There are several factors, including number of cylinders, crank throw spacing(degrees) as well as how a manufacturer numbers the cylinders. A few things to consider, using a V-8 since that is the most discussed here, most V-8s have what are called 90* cranks so every 90* of rotation there is a cylinder at TDC. Now if you divide the 360* of rotation by 90 you see that there only need to be 4 pistons for a complete rotation of 360*. That means that in a V-8 there are 2 cylinders at TDC every 90*. One is ready for ignition and one 180* out from it in the ignition. That allows a firing every 90* and one of the reasons that V-8s are known for their smoothness incomparison to a staright 6. You could conceivably grind a cam and set the ignition so that 2 cylinders would fire simultaneously, creating more power per stroke but have a vibration that was not desirable. Oversimplifying you could say that the more cylinders an engine has (evenly divisible into 360) the smoother it will be. There have been all sorts of combinations used in various vehicles( mostly racing), but the production engineers are usually trying to create the smoothest operation with the number of cylinders in the engine. If you examine the V-6s based on cutting 2 cylinders off of a V-8 you will see that most modern ones are referred to as even fire and the crank is cast so that the firing pulses are even. Early ones, the Buick V-6 in particular, were odd fire. Basicly a V-8 with 2 cylinders removed from the crank and firing order. The Ford racing V-6 while based loosely on the production even fire V-6 is an off fire engine because they make more hp,but aren't as smooth. I remember some of the early Buick engines literally shook the guts apart in the distibutor.
Ther are many components of how a firing order is determined at the factory and this was to give a fairly brief synopsis of what is involved.

 

I believe that in spite of engineers' best intentions it is still trial and error.Take your normal Chev with a firing order of 18436572 - it crosses back and forth until we get to 5 then it fires the pot next door to smooth out the crank harmonics,I know Grumpy Jenkins changed the firing order on his Chevs but I never found out to what or why.
A Holden (Australian GM) v8 has odds on the right, evens on the left with a firing order of 12784563 - 4 follows 8 on the same bank but is not the pot next door. They have a more 'barky' exhaust note, are'nt as smooth to drive and are harder on bearings - not as bad as a 302/351c.
Ever notice how a 289w sounds different to a 351w/c? it's all in the firing order. Listen to a Mack V8 diesel, IH 304/345/392 petrol V8s, VW and subaru flat 4s they all sound like they're missing. The International V8s have a problem with gudgeon pins sliding out and scoring the bore - coincidence. Here we groove the pin bosses and fit spiralox.
The gen 3 Chevs have a different firing order and when uncorked don't sound as smooth as a traditional sbc. 90 degree V6s don't balance as well as 60 deg - how many 60s you see with a balance shaft? Engineering like life is one continual lesson.

 

There's only so many ways to make a V-8 crankshaft that will have a cylinder fire every 90°. There are also different ways of numbering the cylinders. If you're going to swap cylinders in the firing order, they will have to be ones that are 360° apart, like the 4 and 7 or the 2 and 3.
If you were to use the Chevrolet numbering system as a constant, you would find that the Ford 5.0 firing order is the same as the LS1 (18726543), which is a conventional small block 18436572 with the 4/7 and the 2/3 swapped. There is much hype and mystery about 4/7 swap cams, not so much about a 2/3 swap.

 

There's only so many ways to make a V-8 crankshaft that will have a cylinder fire every 90°. There are also different ways of numbering the cylinders. If you're going to swap cylinders in the firing order, they will have to be ones that are 360° apart,.

Exactly
:thumbup:

 

I dont know why I didnt think of those factors that would determine firing order, because now that I think about it, it makes perfect sense. *shrugs* Thanks for the explanation everyone.

Ben

 

You don't want the crank being loaded on opposite ends for the twisting would be very detrimental. If you put them like 12345678, then 8 and 1 are n the oppisite ends, twisting crank and creating vibrations.

The point of 4/7 swap is ease the loading on the crank. There is no power there. It's still just 8 cylinders.

 

If you look at a good inline six, it can be one of the smoothest running engines made. Each cylinder fires exactly 60 degrees apart, and the power is always applied in the same direction. The only disadvantage is the relatively long crankshaft, but that can be dealt with by stiffening the lower end of the engine.

Bruce

 

4 stroke crank

If you look at a good inline six, it can be one of the smoothest running engines made. Each cylinder fires exactly 60 degrees apart, and the power is always applied in the same direction. The only disadvantage is the relatively long crankshaft, but that can be dealt with by stiffening the lower end of the engine.

