TWINCHARGED (Supercharged & Turbocharged) Widebody "WTF-86" 86/FRS *MASSIVE* build :D

[the_one_mike]

Originally Posted by Jaden

Sequential turbos a large one pulling from ambient feeding into the inlet of a smaller one is the most common. They are done in diesels all the time. The confusion on which is the primary and secondary comes from whether you're talking about how the turbos are powered versus the charge.


When I'm referring to the primary I'm talking about the FI system pulling from ambient i.e. ~14.7 psi for sea level.


The primary pulls from ambient and compresses that charge the charge then goes into the secondary at 14.7(or whatever ambient is) * whatever the pressure ratio is for the boost level it provides.


This is the important part. It now becomes a closed system. You can't get any more air than what is provided by the primary. So the flow rate of the secondary charge system doesn't matter, only the PR.


Now in a compound turbo, (Large turbo going into a smaller turbo) the smaller turbo is fed from the exhaust FIRST so that's where the confusion on what is the primary comes in. It's fed first because it will spool faster.


Controlling the boost on a compound turbo into turbo setup is paramount. It's easier with a s/c because the boost is finite for the s/c and you only control total boost output with the turbo.


You don't want a big turbo as the secondary because flow doesn't matter for the secondary, just p/r so you want it to spool as quickly as possible.


Here's why I think that a big s/c as the primary might work better.


Take a look at the compressor maps ogerf a big s/c like an Si trim Vortech


You'll notice that the airflow is broad as fuck. This means that if you use it as a primary even at low boost you have TONS of airflow. Since you're using a quick spooling turbo as the secondary, you can use higher boost at lower rpm and slightly lower boost at higher rpm and have a hugely broad torque curve, which is the whole point of a compound boost setup.


Jaden

I'm definitely starting to pick up what you're putting down. I've been thinking more in terms of compression while you have been thinking more in terms of actual air flow -- which realistically is more important as making boost tends to be the simple part, it's delivering it favorably that becomes an issue.

I also have been reading your other thread and will jump this discussion over there to keep it comprehensive.