Twin Turbo Ramblings
charlie at elektro.cmhnet.org
Mon Sep 17 00:00:37 EDT 2001
Earlier, Andrew Lundy wrote:
> Sequential turbos...
> You have two SAME size turbos. You hook one turbo on each bank of
> cylinders. One turbo is set to spool up at an earlier RPM than the other
> turbo. As you indicated, this early "spool" is to reduce turbo lag. With
> sequential (and generally twin turbos) the turbos used are small. Again, to
> reduce lag!!
> The first car that I saw that did sequential turbos "successfully" (no lag)
> was the 1996 993 Turbo. It's becoming the norm with twin turbo's now!!
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 Smith charlie at elektro.cmhnet.org 614-471-1418
http://www.elektro.com/~charlie Columbus Ohio USA
http://www.elektro.com/~audi photos & technical info
95 S6 Quattro - 24 PSI, RS2 6 speed, and other features
96 Dodge Ram - 30 PSI, w/Cummins turbo diesel
More information about the quattro