Worst V8 firing order?

[andyf]

I've seen a number of posts over the years asking about the best firing order, or the reasons for changing firing orders. It seems there is a rough consensus around the LS1 firing order (18726543) as being the best or one of the best but nobody seems to talk about the worst.

Anyone ever try all 8 firing orders to see what happens? I suppose the cost would be fairly high since some of them are going to require full billet cams.

I'm thinking the worst might be 15736842. That one would fire one bank and then the other bank which doesn't seem good. Also, it would have 3 pairs of cylinders that fire next to each other which also doesn't seem good. Anyone know if a motor ever came with this firing order?

[miniv8]

Did a bit of digging. Please excuse the 2008 op.

This is interresting.
I came across this description of a small oval track car on FB. A quick online search brought me to this thread.
It is as follows:


It was a 4.5 bore, 3.75 stroke, and used 6.5 Carillo rods and 15:1 Venolia pistons. Nothing really new there, but the cam was a custom Reed grind that changed the firing order to 15736842. Basically it was 2) 4cyl engines living in the same block. The reasons for doing this could be a whole separate post, but man did it ever work!

I built a set of custom 180deg 4-2-1 headers for it, and it sounded like a Ferrari out on the track. I also used a front drive magneto to keep the timing a little more consistent. Steve Faria of System 1 filters helped out a lot with the fuel tune. I don't think we ever changed a jet in the injection once we had Steve's tune in it. The engine was good for a little over 900hp and 750 lb-ft, and it made over 650 lb-ft from 3500 out past 7000 rpm. Perfect engine for a direct drive race car.

[PackardV8]

Open-ended questions make for diffused answers. Define "worst".

Worst for a carbureted single plane intake?

Worst for NVH?

Worst for exhaust tuning?

Worst for bearing longevity?

Worst for a flat crank?

Worst for a 90-degree crank?

[engineguyBill]

Open-ended questions make for diffused answers. Define "worst".

Worst for a carbureted single plane intake?

Worst for NVH?

Worst for exhaust tuning?

Worst for bearing longevity?

Worst for a flat crank?

Worst for a 90-degree crank?

^^^^^^^^^^^^^^^^^^^^^^^^^^ THIS ^^^^^^^^^^^^^^^^^^^^^^^^^

As Jack has noted above, there are many things that are influenced by firing order, or is it things that influence the firing order . . . . . . ?? What came first, the chicken or the egg?

[Kevin Johnson]

viewtopic.php?f=1&t=3132#p25969

Firing order
Post by Darin Morgan » Mon May 29, 2006 10:50 am

We have tried every conceivable firing order in the V8 engines and only two showed promise. There was one that showed a small gain ( 6HP-10HP) some where beneficial due to there lack of vibration and the rest where worthless. Now that's with 8 cylinders so the tuning was a far cry better than having just two cylinders. What we found is that if you have the same number of pulses with no change in tuning, you get the same power.
Unless there are advantages with either the induction system tuning or exhaust system tuning, I don't think you will see much of anything other than a loss in power or no change at all. Right now the pulses are evenly spaced so if you have an exhaust system and or intake system that is merged, the pulses might have some beneficial effect. If you go and make the pulses uneven, the tuning will be just as uneven or out of phase with intake valve timing. You also have the added problem of crank shaft shock loads that will be unevenly spaced and could cause some vibrations on an order I am not familiar with which could end up causing premature component failure.

That's all the reasons I can find for you to not do it. Now for the reason you want to do it.
If you have the money and also the time and wish to just play around for the next year or so evaluating these changes, who knows what you might stumble on too. We didnt know what would happen with all those cams and cranks journal locations but we did find about 10HP doing it. By the way, The cost for that 10HP was staggering!

[Walter R. Malik]

viewtopic.php?f=1&t=3132#p25969

Firing order
Post by Darin Morgan » Mon May 29, 2006 10:50 am

We have tried every conceivable firing order in the V8 engines and only two showed promise. There was one that showed a small gain ( 6HP-10HP) some where beneficial due to there lack of vibration and the rest where worthless. Now that's with 8 cylinders so the tuning was a far cry better than having just two cylinders. What we found is that if you have the same number of pulses with no change in tuning, you get the same power.
Unless there are advantages with either the induction system tuning or exhaust system tuning, I don't think you will see much of anything other than a loss in power or no change at all. Right now the pulses are evenly spaced so if you have an exhaust system and or intake system that is merged, the pulses might have some beneficial effect. If you go and make the pulses uneven, the tuning will be just as uneven or out of phase with intake valve timing. You also have the added problem of crank shaft shock loads that will be unevenly spaced and could cause some vibrations on an order I am not familiar with which could end up causing premature component failure.

That's all the reasons I can find for you to not do it. Now for the reason you want to do it.
If you have the money and also the time and wish to just play around for the next year or so evaluating these changes, who knows what you might stumble on too. We didnt know what would happen with all those cams and cranks journal locations but we did find about 10HP doing it. By the way, The cost for that 10HP was staggering!

He did not mention that a reason used for some firing orders being changed is to make the heat in the combustion chambers more even from cylinder to cylinder by changing the coolant / heat absorption within that particular type block; especially with detonation sensitive applications.
This won't make more power by itself but, it could allow other things which may make more power.

