To: Ara who wrote (1048 ) 2/9/1998 12:39:00 PM From: shashyazhi Read Replies (1) | Respond to of 6464
Ara, the airflow through an internal combustion engine is NOT unidirectional, despite your wish that it would be. Various forms of valve arrangements *attempt*, but fail to completely prevent *reverse flow*. Technology involving computer controlled exhaust throttling valves has been available from Japan for nearly fifteen years. One company produced it under two different names. PowerValve is one name and ExUp is the other one. I have a vehicle equipped with ExUp in my garage right now. The exhaust throttling valve never completely closes, as in your "potato" analogy. It is about one- third open at idle, and, as the computer senses rpm increase, it opens fully. The exhaust throttling valve increases the low-end torque of the engine, and the gas mileage is increased from 38 miles per gallon to 45 miles per gallon. The exhaust throttling valve helps to eliminate the flat spot in the torque curve which is caused by *reverse flow* at about 5500 to 7000 rpm. I am sure that if this company ever went to fuel injection, the mileage would get into the middle 50's, because *reverse flow* through the throttle bodies would have no effect. That's right, Ara, I said *reverse flow*. In some engine designs, air passes through the carburetors up to *four* times! And, on each pass, more fuel is added to the mixture, because the carburetor is a dumb device that doesn't know about *reverse flow*. In fact, with the air cleaners off the carbureted engine, a *fog* of fuel air mixture could be seen *outside* the carburetors in one particular design. The manufacturers eventually added a one-way valve between the carburetors and the cylinders, but it took ten years to do it, because the public wasn't complaining about fuel mileage, they were complaining about low-end throttle response. And it took another ten years to get the exhaust throttling valve technology onto the street. It had been thoroughly proven off-road by this company which does research and development for Toyota, but which is also widely known for its musical instruments. And every one of its competitors has adopted an exhaust throttling system for its off-road vehicles. But, then again, I don't know a thing about engines...