27-01-2015, 09:33 AM
Ideally, leave the stop screw as standard for now
adjust the actuator to pull the vnt lever all the way to the stopscrew at 0psi boost
Fit an exhaust manifold pressure gauge - take a feed from the exhaust manifold somewhere before the turbo.
Monitor the relation between the emp whilst the turbo is spooling.
I think on the older gen 1 vnt you can expect to see up to 2x emp to inlet pressure ratio on spool - then ideally as close to 1:1 ratio as you can get when you hit target boost.
Maybe 1.5x emp over inlet pressure once target boost is made will be ok, but the further you let the ratio go up the more pressure you're putting on the turbo to make the requested pressure ratio.
What you really want to avoid is pinning a 60psi emp gauge on spool and having a high ratio of inlet to exhaust pressure ratio when on boost.
Just as bad is having surge on boost / throttle. So if the vnt comes in too early it tries to push more air through the head than it will flow and it surges back through the turbo - this is bad news for the turbo. Irrc on a standard head with something like a 2256v surge was around 25psi at 2k revs, but it will be heavily dependant on the turbo and its surge line. You could have a huge turbo that would surge trying to make 5psi at 4k revs becasue it is trying to shift so much air.
TLDR - get an emp gauge on and go from there
adjust the actuator to pull the vnt lever all the way to the stopscrew at 0psi boost
Fit an exhaust manifold pressure gauge - take a feed from the exhaust manifold somewhere before the turbo.
Monitor the relation between the emp whilst the turbo is spooling.
I think on the older gen 1 vnt you can expect to see up to 2x emp to inlet pressure ratio on spool - then ideally as close to 1:1 ratio as you can get when you hit target boost.
Maybe 1.5x emp over inlet pressure once target boost is made will be ok, but the further you let the ratio go up the more pressure you're putting on the turbo to make the requested pressure ratio.
What you really want to avoid is pinning a 60psi emp gauge on spool and having a high ratio of inlet to exhaust pressure ratio when on boost.
Just as bad is having surge on boost / throttle. So if the vnt comes in too early it tries to push more air through the head than it will flow and it surges back through the turbo - this is bad news for the turbo. Irrc on a standard head with something like a 2256v surge was around 25psi at 2k revs, but it will be heavily dependant on the turbo and its surge line. You could have a huge turbo that would surge trying to make 5psi at 4k revs becasue it is trying to shift so much air.
TLDR - get an emp gauge on and go from there
![[Image: avatar_zpstlcgvhg8.jpg]](http://img.photobucket.com/albums/v363/toastmonster/avatar_zpstlcgvhg8.jpg){kind=avatar}