Here are pictures of the holes that I drilled and
tapped while I had my head off of the car. Read on
from some facts, and answers to common questions
regarding EGT gauges on GLHTs and TDs in general.
An Exhaust Gas Temperature gauge is used to mesure
exhaust gas temperature as it's name impies.
Our motors tend to typically run hottest in the #4 cylender, so that
is where I would reccomend placing the probe. NOTE: According to several
well respected turbo dodge owners with 4 probe EGT gauges, the #3 cylinder
tends to run hottest in their cars. This could be caused by the fact that most
people running stock exhaust manifolds tap the #3 cyl. where it sees
gas from other cyls. as well, and therefore produces a hotter reading.
As the second picture at the top of the pages shows. I have a hole tapped
for the #3 and #4 runners so I can do some testing on my car to see
which cyl. runs the hottest.
Most gauges will use a type K thermocouple which threads into a hole
that is in the manifold. Ideally you would want this
hole to be about 1-1/4 in. from the head.
The probes are most often a compression style fitting, so you can intall the probe
while the head is still in the car by drilling your hole
with your appropreate size bit, and tapping the hole.
The compression fitting will allow you to place the
probe at the depth you need, as many of them are too
long for full penetration into the runer from the
side. The gauge takes the reading from the tip of the
thermocouple, so make sure that it is not touching the
wall on the opposite side of the runner, as it will
read much lower than it actually is.
Most of the fittings used will be a 1/8th-28
NPT fitting. I would reccomend using a magnet, and drilling
slowly to catch most of the metal shavings that result from
drilling the hole. When tapping you could just use a little
bit of grease on the tap to capture most of the shavings.
I would shoot for about 1450*F-1500*F. Some people (Read
Gary Donovan) have run much higher EGTs that this, but the
typical motor SHOULD be safe at this level. Each motor is
different however, so I would keep a close eye on things and
check you plugs regularly to ensure everything is looking