust back pressure (measured at the exhaust housing)," Pre turbo and post turbo back pressure can be influnced by different things. Get data on both and go from there.