Re: 5KTQ Turbo boost question?

[steveb@falcon.kla.com (Steven Buchholz)]

> I recently purchased a 87 5KTQ (137K mi) and was wondering if the
> turbo is peforming correctly. I want to get all engine functions
> working because I am thinking about dong a chip mod!!!!! 
> Here are my observations, if anyone can give me info I would
> appreciate it. Car is in stock condition (turbo, wastegate, ECU
> etc.).
> 
> 1) Is the boost gage accurate? With the ignition switch on and the
> motor not running it reads .8 bar. I figure it should read .832 at
> his altitude (Denver - 5000ft) so this seems correct.

... it isn't really calibrated ...
> 
> 2) From 35 mph in 3rd gear if I floor it the boost comes up to .9 bar
> fairly quickly then at 3000-3500 rpm it gradually increases to 1.0
> bar. If I continue it will creep up to 1.1-1.2 bar above 4000rpm.
> With a shift to 4th gear (still floored) the boost stays at .9-1.0
> until about 4000 rpm where it increases to 1.1 bar on up to 5000 rpm.
> 
> 3) I have rarely seen over 1.1 bar although during a long uphill 4th
> gear climb I did see 1.3 bar once. Isn't the stock wastegate supposed
> to be 1.3 bar?  How fast is the boost supposed to come up to 1.3?

That is similar to my experience, but maybe a bit low ... but then I live 
very close to sea level.  Most of the time my boost peaks at 1.2 with 1.3
showing up occasionally.  Some of the difference could be chalked up to 
the inaccuracy of the gauge as well.  If you really want 
> 
> 4) Can the wastegate spring weaken over time causing it to dump boost
> too early?  I was told this could happen and a new spring from Audi
> Only with increased boost was $50. Has anyone heard of increasing
> boost with a spring only (realizing that the fuel cutoff will still
> happen at 1.5??? bar).
> 
[The reason I decided to post this response to the entire list was the 
subsequent response suggesting using the Schrappnell Knobben (TM) ...]

I agree that the Schrappnell Knobben (S-Kn) would be a good way to get that 
extra boost.  On the newer Audi turbos this would involve disconnecting
the car's existing connection from the WG to WG frequency valve.  If you
live in an area where there are emissions inspections you probably would 
want to do the install in a way such that it would be easy to make it 
stock again (whatever you do, don't simply leave the WG freq valve con-
nection open!).  The one benefit of the S-Kn is also a caveat ... you can 
adjust the amount of max boost that the engine will produce.  This is great
as it allows you to run the engine at a safer level normally, yet have that
"something extra" for those times when you need it :) ... and *that* can be
the problem too ... you have to make sure that you don't turn the knob up 
too high ... and you'll probably want to install a separate boost gauge as
the digital display will not be reading correctly with S-Kn.  

My personal preference on my '88 5kSCQW is the q-list chip club [my name] 
ECU mod.  If you think about it the WG freq valve is doing exactly the same 
thing as the S-Kn is doing, with the possible exceptions that the WG-fv 
switches between pressure and vacuum ... and that it is controlled by the 
ECU, which is looking at the manifold pressure at a different point from 
the point of regulation.  

I fully support both projects ... I have S-Kn for my urQ and QLCC for the 5k.
You have to realize that for either project you will need to hack into your 
ECU [or find someone you trust to do it for you :], so it is not for the feint
of heart.  The S-Kn mods are much easier to install.  The QLCC is impossible 
to discern from stock when it is installed ...

My final point is that you must realize that neither of these mods is guar-
anteed in any way, and that by installing either you are increasing the risk 
of a catastrophic engine failure due to overboost.  You need to decide for 
yourself if the risk is sufficiently low.  If you want guarantees and simpler 
installation, you can buy one of the commercial products (IA, SC, TAP, ???) 
but make sure you know what you're getting for your money ...

HTH! ... and have fun!
Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)