Guess what happened at Pomona...Parity shmarity!!!

Discussion in 'System One Pit Buzz' started by The Zone, Nov 12, 2004.

  1. Norm Drazy

    Norm Drazy Jr. Dragster

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    Gene, The fuel delivery must increase in proportion to the increase in airflow that the Gizmo delivers beyond whatever you are replacing. To do this, we increased the area of both the dribblers and port nozzles by this same percentage. However, the hat nozzles have to be double-dipped. Not only do you have to increase their flow in proportion to the increase in airflow, but you also need to provide an increased methanol/air ratio to the blower (fatten up what goes through the blower) to offset the incresed heat of compression required to compress the increased air flow to the resulting higher boost.

    So, where'd all this come from? It was the result of having put a PSI "D" blower on Jack O'Bannon's Rick Santos-driven car for the Dallas national event in 1997. (I thought I'd died and gone to heaven when we displaced that particular Whipple!) I had initially overlooked the second dip back then, and was confronted with manifold temperatures that were just too high. Remember that back then, very few people had ever seen manifold pressures of 55 to 60 PSIG, and none of those who had seen it had equipped their manifold with a thermocouple. Man, did we ever have to scramble to fix that outbreak of Murphy's law! We couldn't simply increase the hat nozzle area that much, because we'd have drowned the supercharger with excess fuel at idle. Instead, we ran two additional hat nozzles off the port nozzle distribution block. It worked well enough for us to win the race over Mike Gunderson, but it took FOREVER to shut the durn thing off by pulling the fuel shutoff. We finally incorporated the check nozzles in the hat to disable two of them off at idle, and that was when the plan really came together.

    If this idle chit-chat bugs anyone, please let me know, and I'll stow it!

    Norm Drazy
     
    #61
  2. Norm Drazy

    Norm Drazy Jr. Dragster

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    Gene,
    This is a pretty tough question. When a liquid evaporates in air, heat is absorbed and vapor is created. Since the heat absorbed by the evaporation cools and therefore contracts the air, the issue is whether the vapor occupies more or less space than that created by the contraction.

    The heat of vaporization of a liquid in US units is the amount of heat (in BTUs) required to evaporate one pound of it. Methanol has a HUGE heat of vaporization compared to ALL other hydrocarbons. It's therefore the ONLY liquid whose vapor occupies less space than the amount its heat absorption conrtacts it. An interesting side point is that this is the reason that ethanol is so much less impressive than methanol as a supercharged engine fuel.

    So, if we squirt more methanol into the manifold and it all evaporates, and since methanol vapor is approximately the same density as air at any given pressure, the now-cooler air should flow past the intake valve a little more easily and therefore slightly reduce the manifold pressure.

    However, if it doesn't all evaporate by the time it reaches the intake valve, the resulting wet flow adds its mass to the fluid without benefitting the situation by cooling and therefore contracting the air. This makes it more difficult for it to flow past the intake valve and therefore tends to slightly increase the manifold pressure.

    The change in manifold pressure that would result from a 10% increase in the port nozzle flow would be very small if either of the above two cases dominated. However, since they tend to cancel each other depending upon how much of the added methanol actually evaporates, the effect on the manifold pressure varies between very small and zero.

    As for in-cylinder pressure measurements, Kistler makes a high-response, cooled pizeoelectric transducer that I used in college to do just that with a chainsaw engine. I know that Brad Anderson has taken in-cylinder pressure measurements on his dyno. He probably came to the same conclusion that I did: while the data is really interesting, it's not very useful as a tool if your intent is to make more horsepower.

    Norm Drazy
     
    #62

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