Looking for information about building twins. Some don't use wastegates, but I am guessing it is better to use them. The primary is wastegated to around 25lbs? The top charger is than wastegated to limit upper boost? How is the hx35 happy at 50 pounds of boost when it only goes 35 as a single. Or is it total boost minus boost from the primary as what the secondary sees? 50-25=25lbs. Curious how one goes about the wastegating. For those that have built there own, how much does it all cost if you can fab all the pipes yourself. It seems a new HB3t or B2 costs $600-$650. Looks like fun.
Alan

 

Not sure on the total cost. I want to say around $2500, but dont quote me. My top turbo is a S300 that has an internal wastegate. As far as your boost questions, the turbos feed each other so if the primary turbo is putting out 25psi, and the secondary turbo is only putting out 25psi you will get 50psi into your engine. My primary is not wastegated. I recommend the S400 as the primary. It is a little more than a HT3B but spools faster and i like the direction of spin (clock-wise)

Pics are in my gallery

 

I've paid $1800 bucks for two new turbos. The air tubes are cheap, I'm guessing around $100. The most difficult part is the hot pipe off the Hx-35. If you run the S400 or 3B turbo you have to watch on which turbo you pick-up as they lots of different verisions of each. My 3b is a 26cm housing and they are cheap and easy to find. I would put your HX-35 back to its stock 20 lbs. The primary does all the work. Its based on a pressure ratio. If you get a 2:1 pressure increase off your Hx-35 and your 3B puts out 25 psi, your at around 50psi of boost roughly. If you run too much boost on your secondard your drive pressure goes up fast. Most guys try to match both evenly for pressure. There lots of little parts. Exhaust manifold, spacers, oil lines, oil return lines. If you have an auto truck you might have to move the tranny heat exchanger. Good luck, its isn't hard just takes time. I would also use a 3 1/2in air tube off your 35 to your primary. Any bigger it slow down the spool-up.