overboosting (1987 5kcstq)

[Swann, Benjamin R. (BSWANN)]

[So....I can mess with one hose on my 86 5ktq and get more boost? And
at lower RPMs? Why spend all that money on springs, chips , turbos
and downpipes when I get put a calibrated leak into a hose? What key
piece on information am I missing here?
If you could recommend a book containing these pieces of information,
that'd be great. The Bentley isn't exactly a textbook.
-Brian]

Brian,

It is a matter of being able to control.  As you say above "calibrated leak"
- that is exactly the point of the pressure regulator modification oft
referred to as the "schrapnel mod".  You still need some overboost
protection, as the overboost cutoff is not good for your drivetrain among
other things.

IME - I have used the various combinations and have come to the conclusion.
A spring and a chip is the most reliable modification.  Also, the spring
will allow you to keep the wategate clamped longer permitting quicker turbo
spoolup so desired boost is attained quicker.  The spring is a fixed
calibration - once installed, no adjustment necessary.

A proper chip, like SJM or QLCC provides wastegate/frequency valve control,
ignition timing control, fuel mapping and overboost protection tailored for
the higher boost levels.  You would need a chip or other overboost
protection anyway whether you use the schrapnel knob approach, or Spring.
Grounding the fuel pump on all of the time is dangerous and not recommended.

I have a writeup on these and some other inexpensive modifications that may
be helpful:
http://www.homestead.com/Ben_Swann/boostin.html
http://www.homestead.com/Ben_Swann/myaudi.html

If you like playing and calibrating continually, then you may be happy eith
the "schrapnel mod", coupled with a variable resistor mod.  A chip is better
for the engine, however, and more foolproof.

Ben
'5ksctqw (x2):
1) Pearl - combined QLCC chip + 2 Bar SJM spring + schrapnel knob + resistor
mod set for 15-18PSI - additional fueling and other modifications in the
works.

2) Charcoal - recently aquired - Charlie(1.7Bar) spring and fuel pump wired
on with ignition - needs removal and proper installation of chip.  Hits 1.7
bar and goes well though.

'4kscq - Stebro exhaust, 264 Cam, 7 degrees timing advance, Jamex stress Bar
Boges in rebuilt front end.  Awaiting GTQ transplant - someday.