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Re: No replies about safety of turbo mod
Hey-some of you might remember my posting asking if anyone could give their
opinions as to how safe it is to do a wastegate spring mod and bypass the
overboost on the computer. Car has 109k miles on it, '87 5kCST. Also had a
question about how much hp the fwd can take(car is not quattro). I would
really apprecieate people's opinions and there are several others that want
to know too because they are in the same situation.(Not having enough money
to fix the engine if something goes wrong...and engine has lots of miles on
Your opinions please.
Awlright, pay attention this time...
It is <insert your favorite list of trenchant present-participle Anglo-
Saxonisms> dangerous (yea, even stupid!) to bypass the overboost pro-
tection in the ECU. It could very VERY easily cost you an engine. It
is very VERY easy to build up a destructive amount of overboost. The
engine can build up boost far faster than you can react and take your
foot off the gas pedal!
My little story -- "Why I'm deeply grateful for ECU overboost protection"
As I was playing around with my UrQ, experimenting with variable boost
and ECU mods, I was having trouble "making the numbers" agree. I was so
sure that I had the ECU mapped right, and that it *should* be allowing
me 15-16PSI before cutting out. But it refused to go over about 12 or
so PSI before shutting down -- from low rpms, I watch the boost (and the
revs) climb slowly then ever more rapidly to 11-12PSI, and SLAM! the
ECU shut off the engine. Finally, more out of randomness than anything
else, I put a *second* pressure gauge directly off of the ECU pressure
line, and hey, guess what? that <@()#&@&*%#^&@#@#@)*_)($@>ing BRAND NEW
VDO pressure gauge on the dash pegs at 11-12PSI, meanwhile the second
guage on the ECU line screams right up to 16PSI and the ECU shuts off.
(Definitely proved the adjustable boost control was working, too!)
***Thank You Nice ECU, Thank You Very Much!!!!***
Had I choosen to defeat the ECU overboost, rather than resolve this lit-
tle "discrepancy" (trusting the new gauge that seemed very accurate right
up to the point that it quit reading any higher!!!), I would be paying
for ANOTHER engine!
And by the way, once boost reaches 10PSI, it builds very VERY fast after
I dunno about all of the different ECUs that Audi uses, the MAC-02 series
in the UrQs read up to about 16PSI in their stock configuration, so that
is as high as you can run without circuit modifications of some sort.
(I do not consider reprogramming the ECU ["ROM", or more properly the
"EPROM"] as "circuit modification", even though yes you have to desolder
the stock ROM in order to put in a socket/EPROM -- which would certainly
void any warranty...). One of these days (well before the next millenium
starts!) I'm gonna get the "trivial" circuit mod to allow that as well,
at least for the UrQ/MAC-02 series.
Besides the obvious catastrophic spreading of engine $hrapnel everywhere
when you wildly overboost (wastegates do fail...), there is a much more
subtle devastation that can be wrought. The stock ECU sets the ignition
timing based on "stock" parameters, and may not be able to safely cor-
rect for the increased detonation (anti-knock timing retardation) that
wildly enhanced boost can cause. This in turn can result in melted valves,
holes punched through pistons, and other such problems. (NOTE: UrQs do
*NOT* have knock-sensing ignition timing control; they are essentially
purely "static" timing; they do not benefit from high-octane racing gas,
nor do they protect you from low-octane s**t gas!)
So, sure, you can [easily] defeat the ECU overboost, and it'll probably
even work. But springs do get miswound, wastegates do get mis-assembled,
and in general, shit does happen (especially when you have such chimerical
dieties as the Audi Gods looking over your shoulder). Replacing (rebuilding)
an Audi turbo engine is not a cheap experience. (Although, ironically, the
turbo itself is very likely to sail through the whole experience unscathed,
as long as it doesn't ingest any of that pesky $chrapnel floating around...)
Well, that's *my* pulpit-pounding on the subject.