Odd fire engine support?

[Joey120373]

Playing around a bit on the bench with the MRE,

And I did not see any options for odd fire angles,
I have 2- Vtwin engines that could be candidates for a RUSEFI
Conversion, but at least one is a 75degree Vtwin.

I’ll have to double check on the other one.

Just curious if there is, or possibly will be support for odd fire angles ?

Did a quick search of “odd fire” and didn’t turn up anything.

[AndreyB]

Please explain like I am five

How many cylinders? Two cylinders? What is special about this two cylinder engine - is it about spark and injection happening unevenly?

[mck1117]

Odd fire means that the firing interval isn't (720 / cyl count). For example, an even fire v10 would fire a cylinder every 72 degrees, but the viper v10 has gaps (alternating) of 54 degrees and 90 degrees (which you may notice adds up to 72 * 2).

I think we actually do accidentally support odd-fire, because we can set a per-cylinder offset from the standard. So for a viper, you'd set each cylinder to 0, 18, or -18, depending on which one it is in the order. We don't explicitly support odd fire, but I think you could get it to work okay.

[mck1117]

For a "normal" two cylinder, ignition normally happens every 360 degrees of crank rotation.

For some v-twins, the firing intervals are instead 405 and 315. I'm not sure what they are for your particular engine, but you would be able to run a 405-315 by setting the offset on cylinder 2 to -45 degrees.

[Joey120373]

Please explain like I am five

How many cylinders? Two cylinders? What is special about this two cylinder engine - is it about spark and injection happening unevenly?

For this case, yes, 2 cylinders in a V configuration.

An " even fire " V twin would have an angle of 90 degrees between the cylinders, where a flat twin would be 180 degrees.

My KTM has a narrower angle of 75 degrees, so with a waisted spark system, to make the math a lot easier, cylinder 1 would fire on its power stroke, then 75 degrees of crankshaft rotation later, the waist spark would need to fire for cylinder 2.

I think the others have explained it better than i have. And it appears they have answered my question. I just need to find where the cylinder offset setting is. I am used to it being in the base engine settings.

Thanks!

[MHTSOS]

Under ignition settings you'll find per cylinder ignition trim. There you can offset your #2 cylinder by any number of degrees.

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