next »

[mtc]

the fire order is 1,2,4,3

so is 2 cylinder firing at the same time while the other 2 is on the exhaust stroke?

or does the motor fire 1 then 2 then4 then3 and  90 degree?

[Pat Conlon]

Yes, the coils fire 2 plugs at the same time. Left coil fires cylinders #1 and 4...the right coil fires #2 and 3.
That’s why this sequence is called “wasted spark”

[mtc]

Yes, the coils fire 2 plugs at the same time. Left coil fires cylinders #1 and 4...the right coil fires #2 and 3.
That’s why this sequence is called “wasted spark”

are all production 4 stroke 4 cylinders, configured this way?

i read with a cam change( change firing order) this could provide more exit power i.e. traction not that it matter here and now

then why does the 88+ years only have one pick up coil, ? does the upgrade from cdi to the later years TCI have something to do with it?

[Millietant]

Forgive my potential ignorance, but surely the cam doesn't have anything to do with firing order, it just controls the duration magnitude and timing of the valve seems opening. Once the firing order/sequence has been decided, the crankshaft and ignition are the key factors in engine design to facilitate this, with the cam being designed to work with those two factors to optimise power/torque output for the intended use.

[mtc]

Forgive my potential ignorance, but surely the cam doesn't have anything to do with firing order, it just controls the duration magnitude and timing of the valve seems opening. Once the firing order/sequence has been decided, the crankshaft and ignition are the key factors in engine design to facilitate this, with the cam being designed to work with those two factors to optimise power/torque output for the intended use.

unsure

read the paragraph on the inline fours called long bang

https://en.wikipedia.org/wiki/Big-bang_firing_order

https://www.r1-forum.com/threads/who-can-explain-the-big-bang-firing-order-in-degrees.261513/

A twingle is a four stroke twin cylinder engine with an altered firing order designed to give power pulses similar to a single cylinder four stroke engine. It is well known that 4-stroke singles "hook up" better than 2-strokes in the dirt. This is because 4-strokes have half as many power strokes per crankshaft revolutions as a 2-stroke. This creates a recovery gap during which the rear tire regains traction.

[Millietant]

Here's another link explaining the workings of MotoGP Big Bang engines.

https://motomatters.com/news/2008/02/24/guest_column_why_big_bang_engines_work.html

[mtc]

Here's another link explaining the workings of MotoGP Big Bang engines.

https://motomatters.com/news/2008/02/24/guest_column_why_big_bang_engines_work.html

cool thanks, that is one damn good read, need to finish later but good

[Pat Conlon]

Yes, the coils fire 2 plugs at the same time. Left coil fires cylinders #1 and 4...the right coil fires #2 and 3.
That’s why this sequence is called “wasted spark”

....are all production 4 stroke 4 cylinders, configured this way?

No, “wasted spark” was only common on old I-4 engines that did not have a cam angle sensor (CAS)

Once CAS was used there became enough resolution for ignition sequence to become “sequential” meaning one cylinder firing at a time. With one coil for one cylinder this allowed the coil a longer time to charge between discharge events. A smaller coil (like pencil coils used with coil on plug set ups) with larger voltage outputs were the result.
You need a CAS signal to tell the ignition when to fire the single coil.
 A crank signal alone will not give you the proper resolution for sequential ignition.

The same is true with fuel injection.
Without a CAS signal you can not run sequential fuel injection. One injector squirting fuel at a time.
With just a crank signal you can run fuel injection, but it’s run in what is called a “batch” mode, which is 2 injectors firing at the same time, similar to wasted spark....except this one wastes fuel.

Modern I-4 engines have a CAS signal so as to be able to trigger sequential fuel injection and sequential ignition.

Clear as mud?

Big Bang engines involved special crankshaft, cam and ignition designs.

The Digital Controlled Ignition (DCI) on the ‘88+ used 1 pickup because only 1 signal was needed every 180* the ignition digitally advanced the ignition timing curve and selected which coil to fire the “wasted spark” sequence.
(FYI: your reference to CDI.... CDI stands for Capacitor Discharge Ignition, a different animal)

2 pickups were needed on the ‘84-87 Transistor Controlled Ignition (TCI) because the analog ignition could not differentiate which coil needed to be fired at which time, so 2 signals were needed, one signal for each coil.

Hope this helps.

