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On Sun, 2002-06-09 at 08:29, Iamkeen@aol.com wrote: > Hey all. > > I got a general knowledge sorta question here, regarding engine RPM: > A tach gives a reading based on pulses thru an SP wire... "But", I say to > myself, "the plug only fires every OTHER revolution." > So is my tach telling me distributor RPM, and the crank is actually spinning > twice as fast? > NO, the tach does not read the RPM from the SP wire. It reads it from the points wire. This means that it gets 4 pulses for every revolution of the distributor, in the case of a 4 cyl. engine. Therefore, you Tach should be for a 4 cyl. engine, and have the proper electronics in it. (Actually, a analog tach is just a glorified voltmeter.) -- Russ Wolfe '66 FB MT (It drove) '71 FB AT '65 Bug (not running) russw@classicvw.org http://www.classicvw.org ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/