I had some time recently to play with the VNT settings while I am now waiting for the
wastegate to arrive. I am keeping the fueling set at 1/3 turn less than stock 1.6lTD to reduce risk of the boost creeping out of control or doing bad things if the VNT seizes or something before the wastegate gets in.
Previously, when I had the vanes hard-set to all the way open with the fueling reduced, the peak boost was limited to about 12psi (measured at the top of 3rd gear), but the car was not all that powerful off boost, not much torque when the RPMs were low before the boost kicked in. Well now, I installed my nifty new VNT controller with quicker-reacting spring. I initially installed it so it rested at about 50% open, which was a noticeable improvement in making the turbo react better at lower RPMs, and so then I went on and adjusted it so it just sits at 0% open with almost zero spring preload. So basically any pressure applied, even a fraction of one psi, starts the vanes opening, but they rest at full closed when there is absolutely zero pressure. It ended up putting out just a wee bit of boost at idle, although did not seem to be the full 1/3 of a psi strength it had before when I had the vanes more tightly held closed. But now it is obvious that the VNT vanes are definitely moving and the controller is trying to regulate the boost pressure, and it seems to be functioning smoothly and reliably.
With the current VNT controller setting, the boost is quicker to jump to 3-4 or so psi with some throttle application at relatively low RPMs, and the boost climbs more as more throttle is applied and as RPMs rise, quickly up to about 7 psi, then slowly creeping with rising RPMs past then (it seems the vanes must be completely open by about that pressure.) In theory I should be able to see 12psi at the top of third gear at wide open throttle, but due to bad weather and traffic was only able to manage testing the top of 2nd gear, where I saw 10 psi. At freeway cruising steady at 65, it sees a comfortable and controlled 4-5 psi. It is managing to turn out decent powerband, torque, and driveability even with the pump dialed back by 1/3 of a turn! That's because the VNT is giving such a broad boosted powerband and the pump is kicking into "boost pressure / fuel enrichment" mode so often at such a broad RPM range, I reckon.
Oh yeah I also took care of my blown boost tubes problem by flaring the end of the problem hose nipple.
I am noticing when I pull away from stops after sitting idling for a while, there is a small cloud of what looks like oilsmoke left behind. Not good - I wonder if it's valve stems/seals or if it's from the turbo. I will continue to monitor. The good news is that it is clean as can be, never smokes dark diesel smoke at all, whereas before with this was naturally aspirated with the loose timing belt, it had a real smoking problem and we probably would not have even noticed any oil smoke if it was present! I don't know what to do there, probably will just wait it out and drive it more and see if the problem is stabilized or if it worsens, and monitor oil consumption.
I can't wait to get the wastegate on there and pump the fueling back up to stock 1.6lTD levels... I really have a feeling that that this thing is going to rock! :twisted:
PS - one more test for me to try this week before the wastegate arrives... I'd like to try increasing the VNT pre-load by 2-3psi so it doesn't lift off it's full closed position until a little bit longer. Ideally this won't raise the peak boost pressure but will make it reach there quicker and open up even more power and torque at the low to mid RPMs, making the car even more driveable.
