Figured id clear some stuff up with regards to Pure Stage 2 turbos when running pump gas(91 or 93) on the VR30 Q50/Q60. This is completely different when running ethanol which is explained later in the post.
Someone posted earlier this week about an issue he was having with his setup on pump gas. A lot of people were quick to blame his tuner.(It wasn't me but someone who is more than capable)
The issue is not with his tuner but with the design of the turbo itself. These are basically modified turbos in a stock, mostly ported shell. The wheels are much bigger than stock and the center sections are much stronger but the wastegate port and flapper door are still stock size.
For those of you unsure how a turbo works, the wastegate port is an exhaust bypass that routes exhaust gasses away from the turbos turbine(exhaust) wheel to limit and control boost. Since the turbos are driven by exhaust gasses, the wastegate is an exhaust gas control valve. The more the bypass door is open, the more exhaust gasses get routed AWAY from the turbo helping to keep the boost down. The more the door is closed, the more heat and exhaust gas get routed to the turbine to assist in spooling it up and making more boost. These cars have full electronic wastegates. 0mm is fully closed while 8mm is fully open. The idea is to keep them closed as long as possible to assist in spooling the turbo up then opening them as the boost approaches target boost in such a way that prevents over boosting.
The wastegate ports on these turbos are far too small. In order to run pump gas safely, timing needs to be very low. The side effect of very low timing is excessive heat(exhaust enthalpy/energy) in the turbine housing. Increasing the heat also increases exhaust gas velocity(hot gas expands)which also effects spool. The issue with these turbos is, when on pump gas, the timing is so low and exhaust heat is so high causing the turbo(s) to over spool. The wastegate port is too small and unable to bleed off enough exhaust gasses to keep the boost in check. This causes an over boost condition.
On the other hand, the reason the turbos are so laggy (on pump) is because in order to keep the heavy wheels from just taking off and over boosting(which they will do regardless), the gates need to be FULLY open (8mm) for most, if not all of the rev range. So, you get a turbo that takes forever to spool up and once it starts spinning, it just goes to the moon. Adding a higher flowing full 3” exhaust and the problem will get even worse as this will speed up the wheels even further without the ability to slow them down.
As soon as these things go on ethanol, its a completely different story. The timing changes are so substantial that the turbos start to work beautifully. The gates get to actually close early on bringing boost up much faster. Because the timing is so much higher, the EGT(exhaust gas temp) and exhaust gas velocity go way down and allow the wastegates bleed exhaust gas and properly control boost.