XR4Ti Archived Tech Articles

    Factory Boost Gauge Mod - this makes the factory boost gauge more accurate in transient events and displays information more representive of what is going with boost and vacuum.


Post Date:    Tue, 17 Nov 1998
Subject:      Boost Gauge Mod, pitfalls, pratfalls, and results

Summing up my boost gauge modification...

I yanked the gauge cluster out of my 87 XR4Ti.  I was intending just to take
the screw out and put the cluster back into the car.  Didn't work as planned.
First thing I discovered was that I didn't have the right size screwdriver.  I
tried improvising.  Not only did the improvisation get me nowhere, but I
completely screwed up the vacuum inlet to the boost gauge.

I had to get the right tools.  I went to Wal-Mart to get a precision screw
driver set.  Been needing one anyway.  The Popular Mechanics set was a
whopping $2.97.

Came back home and found out for sure that I had terminally toasted the
threads and the end of the boost gauge fitting...  I got a spare gauge cluster
from the garage, and took the boost gauge screw out of that.

The 2.0mm flat blade screw driver did the trick.  Actually, the screwdriver
with a pair of 9" channel lock pliers grabbing the shaft for the rotational
force.  These bad boys were IN THERE.

Be extremely careful to apply heavy, constant pressure downward on the
screw to make sure it doesn't slide out of the notch

After taking the screw out I swapped boost mechanisms in tachs, so I wasn't
replacing a known good tach with a potentially bad one.

Results of the mod:

- It actually seems to go deeper into the vacuum zone when the throttle is
closed and the rpms are above idle.

- the response of the gauge is certainly faster, mostly quicker changes in the
vacuum area as that transient seems to be quicker than the transient of the 
boost climbing.

I guess the best why to describe this mod is this.  The results make the boost
gauge resond more like it is operating at a faster sampling rate.  It responds
to changes much better.

The car isn't any faster.  Who cares, it looks cooler, dammit.  Doesn't make
the stock gauge more accurate, but it kinda does.  Hard to explain.  I guess 
I just can't seem to put the right combination of words together to explain it.

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Update on the modification (22 December 2000)

While no changes have been made since the above article was posted to the 
IMON list two years prior to this update, I have found a better way to 
explain what is changed, in words.  It's amazing how much a little 
mathematical education can expand the mind when it comes to technical 
things like this.

While the stock gauge is inherently inaccurate, by design, the modification 
described above makes the gauge track changes more accurately.  In other 
words, the gauge is capable of displaying a higher rate of change than it 
was previously.  I called it "sampling rate" before.  That isn't really a 
good way of describing this, simply because the gauge isn't digital or 
electronic, it's analog, and the sampling rate is essentially infinite, 
before and after the mod.

I'm not willing to change the article above to reflect this advancement in 
my thinking.  But I am willing to explain it more thoroughly.

Let me sum up in non-technical-speak.  The gauge, with the screw in place, 
isn't able to track the changes in intake manifold pressure as quickly as a 
gauge that has the screw removed.

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Update, 27 July, 2001 - from an offlist email reply:

>   I read about your mod removing the turbo boost gauge screw. Is that
>  all i need to do to increase the sensitivity of the boost gauge?

Amazingly enough, yes.  That's it.  Just make sure you are prepared to 
take the screw out properly (the correct screwdriver and a pair of pliers 
to help turn the setscrew, it's really in there).

So take out the gauge cluster, take out the screw, and put it back in.  If 
you feel like that is too simple, you can replace the vacuum tee to boost 
gauge vacuum hose while you are in there.  They do have a tendency to 
evelop splits in them once you start playing with them.

That's it.  Other than that, the hardest part is getting the vacuum hose 
off the boost gauge nipple.

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Published by Chris Anglin.