Thread: boost lost???

Originally Posted by Blknight.aus

it depends on which way your vanes are setup to swing but if your rod moves out under pressure then you want the arm to just not quite hit the stops when you have the rated boost pressure applied to the waste gate

ideally you want to achieve with the rod adjuster near the middle of its travel.

if the turbo response is too slow (assuming correct fueling rates) then shorten the rod. to delay the actuation of the vanes.

the stop mounted in the cast iron housing is a crub screw with a lock nut. I have not touched this and cant see how the plate DIDNT touch it....im pretty sure it did.

I will check whether the amount im taking about, will either way have the plate open to its maxium. I can clearly see the point where the soot stoped above the lock nut on the actuator rod. And going off the pic I took of the wollowed out rod fitting I think I have my new hole pretty close to original....+ or - 1mm from the end.

the external stop is the limit for the actuation mechanism, If you have the acutator pushing the arm into that too early the extra pressure in the diaphragm can cause it to rupture. the clearance only needs to be minisucle 1 thou of an inch is enough.

the other side of that is...

if you have the arm pushed into the stop too early the extra force generated by the actuator will eventually twist the pin out of the arm.

the rod/actuator is not PUSHING the plate into the external stop...It is PULLING it...hence that is why it is against it in the pic I posted (ricks) and why I was saying that it was against it under minimal boost(idle) as it hasnt enough to actuate the rod off it

Originally Posted by uninformed

thanks Slug...but I think you may have it backwards??? (or I have miss understood you) I dont really know much about turbos.....

when the actuator is in the retracted postion (ie minimal boost = idle) the rod is up and the plate against the stop on the cast iron housing. This stop has not been touched, so whether I leave the adjustmant on the rod as is, or wind it out 3mm, it will not change this stop point. The actuator has a spring inside it so it takes more than 1 or 2 psi to get it to move....

what im looking at is if I have to use 2-3mm of rod movemnt just to get it to seat at the stop postion, I loose this in full extended position.

what is this controling other than the vane angle? ie does the actuator control max boost??? I dont want to run more than stock, which I believe upto 20psi.

Max boost is controlled by the stop screw, this sets the minimum amount the vanes can be closed, remember you don't have a wastegate so this has a major impact on your EMP (exhaust mainfold pressure).
The actuator rod length sets the rate of boost.
it is a fine line to balance the two and i think this is referred to as the duty cycle.
I have never set up a VNT but to my understanding it is best done with a boost gauge and of course someone who knows how.
Hope someone here can steer you in the right direction.

Cheers,
Paul.

Originally Posted by Blknight.aus

it depends on which way your vanes are setup to swing but if your rod moves out under pressure then you want the arm to just not quite hit the stops when you have the rated boost pressure applied to the waste gate

ideally you want to achieve with the rod adjuster near the middle of its travel.

if the turbo response is too slow (assuming correct fueling rates) then shorten the rod. to delay the actuation of the vanes.

tail end around... your stop looks to be the retraction limit, Id set it so that it just starts to clear at about 1PSI....

Originally Posted by harro

Max boost is controlled by the stop screw, this sets the minimum amount the vanes can be closed, remember you don't have a wastegate so this has a major impact on your EMP (exhaust mainfold pressure).
The actuator rod length sets the rate of boost.
it is a fine line to balance the two and i think this is referred to as the duty cycle.
I have never set up a VNT but to my understanding it is best done with a boost gauge and of course someone who knows how.
Hope someone here can steer you in the right direction.

Cheers,
Paul.

so as the engine revs up, the boost increases and the actuator rod extends....this extention and its limit is what limits max boost???

im not sure which way the vanes are positioned at idle with the actuator rod retracted...

Originally Posted by uninformed

so as the engine revs up, the boost increases and the actuator rod extends....this extention and its limit is what limits max boost???

im not sure which way the vanes are positioned at idle with the actuator rod retracted...

With the actuator retracted and engine at idle the vanes are as closed as the stop screw lets them. this is maximising ehaust flows to the turbine.
This is what makes a VNT so much better than a wategate turbo as there is much less energy being wasted.
With the actuator fully extended the boost will be at it's LOWEST.
The overall operation is in some ways similar to a wategated turbo but much more complex and efficient.

Paul.

thanks Paul, so do you think it would be safe to say, that if the rod fitting is set within 2mm of original postion and either way it was against that set stop, I should be ok...as I said I never touched this set stop and I dont think anything would have changed with it. My major concern was over boosting, but I think that max boost wont have changed. I think I will leave the rod set up so I have to put a small amount of pressure in the actuator to fit it up...that means at rest/idle the actuator spring is already compressed a little and should move off a touch quicker...the rod travel length lost here will only affect minimum boost at full extention


clear as mud