A diesel buddy of mine. said once that the bigger turbo compresses the air at a low rpm.. So it dosent need to spool very high if at all. Since it will create more air flow per lb at low boost. The small turbo will reach 15psi and hold there but the air the big turbo is compressing is being double compressed by the small turbo. In essense.. He says that when the small turbo is pushing 15 psi at say 25lb/in on a stock dsm.. with the big turbo.. it would be pushing 15psi at 40+lb/in.

He runs way more power then we ever will.

He says that the little turbo should never try to spool the big turbo.. It more efficiant the other way around.

Close,

But if we are going to use the number 25lb/min, then when the big turbo is applying the 15psi to the inlet of the small turbo, we are actually over doubling the inlet pressure (14.7 atmospheric pressure.) which in turn doubles the lb/min and we would be at 50lb/min at 15psi

Nice! All of these twin charged posts. Get's my creative mind working..

Mike,

How are you running your boost control/wastegate setup?

Currently to make 15 psi I am just using my trusty mbc from 8 years back. Then the outlet side is just t'd and run to both waste gates lower port.

When I reach the point of needing to stop the small turbo and have the big turbo continue to boost I will switch to a pressure regulator on the top ports of each waste gate. Or even better, an electronic controller to run the second turbo/wastegate...

It's been a long time since I looked into all this...at what point would that be?

I honestly don't know yet. Trial and error I guess... I'm sure there is some magical engineering formula, but I really just want a super smooth transition.

I had the small wastegate at spring pressure which was 7. And the large one around 11. And it was far from seamless. It would boost, lag, then boost again. Kinda neat feeling but not what you want...

I'm thinking somewhere between 15 and 20 is the magic number.

I think you should run both wastegate to well 20 psi.. But ya.. You cant reaaly expect anything till you start logging air flows and start taking chances.. And all this with out LINK!

I want to see a pic every time you post here Mike..