5ktq and Boost loss (after MC rebuild/upgrade & T3/K26 turbo) - it was bypass valve!

[Ken]

Wow, I didn't even realize I typed "boost valve", instead of "bypass valve".  Wierd.

I wouldn't necessarily call the valve bad.  Are you sure you are taking the vacuum signal from the correct place?  I understand some of the ports on the intake manifold are not "vacuum" per se, but are some kind of variable-with-throttle-position.  I would check that, since if you are providing less than full intake manifold pressure on the vacuum port, it might let it leak out.  Since your setup is so custom, it's possible the vacuum signal is from the wrong source.

And I was just thinking of one of your original tests, where you disconnected the lower WG hose and punched it to 5k and only got 1.7 bar.

That potentially spun your turbo really, really fast.  If your boost was leaking and your WG was totally closed, who knows what rpms it was hitting.

Just a thought.  I hope nothing bad happened to it.

Congratulations on nailing down the problem.

I like Forge valves so far, but lately people are saying that any piston-type valve with an o-ring seal have some failure mode.  Some people were looking into the "Go Fast Bits" diverter valve, which has a different design that supposedly isn't prone to this failure.  I have no experience here yet, still working on getting the stock valve installed.

Later,

Ken

Quoting Ben Swann <bswann at worldnet.att.net>:
>
> Allright!  Ken wins the lucky cigar!  It was the bypass valve.
>
> I overlooked this completely before since it is/was brand-new.  I
> thought it would at least get me through testing things out.  It seems
> to pass gas at around 1.5 bar which is why I was not obtaining more than > that without really pushing it.
>
> It blew out the cork when I hit the 1.8 bar cutout and shifted.  Now it
>
> acts more like a blowoff valve, since with the cork out you can hear it
>
> start hissing when 1.6 bar is reached.  Ok, I put the cork back infor
> now until I get a proper one.
>
> Thanks all who took a stab at this.  Definately helped expedite finding
> the problem.
>
> So what are the recommendations on bypass valves?  Who has the good
> price on them?
<snip>
> Ken [SMTP:auditude at get.net]
> wrote:
> >
> > [Ben, it really seems like you may have the boost(meant bypass) valve
> hooked up incorrectly.  I would perhaps take it completely out of the
> equation, plugging the holes, and see what kind of boost you build
> then.]