March - April 1998 Lane Racing And Rodding Article By Jim Kaekel, Jr.
For most of us, the 21st century is just around the corner, but in terms of technology the racing world is already there. Just as they did for much of the twentieth century, when they were the first to use such innovations as electronic ignitions, extensive use of lightweight metals and composites, fuel injection, traction control and anti-lock brakes, racers are now heavily relying upon sophisticated data acquisition devices to improve performance and race-to-race consistency. Racing is more competitive than ever, and data acquisition is a very effective way to gain an edge on the competition. Racers are learning that various data acquisition devices can teach them a great deal about their particular car and driving style. Durometers, air density gauges, elaborate weather stations, tach playback recording devices, on-board computers and pyrometers can all provide the information necessary for increased performances.
The pyrometer, in particular, has become an invaluable aid, providing racers with instant tire, track, brake, and exhaust temperatures. Pyrometers are vital to circle track racers, particularly if they race on asphalt. Asphalt racers commonly take tire and track temperature readings to determine if their car is set-up properly. Pyrometers such as Longacre's #50615 Infrared model are very popular and can be used to acquire accurate readings when aimed 3"-6" from the area of the tire where temperature needs to be determined. On an average race day, readings will commonly fall in the high one hundred degree range on the left side tires, where 60% of the cars weight resides, while right side tire readings will generally fall in the low 200 degree range. These readings can help determine if tire pressure or caster/camber setting are correct and most racers will check each tire in three locations on the contact patch; outside, center, and inside, before deciding if their set-up is correct. An abnormally high temperature in the center, may just be caused by over-inflation and the opposite may be true if the temperature is low in the center and high on the inside and outside of the tire.
The pyrometer can also check track temperature, which can change noticeably between qualifying rounds and the feature race and greatly affect handling characteristics on an asphalt car. A hot, sunny day will yield track temperatures in the 250-300 degree range, while a cool night race will show temperatures of around 150 degrees. Lately, even dirt track racers have been seen using pyrometers, especially if they have been experiencing chassis problems.
Drag racers also use pyrometers for checking tire and track temperatures. Though they don't use them to the extent that asphalt circle track racers do, drag racers record these readings use as a tuning aid and for reference purposes.
Pyrometers are also available to measure exhaust gas temperatures. Commonly called E.G.T. (exhaust gas temperature) indicators, the installation consists of a thermocouple, which is attached to an exhaust header tube, and a monitor to display the temperature. E.G.T.'s have been used predominantly during engine dynamometer testing, but racers have begun using them as an additional on-track tuning aid to determine if their fuel mixture is rich or lean, and how well it's balanced from cylinder to cylinder. E.G.T. indicators offered by Barry Grant (#130025 for clamp-on model and #130026 for weld-on) and Percy's (#55100) are primarily seen on drag cars. After a run is made, these E.G.T.'s, at the push of the recall button, will display the maximum temperature attained on that run. The Percy's E.G.T. indicator is designed for use with two thermocouples, so a temperature differential can be determined between two cylinders.
Even with a pyrometer, finding an engine's optimum operating temperature is no easy task. Many factors including fuel mixture, and ignition and valve timing affect engine operating temperature. An engine which is run too rich or too lean may display a low temperature while too much or too little ignition timing can cause high temperatures. If exhaust valves open too soon, potential horsepower will run out the header pipe, increasing exhaust temperature. If the intake valve opens too soon, raw fuel will be introduced into the exhaust during the overlap period (when both the intake and exhaust valves are open) and affect the temperature. Intake manifold, cylinder head port and combustion chamber design also have an effect on engine temperature.
Smokey Yunick, veteran race engine builder and tuner, has determined that the ideal exhaust gas temperature for a properly tuned small block Chevy race engine is 1,450 degrees and an ideal norm for big block Chevys is 1,650 degrees. The difference between the two Chevy engines illustrates the value of the pyrometer for determining exhaust gas temperature because the lower temperature of the small block shows that it has a more efficient combustion chamber design.
Temperatures will vary a fair amount from cylinder to cylinder and you would have to be using a very well flowed and balanced intake manifold and cylinder head to attain readings that are any closer than 25 degrees apart. When installing an E.G.T., it is important that probes are an equal distance - usually 2 inches - from the exhaust flange, with the thermocouple tip about 5/8" deep into the tube.
Using pyrometers as an additional engine or chassis tuning aid will help your efforts in the long run. It will involve some time and patience before you become familiar with what your ideal tire or exhaust temperature is, and you really begin to accurately use this new found information.