Kinsler offers a very complete...
Kinsler offers a very complete fuel test kit to measure the weight of the fuel. It is a good tool for the serious racer.
Depending on the piston’s location when the auto ignition occurs, the abnormal event can be identified as pre- or post-ignition. As lay people, we refer to it as ping, knock, or detonation. In every instance, it’s detrimental to the engine, emissions output, and power. Any Pontiac that experiences abnormal combustion is not giving its all, and depending on the severity and timing of the rogue flame, may actually be self-destructing.
Applying octane’s definition, anything that raises the pressure or heat in the cylinder will test the fuel’s ability to not ignite until electrically induced. There are many factors that promote abnormal combustion, with a dominant one being the compression ratio. It is all too easy for any enthusiast to demonize the compression ratio as the only reason for abnormal combustion, but in reality, an engine is a synergistic approach that is the melding of many different events and design factors. To deem the compression ratio as the only reason for abnormal combustion would be as wrong as to identify a singular cause for a human disease. The end result may be the same, but the impetus for it can often be different.
The weight of the fuel is...
The weight of the fuel is corrected to a standard of 60 degrees F
Out of respect to those who want to tell me I am wrong about compression ratio and its impact on the combustion event, please keep in mind that HPP is not talking about extremes. Without a doubt, street gas will not support a 14:1 compression ratio—that is not what is being stated. We want to know if an iron-head street/strip Pontiac should be built with 9:1, 8.0:1, or a 10.0:1 compression ratio? These are all values that are often mentioned during bench racing sessions. To some, our engine at 9.1:1 is at the threshold of what they call streetable on pump gas. We’ll see.
It needs to be understood that the best running engines enjoy a compression ratio that is high enough to promote good thermal efficiency and throttle response, and be the most powerful without experiencing abnormal combustion. If you lower the compression ratio too much because you believe it’s needed to run on pump gas, then you may very well be giving away the attributes that a higher ratio delivers. If the compression ratio is too high then the Pontiac may not run on pump gas and is no longer really a street car. For this reason, we felt it would be of benefit to the entire community to find the sweet spot on the compression-ratio bell curve using our Mule as the testbed.
Though Rockett Brand Racing...
Though Rockett Brand Racing Fuel supplied specific gravity for each fuel, we confirmed the specification using a hydrometer.
Let’s define the term pump gas. It’s street-legal gasoine that can be purchased by the public. Would any of you think of filling the tank of a nearly 500hp street Pontiac with 88-octane regular? Well, we didn’t fill the tank, but we did pour it into the fuel cell that fed our Mule on the dyno. For a hint of things to come—there are no burnt pistons. More on that later.
We planned to run regular, premium, and 100-octane street gasoline. We saw no value in mid-grade since we book-ended the octane of that fuel with regular and premium. We would dyno the engine with each fuel and make whatever necessary tuning changes required to optimize the combination, as was done with the 92-octane last issue. The same protocol that was established during the initial testing of confirming the results and tuning changes in each direction would be followed.