So . . . in the case of a 1.9L with a coil to feed the tach, does it matter which of these two gauges one uses? -- Rocky J Squirrel
On Sun, 2011-05-01 at 10:46 -0700, mark drillock wrote: > Only diesel engines use the W lead driven tachs, AFAIK. Until somewhat > recently diesel engines had no pulsing signal that represented engine > speed other than from an internal connection point in the alternator. > Alternators meant to provide this signal have an extra lead that you can > connect to. Bosch and VW call this a W lead and Vanagon alternators have > a marked spot on the back of the case for the W lead which may or may > not be actually present. Since gas engine Vanagons don't need the W > signal only some replacement alternators have it installed in the > alternator. This so fewer alternators need to be stocked because the > same alternator works across more applications and the cost of the > rebuilder adding the lead is nearly nil. Since the alternator is belt > driven and often by a compound pulley system there is not any known > exact frequency that means an exact engine speed until the tach is > calibrated for a given pulley setup. > > Mark > > > Rocket J Squirrel wrote: > > I've settled on the VDO "Cockpit Black" series of meters for Mellow > > Yellow's upcoming gauging project. > > > > Looking at eguages's offerings in the 2-1/6'' diameter size, 4000 rpm > > range, I find two very similar gauges. > > > > One is the 333 365, the other is the 333 369. They have very similar > > prices and seemingly the exact same specifications: > > > > For use on 4,5,6,8 cylinder application engines with standard > > coil ignitions, most square wave electronic control ignitions > > with tachometer output terminal, and alternators with "w" > > tachometer terminal. > > > > Eguauges does not know what difference there is between them. After some > > searching, I found this: > > > > 333 365 is 4,000 RPM (400–1300Hz)* > > 333 369 is 4,000 RPM (800–2400Hz)* > > > > where * = For Alternator use only > > > > Can someone help me figure out which gauge will read correctly when > > connected to the coil? Maybe they both will, but this difference of 2:1 > > in the frequency spec gives me pause. > > > > -- > > Rocky J Squirrel > > '84 Westfalia: Mellow Yellow ("The Electrical Banana") > > '74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.) > > Bend, OR > > KG6RCR > > |
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