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Old 11-06-2006, 08:25 PM
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Small carbs are important but the real killer in tunnel rams is the big plenum between the carbs and the runners. Once the air and fuel are mixed in the carb, the worst thing you can do is slow the mixture velocity down which allows the liquid fuel to drop out of the mixture and puddle, flow to one or two runners and not others, etc. The purpose of the tunnel design is to use the 'organ pipe' effect to super charge the cylinders at a narrow design RPM range and divorce the dynamics of weird pressure pulses thru a carb from the intake valve. Exactly the same technology of tuned exhaust headers. This design RPM is usually @ WOT at max power in a drag machine so low velocity isn't a problem. Try to idle one though and all bets are off.

If you want to run one of these things on the street and you want streetability, consider filling the majority of the plenum with something that will reduce the size to that equivalent to a standard hi-rise manifold. this will give you streetability and the power benefits of the longer runners. Devcon plastic steel is great as a filler 'cause it is inert to all chemicals and can stand a bunch of heat. I have used it in modifying intake runner shapes in cylinder heads with great success. The ideal situation would be get one of those tunnel manifolds with the removable top. Then form the filler inside the lower portion of the manifold, grind and sand it to the perfect shape and bolt the top back on. You could even make the insert removable by casting the epoxy paste in the manifold with some sort of release agent (tin foil liner B4 the epoxy would be great).

I did my senior project in college on intake and exhaust design and built a tunnel ram from sheet steel and exhaust tubing in about 1970. I think I was one of the first to make one, sure beat the commercial guys to the punch! Here is a picture of me in the process of making it circa '70. Note the hair!

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