Re: MacBoost

[QSHIPQ@aol.com]

> You know I happened to notice the spec's in Bentley for the cams in the
early
 >5k vs. the later models.  It certainly appears that the cam in the MC is 
 >similar, if not identical to the one in the high compression NA engine
(code
 >NF?) ... I wonder if an MC cam would be of use in a boosted up urQ.  I did 
 >notice that Bentley did not provide cam specs on the WX ...

An MC cam is not really an improvement for the WX....  A 90-91 10vt cam
profile would be...  Remember, all MC's> are hydraulic...
 

 >  Specifically, the turbo application is a variable that can wreak havoc on
a
 > EPROM mod, more so than a cam, btdt with the 272 cam too...  Blanket
 
 >No, the urq's ECU can do nothing to adjust boost, just the ignition timing 
 >at particular boost levels.  The resistor approach simply scales the
mapping
 >so that the modified ECU actually applies the timing at high boost that it 
 >would have applied at a fraction of that boost in an unmodified car.  I 
 >would argue that an EPROM mod _COULD_ have a map that anticipated the
>chang-
 >ing cam timing with RPM because that is an input to the map ... not so with

 >simply scaling the boost input.  Speaking of variable cam timing ... does 
 >anyone know about the cam advance mechanism on the newer Saab turbos?  

Ok, steve...  Though the statement was in regards to cam PROFILE, not cam
timing...  For that the EPROM really doesn't have an input...  To react to
profile, i.e. increased overlap (272 vs stock) the EPROM can't react fast
enough....  My understanding of the Saab cam is that it is a "franco" type
arrangement, not the M3 type....  Crude but effective
 
 >I personally have experience with a _SuperChips_real_EPROM_chip_ modified 
 >ECU in my otherwise stock '83 urQ.  As I reported in the past I was simply 
 >testing to make sure that the ECU worked ... since I had the stock WG
spring
 >I was not expecting to see any performance change.  I was surprised to find
 >the engine had better low-end performance and revved quicker in first gear.
 >I wish I had similar experience with a IA "hack" equipped ECU to see if
that
 >would give similar results ... I suppose I could do this by installing the 
 >Schrappnel Knobben and leaving the regulator shut down ... I'll try that 
 >this weekend.  
>>>>>>  And I have a group A Rally box that does the same thing on the 5ktq,
it gives massive timing advance before boost, then cranks it back on
boost....  The transition is VERY fast, and lag almost non existent....  This
seems to be the answer to the mods, the trick is to get as much timing
advance as possible before boost, then curving it back more linearly ON
boost....  IA doesn't do this to either the early or the late cars in common
for sale form...
 
 >     >>>  I respect your work (hey, I bought a Schrapnel Knobben) but
 > personally 
 >       I prefer the EPROM mod.

 
> I completely agree with the statements that both SK and EPROM are useful
mods.
 >My thinking about the EPROM deal is that there is more than a bit of magic 
 >that is necessary to get to a position where you are able to be able to
tweak
 >the right locations in the EPROM ... and RDH had this figured out quite
some 
 >time ago.  If you look back through his posts, you'll see that he was able
to 
 >address some of the other issues with the engine via EPROM mods (such as
idle
 >and cold starting performance).  Scott M and Orin provided that catalyst
that
 >brought things to the fore now.  

>>>>  And kudos to both....  There is more majic than science in this
execution, we are still talking about the last "nth" HP gain, by definition,
drivability  more than HP...   I personally have been on a quest for 4 years
to find something that "improves" the IA/TAP mods that are available....
 Have driven many configs of engine, turbo and computer tweeks.....  The
computer eprom mods have produced very subtle, though noticeable
improvements....   No doubt, the first is just a boost equation, and looking
at the turbo maps of the k26, it really has no rocket science addressed to
it...  If you aren't running a 2 bar box on a k26 turbo car, the turbo is
never reaching it's peak efficiency....
 
 >I think this is very important, so I am trying to include this caveat with 
 >any posts I make on the subject.  Anyone that is considering modifying
their
 >turbo car to increase the maximum amount of boost that is produced by the 
 >engine needs to realize that these mods do increase the risk of catastophic

 >failure of components in the engine, and furthermore some modifications 
 >alter the effectiveness of the self-preservation mechanisms that were 
 >designed into the engine.  We have a lot of evidence that the risk is
fairly
 >small, but we shouldn't kid ourselves into thinking it is zero.  Proceed 
 >with brain engaged ... and HAVE FUN ... 
  >>

I will second that too...  Beyond 2.0PR, you better do things based on
knowlege, not the addiction for more is better, cuz it ain't....  I can share
that beyond 2.0 PR on a stock audi turbo, you are increasing the INefficiency
of the turbo, and creating a huge back pressure wave on close throttle,
decreasing the life of the turbo as well as the engine.... Forget the dash
guage, those of you with "stage II" boxes, be advised that the pressure
transducer (that measures boost at the computer) is constantly being whacked
at above it's design parameter (2.0bar max)...  When that happens, it reduces
the effective measurement, and then those "testimonials" of 21-22psi boost
levels hit the net (by definition, a 22psi (2.5bar) reading on a guage means
a 2.0 PT is not doing something it wasn't designed to do)....  That's a
2.5-3.0 PT address by definition, and in a stock turbo, you are reducing the
life of engine and turbo, and based on the "hacks" in those "stage II" boxes,
you are asking for trouble, cuz the PT measures the same boost above 12-13psi
(actually a percentage of max boost -so numbers may be different).   Those of
you running the bypass valves to address that wave - make sure you feed the
bypassed air back into the intake of the turbo, that is measured air, and
should not be dumped to outside...  I did some intense research on this over
the last couple weeks....  The talons use a variety of dump valves, the
consensus is that the dump to atmosphere is a track only use (gains of .3 sec
in a sub 13 quarter), the rest of the time, should run closed loop...  You
don't do this feedback, you will get a rich fuel spike which creates either a
backfire on the exhaust side (turbine and or cat life reduced) or the cold
side (turbine or CIS dist life)...  

Having fun is the key...  Make sure it is good and safe fun....  What isn't
is replacing a motor becuz of the addiction to right foot stomping...  Stage
II folks with stock k26, beware....

Scott

HTH
Scott