Bob Wise loads the dyno fuel...
Bob Wise loads the dyno fuel cell with fresh Rockett Brand Racing Fuel. It's a process that would be repeated often throughout the day. Each time the fuel was changed, the system was purged to ensure that there was no residual fuel from the previous test remaining.
There was one problem that first needed to be solved. HPP required a source of fuel other than the local filling station. We needed the actual octane of each gasoline and its quality confirmed. This would not have been possible by going to a local gas station—the octane can be skewed from the pump value since by law that is the minimum octane the consumer is purchasing. So we turned to Rockett Brand Racing Fuel, the supplier of the gasoline for the two articles that ran in the Sept. ’11 issue.
Rockett Brand Racing Fuel is a quality producer of race and street gasoline. The company offers a full line of products to the consumer, and its website offers a wealth of technical information that would be of value to any Pontiac driver. The staff at Rockett Brand Racing Fuel was willing to supply three different grades of gasoline and test them in their laboratory before shipment to RaceKrafters. They confirmed the octane and chemical composition for each blend, and supplied us with 88-, 94-, and 100-octane fuel. With the quality and octane of the fuel confirmed, we were able to move forward with our testing with full confidence that our data wouldn’t be corrupted.
Craig manned the dyno controls...
Craig manned the dyno controls for each pull. With the Depac data system and controls the testing was uniform to guarantee accurate results.
There are a few caveats that need to be supplied, along with a brief review of some terms. Our Mule is a fresh engine; accordingly it doesn’t suffer from carbon in the cylinders or on the piston crowns, corrosion in the cooling system or oil leaking past the valve guide seals or piston rings. It was breathing intake air at the carburetor inlet of around 75 degrees. All of these factors worked to the benefit of minimizing the octane requirement of the Pontiac.
Though you cannot change the weather, you can keep the combustion chambers and pistons free of carbon deposits, the engine in good mechanical condition, and the cooling system working properly. Thus, our test will be valid for the majority of driving and operating scenarios that a well-maintained Pontiac may see.
In extremely hot weather, the engine’s desire for octane may in theory increase. So if you live in a climate that has huge swings in temperature and is normally around 100 degrees F in the summer, you may need to alter the fuel you use during that time of year. But for the majority of the country, that is not the case. A good rule is that as ambient temperature increases, so does octane demand; as altitude decreases, so does octane demand. A cold, high place would require the least amount of octane in any engine to ward off abnormal combustion.
Craig checks the timing after...
Craig checks the timing after an adjustment.
Important terms are octane tolerance and octane creep.
Octane tolerance is the minimum amount of octane required to support normal combustion. It’s usually defined by an SAE standard test protocol. Since the protocol varies, the best thing for the enthusiast to do is to use the driving conditions their Pontiac experiences as the threshold for octane tolerance. There is no use worrying about conditions the car may never see. The facts should be based on your real world and not some engineering standard.
|Fuel||Octane||Specific Gravity||Oxygen Content By Weight||Ethanol Content By Volume|