Re: Power loss at>4800 rpm

["Colin Barfoot" <colin_barfoot@email.msn.com>]

To recap I had a problem when running with boost levels greater than 10 psig
where under full throttle I would acclerate hard to 4800 then accleration
would stop, while boost would stay the same, whether set to 10 or 16
psig(via SK(r)).
I checked the standard advice - full throttle switch -OK, vacuum and boost
hoses OK, timing, spark plugs OK, oxygen sensor OK no improvement found. I
even tried making the fuel mixture a bit richer (so that the tailpipe
carboned up) but to no avail.  Data point is the car would top out at 200
kph (123 mph) up hill or down hill

Then by chance on Christmas eve my starter failed - fixed it followed by the
alternator failing on the way home from work at 9:00 PM boxing day, with the
new starter a ground fault was fixed and the combination of more voltage and
charging circuit ground removed improved things probably 50% so that while
acceleration slowed still it didn't stop and would eventually pick up - a
little above 5500 RPM Data point - top speed  now 205 - 210 kph.

Solution 1: ensure full voltage is available.

The next thing that I did was to have the VW dealer have the fuel injection
set up to stock, i.e I leaned out the mixture quite a bit until it was juct
a couple of degrees richer than stock.   Things were then much improved so
that there is now only a bit of a reduction in acceleration at around 5000
rpm, after which it picks up strongly again.

Solution 2: don't run too rich run just a couple of degrees above spec for
best power.

The next problem was that the TAP silicone hose kept blowing off at the "cam
shaped" lower intake manifold point, it seems that while it wasn't cut
perfectly it stayed on fine for almost a year,but now seems to have
stretched so that at about 10 psig the stretch was enough to pull the hose
off, this also worked to limit power - top speed (up ~ 15  degree hill 200
kph)

Solution 3 used two clamps, one on the hose adjacent to the throttle body to
compress the hose against the manifold and prevent it from stretching and
deforming where it sould pull the hose off the second clamp - arranges so
that the slots (for the wrom gear) dig into the hose as close as possible
tothe cam point on the manifold.
Data point - still accelerating strong at 235 kph (had to slow for turnoff)

Now, I am enjoying the power without worrying about the slowdown when
passing at 4800 rpm.

Hope this helps

Regards,
Colin
86 5000 CD Quattro 325,000 km

PS Clarke P. congratson your 86 Quattro - will you have it out for the
regional slalom championship?