Sharpxmen if I understand what he is trying to do correctly, his "bypass valve" will close completely under boost allowing the MAP to read atmospheric pressure only.
The idea was to close valve on boost and at the same moment to open small valve connected to intake part of turbine, where a little vacuum supposed to be.
the moment that valve starts to open you'll drop boost and will close back
one issue is how you control it
assuming you find a way with some fast switching electromagnetic valves that would open/close in sequence (not mechanically actuated as that would not work) second issue is how do you control the fuel delivery for anything over 0 pressure.
let me explain this last one (i'll simplify the numbers):
your stock map reads 0 absolute pressure to 14.7 absolute pressure (no vacuum, wide open throttle) - the voltage output is 0v to 5v (at idle you'll have something like 1.6 or close to that) - your fuel delivery is based on that range
once you do this mod and let's say you're at 6 psi max boost for a total of 20.7 psi absolute pressure - how do you compensate for the extra air between 14.7 psi and 20.7 psi - you will need more fuel and will not be a set value but progressive as the boost increases
what you need to do is to shift your map output so it will give you 1.6v at idle and 5v at 20.7psi
in reality the stock 1 bar map outputs something like 4.7v at wot
you can do it with a 2 bar map and a volt mod for the map input, but you'll also need a voltage limiter on the output of the MAP so it won't go over 5v or it will set a fault code in your PCM and possibly stop functioning until you reset the computer
the other alternative is to keep the 1 bar map and use an FMU (you'll have to determine the ratio you need)
your stock 1 bar map will only read 1 bar so potentially you can have it in the same spot as the stock one without this bypass valve you are trying to do - i had it that way and it did not damage mine but i can't guarantee you that it won't happen to yours
but regardless, your computer will most likely throw codes if you with one of these options, you will not be able to tune it properly and instead of getting 30% increase in power once you're at full boost you'll get like 10% or best case scenario if you manage to tune it for that specific range your mpg will hurt badly - for the amount of money, time and research you will put into getting it to work you'll be better of buying a piggyback from the start. As i understand this is your DD, if you mistune it you'll risk damaging the engine - if it was a drag racer then you would mostly be worried to get it right in a specific rpm range and mostly at wot which makes it lot easier, in your case you need to make sure it will function properly at all ranges. Your PCM needs to have the fuel trims in a reasonable range or it will never be able to compensate, that's what the fuel delivery table is for.
But, if you decide to go with something other than the programmable piggyback let us know your progress - i'll be interested in finding out how it goes.
