You write:
"We found that with the 1.4mm jet (that we'd set up previously on the road) the boost would rise to 18psi but then drop off at higher RPM. So we decreased the jet size even further..."
The boost map doesn't directly represent the boost level. It would have been because the engine wanted to make max boost at 4800, so the solenoid was closed to lower the boost. Then as revs rise boost tends to drop off so you see the values increasing to try and hold boost.
T28 will struggle to hold anything more than about 16psi above 5000 no matter what you do. Good turbo though - my favourite on an SR. Mr. Nissan chose well!
after the 4 k mark you can open her up.. 5000 + you should be able to use values up near 100 as the t28 flat out will only produce 14psi in these areas.. you might get more but I doubt it.. If machining a restrictor is too hard make an adjustable one.. but year the 1.2mm worked well for me when i did it..
tell me what you think of this document.. I have not had any results from people as yet.. however I did find that the most responsive place is to get the boost signal from the compressor cover on the turbo not post I/C you couls ged even more agressive with the boost control.. would love to see it with an external though.. the results were not as good as my blitz.. but you pay for that.. and full throttle no difference but on partial throttle I got more out of the blitz... tuning the nistune for partial throttle gave me spike on full throttle and vice versa.. if you could add more bleed to the high load areas it would be an awesome system.. but I dont think you can.. the MAp is not 3d.. only 2d..
hey matt is the is the nissan boost map actually 3d or is it just the way nistune represents it.. if that makes sense... I was going to do some more testing with the system.. just havent had the time.. I know my knock sensor is going off for no reason well atleast I think so.. I think it is the worn vct gear that might be doing it.. it seems to jump on light load gear changes..