I have a question, how much boost can hold the greddy twin turbo kit with the stock wastegate and spring? Can hold more than 18psi without drop down the boost on redline?

I see many guys made 18psi of boost or more and use a Greddy TT, but is used the greddy wastegate and spring thats came with the kit or should be make an upgrade to hold this boost.

 

Depends on the boost controller...they will hold a certain percentage more than the wastegate spring.

For me, I run the stock wastegate and push about 30 percent more to hold 8.5. I think once you start exceeding double the spring pressure with a boost controller, probably time to start looking at a higher spring. Makes building boost quicker because of that harder spring pressure initially, so the controller isn't having to fight all the way through.

The guys you see running those high boost greddy numbers probably all have a 13 or 15 spring.

 

with the HKS EVC boost controller and stock greddy wastegate springs, i am maxed at 14.5 psi, it just will not go any higher. it will occasionally spike 15-15.5 psi if i load the engine just right, but it only taps that for a brief moment and comes right back to 14- 14.5

matter of fact, that is the only reason i am not running more boost/power. one of these days when i feel like actually working on the car again i will install my badass SGP 3" downpipes and wastegate relocations with some tighter springs, probably gonna put in around 9psi springs and tune her up to 18psi or so.

 

Charles is right. Depending on the boost controller, the boost curve gets a little jumpy if you try going much further than 15psi. Your best solution, is to install a set of 1 bar WG springs, which produce about 12psi effective pressure the manifold. Assuming you are running a built motor, 12psi is good base boost level for the majority of folks. Then you can use your boost controller to raise the boost to 20psi+ easily.