Twin Turbo Ramblings

[JShadzi at aol.com]

I agree, cars like the S4tt and 911t use two turbos that feed one bank each.  
They spool at the same time, and create equal pressre.

True sequential twin turbos such as the RX7 use two different sized turbos, 
and the turbos actually transition from one to the other, and never operate 
simutanioulsy because the airflow is actually blocked off and diverted 
through the other turbo.  This of course creates tons of compelxity and extra 
componentry, it is questionable whether there are any major advantages over a 
well designed conventional turbo system.

An interesting thing to note, though twin turbos are though to spool faster, 
it is actually a much less efficient way to turbocharge an engine.  The heat 
energy is split between two turbos instead of one.

Javad Shadzi
80tq.com

In a message dated 9/16/2001 8:09:59 PM Pacific Daylight Time, 
charlie at elektro.cmhnet.org writes:

<< 
 There are two different ways of engineering a "Twin Turbo" setup, not 
 getting into tractor pull configurations that actually have one turbo 
 blowing thru an intercooler that feeds a second turbo that blows through 
 a second intercooler that then supplies air to the engine ...  usually at
 a very high pressure..
 
 The one you describe has the turbos in parallel, with both of them
 acting in unisen.  As in the S4tt, A6 2.7tt, and Porsche twin turbos.
 The advantage of two smaller turbos (one working from each bank of 
 the exhaust) is that the smaller turbos spin up faster and there is 
 less lag, plus the exhaust path from the exhaust ports to the turbo 
 is shorter and the exhaust gas thus has less chance to cool down.
 I don't think this configuration has one turbo spin up before the 
 other one, as you noted they are both the same.
 
 The other configuration is with the turbos effectively in series, but 
 with a small one acting quickly at lower rpms, and with a larger one
 taking over at higher rpm.  I believe the twin turbo Mazda RX7 has
 this type of setup.  The advantage here is that the smaller turbo 
 builds pressure at low rpm without lag, and the larger turbo takes 
 over at higher rpm when more air mass is needed without heating the
 intake air as much.
 
     - Charlie
  >>