[Vwdiesel] Turbo vs. Non-turbo [was My TURBO test (more scien tific)]

[Tyler "Casioqv" Backman]

Exactly, it depends on the turbo setup, this is what I am saying. With a
properly sized turbocharger, you can make full boost at any rpm you
want, but there are tradeoffs. At the factory, VW decided to put a
rather large turbo on their motors (for the displacement) and therefore
they cannot produce full boost instantly at low rpms, but must first
reach higher rpms (with more throttle as James Hansen said). This is not
reaching full boost at any rpm, because your rpms are increasing to a
level capable of flowing enough air for the turbocharger to provide full
boost. Just look at a turbo compressor map, and see that high boost at
low flow rates puts a compressor above it's surge limit, and are
engineered to not occur on modern turbocharged engines (by sizing the
turbo properly). Many engine manufacturers combat this problem by having
2 turbos sized differently, so that full boost can be obtained at lower
rpms. Commercial volvo diesels have a small clutched supercharger, that
disconnects at higher rpms, but provides almost all the boost at low rpms.

Shirley, Mark R wrote:
> Uh, yes it can.  It depends on how you setup the system.  Boost is caused
> by turbine rpm on the turbocharger.  If you set the exhaust housing size
> small
> enough, you can reach full boost at lower rpms, even with lower loads.  For
> example, If I took my trucks' exhaust housing, which has a 0.96 A/R, and
> swapped
> it for a 0.65 A/R housing, I would incur more boost at a lower level.  The
> A/R
> value is a ratio of inlet area to radial distance to outside wall of the
> housing.
> Note however, it's a tradoff between making the housing small enough for
> good
> boost response, and so small, it restricts flow at upper rpm ranges.
>
> James' original assertion that Cam timing, lobe height, runner length and
> volume,
> etc defines torque peak and VE for an engine is correct.  A turbocharged
> engine
> and a NA engine with the same basic hardware will produce torque peaks at
> the same
> rpm, the only difference is that the peak will be higher on the Turbo.  The
> VE will
> however be different throughout the rpm range.