Re: "Blue" wastegate spring

["Scott Mo." <scottmo@teleport.com>]

Phil,
> 
> C'mon, guys - someone _must_ know what blue colour coding means on a >wastegate spring.

I don't have a match for this spring with a blue paint mark you
described previously with the length of 75.5mm, OD of 36.5 mm OD, 30.5mm
ID, 3mm wire. The US ur-Quattro stock WG spring is aproximately 68.6mm
long, 40.4mm OD, 33.3mm ID. I have never seen the euro ur-Q spring to
make a comparison....

It is tough to really compare springs just by their dimensional
information unless you know the material it is made of or what the
spring rate is. One way to compare different WG springs is to check the
load it supports at a given compression and calculate the rate. 

I normally measure the WG cap and perch dimensions to figure out the
installed height of the WG spring. From this information you can then
test the load of each spring at this compressed height. A electronic
bathroom scale actually works pretty darn good at estimating this load.
The US ur-Q has an adjustable WG spring perch which normally is set
higher (spring is compressed less) than what the 1986-88 5000TQ WG perch
does.

If the installed WG spring tension is higher than stock then you would
normally see the behavior mentioned, where the WG solenoid duty cycle is
shut off (Test LED light stops blinking) as the engine speed climbs at
WOT. 

The ECU senses that enough boost or too much boost is being made so it
shuts off the WG solenoid. When the WG solenoid is shut off and connects
the upper WG cap to the intake boot at the turbo intake, the WG upper
cap will see a slight vacuum at sustained WOT operation. This will
reduce the boost ~0.1 bar over what the WG spring alone will make with
the upper cap connected to atmosphere.
HTH
-- 
Scott Mo.
1989 200TQ
http://www.teleport.com/~scottmo