RE: Overboost defined - long

[Scott Mockry <scottmo@teleport.com>]

Scott,

>I'm intrigued by the claims of audi, Scott, since a second or two of 
>"overboost" readings really isn't affecting a measureable time. 

Well, these are not "claims" by Audi, as the overboost is a "reality" that
is a result of the feedback control system and it is something that can
easily be measured or observed.

Having a boost profile that has more area under the curve, "IS" going to
make a difference if you imagine that boost translating into a Torque graph
with more area underneath it. Whether you can measure the difference
"accurately" and repeatedly, is another matter.

>In fact, to 
>test this, I tested a 1.8bar HKS mod (1.8bar peak) to a 1.8bar ecu mod 
>(2.0bar 'overboost' seen).  

I have not tested the HKS boost controller, so I can't comment on what the
boost output graph looks like, versus the boost output with the stock MAC11
boost controller solenoid. If the HKS provides a longer time in overboost,
and gets the boost ramped up quicker, then it surely could result in a
quicker 1/4 mile time. 

Getting consistent 1/4 mile times with the quattros can be tough to do and
require making a lot of runs with the same setup. The cheaper G-analyst
(G-Tech-Pro) didn't give me consistent results for the 1/4 mile times when
used back to back and compared to the actual time slips at the race track.
I don't know how the comparisons were made, but the ability to make
repeatable, accurate measurements, should always be kept in mind.

>It seems apparent, that audi is liberally using the "overboost" readings as a 
>good thing ("...can be obtained" doesn't at all mean it 'is' or is a 
>measurable "feature").  Not sure I agree or disagree, the side benefit might 
>be a slightly higher instant reading, but translating that into some sort of 
>"performance" really is stretching the argument, SAE paper or not.  A peak 
>reading that immediately falls, is a tough argument to measure, more 
>specifically, it doesn't really make a difference.  

Well, to say that "it doesn't really make a difference" is pretty silly. I
can't imagine finding too many people who would look at the boost graph of
the two different scenarios (with and without the ECU controlled boost) and
think that the profile which goes higher and stays higher for 2 seconds, is
going to have NO difference? 

Translate that boost graph into a torque output graph for the same
scenario, can't you imagine that the torque is going to be higher when the
boost is higher? 

When you are doing a 0-60MPH run, that lasts only 6-7 seconds, do you think
have higher boost during a few of those seconds will make a difference?
>
>WRT what you posted on the 944turbo cars, I'd be careful here Scott.  Several 
>in the dodge technical department found out that this modification to the 
>2.2l turbo cars (boost bleed mod) gave some lean fuel results, and warnings 
>about this modification were widespread.

I did not do the modifications to these 944 Turbos, as I said, the mods
were from a "particular tuner" and I have told the owners, that I don't
recommend doing this. They have been told by others that headgasket failure
is common with this "Overboost" mode.
>
>Overboost cutoff and overboost mode have accepted defintions in the turbo 
>arena.  Using a slow feedback loop WGFV control system in the context of 
>"overboost" is a great technical spin of terms, but really isn't a correct 
>presentation, IMO.  The proof is in the simple and cheap HKS pudding.

Well, the term "Overboost" certainly can have different meanings for
different people depending on the context of the conversation. The brief
"Overboost" found in the 10V Turbo is due to the Feedback control system
particulars, the 15 seconds "Overboost" mode found in the 1992> S4/S6 is
due to the programmed values inside the ECU and is much different in its
execution. This doesn't mean that my definition when applied to the 10V
turbo is somehow incorrect, as my boost graphs surely show that it exists
as defined by me.

Over and out
Scott Mockry