Manual Boost Controllers (MBCs) are the cheapest way to get more power out of your turbo. Please do a Stage 0 first!
This link has a good ‘how to’ on boost controllers for Volvo turbos. With the ECU controlling the boost you may not get what you want with a MBC.
I plan on running his setup with Voodoo IV controllers once I get my other issues resolved, exhaust installed and upgrade the ECM.
I’ve had a $80 Hallman ES MBC in my 850 T5 for months and it’s great. Yes, you can make one for $20. If I could do it over, I’d go that route. It’s just a dead-simple mechanical device that either works or doesn’t. You’ll know the second you accelerate from your driveway if you’ve gotten it terribly wrong. IF you have a boost gauge.
It boosts to 15psi in 2nd, 3rd, 4th gears, and up to 10psi in 1st. Stock T5 behavior is 10psi in any gear. I do not have an ECU remap/chip/tune. I do have an R ECU. I do not get fuel cutoff until ~90mph / full throttle.
I do have a boost gauge. I would feel very uneasy using an MBC without one.