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Power, WGs, boost control.
I think there are some people out there with the wrong idea of how the Audi
turbo systems work.
Here are a few facts as I see them. If I'm wrong, help me out. I knew you
1. The wastegate acts as an exhaust bypass valve. It does not bleed off
boost, but rather diverts exhaust gases from the turbo hot side. The exhaust
takes the path of least resistance and goes out the exhaust system when the
WG opens, not through the turbo. If you want, apply air pressure to the
bottom of the WG and watch it open. No air will leak out. Just BTDT with
a spare 20Vt WG (same WG as the 10V, just uses a different spring)and my new
compressor at ~ 50psi. :)
2. You won't overspin a turbo with the WG open. In fact, it gets to slow
down, so it is very happy. :) See above.
3. The 10V WGFV _can_ hold the WG closed at well over the stock spring
level. As an experiment, I used the above mentioned WG, the stock hose
going to the bottom side of the WG and a tee with a restrictor going to a 3mm
ID hose connected to the top side. The results were interesting. The WG
would initially open, then close as the restricted side (top) pressure
equalized with the bottom. Makes sense. My conclusion: The WGFV can hold
the WG closed, but there is a time delay. This keeps boost delivery smooth
as it cycles. A heavier spring deadens this reaction and raises pressure at
which this will occur. Hence cars with stiff springs (IA, TAP, Charlie
springs) have better, or shall I say quicker, "boost response". In the Audi
10V this time delay is enough when combined with other factors to keep the
boost levels smooth and constant without overshooting computer set limits.
The 20V don't use this sort of time delay in the control system, so things
can happen quicker. The engine management systems on those cars are also
much more sophisticated and powerful.
BTW, make sure everything is well clamped if you try this. Those hoses hurt
when they come flying off. BTDT, ouch.
One subject that I have never heard addressed is that exhaust pressure opens
the WG. If manifold and turbo restriction is low, there will be less
pressure on the WG port, and therefore it will take more on the top chamber
to open. Wow, there's alot of stuff working together here...
4. You don't need 25 psig to develop big hp. The total breathing system of
the engine must be addressed, i.e. intake, exhaust, fuel and heat and how
efficiently each is delivered or expelled. Raising boost gets you more power
to a point, but running too much is like trying to force an elephant through
a man hole. Not to mention putting man holes where they shouldn't be. No,
haven't BTDT and never hope to.
5. You will not get 400hp just by adding a "super-duper-Boostmeister" chip.
See #4. Audi has done a pretty good job from the factory at making a
relatively powerful and _reliable_ engine. If you look at the chip tuners,
most everyone simply modifies the stock parameters a bit. If it works...
Check out what the Diamond Star, Honda, Toyota and other tuners do. They
have to REALLY beef up their motors to get big hp. We are just lucky the
Audi I5 is as stout as it is to put up with the abuse modded cars deal with
running stock mechanicals.
That's the way I see it. Correct me if I'm wrong. Oh yeah, didn't have to
add that did I?
'82 Not So Ur q 3B2B