Been chasing an issue with the car all day. Think I've finally got it pinned down, just wanted to see what you all thought and make sure I'm going down the right path...
Initially I was seeing a steady 12psi with boost gauge all day long, but MS's MAP sensor was showing something really weird- spools up to 100psi or so, then around 5k, it ramps up to 13 and stays there till redline. Does seem to start fluttering a lot though closer to redline. Boost gauge and MAP sensor using the same source. Using a hallman MBC. Does the same sorta thing spring pressure only..don't suspect the mbc being any sort of issue or contributing factor.
Upon further investigation (should have caught this earlier, but I didn't), I'm having to use usually high VE values in the 4000-5000 RPM range (where the low 11psi spot is in datalogs), in order to maintain target AFR. Around 5k the VE values actually decrease and seem to go back to 'normal' (I am running a bit rich up top, still need to finish the tune for sure).
So my logic is that, for whatever reason in that 4000-5000 region, actual air entering engine > measured by the MAP sensor. Spool up is fine, 12psi @ 3800 in a 2871 w/ big turbine housing. If it were a big boost leak in the IC piping I'm thinking it would be hurting spool a lot, and actual and measured air would probably be the same/very close. So, pretty sure I have some sort of leak in my vacuum tubing, probably close to or at the megasquirt, since the boost gauge (which is tapped off same source) seems to be reading steady and consistent. I'm still kinda perplexed as to why it would only be 'leaking' from 4000-5000 though, and appear to go away above that?
I did a quick check of all the fittings, hoses, IC pipes and everything seems OK.... going to make a real boost leak tester this week to actually test this stuff out. Am I on the track you think? Driving myself crazy today trying to figure all this stuff out. Here's a datalog that shows the Boost/VE stuff I was talking about....this is very repeatable. Boost gauge always showing a steady and consistent 12 psi.