Can someone check my thinking here?

I've never really thought about any engine with more than 4 cylinders, but was trying to sort out a niggle with the mondeo tonight and started thinking about V6's and bigger...

Does each spark must move the crank 180 degrees as with a 4 pot? Surely it must do?

Therefore, on a V6, does the crank rotate 3 full turns before the engine has done a full firing cycle (i.e before #1 is back at TDC ready for another spark), and so a V8 must go 4 crank rotations?

How in the hell does a 5 cylinder lump work?

Please help, or I'll get no sleep!

Neil.

 

no, it will fire 3 per rotation, it just sparks more often :P

 

That wasn't particularly well-written Mr Galbally, but I think I follow what you mean

i.e. TDC is 120deg not 180deg apart as per a 4 cylinder?

 

Firing angle = 720 divided by number of cylinders

 

Simon, so basically there are always two full crank revolutions for a firing cycle?

If so, then that pretty much answers my questions!

Something else you may be able to help with actually if you wouldnt mind?

Am i right in thinking that if you were to watch the voltage on the -VE coil terminal, you would see 0V as the ECU charges the coil, with short peaks of close to battery voltage as the ECU breaks the coil down?

Cheers!

Neil.

 

4cyl - in 1 spin of the crank it fires twice at 180degree increments
8cyl - in 1 spin of the crank it fires 4times at 90degree increments

instead of 2 pisons up, 2 pistons down all the time ts 2 up, 2 down 2 half up 2 half down

hey, is the glass half empty?

 

Neil S,

Correct BUT you will NOT see this correctly on a voltmeter as the pulses
are too fast for ANY meter to register correctly let alone the human
eye to see them.
You would need an oscilloscope of some description.

 

Jim Galbally,

Dare you to explain 5 cylinders in a 4 stroke engine

 

Simon - I am indeed using a hand held scope

I'd never considered any of this before the stupid runaround started misbehaving

Cheers Again!

Neil.

 

simon,

www.howstuffworks.com

 

good answer

 

I know on aero piston engines the firing order is always stamped on the inlet manifold, not sure if this is the case with cars as well.
But as said above, as long as you're still talking 4stroke engines the basic principle will be the same, ie 2 full revolutions for each spark with it firing somewhere before top dead centre on the compression stroke.

 

Jim Galbally,

Lazy git Good site though