Is my math right? A 4 cycle engine at 2500 rpms fires each cylinder over 20 times a second?

[Kern Dog]

I was talking with my nephew today about how amazing that engines are and how it seems like everything has to go right for them to run as well as they do.
I told him that at freeway speeds when an engine is running at say....2500 rpms, each piston fires about 20 times a second. I based this on the cylinders firing on every other revolution given that this is a 4 cycle engine. That cuts the 2500 number to 1250. Then divide that by 60 to show what each second would see in terms of each cylinder firing.
I came up with 20.83.
This is something that I have never looked into this deeply before.
If this is true, if you shift at 6000 rpms, you're firing the pistons at 50 times in each second.
If this is true, that really is amazing.

 

[Jerry Hall]

First off a 4 cycle engine fires once every 4 revolutions. So 2500 divided by 4 divided by 60. 10.42 times a second if I'm thinking right. Still amazing.

 

[Kern Dog]

First off a 4 cycle engine fires once every 4 revolutions. So 2500 divided by 4 divided by 60. 10.42 times a second if I'm thinking right. Still amazing.

Are you sure about that? 4 cycles are Intake, compression, combustion and exhaust evacuation. That happens in 2 revolutions of the crank.

TDC to BDC for intake.
BDC to TDC for compression.
That is one revolution.
TDC to BDC for combustion.
BDC to TDC for exhaust evacuation.
Two revolutions.

I'm not arguing, I'm trying to wrap my head around this.

 

[Richard Cranium]

At 2,500 RPM, a spark plug in a four-stroke engine fires 1250 times per minute per cylinder. Since a four-stroke engine has two rotations of the crankshaft for each firing event, each cylinder fires once every two revolutions. Therefore, for a 2,500 RPM engine, each spark plug fires 2,500 / 2 = 1250 times per minute.

Divided by 60 = 20.83333