Air Shrouded Injectors (and low boost)

[Mike_Buckham at ptk.pioneer.co.uk]

Humble pie anyone? I've eaten loads, so I've got plenty spare. It turns out
that within the 3 months I have owned the car, the michelin man hose has
indeed developed a split. I checked it when I first got the car when
looking for a different problem. Thank you Ken and Nate for your help and
consideration.

I took the hose off on Saturday, cut it in half (where the split was) and
clamped a piece of plastic drain piping in the middle as a temporary fix.
With the bottom wastegate hose disconnected, I was totally shocked at how
quickly the boost built up. I saw 1.9 BAR on the dash pressure gauge
(momentarily) before the ECU decided that enough was enough. When I
reconnected the bottom wastegate hose, it held a nice steady 1.4 BAR unless
I was on full throttle when it allowed me 1.5 BAR. Also, I managed to
average 27mpg when travelling at 80mph on the motorway and at least 30mpg
when going round town. Amazing. I still have a dubious knock sensor though.
The ignition timing keeps retarding and causing power loss so I might just
get a new one.

Cheers, Mike.




                    <auditude at cox.
                    net>                 To:     Nate Stuart <newt at newtsplace.com>
                                         cc:     Mike_Buckham at ptk.pioneer.co.uk, quattro at audifans.com
                    21/02/2003           Subject:     Re: re: Air Shrouded Injectors (and low boost)
                    17:56






Nate Stuart <newt at newtsplace.com> wrote:
>
> If I remember correctly. the wastegate actually gets it's pressure
> reference before the throttle body, on the same line as the idle
> stabilizer.So when you drop the throttle shut the WG sees a surge in
> pressure and opens up. Though if the line was plugged as he mentioned
> before this is all a moot point.

Okay, that's much better.  This is what I originally thought, and I was
going to post some about it, but then I remembered where the lower chamber
hose goes to, and didn't want to post the wrong thing so I changed it.

So, what I was going to post when I hadn't convinced myself incorrectly on
the WG's connection, was that without a bypass valve, you not only slow
down the turbo from the buildup of pressure after the turbo from the
throttle closing, but also because that buildup of pressure opens the
wastegate which stops/slows the spinning of the turbo by the exhaust gases
as well.  That's a lot of wasted momentum.

So, a bypass valve really helps keep the turbo spooled in more than one
way, on the intake side and on the exhaust side as well.  I didn't realize
this until for a short moment this morning before I thought I was wrong.
Anyway,

I think that's interesting, as prior to that I was only thinking the
benefit of having a bypass valve was all based on reducing a slowdown of
the turbo that was all caused by the intake side pressure spike.

Ken