I have been looking into the BBS twin turbo kit. It has internal waste gates.

If I understand correctly you can adjust the boost using the pressure line going to the diaphram.

Also, I have read for higher boost applications that sometimes an internal wastegate may not be big enough to bleed off pressure at hi boost. Is it possible to add an external if necessary to fix such a problem?

Does anyone know what would be the max reliable amount of boost you could get out of the set of Garrett TBO3 turbo's that they use in the BBS Design? (of course when I am talking high boost it would be intercooled, I am just asking about the turbo's themselves)

You adjust boost by changing the spring pressure. When the diaphram pressure overcomes the spring force the valve opens. On an internal WG you adjust spring preload by changing the length of the rod going to the valve. With an electronic boost controller and a boost control valve on the pressure line going to the diaphram you can raise the boost pressure over the spring setting.

Yes

Cool, Thanks for the reply JoBY.

What you are referring to is commonly called 'boost creep', when the WG can't divert enough exhaust.

You can port the passages and have bigger valves installed on the internal WG's, though I don't know how much bigger you could go on said T3's. I'm not sure of the price difference, but I don't think it's as much to do that as doing an external setup (two external WG's, welding, etc).

I don't know how much boost is doable before these particular turbos will creep, but I'll let you know when I get my setup done sometime next year. The kit is paid for (months ago) and almost ready to be shipped.

Like JoBy said, you can adjust the boost any of those ways.

As for the max reliable amount of boost, it's largely dependant on how high your setup will rev and how much air it's capable of flowing. Just as an idea, I plan on running 15 intercooled psi to 5500 rpm on stock L98 heads/cam/tpi with ~8.7:1 forged internals, then on same setup but with an HSR, to 6000 rpm. It should work fine like that (next setup will have and need bigger turbos). I did order the .63AR/stage III turbine side though, if you get it you should too.

Here's the compressor map for the T3 60 trim compressor wheel.
Hope this helps.

Thanks for the awsome response!
Please keep me updated on how it works out.