The GM performance enthusiast quickly recognized and embraced the benefit of instrumented testing in its ability to extract the most power from an engine. This was in part due to the acceptance of programmable stand-alone EFI controllers and the need to completely map the fuel and ignition curves.
Prior to the expansion of chassis dynos into almost every area of the country, the dangerous and ineffective practice of tuning on the street was often employed. Not many dragstrips offered "test and tune" days, and when they did, were often very crowded and required a great deal of waiting time in between verification of the calibration change. This delay often brought a change in weather conditions that would skew the data. The chassis dyno quickly became an EFI enthusiast's dream come true.
Even with this level of acceptance, many do not use their dyno session to its fullest potential and often come away frustrated, confused, and disillusioned. Recognizing this, GMHTP prepared this overview of the steps and thought process that is required for an effective day spinning the rollers.
Finding A Dyno Shop
The first step in having an effective dyno session is to find the proper shop. Though there are many different brands of chassis dynos (all being capable of doing the job), the shop is the key component often overlooked. The process begins by identifying what your particular needs, level of involvement, and skills are. Are you someone that just wants to drop the car off and have it tuned or do you want to be a dynamic part of the process? Are you only interested in purchasing dyno time along with the operator and you will execute all of the tuning decisions and processes? All of this needs to be established with the shop before you show up.
Other considerations when choosing a dyno facility are: do you need four-wheel-drive capabilities? Can your car fit on the dyno, or if it is an above ground unit will it have sufficient clearance to drive up the ramps? If you are looking to perform complete mapping of the fuel and ignition tables, then a dyno with a brake that can hold the engine at a fixed load is crucial to your success. An inertia-only dyno will make it very difficult to calibrate and tune at part-throttle and light-load operating modes.
It is often a good idea to visit the prospective shop and have a look around and speak with the staff about your requirements. Look for clear access to the dyno rollers, a sufficient sized fan to cool the engine (not a box fan from the discount store), and if the shop is going to do the tuning, do not be shy about asking about their qualifications for your type of vehicle. A business that is very well versed on working with Fords may not be the best choice for your GM car.
For the business owner, the dyno is only one part of the investment required. Many of the better tuners have available PCM-based data acquisitions systems that will interface with the dyno software and provide serial data along with horsepower and torque results. The ability to accurately monitor the air/fuel ratio is also very important. A wide-band and fast-acting air/fuel ratio meter employing at least a five-wire oxygen sensor should be part of the dyno cell along with the ability to print or graph this information in relation to the pull made. If the shop shows you a cheap, OE oxygen sensor-based meter, that facility is not good for much more than providing horsepower and torque numbers.
Discuss your needs and ask if the shop can provide these services. Review the appointment and cancellation policy. Confirm the level of involvement you desire along with the total fee for the shop's services. Since tuning is often a trial and error based function, it is very hard for the business to provide a flat fee for dyno time. Many shops have a flat charge for the first hour and then a reduced rate for each consecutive hour spent on the rollers. You need to understand this.
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