If you use a Demon or Holley-style modular carburetor, a power valve with a lower vacuum opening (more throttle angle required to evoke enrichment) will improve fuel economy.
Drain the oil. Some of the chemical will have leaked past the rings and into the lubricant. With fresh oil installed, start the engine and take the car for an aggressive drive to blow out the carbon. The exhaust will smoke and have an odor on start-up. If you live in a populated area, you will want to drive away immediately to avoid complaints from the neighbors. This procedure may need to be repeated one or two more times, and if scheduled when an oil change is due, will not be a financial burden or waste natural resources.
With the pistons and combustion chambers relatively clean, you now need to attack the IVD. If you own an older Pontiac that is easy to work on, the most effective method is to remove the intake manifold and valve covers, and loosen the rockers so all the valves are closed. Then use either the spray or liquid to cover the intake valve with Top Engine Cleaner. Let the chemical soak the same amount of time as for the piston. If you can have access to the intake manifold runners by only removing the carburetor, then you can leave the intake manifold on the engine and accomplish the same thing.
Reinstall the rocker arms, valve covers, and intake manifold. Pull the spark plugs and disable the ignition. Crank the engine over by hand to get the chemical out. You do not want to hydraulically lock the engine, so do not use the starter. Reinstall the spark plugs, start the engine, and go for a drive. There is no need to change the oil since the cleaner will not sit on the pistons long enough to leak past the rings.
Keep in mind the GM chemical is very strong and will dissolve any paint, so you do not want it to splash on the fender when purging the cylinder bores. That is another reason why HPP suggests turning the engine over by hand.
Racers check the specific gravity of the fuel. Street gas will vary in density with each shipment from the refinery. Octane is mandated by law, but density is not.
A good, synthetic, light-weight oil should be used with an API rating of GF3 or better. Any Pontiac, even an older one with stock bearing clearances, can get by with a modern 10W-30 synthetic. Forget about the days of running 20W-50. [See the oil story in this issue for more info on vintage Pontiacs and oil.--Ed.]
A switch to high-quality, low-friction synthetic lubricants for the manual transmission and differential will also cut fuel losses. Synthetic automatic transmission fluids are excellent for allowing extended drain intervals, but do not offer any fuel economy benefit.
Pay attention to drag from calipers and misadjusted drum brakes. Remove the calipers, and polish and lubricate all slide areas with a synthetic brake grease. Check and repack the front wheel bearings when applicable.
Find a good alignment shop that will make sure the front wheels are set to specification and not dragging and wasting fuel.
Make a weekly habit of adjusting and maintaining the proper tire pressure. Modern radial tires usually ride best with the prescribed air pressure. Keep them filled up to specifications or no more than 2-4 pounds above. Always check the pressure when the tire is at ambient temperature and not in the sun. A good time is in the garage in the morning. Make sure your tire gauge is accurate.
Keep the body of the car clean and waxed, especially if you do frequent highway driving. There is a reason airlines wash and wax airplanes, it cuts the wind drag over the wings and fuselage. Highly waxed cars do use less fuel.
Remove any excess weight you carry in the vehicle such as a toolbox, golf clubs, and so on. You would be surprised at what is in the trunk of some people's Pontiacs! GM engineers state that every 100 pounds of excessive weight can create a fuel mileage penalty of up to 2 percent.