1st Gen R53 Cooper S VGS Mod with negative consequences.

Having the day off today, and doing some reading and researching I figured, why not? I ran up to the shop and prop the tool box open and started with the VGS mod. In theory it makes great sense, my old turbo cars were setup similarly. Use a post-intercooler boost signal source for the wastegate so it gets the most accurate reading to whats entering the intake manifold.

Anyways, I perform the VGS mod per instructions and popular writeups of the internet and common sense. Took our shop scan tool out and entered a live data mode to see the MAP sensor readings. I registered 41.93inHg on the map sensor at WOT and about 5500 RPM.

After doing some simple math, I came up with 41.93inHg = 20.5 psiA which is not including the subtraction of atmospheric pressure (14.7psi) to come up with a WHOPPING 5.8 psiG! Thats 5.8psi on a boost gauge! Bone stock 02 MCS, no pulley nothing! Ambient temperatures were about 46 degrees Fahrenheit. THERE ARE NO VACUUM/BOOST LEAKS AT THIS TIME! ALL LINES SECURED WITH ZIPTIES!


Does that not sound extremely low even for a stock pulley MCS? What could cause it to drop from the stock measurement of around 8-10psi?