[urq] Piggy back wastgates?

[James Bufkin]

Justin,

I'm not an expert on this system, but I've made inquiries to a few people 
about how it works and I'll relay as much information as possible here.

I don't have the 2nd wastegate hooked up to anything at the moment.  The 
exhaust manifold is vented into the piggybacked manifold so the manifold is 
fully functionaly, but I have installed a solid copper gasket at the 2nd 
wastegate as a cap.    I left the 2nd manifold on there to hold the copper 
cap in place.  I have seen other Audisport retrofit installs with a steel 
plate bolted to this orifice to dubunk the system.  The bottom of the 2nd 
wastegate would connect to the U-pipe between the turbo and intercooler.

Basically the system allows intake charge air to enter the exhaust stream 
via the wastegate.  Its controlled by vacuum pressure post TB with some 
other electronic vacuum control not yet determined.  The wastegate will be 
open at idle introducing O2 in to the exhaust stream which results in a 
very marked increase in turbo RPMs  which means more CFM airflow.  To 
prevent turbo surge the unused air is vented into the manifold which 
provides O2 gases for post combustion or a rich mix.   So for example the 
turbo is always providing some very high CFM number.  The wastegate merely 
dumps whatever air the engine can't consume into the hotside.   The 
complicated part is controlling the balance between the exhaust manifold 
pressure and the intake manifold pressure to keep flow going in the right 
direction.

Described by Bruno, A car so equiped would idle at about 4000 rpms.  Boost 
pressure is instant and power is fantastic with NO lag at all at any 
RPM.   The problems encountered is that the system burns up exhaust valves 
and exhaust manifolds rapidly.   Bruno said within an hour.  So, the system 
isn't normally seen on any S1s anymore.   And more often than not a close 
examination of most S1 E2s with the tubular Lehmann manifold will have the 
2nd wastegate removed or the piggyback manifold removed.

The two turbos I got with the manifold had #9 K27 hotsides.  Interestingly 
enough, I saw a picture of a #9 K27 hotside used on the Safari rally of 
1982.  This stamping number on the turbo was visible and this was on a 10V 
car which supposedly had less lag than the 20V cars.   The #7 was used on 
the SQ which is what is on my car now.   Lehmann thinks the #9 is good for 
racing and the #7 is too small unless I want to drive like an old 
man.  LOL   What is interesting about all this, is the choice of hotside 
size that was used on the various cars.   I think the #9 on a 10V is very 
large; however, the picture clearly shows that this turbo was used on 
10Vs.   Its possible they used a larger hotside on the final version of the 
system to reduce exhaust temps.  And since they used #9s on 10V cars(via 
the picture) they might have  gone even larger on the S1s which might not 
have been the right thing to do.    I haven't driven my car with a #9 turbo 
so I can't compare, but I do like the lag characteristics of the K27 #7 
very much.   Its not bad at all.

Could the system be made to work without destroying valves?  Possibly.   I 
havent given it alot of thought recently.  I'm happy with the turbo on the 
car and its lag characterisitics.   According to a few SQ owners they get 
full boost around 4K and thats about where I'm at with my setup.   The RS2 
with the #6 was making boost by 3500 rpm or so.    Very decent.    Lehmann 
says the #9 is about 500 rpm later so I would expect around 4500 rpm.   The 
#11s and #13s which might have been used on the 20V rally cars would push 
that to 5K or higher which would validate the complaints the drivers made 
on the lag characteristics when the power got that high.  However, this 
anti-lag system could possibly work to remedy that if a large hotside is 
used to control temps and pressures.

I bought the stuff from Ned Ritchie.  The manifold holes had been plugged 
and the piggyback was detached.  The wastegates were functional.   The 
manifold itself had numerous hairline cracks and was slightly warped on 
most flanges.  It had been repaired in the past already.  Surely a sign of 
very high heat and possibly dabilatating the manifold for good.   I took it 
to a master welder and machinist who also legally rebuilds deactivated 
class3 MGs so he knows his way around welding shit back together.  I milled 
over the idea of ditching this manifold completely in lieu of a tubular 
manifold from Sam Yeo's car now owned by Fru-T-pants.   In the end, I 
decided to at least attempt to repair the manifold and put it back together 
like it was supposed to be.  Over the course of a day he was able to slowly 
weld up the cracks with some very fine and long pencil TIG attachments.  We 
were also jetting argon on the inside of the manifold.   We tried not to 
use filler rod, cause the metallurgy on the manifold was definately an 
exotic alloy.   I had the surfaces decked and so far it looks okay but I 
haven't stressed it too much.  I want to complete the brace down to the 
motor mount before I go much further.   The two turbos are dated 6-5-85 and 
are 3 and 4 from a run of 15.  They were K27 #9 hotsides with a 3450 
compressor wheel in a K29 housing.    If I recall, a mechanic who worked on 
the 85 pike's peak car got these damaged parts as partial payment.  They 
were used on test runs up the hill.  I think Ned got them via barter for 
his services as well.

Sorry for the length of this blurb.
James