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

[Bill Lawry]

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



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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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