You adjust preload by changing the length of the actuator arm using the turnbuckle at the end. If you shorten the arm, then the spring in the actuator is preloaded when the wastegate is closed. That means that greater boost pressure will be needed to move the wastegate puck off its seat. However, the rate of the spring remains unchanged so once that preload is taken up by hitting the threshold boost pressure (which is higher than with no prelod), the actual travel of the wastegate arm will remain the same as it would have been without the preload (minus the preload distance). A higher pressure actuator (like the 25 psi unit) has a stiffer spring and therefore the rate of actuator arm movement is less for a given pressure even with no preload -- which is why a softer but preloaded wastegate actuator might have a similar crack pressure to a neutrally installed higher rate actuator but have fewer issues with boost creep when used close to the minimum pressure (because the wastegate is open wider). The advantage of the higher pressure gate is that when preloaded it can have even more seat pressure (spring pressure when closed) and thus is less likely to "blow open" from turbine exhaust pressure (which can cause laggy spool and lost power due to exhaust energy being "wasted" when you want it going through the turbine wheel).

Hope that made sense!

 

I truly appreciate this explanation. Thanks, EVO8LTW

 

Well, I checked the actuator preload on my car and found that it wasn't as much as I expected. It was basically one full turn (2 half turns) from neutral. I tightened it one full turn and took the car out to see where that put me. At low RPMs my boost hit wastegate pressure of 20-21 but it crept to 28 psi on the top end even with only 2 turns total on the preload. That's the highest I've run the car on boost up top so far (still getting my tune dialed in little by little), even though I've been running it higher in the mid-range. Good news, VDR reported over 500 whp with that treading into higher boost levels on the top end. Bad news, my 3700-3800 studder is still there.

This almost feels like its missing in that narrow RPM range. The AFR goes rich when it happens and the boost dips below wastegate pressure, so I think the car is actually misfiring. It's also very consistent about the RPMs that happens in. I just wonder if this might be a stock ECU SD gremlin of some sort. It did it on stock ignition and I recently added a Spoolin UP COP (and fresh plugs), and that made no difference. If it's not the actuator, not the ignition and not the BOV, there's no much else to adjust. I might just have to tune it out with the WGDC table (after reducing my preload to my previous level), as much as it hurts me to lose torque in that range.

 

yes im running the 25psi gate and thats what it does. I dont mind it cause I use e85 and sometimes 93oct but still...... That is with me pretensioning it a few more mm then what FP had it set to. When FP checked it out they marked it off as a 25-30psi gate.

 

and if you want to preload it a lot you pressurize the actuator so it allows you to slip the arm over the flapper arm thats how mines done.. clearly mine would suck if i was using 91oct though. nice explanation though.

 

What O2 housing?

 

I pressurized my actuator today when I adjusted it. I've always fought with the arm, tugging and pulling, killing my fingers, endangering my radiator, etc. And then today it hit me -- "just pressurize the wastegate dummy"! So, I ran a rubber hose from my tire to the wastegate and used that to take the tension off it. Soooo much easier to adjust that way!!! It also shows you how much actuator movement there is at a given pressure (since it's easy to adjust the tire pressure if you have an air compressor in your garage).

 

It's a Helix, which is basically just your typical ebay housing.

 

Thanks for explaining it. It makes sense now.

 

Could this be your problem ? To me it does not sound like a WGA issue, but hey what do I know ...

 

Are you refering to the possibility that a too small merge hole might be causing his boost problems?

 

a bit off topic, but since you guys all seem to understand the workings of our WGAs, i'll give it a shot:
no matter what my WGA is preloaded to (i've tried it everywhere from neutral to threaded all the way down), i end up at 16-18psi of boost with my Forge MBC. i can get the boost to reach pretty much anywhere i want (25psi right now), but always tapers to the 16-18psi.
do i need to cut the arm down for MORE preload? is my MBC bad? i have the "heavy spring" in the MBC (assuming Forge sent me the right one). i added a "helper" spring to my WGA in addition to tightening it all they way down.
any ideas, guys?

 

You are right in assuming that you need to shorten the threaded end of the actuator rod. Measure and cut just 3/8" off the threaded tip of the actuator rod. It is a relatively simpe proceedure and can be done carefully with a hacksaw. If you are careful then you shouldn´t even need to touch up the threads with a file.

 

i figured that could be it. i've read quite a few people mentioning how they have had to cut the arm down. i'm guessing the end bottoms out before making it to the bottom of the threads?
i wouldn't suppose anyone's done this while the WGA is still in the car? LOL

 

I know this thread is a couple years old but if anyone else is having an overboost issue with there 25psi wastegate actuator, I referred to this while using googling the 25 psi vs 18 psi unit from Fp with my red turbo. I couldnt stop boosting over 30psi with the unit even with zero preload and the boost controller taken out of the equation. I ended up just throwing the stock actuator back on and im boosting right at 20 psi.....Ill hang on to the 25psi unit for when I have my block built up and tuned for big boost.