Cheers

[mtc]

Yes, the coils fire 2 plugs at the same time. Left coil fires cylinders #1 and 4...the right coil fires #2 and 3.
That’s why this sequence is called “wasted spark”

....are all production 4 stroke 4 cylinders, configured this way?

No, “wasted spark” was only common on old I-4 engines that did not have a cam angle sensor (CAS)

Once CAS was used there became enough resolution for ignition sequence to become “sequential” meaning one cylinder firing at a time. With one coil for one cylinder this allowed the coil a longer time to charge between discharge events. A smaller coil (like pencil coils used with coil on plug set ups) with larger outputs were the result.
You need a CAS signal to tell the ignition when to fire the single coil.
 A crank signal alone will not give you the proper resolution for sequential ignition.

The same is true with fuel injection.
Without a CAS signal you can not run sequential fuel injection. One injector squirting fuel at a time.
With just a crank signal you can run fuel injection, but it’s run in what is called a “batch” mode, which is 2 injectors firing at the same time, similar to wasted spark....except this one wastes fuel.

Modern I-4 engines have a CAS signal so as to be able to trigger sequential fuel injection and sequential ignition.

Clear as mud?

Big Bang engines involved special crankshaft, cam and ignition designs.

The Digital Controlled Ignition (DCI) on the ‘88+ used 1 pickup because only 1 signal was needed every 180* the ignition digitally advanced the ignition timing curve and selected which coil to fire the “wasted spark” sequence.
(FYI: your reference to CDI.... CDI stands for Capacitor Discharge Ignition, a different animal)

2 pickups were needed on the ‘84-87 Transistor Controlled Ignition (TCI) because the analog ignition could not differentiate which coil needed to be fired at which time, so 2 signals were needed, one signal for each coil.

Hope this helps.

Cheers

dci,  since it's got 1 pickup, it sees the rotor every 360 degrees no? unless those little protrusions, every 90 degree triggers it?

[Pat Conlon]

Good catch, I think you’re right....I need to look at a rotor to be sure....

[fj1289]

The camshaft absolutely determines the firing order - it determines when each cylinder is on the intake, compression, power, or exhaust stroke.  Now, that said, the ignition doesn’t care if cylinder 1 fires “before” or “after” cylinder 4 since it is going to fire both plugs each time anyway.  

Actually each “pair” fires 360 degrees apart - the total engine cycle is 720 degrees, not 360.  The “off” pair fire 180 degrees out from the other pair.  

The FJ runs a 1-2-4-3 firing order.  A lot of other four cylinder engines (mostly car I think) use a 1-3-4-2 firing order.  The difference is determined by how the camshaft lobes are arranged on the “bump stick”.  

There is a guy that has cut and rewelded the camshafts of his FJ in order to make a “Big Bang” engine - 1&4 fire, the 180 degrees later 2&3 fire, then 540 degrees later 1&4 fire again.  Looking for that article again.  Why did he do it?  What was the purpose?  For him, it sounds good!  Lol

[Pat Conlon]

Thanks Chris, yea, a FJ Big Bang motor....holy crap....
Q: on the ‘88+ ignition rotors, were there 2 timing nubs or just one?

[fj1289]

Thanks Chris, yea, a FJ Big Bang motor....holy crap....
Q: on the ‘88+ ignition rotors, were there 2 timing nubs or just one?

I don’t remember - mine now have 23 (24-1) or 22 (24-2) or 11 (12-1)!   

Pretty sure they have 4 - 3 shorts and one long.   

The rotor pattern isn’t that important - what is important is the “decoder” reading the wheel. 

[Pat Conlon]

You’re running batch injection, correct? 

[fj1289]

Yes - but the new system on the race bike allows me to run “untimed sequential”.  Biggest advantage is allowing for only 1 injection pulse per engine cycle from each injector — allows it to idle well on 990cc/min injectors!  Normal batch firing requires 2 injection pulses per injector - and doubles the minimum amount of fuel you can inject at idle - too rich to idle in my case.

The “untimed sequential” might end up injecting on the intake stroke or the exhaust stroke.   May make a little difference on idle quality or emissions, but really doesn’t matter for power or torque since the injection time increases while the time to inject is decreasing.  Even on the idle - you probably won’t notice anything other than a change in the AFR of a couple tenths. 

Also - a lot of engines that use sequential injection still use waste spark (you can tell by the siamesed coils in the coil packs. 

My coils are wired for sequential,  but are fired wasted spark without a cam sensor to determine engine cycle.