Bruce

That's right, about 6 cyl. engines firing 60 degrees apart, if you're talking camshaft rotation, but it takes 2 revolutions of the crankshaft ( 720 degrees )to make one revolution of the camshaft ( 360 degrees ), so the firing of the 6 cyl. is 120 degrees of crankshaft rotation--- which is one of the reasons why 6 cyls. have such good sustained low end torque. :welcome:

 

The camshaft has a lot to do with the firing order like on some 302 Fords they use the 302 foring order some of the cam use 351 firing order and some of the chevy V-8 engines we have used some 4-7 swap cams.

 

I would like to point out that the smoothness of an engine is based on the weight of the flywheel which maintains momentum between firing pulses.

There is noticable difference between a 10 pound and a 40 pound flywheel on the same engine.... not to mention the bogging when starting out using the light flywheel.

Regardless of firing order on a modern 90* V8.... two adjacent cylinders will always fire consecutively.

Sometimes changing the firing order by regrinding the cam sequence helps power because the intake manifold becomes more efficient by changing the pulse pattern/ fuel distribution, especially with a single plane intake.

Ford changed the small block firing order to reduce front main bearing knock at idle because the fan belts pulled the crank over to cause a noise. It also reduces crankshaft twist under heavy loading. The Ford engineer who designed the change told his story in a hot rod magazine several months ago.

 

Trick topic.In my opinion no matter what you do to the camshaft or firing order,if a V8 has a two plane crank it will always end up with neighboring pots firing in sequence.The only way out is to have a single plane crank.Then you still end up with two pistons at TDC at once but the firing order will always be jumping banks.And I imagine it must be cheaper to build flat cranks.Why the big 3 did not do it?...

 

Trick topic.In my opinion no matter what you do to the camshaft or firing order,if a V8 has a two plane crank it will always end up with neighboring pots firing in sequence.The only way out is to have a single plane crank.Then you still end up with two pistons at TDC at once but the firing order will always be jumping banks.And I imagine it must be cheaper to build flat cranks.Why the big 3 did not do it?...

A single plane crankshaft was used on the Curtiss-Wright OX-5 and OX-6 series engines back in WWI. (water cooled 90* V8, aluminum block with removable cylinders like a Corvair, true hemispherical combustion chambers, gear drive camshaft, and ........ BEEhive valve springs.) Sounds awesome with zoomies. :thumbup: I built 2 in 1984.

FYI something like 400 cubes (I have to look it up) and 5-6/1 compression making 90 to 100 hp at 1475 rpm factory redline.

And you thought people were just inventing this schtuff the last few years...

A single plane crankshaft was also used in the late 40s race car cranks called a Norden crank, I think. Mostly flathead Ford V8s I think.

Can you spell V I B R A T I O N ?

 

A single plane crankshaft was also used in the late 40s race car cranks called a Norden crank, I think. Mostly flathead Ford V8s I think.

Can you spell V I B R A T I O N ?

They also used them in some Indy engines back in the 60s....I think Bruce Crower experimented with them in his Indy endeavors. It basically makes a twin 4 cylinder...and as xntrik says... Vibration is the big boogie man. I think they generate a lot more torque but do have a hell of a vibe as speed increases. It's been a long time ago, so I am not sure what they did for balancing. It was probably not very successful since it was never continued.Novi's used them as well, I believe. Most things have been tried, but for some reason weren't viable at the time, later on to re-emerge as technology/metallurgy or whatever progresses. 4 valve heads are a good case in point, they have been around since the early 1900s,but the ability to produce them and make them work was not available at the time...now, they are everywhere.

 

Yes I have read about them at Indy too.Even dragsters tried them.But this aviation one must be awesome.Pictures?

In the 90s I was in NJ restoring sports cars.We got a customer from South Africa with a Ferrari GT4 and it had a 3 liter 4 cam V8 midship.It used a flat crank,2 distributors of 4 cyl each and carbs.And trust me it was absolutely silk smooth from idle all the way up to 7500 rpm.Firing sequence always jumped banks.No chance of spark cross over.

