87 savage wrote on 06/25/12 at 16:27:10:360k+ That sure is alot to ponder! So, all that being said, I'm not trying to play devils advocate, just trying to figure it out. How is it that the tach that EJID posted a link and pic for will work with the savage single cylinder. The ad for it says: "THIS TACHOMETER IS DESIGNED FOR DUAL FIRE IGNITIONS ONLY" and: "THIS MINI TACH WILL WORK ON ANY V-TWIN WITH A DUAL FIRE IGNITION!!" and: ITEM FITS SUZUKI MARAUDER, INTRUDER AND BOULEVARD MODELS
So does "Dual Fire" mean that it fires every stroke? Or does "Dual Fire" just mean it fires both cylinders. And how will it work with a Vtwin and a single at the same time? All so darn confusing!!
If the tach that EJID refers to works on a Savage, it is by virtue of the fact that on the dual fire Vtwins each cylinder fires every OTHER time (i.e., camshaft driven trigger). This would work on the Savage because it fires EVERY time, but is one cylinder. In other words, a dual fire coil still fires once per rev (like a Savage) because it fires both cylinders, but every other time. So the Savage "looks" like a VTwin dual fire system. This starts to get technical because on a VTwin the firing is NOT 360 deg symmetrical. For instance, on a 45 deg VTwin if you had a degree wheel attached to the crank what you would see is...
1st plug fires at 0 deg
2nd plug fires at 315 deg (360 - 45, note this is the 2nd firing within a single 360 deg rotation)
1st plug fires again at 720 deg (360 x 2, but 405 deg lag behind previous cylinder)
2nd plug fires again at 675 deg (315 + 360)
For this reason a dual fire VTwin will actually fire TWICE within one 360 deg rotation and none in the next 360 rotation, even tho there are two cylinders. Now that it's all cleared up
. In the description for this tach it says it works on Boulevards, but I think they mean VTwin boulevards. It is just by luck (or cheaper design) that the Savage fires each rev, which makes it work. On the other hand, they may be smart enough to realize what I've just stated and have already taken the Savage into account (firing every rev). Keep in mind, even if a tach is "made" for one cylinder, the mfr must state whether it is designed for 1 fire or 2 fire per revolution. Otherwise, you get half or double the reading expected.
Hey, I'm an engineer - don't dare ask me the the time of day - LOL.
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