Need explanation on actuator adjustment.

POWERSTROKE · November 6th, 2009, 13:31

Hi all,

I have my car reasonably set up now. I have a question just for my own knowledge. It is said that the "actuator should crack open at 3"-5"HG and fully open between 18"-22" HG". Mine is set for 4" and 20.5"HG. I have tested my N75 control and it is in between 0"-25.5"HG. So both of my numbers are in between the high and low. Good control. Now, all i want to understand is what these numbers mean? What if I had it set up the actuator to open at 3" and fully open at 18"? What would my drivability difference be? Or 5" and 22"? What I am seeing is that of you set it to open at a certain point, you have zero control where it will fully open and vice versa. So what numbers are more important, and what really matters.

jcrews · November 6th, 2009, 13:48

I have RC2 with PP520 nozzles. The actuator went bad on my turbocharger, so I put a new one on. Previously, I had adjusted the old actuator quite a bit (longer). I set the new one against factory settings (17.5" to drag a 0.05mm gauge, and 18" to capture it), and boost went off the scale, as expected, under heavy load.

So, I fell back on adjusting it longer and longer until the response was correct. I just had to drive around a bunch to get it mostly dialed in. The initial adjustment is important, but, especially with a modification or two, additional adjustment could be necessary to match the turbine response to the engine's configuration. The only good way I know of to accomplish that is to try different settings until you converge upon the right one.

POWERSTROKE · November 7th, 2009, 04:12

Thanks jcrews. My initial question was only because i think it is mechanically impossible for me to have the initial open at 4" and full open at 18". Mine opens at 4" and doesnt fully open until 20.5". So, I have to live with either the first or second figure being where it should be.

jcrews · November 7th, 2009, 13:24

A start pressure wasn't specified in my TSB.

POWERSTROKE · November 7th, 2009, 14:42

This is true about start pressure and the tsb. But I have read every single article on this site and everyone says between 3" and 5"HG start to open. So I can forget the crack pressure and just shorten the rod to fully retract at 18" HG. What will I gain or lose by changing from 20.5 to 18hg full open? I do believe from a mechanical point of view that the N75 is the arbiter of what vacuum pressures will work. As long as you have an N75 that cycles a few points ("HG) higher and a few points lower the the open and close pressures of your vnt actuator than I would think, in theory, you should be fine....