I was looking at the Haynes manual on my car, and I believe that the book said that the firing order was

1-3-2-4

 

However,

 

It doesn't seem right that there is only one cylinder firing at a time.  I would think that 2 cylinders would be firing and 2 exhausting per engine revolution. 

 

Can anybody help me with this?

 

Thanks.

 

 

Your assumption on the  differing firing order is incorrect as this is a 4 stroke (2 rpm) engine and this is how they work

 

Correct - one cylinder fires at a time for every 180 degrees rotation of the crank  one cylinder exhausts one is under compression and one is under induction

 

Correct - 2 cylinders firing strokes / 2 exhausting strokes  every revolution of the  crank   ie the cams turn one revolution  to the crankshafts 2.

 

ie for all 4  cylinders to fire (and complete 4 srokes) the crank has / has to turn 2 revolutions

Edited March 21, 201610 yr by subnz

Asking about plug firing, I'm guessing you read that each two plugs fire at the same time?

 

Its a waste spark ignition system.

Each plug pair is fired at the same time, but one of the plugs is fired on the power stroke of one cylinder, while the opposite plug is fired on the exhaust stoke of the opposing cylinder. The spark on the exhaust stroke doesn't actually do anything, thus it is "wasted". Hence the name.

Flat plane crank engines fire 2 at the same time, like Ford's new 5.0L engine. In those engines like the 8 cylinder, it fires more like a dual 4 cylinder engine, where 2 pistons mirror each other throughout the combustion cycle, vs. more traditional V8's that fire each piston at it's own time. A 4cylinder flat plane crank, would fire like a dual 2 cylinder engine.

That may be true of the ford, but in traditional 4 and 6cylinder flat engines each cylinder fires at separate times.

Subaru does not fire two cylinders at once.

Two spark plugs receive a spark at the same time, but only one of those is on the power stroke for its cylinder.

(I always wondered if anyone modded a soob engine into a 'big bang' motor - kinda doubt the crankshaft would last long.)

 

 

 

I think this is how our engines fire;

 

Edited March 21, 201610 yr by 1 Lucky Texan

That may be true of the ford, but in traditional 4 and 6cylinder flat engines each cylinder fires at separate times.

Subaru does not fire two cylinders at once.

Two spark plugs receive a spark at the same time, but only one of those is on the power stroke for its cylinder.

 

I was referring to flat plane cranks, not boxer engines in general. Very few engines run a flat plane crank, though it might get popular. Ignore the music and watch this as it shows how a flat plane crank works vs. cross plane. The flat plane demo shows a typical V8 and each cylinder is "paired" with another in the combustion/exhaust event. It changes the sound of the engine, the ability to rev, the powerband, etc.

 

EDIT: NVM 

Edited March 21, 201610 yr by Bushwick

(I always wondered if anyone modded a soob engine into a 'big bang' motor - kinda doubt the crankshaft would last long.)

 

 

 

I think this is how our engines fire;

 

This is what the book says, but it's hard for me to understand why they wouldn't fire one cylinder on the right side and the next cylinder on the opposite side.  It doesn't seem balanced that you would fire one on the passenger's side, then fire the next one on the passenger's side.  It seems like it would be more balanced to fire opposite sides alternating.

it may have something to do with cylinder scavenging or 'yaw' vibration/oscillation or ?????

 

flat 4 boxer engines eliminate one entire set of vibration harmonics that plague in-line 4s anyway so, I'm guessing they have a good reason.

 

check the graphs on page 15 here; http://www.surrealmirage.com/subaru/files/SAE_boxer.pdf

It is not intuitively obvious, but the combustion event adds so little to the dynamic forces of the pistons, rods and crank moving that it doesn't make any difference to the balance to fire both pistons on the same side consecutively.

 

Also, if you look at it, that is the way it has to happen. 

 

Imagine if the firing order was 1-4-2-3.  This goes from left to right, but then has to fire 2 after 4, as that is when the #2 piston is coming up on TDC on compression.  Then it goes from 3 to 1 to  restart the cycle, so it is the same as if it went from 1 - 3 at the beginning. 

 

Overall, it is 6  to one half dozen of the other. 

Edited March 21, 201610 yr by robm

It is not intuitively obvious, but the combustion event adds so little to the dynamic forces of the pistons, rods and crank moving that it doesn't make any difference to the balance to fire both pistons on the same side consecutively.

 

Also, if you look at it, that is the way it has to happen. 

 

Imagine if the firing order was 1-4-2-3.  This goes from left to right, but then has to fire 2 after 4, as that is when the #2 piston is coming up on TDC on compression.  Then it goes from 3 to 1 to  restart the cycle, so it is the same as if it went from 1 - 3 at the beginning. 

Overall, it is 6  to one half dozen of the other. 

 

Agree don't think it matters too much what the firing order is - the oppositely opposed configuration of boxer motors means that they are perfectly dynamically

balanced  (smoother - less vibration etc)

 

Compared to In-Line and V configured engines  which need counter weights on cranks etc  

(I always wondered if anyone modded a soob engine into a 'big bang' motor - kinda doubt the crankshaft would last long.)

 

 

 

I think this is how our engines fire;

 

 

Imagine turning this boxer 4 into a 2 stroke ie 4  power strokes every turn of the crank  

Edited March 22, 201610 yr by subnz