would it work?
 

would a setup work having a small turbo off the manifold and a larger turbo downstream mounted similar to the STS idea? combined boost would be about 14psi. what do you guys think?

If I was a smart ass I would say to put 3 turbos on and get up to around 15 PSI...

Dual turbos isn't the best way to do it.

yes it would work. theres an answer to your question. is it more efficient then running a single turbo at 14psi not really gunna notice a huge difference. if you went higher boost then you might. but yes it would work jut like a twin turbo setup.

anyone else?

why do you need it? ive seen someone running twin turbo setup on m.net but if i recall correctly they didnt see any improvement at all.

Turbotim as the twin turbo setup here and it looks cool but wants to go bigger.
I think a better example of what you're talking about would be the RX-7 twin turbo. Pretty sure it's all one unit but one is for low end and the other is for top end. Most of those guys end up Upgrading to a single turbo because it's more efficient and easy to work on.
I don't see the point it making something harder than it needs to be. A T3s60 spools quickly and produces lots of power and they're not very expensive.

Wouldn't this be considered a two stage turbo set up? Small turbo spools for the low end and the big turbo for the high end? I believe Alfa Romeo has a two stage turbodiesel engine.

The only way to do it correctly though is to have the exhaust gasses going to the smaller turbo cut off and divert to the larger one are some set point. IE complexity.

Well, I have almost all of the parts I would need on hand, so a small td04 9b off the manifold with a t3 downstream would work nicely. 7-8psi at just over 2000 rpm, 14psi from 3200 rpm to almost redline. When I pop the hood people will just see the tiny turbo, lol.

Should I run a collector before the intercooler with a single inlet, or run a dual inlet intercooler?

Why can't the downstream turbo run off the expelled gas from the first turbo?

It would slow down the gas velocity tremendously, and also lose alot of heat energy in the first turbo. You might as well be running a single rear mount turbo if thats what you want.....its been done :P

A 2.5in exhaust should allow enough hot exhaust gas to be forced through by the first turbo to spool the downstream turbo. It would be a lot hotter gas and more flow to the second turbo than just having the rear mount turbo by itself.

Or have it divert via an external wastegate.

I'll take some measurements and see what might work.

your small turbo will run out fo steam fast, and when it does so, it simple becomes a restriction in the exhaust flow. Then it will start to produce hot air out of the compressor housing with no addition boost, and raise the EGTs.

it needs to be bypassed once the second turbo is spooled so the exhaust bypasses the small turbine and flow directly into the larger one.

fwiw, i think using a T3 as the large turbo is a retarded idea. the thing can make 15psi by 4000RPM. The boost onset is 1500-1800RPM.

why make something more complex for no reason?

a friend of mine created a parallel/sequential big 16g twin turbo set-up for his DSM. it worked, sort of... at anything under 10psi both turbos would spool perfectly fine, but once he went over 10lbs the second turbo would just start to surge and never make any useable boost. so in the end, he had an incredibly complex (but unique) set-up that had mediocre at best performance. he spent years researching and designing this set-up, only to be frustrated and disappointed in the end.

so basically you can do it, but is it worth the frustration?

Another thing is that when the bigger turbo takes over, the smaller turbo gets exhaust gasses routed around it. That is good, but what happens to the charge air? You just have a boost leak through the compressor of the smaller turbo.

I choose turbos that were too small (Garrett has incorrect compressor maps on their website, their catalog has it fixed, dumb). They'd rock with the next-size-larger turbos. 240rwhp and extremely linear torque as it is now is fun though. If i was smart I'd leave the car A L O N E.

I'll be attempting sequential after my other projects are done, probably over the winter. I already got the turbos and part of the manifold modeled in solidworks. If it don't work, I'll throw it away and just use one turbo. I'm too old (gasp) to get too fustrated.

the smaller turbo will still be boosting and pushing air through, so not sure what you meant?

It's not the best idea. Enough said.