how many firing sequences for 90* V-8

[dave brode]

All,

Anyone correct me if I'm wrong;

I notice that Ford guys like to think that GM stole their 351W/"HO" firing order for the LS engines. Note that Cadillac used it in '63. The '63-'67 Caddy is labelled like a 18436572 engine, but order is 1-8-7-2-6-5-4-3 [see 4-7 and 2-3 swapped]. Caddy also used that sequence in '68 up family. They labelled cylinders differently, so it takes some head scratching to see it. Anyone know of an earlier engine using that firing sequence? If so, I'll yield, but if not, said firing order shall hereafter be called the '63 Caddy firing order.

1. The old common "18436572" sequence

2. '63 up caddy, "HO"/351W ford, 18436572 engines with 4-7 / 2-3 swap and LS are same sequence

3. The 18436572 engines with a 4-7 swap are same sequence as Flathead ford.

That's three different sequences. Are there more?

Dave

[MadBill]

Potentially, are there ever! Assuming an SBC cylinder numbering convention, and starting with the basic 18436572 sequence, after #1, you could fire 5 instead of 8, so that's two. Next, you could fire 7 instead of 4, so that's three. After that you could light off 2 instead of 3, so four. Back to #1, you could have fired 8 first instead, so that's four more... It goes on, but there's around a dozen possible, including a double-fire combo: 1 AND 6, 8 AND 5, etc...(Might be just the thing for loose dirt...)

[Nick Campagna]

http://en.wikipedia.org/wiki/Firing_order

[dave brode]

Nick,

I saw that page, but it really doesn't indicate very much, as there are so many different labeling methods used by various car makers. It seems that Cadillac could not decide on how to mark their cylinders. The '63-'67 are labeled like a common 18436572, and it's clear that they have a 4-7 / 2-3 swap. The '68 up is actually the same sequence, but since the cylinders are labeled differently, it takes some pen and paper time to see that for my little brain. Ford used at least three different sequences, but at least they assigned the same numbers to the cylinders.

Fwiw, here's a chart with some popular engines. Looking at the LS chevy, you see it's same as '63-'67 Caddy, easy to see, same labeling. Re-label the '68 up caddy, and you'll see it's the same sequence [why did they feel the need to re-label?]. Re-label the "HO" ford [and mod] like a GM, or vice-versa, and you'll see it's the same too.

http://blogs.hotrod.com/msd-ignition-co ... z2ctpYZCRA

Re-label a GM 18436572 engine like a ford, or vice-versa, and you can see that a "4/7 swap" 18436572 engine is like a flatty sequence.

Re-label a 289/FE/429 etc and you'll see it's same as a 18436572 GM/mopar

Haven't looked close at the nailhead and Y block yet. I wonder about old V-8 Packards and such.

It does seem a bit odd to me that mopar stayed with the 18436572 sequence, where most others are the "4-7 / 2-3" swap now.

I realize that MadBill is right about what's possible, but I wonder how many firing sequences are actually in use? Why do I care?

Dave

[PackardV8]

That's three different sequences. Are there more?

One, there's the cylinder nomenclature issue not uniform from one manufacturer to another. This complicates the easy comparison.

Two, the wiki reference gives eleven:
1-8-4-3-6-5-7-2
1-8-7-2-6-5-4-3
1-3-7-2-6-5-4-8
1-5-4-8-7-2-6-3
1-6-2-5-8-3-7-4
1-8-7-3-6-5-4-2
1-5-4-2-6-3-7-8
1-5-6-3-4-2-7-8
1-5-3-7-4-8-2-6
1-2-7-8-4-5-6-3
1-2-7-3-4-5-6-8

Three, engineers will have to check the math, but there are about 40,320 possible 90*V8 firing orders.

Obviously, some have been found to work better than others.

[dave brode]

Mr. Vines,

The wiki list of 11 *could* be only three actual sequences used, but those three sequences and different combinations of labeling equal the 11?

To this point, I see only three sequences used.

#1 common 18436572 sequence
#2 Flat head ford, 18436572 with 4-7 swap
#3 '63 Cadillac, HO ford, LS, 18436572 with 4-7/2-3 swap

More late night "I should go to bed" activity required.....

How are the V-8 Packards labeled, which sequence?

Dave

[ap72]

Do any engines fire two cylinders together? Would there be any advantage to this?

[Ken_Parkman]

There are a bunch more factors to consider.

"Flat" cranks are inherently shakers as the secondary forces cannot be cancelled, so conventional engines ignore a flat crank and use a 90 degree throw crank. A 4 stroke is a 360 degree cycle, so an 8 cyl uses 90 degree firing pulses for even fire, explaining why the block bank angle is 90 degrees. Mechanically cylinder pairs are on the same crankpin, so that is another design requirement as paired cylinders must fire either 90 or 450 degrees apart in the cycle. Then you want to cancel the shaking forces and moments as much as possible, and (barely remembering my machine design - it was a long time ago) some crank configurations cancel them all except for the secondary moment. Last one I can think of is the firing order has an influence on the crankshaft torsional vibration excitation orders, and probably some firing orders are better than others for crank vibrational stress. This last one is the reason I think some firing orders seem to make more power, the crank vibration signature may be "better" matched to the rest of the engine.

