UrS4 race motor meltdown. Advice?! Parts?

[Leigh Anderson]

Hi all,

need some help scoping out cause, ideas, costs, options to fix re a '92 UrS4
motor meltdown...

This concerns the moto/speedvision cup '92 S4 purchased from TAP (1st big
mistake was trusting TAP). The car arrived from Florida, with supposedly
"fresh rebuilt 440-HP" engine*. However, right off the truck, it was
blue-smoking some, was missing lots of high-HP parts, such as the RS2
injectors and MAF. Replaced the stock injectors and MAF with RS2 units,
fixed multiple intermittent-faulty sensors, tightened a finger-loose knock
sensor, finally got it running OK. Did a leakdown test re smoke, but test
was OK.  Suspected hybrid turbo oil seal leak at this point. Decided to run
the car despite
variable amounts of blue smoke that appeared for a few minutes at some but
not all startups.

Argghhhh!!

At PIR event, don't know the cause, but a valve head broke off, and bounced
around at high velocity, in #2 cylinder.

- The cylinder wall is scratched a little but easily salvageble with honing
etc. there is no wear-lip at top of cylinder at all.
- The piston is badly eroded and 1/3" holed, thus metal bits distributed
throughout engine
- The head chamber is chewed up and eroded pretty bad. Either get a new
head, or do major welding to add material back + machining salvage job?
- looks like oil/melted-aluminum slurry went through the hot side of the
T4-K27 turbo, but blades may be OK, needs more looking into, at least
cleaning.

Situation: After about 20 minutes of the Audi PIR event track session,  car
had completed a nice strong pull up to neighborhood of but not beyond 7000
rpms, pulling hard and smooth_right _through to the braking point about
115mph (definitely below rev-limiter), lifted off gas for PIR turn #1, onto
brakes hard down to 50mph or so, went to blip gas for downshift, surprised
by hardly any/no engine rpm response. coasted through PIR's chicane, felt
like motor was in "limp mode", then there was a sudden 100 yard plume of
dense blue smoke out tailpipe. turned off ignition and coasted onto grass
behind flag station. No fluid leaks or smoke at that point. (With full-face
helmet on and noisy race car sound level, never did hear any mechanical
distress sounds.) Note: always used 104 octane unleaded fuel. Topped off
with synthetic oil, good oil pressure.

I suspect that the valve train was somehow weak, or very race-used before
it arrived, or put together wrong perhaps, and cumulative stress somehow
caused the valve failure at a fairly random moment. Usually this kind of
valve failure is caused by a severe over-rev +_immediate-failure at the
exact moment that over-rev occurs. Absolutely not the situation here, so its
a bit mystifying as to the _exact cause. (Also not a lean fuel/detonation
piston-punch-thu)   Would like to figure out cause.

Here's my questions:

1. theories on the cause? additional diagnosis/examination to try? I'm
dead-nuts sure the failure point was NOT the usual over-revs cause. Its
possible there was over-revs in this motor's lifetime, but NOT close in time
to the point of failure.

2. ballpark $estimates to fix motor? any BTDT? fortunately, we've got some
great non-dealer audi-capable mechanics around here, so we can ask them too.

3. suggestions for better than OEM brands/sources of pistons, rods, valves,
head bolts, etc. etc. to consider as long as motor is being rebuilt from
bare block anyway?

4. Best source for new/used good 20V head? any for sale?

5. would we be better off $-wise parting out this motor and buying a used
motor to bolt on good parts? any used UrS-car motors for sale? what do used
motors go for? (i know they're scarce)

TIA,
Leigh

QUATTROS UBER ALLES!