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Here's how the story goes, it may get a bit confusing so i'll be as descriptive as possible.

I own a Greddy 18G with its factory WG actuator. Before my tune I decided to purchase a 14psi wastegate actuator from ATP turbo and swap the WG's in order to be able to reach my goal of 22psi.

On the day of my tune, I didn't realize that I had installed the ATP actuator with a bit too much slack on the flapper and made only 8psi initially not hitting my desired 22psi until really late in the powerband, say 5500rpm or so where it was useless. Bear in mind this ATP actuator was supposed to be no less than 14psi out of the box. Basically it was leaking boost until enough pressure built.

I should also note at this time that I have an S300 and PWM boost by gear.

Now...the day after my tune, I strap the 18G factory wastegate back on and make 10psi in first gear at a more desirable RPM basically how a greddy 18G would spool, nice and early. 3rd gear I'm now hitting 17psi, which is nice but i'm tuned for 22psi..something the factory greddy actuator just will not reach.

Changing variables:

So yesterday I install the ATP 14psi actuator again, this time properly. Nice and tight over the flapper, not allowing boost to escape early on and building pressure like an 18G should

1st gear - 14psi, great
2nd gear - 16psi, great
3rd gear - wanting to go passed 22psi and car going into boost cut.
didn't even proceed going through the rest of the gears as i'm sure this issue would persist.

I'm trying to make sense of this because my boost by gear is set to only make has high as 18psi in 3rd gear and 22psi in 4th and 5th.

So why this spike? why won't it hold at 18psi in 3rd?? could it possible i got overzealous with the tightening of the actuator rod on the flapper as to eliminate the boost creeping out into the exhaust? so much in fact that now the flapper doesn't want to open enough??

however if this is the case...then why no significant boost cutting spikes in 1st and 2nd?

thanx in advance to anyone that takes the time to read this and lend a hand.
 

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Whats the duty cycle in the different gears? I assume you have adjusted them when you changed actuator?

Another thing to think about - If you make boost significantly earlier now then what you did when you got tuned, you should be careful, as that part of the map was never reached on the dyno. At the best the tuner had to guess what kind of numbers to put into the cells, or he just left them alone.
 

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i'm going to say you'll always have this issue with the internal WG.... its a known issue with the mitsu housing inparticular.

you need to start by adjusting the boost vs gear pwm settings though and see if it helps.
 
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