By the time you sort this stuff all out I'll bet there are only a few true usable firing orders, and those are the ones you see out there.

[PackardV8]

It seems the OP is asking what existing production engine firing orders have been used in production 90* V8s. We're just having some fun with the possibilities.

By the time you sort this stuff all out I'll bet there are only a few true usable firing orders, and those are the ones you see out there.

Yes, that's a given; things are the way they are because that's the way they are. That engineers have winnowed through the many thousands and chosen the best few doesn't change the fact other possibilities exist and are "usable", just not the best choices. The now-popular 4-7 swap wasn't out there not that many years ago.

Mechanically cylinder pairs are on the same crankpin, so that is another design requirement as paired cylinders must fire either 90 or 450 degrees apart in the cycle.

That used to be true, but as GM and other even-fire V6s have shown, it's no longer a requirement for any two cylinders to be on the same crankpin.

so conventional engines ignore a flat crank and use a 90 degree throw crank.

There are more 180* crank V8s currently in production than we'd have ever believed if we just read the textbooks.

[andyf]

There are just 8 possible firing orders when using a standard crankshaft. If you go with a flat crank, or a split pin crank then you can use more firing orders.

Some of the 8 possible ones are really odd. As far as I know, there are just the 3 primary firing orders in use. I'm sure people have tried more of them, but we usually only see the common 3. To really know the answer you have to ask the cam guys. Chase at Crane has probably seen it all, I'm sure he would know if people have tried the other firing orders.

[Ken_Parkman]

I remember working out the shaking forces mathematically and vaguely (machine design really was a long time ago) remember the bad secondary forces in a 4 cyl or flat crank 8 were related to deck height, explaining why the smoother honda's and such have such short decks and rods. And why some of the big 4's shake so bad. Was for a drive in a model A last week - that thing shakes! I have a buddy who has a 328 Ferrari and I keep telling him how stupid the Ferrari engineers were to make such a dumb engine and for some reason he takes offense. But I guess there are a lot of 180 degree cranks out there - almost every 4 cyl and a lot of very small V-8's.

I still think it is kinda dumb on a V-8 when you can do it right, but certainly the Ferrari guy's disagree with me. But I also think it's kinda dumb to design an engine that small a displacement when a pushrod engine will make much more power in the same space and weight. For sure that will bring out the people that disagree!!

BTW I'm pretty sure the 4-7 swap is the old flathead when you number them the same, so it's been around for a long time.

True about the offset crankpin, but that's another solution to using the wrong engine configuration when they needed to get a 120 degree firing pulse with a 90 degree bank angle. And then there was the "semi-even" fire V-6. Of course a V-6 is an engineering aberration altogether. 3 firing planes cannot possibly have the forces cancelled, and the block bank angle should be 120 degrees. Have to admit apply enough technology and they work pretty good, but it took a lot of effort.

The mistake on my first post is the 4 stroke cycle is 720 degrees - so an 8 needs a 90 degree firing pulse for even fire, and a 6 needs 120 degrees.

BTW Jack, I finally got a chance this week to drive my dad's 55 2-ton Stude that you helped us find the OD tranny for - THANKS. He has turned it into a car hauler and it works pretty good. The OD tranny is a huge improvement as you can almost keep up with traffic now, but the shift pattern sure takes some getting used to. This weekend he is going to a show driving the 55 Stude with a 53 Henry J on the back and hauling the 45 Stude Weasel. That should be a sight on the highway!

[andyf]

It is fairly easy to make a list of the 8 possible firing orders.

Start with 1, then the next choice is 5 or 8, the next choice is 4 or 7, the next choice is 2 or 3, then you have to pick 6, then you choose 5 or 8 again (can't duplicate if already picked), 4 or 7 (can't duplicate), 2 or 3 (can't duplicate)

If you print them out you see how it works.

15436872
15426873
15736842
15726843
18436572
18426573
18736542
18726543

That is all there is. Everything else is just a renumbered version of the same thing. The Wiki article is wrong since it mixes and matches cylinder numbering in with firing orders. Someone should correct that article.

The 15736842 would probably be a real paint shaker. First one side of the engine fires then the other side fires. I can just imagine how hard that engine would rock back and forth.

[Nick Campagna]

For us short school bus people, what numbering system are you using ?

[dave brode]

Andy F,

I figured the flat crank would come up. I should have said, my question is looking at normal V-8s.

Ken,

Yes, the flathead is same as 18436572 with 4-7. I see guys all the time stating that a 18436572 engine with a 4/7 swap is same as "HO" ford [they like to call it that], but not so.

On the subject, there is somthing nice about the sound of the HO ford, and the LS engines, and a cadillac with same sequence sounds the same. I can't say that I have heard a 18436572 engine with just a 4/7 swap.

Thanks for the input, fellows.

Dave

[MadBill]

I'm thinking there's a SpeedTalker with the initials DM that could tell us first hand about testing every possibly firing order in a 500" V-8 ...