[mkiv] EGT - Two BIG questions re probe placement & compensation

[Shawn Davis]

Unfortunately I don't know of a correction factor you can use to account for
your placement of the EGT.  What I would suggest is:

A) Move the EGT upstream of the turbo as you suggested.  A big function of
the turbo is to extract energy from the exhaust gas stream so you're
measuring way too late.  You have a temperature difference as well as a time
lag between your measurement and the combustion.

B) Do not use EGT as a measurement of A/F.  While there is certainly a
correlation and EGT can be used as a safety measure, there is no reason not
to directly measure AFR with a wideband sensor.  The wideband senor output
can be run directly to the AEM EMS for logging and logic driven tuning.

Shawn

On Tue, Mar 18, 2008 at 1:23 AM, Bill Lawry <inov8tn at gmail.com> wrote:

> Hi -
>
> When you want the best go to the MKIV list.
>
> OK, the OEM twins,  air box and exhaust are out and a single with
> FMIC, BOV, exhaust, AEM EMS, and a huge air filter are in. Performance
> is excellent if you don't count starting, idle or cruising mpg. You
> guessed it - acceleration is awesome! Roughly 500 rwhp w/ stock fuel
> system and pump gas.
>
> But this question is about determining actual EGT
>
>   1) Under cruising and
>   2) Under WOT
>
> When the probe is (obviously) not in the combustion chamber.
>
> Right now the EGT probe is mounted about 4" downstream of the turbine.
>
> Is there a table or rule of thumb that will tell me how to compensate
> for not having the EGT probe in the combustion chamber? Mine is just
> after the (new) SP58GT single so there's heat that will be lost to the
> valve(s), head, header pipes, and turbo that I'll need to compensate
> for if I want to know the EGT so I don't burn valves or pistons.
>
> I want to know absolute temps so I can have the dealer lean out the
> mix and tweek the spark when under cruise control (light load) to get
> better mileage.  I do a lot of highway driving and I can't afford a
> Prius.
>
> The AEM 1100 EMS should be up to this.  Some on the AEM list claim a/f
> up to 16:1 w/o damage.  I don't think I'll want to get that aggressive
> - 15.5:1 maybe. I want to get up highway hills under Cruise Control
> without burning anything but gas
>
> The SP58GT turbo is of course mounted right at the collector.  And as
> I said the probe is a few inches downstream of the turbine.  I'm told
> that while cruising the turbo won't be removing much heat from the
> exhaust so it shouldn't be much of a factor under light load.  This
> seems reasonable to me how about to you?
>
> Can I just consider the turbo to be X inches of pipe?  What's 'X'? What'
> pipe?
>
> So Question # 1 is: How much temp will I lose going past the valves,
> through the block, the header pipes, the turbo, and a little more pipe
> under cruise?
>
> Do you have any idea of the accuracy of the compensation so I can
> build in some safety factor?
>
> Outside of NASA is there some way to calibrate this setup?
>
> And now for the 'extra credit' question (#2):
>
> Are there different compensation factors I can use for WOT
> measurements or should I press hard for the dealer to move the probe
> to the inlet flange of the turbine housing to get the turbo with all
> of its variations out of the 'equation'?
>
> I understand there is enough 'meat' at the beginning of the turbine
> housing to thread mount an EGT probe without needing a weldment.
>
> Will this impact WOT performance very much - how much?  Enough that I
> should to move the probe downstream of the turbo after I get things
> setup?
>
> Thanks in advance.
>
> - Bill
> '93 BPU+ *and* drivability
>            *and* better mpg
>            - Soon, I hope :-D
>
>
>
> Sent from Gmail for mobile
>
>
>
> On 3/16/08, Eric Typpo <etyppo at comcast.net> wrote:
> > I usually had my V700s on the car for a day or two before and after
> track
> > events, and was always happy to put my street tires back on.  They
> tramline
> > quite a bit and ride considerably harder than street tires in addition
> to
> > throwing up debris.  I wouldn't use them as street tires.
> >
> > Eric
> >
> >
> > >
> > > I been through several sets of V700's and now V710's.  Frankly I would
> not
> > > try to use tires in a manner they were not designed for.  You will be
> > > disappointed on both the street and the track.  After you drive the
> track
> > > tires like V700's on the street, they will be crap for the track and
> vice
> > > versa.  And you won't get many miles out of those tires on the street,
> or
> > > anywhere.
> > > Bite the bullet and get a second set of wheels (stock or other) and
> mount
> > > the track tires.
> > >
> > > Larry
> >
> > _______________________________________________
> > Mkiv mailing list
> > Mkiv at mkiv.com
> > http://www.mkiv.com/mailman/listinfo/mkiv
> >
>
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