Tom’s Corner – The Technology Behind Smokey Yunick’s Hot Vapor Fiero

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After having presented an article on Smokey Yunick’s ‘ hot vapor engine’, I will attempt to explain how this technology works. Normally different parts of a standard non=homogeneous air/fuel mixture burns at different rates within the same cylinder creating turbulence and colliding flame fronts. Under normal running conditions, cooling the intake charge to create higher mixture density is beneficial to keep some of the fuel molecules from undergoing spontaneous combustion or denotation.

Smokey installed a heat exchanger under the carburetor that used hot engine coolant exiting the motor to warm that mixture to around 200 degrees. Then the air/fuel mixture flowed through a second stage generator, an exhaust driven turbine wrapped in exhaust gas ducting. He called this devise a ‘homogenizer’, but it was really a turbocharger underneath that fancy ducting ! Not only did this devise generate boost, it also served as a one way check valve to keep the expanded hot gas from back flowing out of the carburetor. Then from the turbine the mixture flowed through an intake manifold also wrapped by exhaust ducting to reach its final super-hot temperature. Smokey’s engine had all the usual hot rod items of the period such as trick rings, forged pistons, Carillo connecting rods and so forth. One of the key secrets is the exact tune-up or technique used to get the engine past the detonation threshold to the super-hot, super-lean running condition. In short, an engine makes its most power running on the verge of denotation.

The key seems to be getting safely past 2250 degrees so not only is the tune-up critical…some special cam shaft timing is involved as well. Typical small block GM engines run very reliably at 1750 degrees F stabilized exhaust temperature. At 2250 degrees you are definitely in trouble from engine destroying denotation.So if you can get it to 2600 degrees or beyond you can control the burn rate of the hydrogen molecule in the fuel which is the major radical in the gas which causes denotation, you will make more power without denotation. Since the fuel economy standards are to be raised in the next 10 years, the auto makers are getting heavily involved in ‘heat vapor’ technology. Smokey was way ahead of his time and experimenting on a Fiero is another reason why this car is considered a true time capsule by the automotive industry ! I hope you enjoyed this small part of Fiero trivia.

Editors Note: Sorry for the delay in part two of Tom’s series on Smokey Yunik’s Fiero. Entirely my fault as I was busy looking for a new day job. There was lots of debate regarding the Smokey Yunik Fiero when the Tony Allers re-creation was re-discovered. You can read some of that debate at http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20090219-2-070301.html . The car even made an appearance at one of Ed Parks open houses at The Fiero Factory. — Jeff Jones, Editor

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