Twin Turbo Ramblings

Dave Eaton Dave.Eaton at
Tue Sep 18 18:59:50 EDT 2001

another downside of the twin sequential turbo can be the mapping of the
turbos.  as anyone who has driven the subie legacy gtb, b4, and rsk knows,
there is a noticeable "flat spot" (for want of a better word) at around 3k
rpm when the 1st turbo is all done, and the 2nd isn't yet up to puff.  this
is disconcerting, as this is usually about the revs you are at on the open

'95 rs2
'90 ur-q

-----Original Message-----
From: JShadzi at
Date: Mon, 17 Sep 2001 00:45:52 EDT
Subject: Re: Twin Turbo Ramblings

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
componentry, it is questionable whether there are any major advantages over
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

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