Mike, you are right. The intake manifold is a common vacuum chamber to all cylinders. The 413 is no different than any other engine in this respect. Only multi carbureted engines (like one barrel per cylinder) may have isolated vacuum. So, Hugh, even the 392 would have a common vacuum. Further, I doubt a small loss of compression in two or more cylinders will have a serious impact in the total engine vacuum. Remember, the vacuum is created by the suction during the intake stroke and the closed throttle. However, Hugh, it was a suggestion worth discussing. D^2 Quoting mike sutton <mikanlin62@xxxxxxxxxx>: > Unless the intake manifold and port for the car that has the potential > booster problem ( 59? ) are radically different from 95 + percent of the > other Chrysler products, the vacuum for the booster is ported from the > intake manifold and is common to the entire intake. Ill grant that the port > is probably closer to number 8 , or is perhaps between numbers 7 and 8 > depending on the intake style, but the booster takes advantage of the entire > volume of vacuum available. I highly doubt that the design of the intake > manifold directs vacuum from only one cylinder in a V-8 engine. > > Mikey > 62 Crown Coupe > > >