 

There actually is a rationale and design guideline for firing order. I took a engine design course in college so long ago I don't remember the details - but net is that dynamic balance is important. When a piston fires, the force is not only on the connecting rod to crank but there is also a reaction force on the head. When & where these forces occur matter to both the dynamics of the rotating assembly and the block. Net is the vibration of the engine is not necessarily just the result of when pistons fire as function of angular position of crank but spacial position of pistons in block. I remember an example of a 4 cyl tractor engine which was best balanced when the pistons fired in 2 bursts 90deg apart (instead of every 180 of crank). Some of you may remember old tractor engines with a funny ba-bap sort of sound. Modern V-8 are actually not a good design for a smooth, vibration free engine - they were designed for power in a smaller space. Striaght 6s are inherently a smoother engine design. I believe horizontal 4s with opposed cylinders are better - like the old corvairs? Anyway, there's a bunch of stuff on web if someone is interested.

 

Corvairs were flat 6s - not 4s. Subarus sound like they are missing and suffer a relatively short engine life - not just the turbo models.
Why did Rolls-Royce chose 18436572 with odds on the left as their firing order? (when they made their own engines) - because like Cadillac first and other GM divisions later they found it to be smooth. Funny how Pontiac moved the r/h bank forward of the left so #2 was ahead of #1 on the crank, a bit like Ford and M/Benz who put #5 ahead of #1. Trivial maybe but it looks silly when you pull the pan and are confronted with 51627384 instead of 12345678.
As spring pressures rise in HP engines camshaft harmonics can be transfered to the crank via the timing chain/gears. Grumpy and others ran front mount ignitions in the 70s to reduce spark 'scatter' through camshaft flex. Now with crank trigger ignitions it's less of an issue.

 

Ian.Holden engines seem to have blocks similar to Chevy.Cylinder heads though are different with valve arrangement and port design of their own.Could a Chevy camshaft be used on a Holden? I think not so.Do you see any advantage?

 

Paulo, Holden V8s are more like an Oldsmobile in appearance but have an external oil pump like a Buick. Other than some late 90s hiperf 5.7l engines most were either 253 or 308 ci. In 1985 CAMS ( chaps against motor sport) brought in the european group a formula so Holden destroked their 308 to 304 to fit in an under 5 litre class.
Anyway, when people started stroking the 308s in the late 70s they used modified 272 y - block Ford cranks which proved brittle at high revs or 'pilled up'. The next attempt was to weld a Holden flange to the rear of a Chev crank which was not a job for the faint of heart. This also required a billet cam ground to a Chev firing order and smoothed them out but it was costly - My 400sbc cost me less than a billet cam.
Finally in the 90s we started seeing afordable cast iron and forged steel cranks available but they are in the Holden firing order of 12784563. As our cars are rhd the r/h (drivers) is the leading bank numbered 1357 so, like a Chev in a lhd car #1 is on the drivers side and with the sump off you see it numbered 12345678 from the front - sensible huh?
My daily driver is a 96 Holden Statesman with the standard efi 304, it's as smooth as a windsor re harmonics but not as smooth as a sbc - I only bought it because I'm way behind on my 72 HQ Holden ute (407/t700 9in body off) project and I got so sick of driving my old Range Rover on sealed roads. Other people will disagree but if I were building a high reving (over 8000rpm) v8 it would have a Chev firing order.
BTW cams call themselves the CONFEDERATION of AUSTRALIAN MOTOR SPORTS but most racers refer to them by the title I used earlier. Of course 'chaps' is not the word we use but it starts with the same letter.

Seeya, Ian.

 

OK mate.So this is a totally different project! Amazing the things done in Australia.In other words no parts from Chevy will fit this block,heh? Headers,manifolds,cams have to be made specifically for it.Must cost more than usual.

Now concerning the Confederation Against Motor Sport,if I get it,you guys must suffer from the same disease Brasil suffers.Here we also have a stupid Confederation that monopolizes the sport and ruin it by doing so.They are FIA disciples,that entity that tries to rule the sport worldwide.God bless America where any club can rent a track and run it's race without giving a damn to fia.

 

Fortunately more and more tracks are ignoring cams and our 5l v8 supercar series is so popular that they can now dictate terms to cams.
In drag racing, a few tracks like Heathcote in Victoria run their own show without approval from ANDRA (Australian national drag racing association) which allows for more Outlaw street/Nostalgia/Blown Outlaw type events. As there are only a few genuine sub 5 second fuelers in the country we only see them at 3 tracks - Willowbank in Queensland, WSID in New South Wales and Kwinana Motorplex in Western Australia.
Oh yeah, this thread is about firing orders. Funny how all Mercedes Benz M116/117 V8s had a dot below the 6 on the id bands on the #6 spark plug wire, they also had a line scribed under 6 on the conrod - this was obviously to avoid confusion with #9. Sad part is they didn't build V12s (pass car) until AFTER these engines went out of print. Good drugs in the engineering shop?