Bonneville America Forums Forums Technical Forums General Tech Pulses per Revolution (PPR)

Is there anybody out there know the number of ignition pulses per revolution of the BA 790 engine? Also does the PPR change over a certain RPM, if so at what RPM?

Thanks in advance, Andy

Not sure if this helps, but one plug fires twice within the 4 cycles --
once during the exhaust cycle, and once during the compression cycle.

One cycle = one RPM -- and, 4 cycles = 4 RPMs,
for tachs count each & every full rotation of the crank as one unit

One spark plug receives 2,000 impulses to fire at 4,000 RPMs.

Two spark plugs each receive 2,000 individual impulses to fire at 4,000 RPMs, so in the case of the 790, were talking a total engine / both plugs scenario of 4,000 impulses to fire the plugs at 4,000 RPMs.

I strongly believe that the firing ratio of 2 pulses per 4 RPMs per spark plug X 2 spark plugs remains constant throughout the entire engine operating range.

More about wasted spark, from the new King of Darkness -- Gill
http://www.gill.co.uk/products/digital_ignition/Introduction/8_wast_spark.asp

If each plug fires twice in 4 cycles then it would be once per rev. I am not saying that is what it does just making it simple. Being 1 crank sensor and 270º firing I would think each gets 2 pulses but I don't know that for sure since the CDI may split that up between the coils so each only gets 1 at different times per revolution. That being 2 revolutions per 4 cycles.

Yeah - I'll edit the original first sentence from "each" to "one" so as to make it relevant to one plug at a time.

Thanks.

If we're talking about both plugs, wouldn't that make 4,000 fires in 4,000 RPM?

I get confused with the modern math.

There's one pulse for every two revolutions of the crank. There may also be a "waste spark," not required for engine operation. Why do you ask?