MegaManual Math Issues??

[evotunedscc]

In the "How Megasquirt Works" section (http://www.megamanual.com/v22manual/mfuel.htm#reqfuel), about half-way down the page (several paragraphs following the fuel equation) it's explained that

"For example, in a pretty reasonable worst case, 1500 Hz is about 4 times the IRQ ("interrupt request") rate (6000 RPM * 8 cyl = 400 Hz). So on a V8 at 6000 rpm, the fuel pulse width is updated 4 times between each spark event (and 8 times between fuel injection events, if running 2 squirts). MegaSquirt-II doubles these, as would running a 4 cylinder (since there are half as many events at a given rpm). At 600 rpm, you have 10 times as many updates per ignition/injection event."

The 6000 RPM*8 cyl = 400Hz is throwing me--I would expect this to be 800Hz. (6000rev/min) X (1 min/60sec) x 8 cyl = 800Hz. Can someone explain this?

Thanks in advance.

[Bernard Fife]

etscc,

For a 4-stroke cycle engine, there are two revolutions per spark event (per cylinder), or per intake stroke for fuel, so you have to divide 800Hz by 2.

So you need to add a factor of (1spark/2revoutions) to your calculation to get:

(6000rev/min) X (1 min/60sec) x (1spark/2revoutions) x 8 cyl = 400Hz

Lance.

[evotunedscc]

Understood. Thanks for your help.