MicroSquirt.com read only forum (Jan.15,2018)

Alirght, I'm fairly new to this tuner world,I bought a garrett t25v used for my sandrail, it has what looks a waste gate but has no adjustments, what is it set for, can i buy an adjustable one?

Thanks
Brendan

It should be set somewhere under 10 PSI (I think). It may be adjustable already- the GT28 on my Miata has a bolt on the rod, you loosen it and turn the entire rod to adjust boost, then thighten it back up. If it's not adjustable, a cheap boost valve , AKA "manual boost controller" is what you need.

The length adjustment on the wastegate actuator is not meant to adjust the boost level, rather just to allow the wastegate to be adjusted to be fully closed. They do effect a small measure of boost adjustment because the spring force changes slightly as it is stretched but usually only +/- 1 or 2 PSI and you risk overboosting if you go too far (because the wastegate can no longer open fully). If there is no adjustment provided for , it is of no consequence.
As mentioned previously, get a boost controller of some sort if you wish to increase the boost level. you will need a new wastegate actuator if you want to decrease the amount of boost (or use an external spring to take some load off the wastegate).

Well, I went from less than 5 to about 8 (limited by stock spark for now) by adjusting my wastegate, so it worked for me. Yes, you are right- trying to adjust it really far won't work. Also, you don't stretch the spring to increase boost, you compress it by shortening the rod. That means there is more load from the spring, as it is compressed further, so it takes more exhaust pressure and more boost pressure on the diaphragm to open the wastegate. This is analagous to changing the spring in an external wastegate, or screwing in the top of a blowoff valve. You can also use washers and spacing to lower boost on a non-adjustable rod- not that you would ever want to.

Of course, you want a boost controller, I am thinking about giving MS a go with a DSM valve eventually. There is obviously no way to adjust your wastegate while in the car, and an electronic boost controller will make your turbo spool faster due to the partial elimination of wastgate creep (ever notice how the spool slows down a little when you approach max boost?). They are NOT cheap though, usually a couble hundred (when a $200 MS can run your entire car, $400 for a box that PWMs a solonoid based on MAP seems just a little overpriced).

just to give warning: adjusting the rod is NOT a good way to do this. What you are actually doing is changing the preload on the flapper valve, and changing the flapper valve movement range, but what you aren't changing is the spring rate. This creates the following problems:

If you increase tension, you reduce the amount the valve can open, this will cause the boost to creep at higher RPM's. IE, it'll see max boost at 10psi for example, then will creep up to 16psi. This is due to the flapper valve being limited and this restricts the venting of teh waste gate

The alternative, stretching the rod will leave very little tension on the flapper, and the oppositive of the above will happen. It will spike the boost high at initial boost, and then bleed pressure at higher RPM's. IE, spike to 15psi, then fall down to 10psi later.

The proper way to setup a internal waste gate setup is: start without a boost controller. Set the tension on the rod so that you have even pressure, no creeping at all RPM's and loads. Then install the boost controller and tune it to whatever PSI you want. If you max out the boost controller, there is no way around it, you simply need a higher spring rate in the waste gate, but you will be quite surprised how much PSI you need before that starts happening. I've seen 25psi on my T3 and had more left in the boost controller.