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how many cyl do you set a tach to on a rotary??

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Old 01-05-03, 10:18 PM
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Flinstone Power

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how many cyl do you set a tach to on a rotary??

i just bought this http://cgi.ebay.com/ebaymotors/ws/eB...tem=1876195578

and was wondering how i set it for a rotary.. thanks
Dave
Old 01-05-03, 10:20 PM
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i believe you set it for 4 cylinder
Old 01-05-03, 10:28 PM
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2 rotor wankel = 2 cylinder 2-stroke = 4 cylinder 4-stroke, because they each fire twice per output shaft revolution.
Old 01-05-03, 10:30 PM
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Yeah, if you go off the leading coils. The trailing coils fire half as many times (each) as does the leading (twin outlet) coil. So, the leading reads like a 4-cyl, while the trailing reads like a 2-cylinder. I think the factory tach reads off the trailing coils, though.

Ren
Old 01-05-03, 10:36 PM
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Flinstone Power

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thanks guys
Dave
Old 01-05-03, 11:21 PM
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FD > FB > FC

 
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yep a 13b = a 4 cylinder and a 20b = a 6 cylinder
Old 01-05-03, 11:24 PM
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but you go off the trailing to set up a tach or a tach light.
Old 01-05-03, 11:44 PM
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If you take your tach input from the trailing coils, you set it at 4 cylinder (stock tach runs off this input, and I believe a connector is already ready to connect).

You can wire it into the negative signal from the leading coil, but if so, you must set it as an 8 cylinder,.
Old 01-05-03, 11:45 PM
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Originally posted by fastrotaries
but you go off the trailing to set up a tach or a tach light.
Stock does. You can go off of either with an aftermarket.
Old 01-05-03, 11:47 PM
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Originally posted by turboren
Yeah, if you go off the leading coils. The trailing coils fire half as many times (each) as does the leading (twin outlet) coil. So, the leading reads like a 4-cyl, while the trailing reads like a 2-cylinder. I think the factory tach reads off the trailing coils, though.

Ren
This is incorrect. The leading coils fire twice as much as the trailing due to a wastespark every revolution, and would read as an 8 cylinder.

The trailing coils fire twice each for every two revolutions, so it would read as a four cylinder, not a 2 cylinder.
Old 01-05-03, 11:55 PM
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I did say I think. Since I haven't seen my FC's in over a year, I can't remember for sure. I knew the leading coil fired twice as often as the trailing, and that there is a wire on the trailing for the tack hookup, I just couldn't remember what it was set up to read.

Ren
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