http://ww2.justanswer.com/uploads/JCTech012/2010-05-25_215739_How_To_Build_a_High_Performance_Cummins_Diesel.pdf
Here is the article I read on building high performance diesel engines. Quote from the bottom of page 4:
"Now we will concentrate on pyrometers, manifold pressure, liquid-filled
fuel pressure and air and fuel filter restriction gauges. These five gauges work
in unison to monitor your engine as you drive. It's like having a portable dyno
in your cab at all times. With the gauges, we can diagnose ninety-five percent
of all power problems over the phone."