WRX vs. 1.8t

[nealtovsen@yahoo.com (Neal Tovsen)]

> So, is that clearer, or just gobbledygook?

Yes, clearer. But yet, gobbledygook! Hehe.

The difference between measuring MAP vs. MAF has
always confused me, so that is definitely where the
problem lies.

I don't quite understand why a given absolute pressure
value in the manifold doesn't directly relate to
density of the fluid. In my mind, density should be a
simple factor of pressure. If it did, it would make
MAP vs. MAF irrelavant, which you say isn't the case.
But I'll admit that I need to learn more here...and my
physics book has been collecting dust on the top shelf
at home for years. :)

Neal

--- Dan Bubb <jdbubb@ix.netcom.com> wrote:
> Let me see if I can explain a little better.
> If you have a mechanical wastegate or the ECU
> controls the wastegate for
> a set value of manifold pressure then the maximum
> pressure in the
> manifold will always be the same. Let's assume 15
> psi. Then at sea level
> manifold absolute (as oppossed to "gauge") pressure
> will be 30 psi (just
> assume ambient is 15 psi for this example). i.e.
> manifold pressure +
> ambient pressure. Now if you go to Colorado Springs
> the ambient is 12
> psi. An NA car will have 80% (12/15) of sea level
> power. Our boosted car
> will have 90% [(12+15)/30] of sea level power.
> My 98 Audi 1.8T doesn't even have a manifold
> pressure sensor. All it
> does is measure MAF and adjust the wastegate to
> acquire a set MAF value
> at WOT. So, on a humid day where air density is down
> it will run higher
> manifold pressure for the same MAF. Same thing at
> altitude. If ambient
> pressure drops then  MAF will drop if the manifold
> pressure is at a
> fixed boost level, but the Audi is only looking at
> MAF and adjusts
> manifold pressure up to, again, reach the desired
> MAF value. So, if the
> Suby ECU controls MAP and the Audi/VW ECU controls
> MAF then the Suby
> will be at 90% in the above high altitude example
> and the Audi/VW will
> be at 100% minus some amount associated with lower
> turbo efficiency at
> higher pressure ratios.
> I don't know whether the Suby ECU controls MAF or
> MAP, so this is all
> conjecture. Also, athough my 98 Audi doesn't have a
> MAP sensor, later
> Audi/VW's do. I still think they control MAF and not
> MAP, but I could be
> wrong.
> So, is that clearer, or just gobbledygook?
> Dan 
> 
> Neal Tovsen wrote:
> > 
> > I'm not quite sure I follow this, but I know this
> is
> > getting over my head technically so I could be
> plain
> > wrong...
> > 
> > I think you're saying the early 1.8t measured the
> MAF
> > and adjusted the wastegate via the ECU instead of
> a
> > self-controlled mechanical wastegate. But
> mechanical
> > wastegates are driven by a diaphram...isn't that
> > basically the same thing? Boost is pressure, which
> for
> > the same fluid should equal density. Thus, for a
> given
> > volume/path and speed boost should be directly
> related
> > to MAF. Or am I missing something important? 15psi
> in
> > the manifold at 5000rpm is 15psi at 5000rpm,
> > regardless of what the air pressure was *before*
> it
> > was compressed.
> > 
> > Neal
> > 
> > --- Dan Bubb <jdbubb@ix.netcom.com> wrote:
> > > The early 1.8T's didn't actually measure and
> control
> > > boost pressure.
> > > They measured mass air flow and adjusted boost
> > > pressure to control that.
> > > I don't know if the later 1.8T's control boost
> the
> > > same way or measure
> > > and control boost directly.
> > > The net upshot is that at higher altitudes the
> VW
> > > engine will run higher
> > > boost to attain the same mass air flow the
> engine
> > > would have at sea
> > > level. So, power declines at altitude (mostly
> due to
> > > turbo inefficiency
> > > at higher pressure ratios), but not much. If the
> > > Subaru directly
> > > controls boost then it will loose more power
> than
> > > the VW at altitude.
> > > Maybe that explains it. Or maybe the Suby driver
> was
> > > lost in turbo lag?
> > > Dan
> > >
> > > -------- Original Message --------
> > > Subject: WRX vs. 1.8t
> > >    Date: Thu, 24 Oct 2002 12:59:12 -0600
> > >    From: "Brandon Smith"
> <SCIROCCO_SPEED@msn.com>
> > >      To: "SCIROCCO-LIST"
> <scirocco-l@scirocco.org>
> > >
> > >  Okay to make myself clear, here in tha
> Mountains of
> > > Colorado (well not
> > > really, but still over 6,200 ft above sea
> > > level...like the base of Pikes
> > > Peak) its just been my experience that the 1.8ts
> are
> > > faster than the
> > > WRX....why??? assuming because of the turbo lag
> of
> > > the WRX.   Up here
> > > the 1.8t pulls harder.  guess maybe VW had
> visions
> > > of their european
> > > customers driving around in the Alps a lot.? but
> for
> > > some reason, a
> > > 150hp 1.8t in a VW seems to pull harder in the
> first
> > > few gears than a
> > > 180hp Audi ???-Brando
> > >
> > >
> > >
> >
>
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