[TitaniumTT]

Sounds like a VERY intreresting project! I like the thought that went into it. Unfortuneately for me, I only hav the option of running one stepper motor with the Motec that I'll be using. I was going to use it for the OMP but I like the throttle body butterfly for the intake idea more. I suppose I could use an internal style wastegate actuator connected to a butterfly valve as well.

My main question would be, how would the turbo's handle working against each other? The larger T4 turbo in your example would be moving more CFM at the same boost pressure as the T3 style. Pressure is pressure and if held constant between the turbos, would the T4 over power the T3 in anyway?

The setup I had in mind is similar. Here's the setup that I'm contemplating

Two equally sized turbo's as far as compressor goes. Possibly changing the A/R on the secondary turbo to reduce the inherent backpressure that would be created between the two turbo's. Basically what I'm contemplating is an equal length mani with a T3 flange and the largest WG possible right under the flange. The primary turbo would get the full brunt of the rotary exhaust. This primary turbo MAY be gated on the snail, and if so, that WG will run to the DP, I don't think the will be necessary though. Routing from the turbines exit of the first turbo is plumbed directly to the turbine inlet of the secondary turbo. The first WG is also plumbed back into that same exhaust stream allowing the exhaust energy to be split. There is a second WG below the turbine of the secondary turbo as well. This WG is vented directly to the actual DP. That's the exhaust side of things.

The intake side is rather simple as well. THe primary turbo is plumbed directly to the intake track. THe secondary turbo will have a vent valve placed between the compressor discharge and a TB style butterfly valve to keep the two turbo's seperate.

Play by play -

Theory being that when you floor the go pedal, the smaller turbo gets the full power and flow of the exhaust and such will spool VERY quickly. The WG associated with that turbo keeps the primary turbo;s boost in check. The secondary WG will COULD be open at this point to reduce the backpressure between the two turbo's to allow for a bit faster spool in the lower RPM's. (If I need to build seperate vac and boost storage tanks to aid in this, so be it. Easy enough to do, They're on my setup now actually) As RPM's and EMAP increase prior to the first turbo, the primary WG will open to keep the primary's boost in check, when the prim WG is fully open, the secondary will be in charge of controlling boost in the entire system. Once the secondary turbo begins creating boost, the seconday WG will most likely begin to close to aid in the secondary creating boost. Once boost is realized in the secondary turbo, the vent will close, the butterfly valve will open and both will be running in parrallel. The point of the second WG on the snail of the first turbo would be to vent the exhaust energy from the first turbo if the difference in flow of the exhaust system was such that the primary was receiving more energy than the first.

In my Datalogs of the stock sequential system, the rear turbo will always run hotter by ~75-100*. I've switched signals, repeated runs and gotten the same result so I know that it is not a function of different sensors, wiring, or signal amps. My theory is that the exhaust flapper in the rear of the housing creates enough resistance to increase the backpressure there, keeping the gas hotter. There is a direct correlation with the seperation of EGT's and EMAP.

The system that I am proposing is very similar to the stock sequential system. In my eyes, the drawback to the stock system is two fold. The inability of the hitachi turbo's to tolerate more than 15-16 lb's of boost reliably. More important though is the exhaus mani itself is a convoluted mess. A tubular mani in my eyes would yeild significant gains.

The plumbing would be a bit of a chore. However, I believe that after scouring the goodridge catalog, they offer enough fittings to allow for a somewhat neat packaging. I would run one -3 line to the top of the turbos and hope that I could get the CHRA's in a banjo fitting and just use an on-the-run type fitting to feed the second turbo. Drains are pretty simply if you're using an RE or an REW block, there is a drain for and aft. I would use the outlet/inlet of the WP housing to cool the first turbo. Perhaps use the nipple on the rear housing to cool the rear turbo and just weld a second -6 bung on the waterpump inlet. Although I do plan on using an REW WP housing, I plan to take the T-stat housing and outlet off and build my own to suit my needs. In that case the AST would be contained there and I would just have a ton of fittings welded on to it. I think the exhaust plumbing would be much more of a headache than oil/coolant plumbing it thats what you guys are reffering to with the plumbing nightmare comments. Hardlines would be awesome to have here as well and are very easily made, even when using banjo fittings.