Within the Pontiac community there are enthusiasts who adore Ponchos but are also very familiar with other makes of engines, and I am one of them. I make no effort to hide that I am an engine guy above all else.
Over the years, the Pontiac cylinder head design and combustion chamber have often become a target of ridicule by many engine people. It does not take long for the conversation to drift toward the chamber shape, port design, and spark plug location in relation to the bore center. The truth is that by modern standards the Pontiac cylinder head design is outdated. The problem being the human element is skewing this opinion.
It is not fair to compare a 35-plus-years-old Pontiac head design to a 2012 design, such as the latest LS series engine. Technology has advanced greatly since the Pontiac cylinder head was developed. But if you look at competing brands from the same era, the Pontiac cylinder head is seen in a different light. The Mule engine build has shown that to me with clarity. Let me explain.
I never doubted the Mule’s ability to make power, but I was cynical about the thermal efficiency, fuel consumption, and the octane tolerance.
Any engine with a 4.185 inch bore and an O.E. cast-iron cylinder head that can make just shy of 500 horsepower on 88 octane fuel with only 32-degrees of ignition lead and a BSFC of around 0.38 needs to be applauded.
A good qualifier of any engine is the amount of ignition lead required to produce peak torque. The slower the combustion chamber burn rate, the more lead is required. Granted, a modern LS engine would make the same power with 20 degrees of advance. A 1975 (the year of our engine) Chevy, Ford, or Mopar would need about 8 to 10 degrees more timing to make like power if it even reached that level. Likewise with only 9.1:1 compression ratio, I thought the BSFC would be around 0.43.
I have always loved and respected Pontiac engines but did my fair share of doubting the cylinder head. The Mule has changed that for me. I hope that you too can look beyond the power numbers and with pride know that a Tin Indian is a force to be reckoned with. I am enjoying my meal of crow and could not be happier to be wrong.—Ray T. Bohacz