Too much of a good thing(boost)

[Bernard Littau]

Hi Ryan,

Sounds like your lower wastegate hose is fine, as is sounds like the
wastegate is doing its job correctly when you have the top chamber vented to
atmosphere.

The addition of any pressure to the top of the wastegate will increase the
allowed boost.  Sounds to me like your pressure regulator is still allowing
some pressure into the top of the waste gate even when you have it at
minimum.  At 5psi min (5 psig), that's 0.31 bar it is still adding to the
1.6 from the spring, making potentially 1.91 bar boost.  Add in a little
rounding error on anything and I can see where you would hit the 1.95 bar
cut off.

Tee in a pressure gauge with a long hose and measure the pressure at the top
of the wastegate while you are driving.

Best,

Bernard Littau
Woodinville, WA
'88 5ktq


> Hello all, I have been trying to figure out a
> problem I have had for a couple of months now.  One
> day a boost problem showed up on my '87 5ktq.  First
> off, let me say that I have a QLCC chip, 1.6 bar
> spring, adjustable wastegate spring seat, and bypass
> valve installed between the IC->Intake hose and
> turbo cold side intake hose.  This combination
> worked very well until shortly(not immediately)
> after I modified the wastegate to be adjustable.
> The condition is such that if I apply more than
> about 1/2 throttle in most gears, the boost will
> quickly rise and go right up to the 1.95 bar fuel
> pump cutout.  Especially in 2nd and 3rd gears.  In
> trying to diagnose the problem, I disconnected the
> WGFV->Wastegate vacuum hose, not plugging the
> wastegate or hose.  This had the effect of limiting
> the boost to 1.6-1.7 bar, so I assumed that the
> spring was doing its job and opening up the
> wastegate at the prescribed boost level.  This led
> me to conclude that the WGFV, its electronics, or
> one of the lines leading to it was the problem.  So
> I thought, why not just eliminate it and go with the
> Schrappnel Knobben(tm)?  Which is what I did
> tonight, using the Sears valve that's recommended on
> Ben Swann's "boostin" webpage write-up by Paul
> Timmerman himself.  I connected the input for the
> valve to one of the nozzles on the top/rear of the
> intake manifold, and the output to the top nozzle on
> the wastegate.  The arrow on the valve points toward
> the wastegate.  I blocked off the vacuum line that
> led from somewhere in front on the passenger's side
> to the WGFV, and connected the line that led from
> the intake to the wastegate to the other line that
> led from the intake(right next to it).  I assumed
> that this was effectively creating a closed loop,
> and provided more or less the same result as
> plugging it.
>
> Here's the problem... I get the same result as when
> I had the WGFV attached... even when I turn the
> pressure regulator all the way down! (in the "-"
> direction)  I thought that with the regulator all
> the way down(5psi min), the top of the wastegate
> would actually see less pressure than if it were
> vented to atmosphere, and that the wastegate would
> open sooner.  This problem is really annoying, and
> forces me to drive with a light foot.
>
> I know that the WG diaphragm is in good condition,
> as it holds pressure/vacuum.  The only thing that I
> can think of is that there may be a problem with the
> line going to the lower half of the wastegate.   The
> line is physically in good condition, but could it
> be plugged?  Would that cause this result?  The
> thing that really baffles me is that the wastegate
> seems to work fine when I vent the top half to
> atmosphere, so I don't think it could be that the
> wastegate is stuck.
>
> I've been to SJM's website, and gone through the
> tests, and everything seems to check out fine.
> Especially now that I have the WGFV eliminated and
> manually adjustable pressure regulator installed,
> what could be the problem?
>
> Any help would be appreciated.
>
> Thanks,
>
> -Ryan
>
>