[Walter R. Malik]

(double post)

[miniv8]

Scrounging for information on the 15736842 firing order I found some suggestions implying Warren Johnson tested it in ProStock.
the results where basicly inconclusive performance wise, but by the way it sounded, everybody thought it was a flat plane crankshaft.

it might not be suited for a single carb manifold application, but with a tunnel ram, ITB's or a blower, it might make for a fun different runner. If it doesn't instantly kill the mains that is.

[ptuomov]

I think there are six possible crossplane V8 crankshafts, but only two are used. Why?

For the two that are actually used, the possible firing orders are these:

56D086FF-67F8-4EAD-806A-CACCA20F09DB.jpeg

[Truckedup]

Why was 18436572 popular for many earlier OHV V8's?

[dannobee]

The story that I heard years ago from an old time GM engineer was that they assembled 4 engines with different firing orders, ran them all on the test stand at idle, and the lead engineer "evaluated" each by putting his hand on each of them and "determined" that the 18436572 was the "smoothest." Dunno if it's true or not, but the old guy stuck by his story. And by the disdain he had in his voice when he told the story, he sounded pretty pissed about the whole process.

[ptuomov]

Here’s Porsche external doc on firing order. They or the browser failed to translate it back to characters from type set and fls and fis are missing...

https://newsroom.porsche.com/en/technol ... 14034.html

Differing firing orders depending on the manufacturer
While the firing order determines the crankshaft rotation angle traveled between the ignition of two cylinders, the firing order defines the unique sequence of the cylinders in succession. As fixed geometric variables, the bank and crank angles only allow certain orders. The respective configuration defines which pistons reach their top dead center. The firing orders of flat- and cross-plane engines therefore differ in principle. Nearly all modern flat-plane V8 engines fire in identical sequences; in cross-plane V8 engines, by contrast, one generally finds manufacturer-specific firing orders. This takes into account a circumstance that can lead to slight confusion: worldwide there are different definitions as to which cylinder is counted first and how the other combustion chambers are numbered. This would seem to result in different firing orders. Removing the effects from the different cylinder counting methods, the variance in firing orders drops markedly.

If one begins the cylinder count in each case with cylinder 1 according to DIN 73021, there are a total of eight theoretically possible firing orders for each rotational direction in a flat-plane V8. With a cross-plane engine, the total is 16, as here the angle position of the center crank pin is interchangeable. However, not every theoretically possible firing order is implemented in reality. The objective is always the best-possible compromise between the following criteria:

> Gas cycle 

> Stress on the main crankshaft bearings 

> Vibration stimulation of the crankshaft drive through deformation of the crankshaft under loads 

> Rotational irregularities 


Porsche Engineering carefully examined the question of the optimal firing order for both flat-plane and cross-plane V8 engines. Nearly all flat-plane engines reidentically, with alternation between banks always a possibility even with a deviating ring order. The result for cross-plane variants was likewise no surprise: particularly with a focus on maximum robustness of the crankshaft bearings, the firing order 1-3-7- 2-6-5-4-8 is the best choice in view of all characteristics — which is the firing order for all Porsche cross-plane V8 engines since the 928. Even so, the other implemented firing orders also have their justifications; here the objectives of the manufacturers in terms of their conceptual decision do vary. The results of the analysis also revealed another interesting point: There are certain ring orders that have never been implemented in reality but which also demonstrate exceptional balance in the fulfillment of the specified objective criteria.

[dannobee]

So it ends up being like the man who carefully analyzes the attributes of four different women and ranks them based on dozens of criteria such as culinary skills, lineage, religion, education, potential for generating income, personalities, and the like, and after carefully weighing the data, ends up marrying the one with the biggest tits.

It simply doesn't matter enough to lose sleep over.

Directly related to firing order, but for a far more devious reason, some tracks have "claimer" engine rules on lower division cars, whereby one competitor can "claim" the engine of another for a price agreed upon in the rule book. If one changed the firing order, the other would play hell trying to get it to run right. Another way to circumvent "claimer" rules was to externally balance the engine and keep your balancer, flywheel and clutch.

I always hated such claimer rules. You can tell which side of the fence I was on.

[NewbVetteGuy]

What would be the extreme edge cases where a change in firing order would be more likely to see more gains?

I think there’s something to be learned from scenarios where it’s likely to make a difference.


I’ve heard that firing order changes can be a big deal with GM TPI engines; wondering if it’s because it’s very easy for them to be induction limited by the poor flowing intake; I’m thinking the contention for air from adjacent cylinders is a bigger deal in this situation potentially.

What about when you have to use certain log exhaust manifolds? I’d think two adjacent cylinders dumping exhaust into the same log manifold could be a situation where a firing order might eliminate an exhaust limitation then...

Adam

[ptuomov]

What about when you have to use certain log exhaust manifolds? I’d think two adjacent cylinders dumping exhaust into the same log manifold could be a situation where a firing order might eliminate an exhaust limitation then...

There is no crossplane V8 firing order that makes the exhaust work right for a manifold. All of them are irregularly spaces with 180 and 90 degree exhaust blowdown interference. The options are LS7 collector which dumps into a large plenum, Coyote manifold that intentionally combines the 90 degree spaces pulses as close to the head as possible, or two separate manifolds per side configured like tri-y like BMW sometimes does.