[s-cars] Underdrive pulleys?

[Paul Gailus]

A couple things to consider are:

1. Is the 2.7T motor "internally balanced" so that
a neutral balanced pulley is appropriate?  I assume that
this is true, but you night want to find out for sure.

2. The lightened underdrive pulley may have little or no
torsional damping. The OEM damper (harmonic balancer)
has very likely been tuned to absorb the resonances
that are specific to this engine. Undamped resonances
can cause a lot of extra stress leading to metal fatigue,
bearing wear, and all sorts of bad things. With the short
crank on the 2.7T V6, it's possible that the major resonances
(critical frequencies) could be high enough that they occur at
RPMs beyond redline. If this is the case, the engine might
survive for quite a while without a damper. But why risk it?

The flywheel inertia and crankshaft typically resonate
at frequencies that are below idle speed. At the higher
frequencies where the harmonic balancer is effective,
the flywheel is so masive that it essentially doesn't move
at all. So the requirements on the harmonic balancer should
be relatively independent of the type of flywheel used.

Paul


----- Original Message -----
From: Joseph Pizzimenti <pizzoman at yahoo.com>
To: <s-car-list at audifans.com>
Cc: <quattro at audifans.com>
Sent: Thursday, December 12, 2002 11:49 AM
Subject: [s-cars] Underdrive pulleys?


> I was wondering what detrimental effect, if any, would
> a lightened underdrive pulley have on the drivetrain?
> Would I bend rods and/or twist the crank?  These
> pulleys are zero-balanced, would using these with a
> stock dual mass flywheel damage anything?
> This is going on a 2.7T motor, otherwise stock with
> the exception of engine management and exhaust
> modifications.
>
> Thanks