Dyno Tuning Basics - Jets, Timing, Camera, Action

***Ed Blown Vert*** · 04-09-2008, 10:00 PM

Dyno Tuning Basics - Jets, Timing, Camera, Action

As you gaze out your window and wonder when winter will finally break-at least enough so that you can safely open up the garage and fire up your Pontiac without fear of engulfing it in a swirling maelstrom of snow and ice-take solace in knowing that there is a way to test the effectiveness of your "winter" performance upgrades without hitting the dragstrip.
For those lucky few who live in climates that support year-round dragstrip operation, hold off a few minutes before heading out the door to test again. While dragstrips are certainly fun, and in many towns a great place to meet and participate in the Pontiac hobby, they do have their limitations for A-B-type testing of performance products.
Since new or modified engine combinations often require extensive tuning, it may take 10 quality passes or more to get your combination dialed in. Invariably, things don't always go as planned. In many cases, you end up waiting and getting in only three runs, of which one was invalidated due to poor traction or some other variable. By the time you arrive back home, tired and frustrated, the mental financial calculator has already clicked off $100-$150 of wasted funds, paid for tow vehicle fuel, race car fuel, food and gate fees.
Sure, you can head back out at the next available time or try another track, but what happens if at the next date the weather is 20 degrees warmer and the barometric pressure has swung wildly? Will the changes that you made following the first testing session show improvements or will you simply be compensating for other variables, and continue chasing your tail until the perfect set of circumstances allow you to get your Pontiac dialed in?
For years, the only methods available for hobbyists to test their high-performance modifications included a street-based "seat-of-the-pants" approach or the dragstrip. With the introduction of the inertia-based chassis dyno, the Dynojet and the iconic Dynojet 248 model, dynamometers offer enthusiasts and tuners alike a tool to measure horsepower and torque in a controlled environment.
Now a mainstay of both the aftermarket shops and the OEMs, chances are there is a performance-oriented business in your area that will provide you with dyno-tuning time so you can objectively quantify a baseline, then make changes to optimize your tune.
Regardless of the brand or technology employed by the "chassis dynamometer," the object of dyno tuning is to allow you to get your Pontiac dialed in so that when it's driven on the street or the track, it's very close to being optimized. Whether it's equipped with a classic Pontiac running a traditional carburetor and distributor, or the latest LS-offering from GM, the same principles apply. Optimize the fuel delivery system and ignition timing for maximum safe power.
Strap yourselves in as we roll on over to Real Performance Motorsports (RPM) in Lewisville, Texas, and dyno-tune Floyd Hand's '66 Tempest. Is there power to be gained by tuning this well-sorted out combination or will we simply be spinning our wheels?
Recommended Tools: Timing light
Standard wrenches
Screwdrivers
Automotive diagnostic tools

Recommended Parts and Supplies: Carburetor tuning supplies
Carburetor gasket(s)

Dyno Preparation
Preparing to dyno-tune your Pontiac requires forethought. Ensure that your car is in top operational condition, gather your carburetor tuning kit and timing light, and call up your favorite shop to schedule an appointment.
Market rates dictate how much it will cost but in general, expect to pay between $100-$150 per hour for dyno tuning. Tuning time depends on myriad factors including the current tune of the combination, as well as the tuning ability of the dyno operator and enthusiasts involved. For most, a single hour session is often sufficient to optimize power, assuming that quick changes, such as carburetor jetting and timing adjustments are all that are required.
According to Keith Lohse of RPM, "Enthusiasts who have never put their car on a chassis dyno shouldn't be put off by the Internet stories of people damaging their engines. An engine and drivetrain that are in mechanically sound condition will experience no additional risks over what would be experienced on the street or track. At least in a dyno environment, we carefully watch the air/fuel ratio and immediately shut off the car if there is even a hint of a problem. In addition, topping out the car on a dyno is far safer than doing so on the street."
Dyno Results
Tests were conducted on a Dynojet 248 chassis dynamometer equipped with a wide-band O2 sensor. All horsepower and torque readings were converted back to SAE. Average horsepower and torque were taken from 3,900-5,900 rpm. In both the baseline- and dyno-tuned configurations, the peak horsepower and torque numbers were recorded at the same rpm levels. Peak horsepower occurred at 5,850 rpm, while peak torque registered at 3,950 rpm. Since the Tempest was equipped with a Turbo 400 automatic transmission and a 3,200 stall tight 10-inch Continental torque converter (Jim Hand Special), the car was pulled in Third gear. Rather than simply romping on it, which caused the car to downshift into Second (and invalidate the dyno pull), the throttle was eased down until just over 3,200 rpm, then mashed to the gunwales.
Info Baseline Dyno Tune Intake Air Temp Deg 97.5 104.7 Vapor Pressure (In.Hg) 0.39 0.38 Barometric Pressure 29.29 29.16 Correction Factor (SAE) 1.04 1.05 Air/Fuel ratio Avg. 10.7 11.8 Baseline Dyno Tune Gain Horsepower 354.9 383.2 28.3 Average Horsepower 321.2 343.2 22.0 Torque lb-ft 427.9 455.6 27.7 Average Torque lb-ft 351.7 375.3 23.6
Conclusion
After establishing a baseline for horsepower, torque and air/fuel ratio on the Tempest, a series of changes were made to the carburetion and timing in order to enhance driveability along with overall power and torque. When complete, the Pontiac picked up peak horsepower and torque to the tune of 28.3 and 27.7, respectively. More important than the peak numbers were the gains in average horsepower and torque, as those are the changes that can be felt on the street and track as the engine accelerates through the power band.
Keith Lohse of RPM states, "As the generation that grew up tuning and racing carbureted powerplants such as the Pontiac dwindles, we are seeing a greater influx of cars that are either overly rich or dangerously lean coming into the shop. Since a carburetor and distributor are 'wear items' and are not capable of self-adjusting like the late-model EFI-equipped cars, a car can go out of tune with minimal use. Even with highly-skilled tuners-such as Floyd Hand and Marty Parker-due to the demands of everyday life, there just isn't enough time available to take repeated trips to the dragstrip in order to get the car tuned again. In a normal 1-hour tuning session, an enthusiast can generally get their car tuned well enough so that when they return to the track, they are very close from an optimal performance standpoint."
After reflecting on the dyno session, it strikes you that the chassis dyno is simply a tool for tuning, and the real expertise is what both the dyno operator and enthusiast bring to the table in the way of experience and tuning ability. Rather than simply trying to optimize overall power or torque, RPM carefully watched the car's air/fuel ratio under various throttle conditions in order to improve the overall driveability of the car and consulted with the tuners on a recommendation in order to optimize performance.
Although the snow may be swirling, it may be worth considering dyno tuning your Pontiac. It doesn't matter if you run the same combination for 10 years or have recently installed a new set of cylinder heads and camshaft, isn't it worth knowing that when you roll your prized possession out onto the streets or drop the hammer for a pass down the strip that you will be doing so with the confidence that you have objective data to rely on?
Knock the toboggan out of the way, check the bearings on your trailer and spend an hour with your friends or club members engulfing yourselves in the melodious rhythms of a Pontiac engine singing a song that's music to your ears and uplifting to your spirits.

Photo Gallery: Dyno Tuning Basics - Jets, Timing, Camera, Action - High Performance Pontiac

Read More | Digg It | Add to del.icio.us

More...