In response to a request for opinions on how to safely boost a V70, MVS user pkplok posted this link which is specifically about boosting Volkswagens but should work for Volvos as well.
Additionally, user SweedSpeed posted the diagram below which shows how to allow the ECU/solenoid to regulate boost in lower gears while utilizing the manual boost controller in higher gears.
Post by csbrianp » Mon Apr 13, 2009 9:01 am3barracing.com sells Manual Boost Controllers for $40, the install in minutes and help increase the boost on your turbo. Beware, the 850 turbos have a fuel cut at 15lb of boost, so after installing your MBC if your car really starts accelerating quickly (and it will) then shuts down you have the boost too high. Even if you turn the boost down you still might hit fuel cut on cold mornings.
Post by volvslow » Tue Jan 05, 2010 8:00 pmi just received mine today actually! got it on ebay. i did some research on the cheap, no name brand manual boost controllers on ebay (oh you know they say “high performance turbo controller” on em). turns out some folks have written good reviews about them. its black includes the control valve, extra long vacuum tubing (to install in cabin), mounting hardware, etc… it controls 1-25 psi. 18.00 usd. probably going to drill a hole in one of the blank plates behind the steering wheel under the cluster and mount it there. figured i set it at a conservative 10psi. there is one that is cheaper. it just doesn’t include enough vacuum line to run it in the cabin. but i see this being difficult to adjust. example: floor it 50mph and watch the boost gauge, stop, pop hood, get out, open hood,adjust little knob, get in, floor it to 50mph watch boost gauge, stop adju………get a boost gauge if you don’t already have one.