V8 Firing Orders

[Lou Scannon]

Out of curiosity I have been "collecting" V8 firing orders. So far I have found 5 unique firing orders for a conventional 90 deg bank angle cruciform crank V8. For clarity, cylinder numbering is from the front of the engine to the back, so odds are on one bank, evens on the other.
They, along with their twins (cylinders numbered back to front), Ford numbering system equivalent, and a partial list of engines that use them are:

Original Twin Ford
12784563 15436872 15486372 Ford Flathead Lincoln Flathead Ford Y-block Lincoln OHV Buick Nailhead
18547236 14527638 18364527
18736542 12634578 18654273 caddy flathead Olds OHV
18726543 12734568 15426378 MEL wedgeblock Ford FE
18436572 15634278 13726548 Caddy OHV Desoto Firedome Chevy smallblock Pontiac Mopar B AMC 1st & 2nd gen Olds 2nd gen Porsche 928

 

[FoMoCoMoFo]

It's beautiful, But.. I don't see my favorite ford firing order 15426378 represented. numbered front to back looks like 12734568 ( I suppose front to back makes more sense, but far be it from me to question the wisdom of our ford ) probably just a mix up in the translation.

 

[crysta1c1ear]

12734568, reading left to right

It just looks weird to me when you get two cylinders on the same bank firing one after another, like 73 and 68 in the example above.

 

[FoMoCoMoFo]

there it is ! yes at 68 they are right next to one another. it happens at 31 in 2 of the others above. the point of some of the earlier posts is that it has to happen somewhere. so 18547236 in the middle above is the oddball. what goes on there ?

 

[patprimmer]

Maybe it (18547236) has a flat plane crank.

Regards

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[patprimmer]

Or maybe it fires at around about 120 deg before or after TDC on one cylinder.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[NormPeterson]

Ford cylinder numbering scheme with #1 cylinder on the left side of the engine (typical GM), with the middle throws opposite hand to the original SBC?


Norm

 

[kenre]

And the firing order of a Detroit Diesel 8v71 would be?

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[Lou Scannon]

The 18547236 order I got from a post by the esteemed Greg Locock in this thread:

http://www.eng-tips.com/viewthread.cfm?qid=82875&page=58

It is a translation into conventional numbering of Greg's posted Bosch 18364527 order.

 

[Lou Scannon]

A two-stroke V8 (e.g. DDC 8V-71) firing order would likely be quite different from a 4 stroke firing order, whether 360 or 180° crank. A 4 cyl two-stroke already has a two-plane crank and even (90° separation) firing order so ideally a two-stroke V8 would have 45° phase separation for the whole engine and 90° phase separation on each bank.

 

[kenre]

hemi,

this is the firing order, 1L-3R-3L-4R-4L-2R-2L-1R

Not sure on cylinder numbering.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[Lou Scannon]

As expected, the 2-stroke V8 firing order does not have any consecutive events on one bank. Using conventional numbering, it would be 16587432. You can see opposite cylinders are paired. That's probably an inherent feature of a two-stroke 90° V8 with 45° offset crankpins, which I'm guessing is the configuration.

 

[iolair]

Historically, maintaining the correct A/F ratio of the 5/7 adjacent firing clyinders has been a problem because of their location in the firing order and as it relates to cylinder cooling or the lack thereof.

The 4/7 swap simply moves the adjacent firing cylinders to the front of the engine, thus they get first shot at the water pump and it makes it easier to jet the motor when carbs are used. Obviously, the 4/7 swap is not as critical if a reverse flow setup is employed.

John

 

[patprimmer]

Most of the SBC I have seen put the water into the front of the block AND out of the front of the head.

The holes in the deck are designed to restrict flow enough to stop high flow due to shortcutting of flow at the front and stagnant water water at the back.

This would suggest the coldest cylinder but the hottest head at the front. This would suggest 4/7 swap has no advantage nor disadvantage, except to line the pockets of cam grinders and to cause a non standard firing order that may lead to incorrect wiring of spark plug leads.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[iolair]

Actually, with the 4/7 swap, the average temps of the 4/2 cylinders are always cooler than the 5/7 cylinders.

I would suggest you stop suggesting and start measuring!

Regards

 

[patprimmer]

Then how does reverse flow change the situation.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

Also, many who do the 4/7 swap have highly modified engines and therefore quite likely have different temperature profiles across their engine, so measuring one or two examples would not be an accurate representation. This swap is quite popular in drag racing where they often do not even circulate the coolant and sometimes use no coolant other than ambient air and rich mixture.

Also, in a pair of cylinders, if one goes lean and therefore possibly hot, the other goes rich and therefore possibly cold, so we get one hotter and one colder, so how does colder water help the cold cylinder.

If the hot cylinder were to go into detonation, I could see your point, but I have never seen a detonation problem cured by the 4/7 swap.

I have seen detonation or chamber overheating problems cured by directing water flow to hot spots by changing water inlet or exit points or by changing the size of water passages in the deck. I have more often seen them cured by simple jet or nozzle changes.

I have only ever measured individual chamber temperatures by spark plug reading as that indicates the temperature inside the chamber, not way out in the water jacket.

If I was having trouble controlling temperature around a particular cylinder, I would try to correct the water flow rather than change firing order.

On a SBC I put my effort in this regard into getting more water between 3/5 and 4/6 as that is where exhaust heat causes gaskets to blow with std exhaust valve layout.

I fix charge robbing problems in the manifold, not the camshaft.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[iolair]

With a single-plane or common plenum intake #5 will rob #7, aggravated by #7 running hot unless the 4/7 swap is employed. Adjacent firing cylinders are very difficult to jet properly...if #7 is just right the rest of the cylinders will be too fat; if the other cylinders are just right #7 will be too lean and if #7 is lean and hot it will detonate. The 4/7 swap helps lessen the possibility of detonation due to the cooler cylinder pair.

Look, its no big deal....people have been doing it for 30 years or more and it does not cost extra if the cam grinder has masters with the 4/7 lobe setup. I admit, I have not kept up with the latest technology and don't know what they are doing now.......and I certainly no longer use carbs.

You stated you could not find a plausible reason for the 4/7 swap and I simply gave you one that worked in the day.

John

 

[iolair]

Note that the LS7 and the 4.6/5.4 Modular motors have moved their adjacent firing cylinders to the front of the blocks.

1-8-7-2-6-5-4-3 - LS7

1-3-7-2-6-5-4-8 - 4.6/5.4

Coincidence?

John

 

[larrylcoyle]

While I am sure there are certain combinations and conditions where the 4/7 lobe setup "really works", I am just as sure that the cam manufacturers are "using" this as a method to sell additional camshafts. I also put this in the same category as the Beehive and Conical valve springs that have re-appeared on the market. And then there is always the Vibration Absorber Carb spacer if you need something else to think about.

Larry

 

[Lou Scannon]

You bring up conical springs... interesting, that reminds me that production Oldsmobile Rocket engines in the late 50's - early 60's had conical springs, if I'm not mistaken. They must have had a good reason to do that in mass production - any guesses?