The actuator holds the VGT closed until 6-7 psi, then spool slows down. Its weird, driving normally you can't really hear much exhaust note wise the only thing you hear is the turbine wheel whistling, keep in mind this is through 8" of exhaust. Once it hits 6-7 lbs, the note changes totally, the rack is open fully by ~10-11 lbs I beleive. It sounds sort of like an electric cutout opening, but not as loud. I think even though it has a huge hotside the vanes still help quiet it down, but make it whistle more. Go under and overpass and it sounds like a jet flying by.
Here is a log from ~70mph cruise in 5th gear showing the transient response. 70kpa, to 9psi in about .95 seconds at ~3000-3100rpm.
It spools a good 1000-1200 rpm faster than the small 8 blade HX40 in the .55A/R bullseye housing I had on the car before. Even with the VGT open fully which is somewhere far above 1A/R. Over 3500rpm or so the boost keeps climbing, by 4400 rpm it reaches 24lbs and climbing rapidly. I'm really glad I included the external gate. I'm waiting on a 14.7 lb spring I ordered to hook it up to a boost source, so it will be a little while till I can do a full pull.
Anyone able to calculate the A/R given the nozzle area and wheel diameter?
Open is the wheel given below and opens to 25cm area. I'm going to clay another turbo I picked up to see how tight it squeezes. I know it has to be pretty small given the fact the 6.7 cummins uses the turbo closed up as an exhaust brake and the stock 5.9 turbo is a 9cm housing and doesn't act as a brake.
Wheel measurements
Turbine
EX 2.357
IND 2.755
Compressor
EX 3.38
IND 2.37
Compressor is as close as I can measure since its a 7 bladed wheel. Measurements similar to the large 6bladed HX40.