wastegate acuator

[talon_frost]

how tight should the acuator rod be ? should it be as tight at it wil thread in to the acuator or should it be loose?

 

[Mr Peepers]

It should be pulling the lever very tightly when installed, but not to the point where it is pulling the rod out more than 1/16".

 

[JusMX141]

By adding more tension than necessary to the wastegate arm you're preloading the spring which is delaying the opening of the wastegate, and raising the boost level.

Adjustable wastegate arms were previously the only way raise or lower your boost level until the boost controller became a popular item. Basically if you had an 8psi actuator you could run no less than 8psi when the arm was at it's loosest setting, and the boost level would raise slightly as you'd shorten the rod.

The downfall to this method is that by preloading the spring heavily to achieve a very high boost level you're taking the responsiveness out of the actuator. Many times if you have too much preload on the actuator you'll see a slight spike in boost pressure prior to the wastegate opening before it drops and settles to the desired level.

Many of today's solid-rod actuators (like those found on the T25 and 14B/16G) cannot hold much past 18 or 20psi before they begin begin to open on their own. The only way to control this is to use washers to shim underneath the mounting tabs of the actuator and add a bit of preload to the wastegate system. Of course there are tons of variables that determine the final pressure at which a wastegate will open- wastegate hole size and flapper size being the two biggest factors.

You'd be surprised- once you reach higher boost levels, wastegate arm travel and flapper size have absolutely NOTHING to do with controlling the boost level. If the wastegate opens as much as 1/4", the boost level will be limited. For those who think bigger flappers are better at higher boost levels, take a look at a 16cm2 Holset turbine housing for a large diesel truck running 35 or 40psi....the wastegate hole itself is barely big enough to fit your pinky into, and the flapper is about the size of a nickle.



Recently we ran into an issue on my buddy's car when trying to achieve anything over 18psi. The car has a 34mm internally-gated FP Green and we were using a T25 actuator (the turbo had a welded flapper when I got it, be he wanted to go internal and the T25 actuator was the only one I had that would fit properly.)

Anytime we tried to boost past 18psi, the flapper would blow open. The car has an external dump for the wastegate chamber, so we could hear when the wastegate would open....no hiding that. I began shimming the gate tighter and tighter and we were getting the same results. We were down to 1/4" of arm travel, and I had the boost source going to the actuator completely disconnected- same result. I ended up getting a universal AGP actuator with a much stronger spring and an adjustable arm and manufacturing a bracket to hold the actuator head.

The first time out with the new actuator the car made 28psi....I had far too much preload on the actuator arm. Plently of tuning later, we've found a sweet spot between the actuator having enough spring strength to hold the flapper shut and just enough preload that there isn't a huge spike in boost. The boost now spikes to 23-24psi before settling at 22 and holding it rock-steady to redline.

Lesson learned: If you want to run more than 20psi and have absolutely no issues controlling boost, an external wastegate is highly recommended.