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It looks like the LS firing order is for people like me. Fire the corners and then fire the middle. I would start on #3 and fire kind of like a torque sequence 3-4-5-6-2-7-8-1. The engine might run backwards, but the firing order would be neat and tidy. :D
 

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Discussion Starter #22
It looks like the LS firing order is for people like me. Fire the corners and then fire the middle. I would start on #3 and fire kind of like a torque sequence 3-4-5-6-2-7-8-1. The engine might run backwards, but the firing order would be neat and tidy. :D
That reminds me of a guy I used to work with who was a volunteer foreman at once time. He said that one of the fire trucks they had in the station was a very old one with a deisel engine. He said that once in awhile when they would start it up, it would actually run backwards, and they would have to shut it down and fire it up again. I don't know if that's possible, but that's what his claim was.
 

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I guess this guy has to go back to fix his fingers.
 

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That reminds me of a guy I used to work with who was a volunteer foreman at once time. He said that one of the fire trucks they had in the station was a very old one with a deisel engine. He said that once in awhile when they would start it up, it would actually run backwards, and they would have to shut it down and fire it up again. I don't know if that's possible, but that's what his claim was.
Possible. If you overload some diesels to the point of stalling, sometimes they will run backwards. Seen it and had to implement solutions for it a few times.

Your example likely had a weak injector or two.
 
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I thought the whole issue is swapping the firing order was for fuel distribution as per Ricky Smith

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Discussion Starter #29
For GM engineers to go from the decades long used old firing order to the LS firing order, I'm sure they did extensive testing and there was some improvement in crank stress, heating, intake turbulence, exhaust pulse, something that made the change worth it.
I'm not as confident of engineering actions being valid all the time as you are. I work in a giant aircraft manufacturing place for the past 39 years as a transmission gearbox Leadman/mechanic. The place has military contracts and has been in biz since the 1940's, and I've seen engineering design changes for the mere sake of change itself even when the end result is worse than the alleged issues it was supposed to fix.

And once the time and effort for the change was made, the decision to impliment it never gets reversed regardless of how bad it might turn out to be. Kind of like when congress writes and votes in a new law for us all to have to obey. Once it's completed, and implimented, they rarely reverse it no matter how bad it turns out to be. Because for them to do so would mean that they have to admit that they were wrong. And it seems that many engineers do NOT see the truth and value in the old saying: "if it aint broke, don't FIX it". Instead, many of them want to make a name for themself or perhaps justify their position by coming up with a "NEW" method or design, just for the sake of it being "new".

Because of this, sometimes things are OVER-engineered and create more problems than they're worth. But the engineers involved usually cannot admit that to themselves, let alone admit it to their supervisors, nor to their customers. It becomes a stubborn ego thing for them. Kinda sucks for everyone really, including the end-user/customer. The LS1/2/3/6/7 platform's big improvement from a performance standpoint was/is the cylinder heads with their catherdral port design, IMO. It obviously improved airflow. But I'm not so sure that the firing order was worth the change. JMO though. Like I said earlier, I wasn't even aware of that firing order change of the LS engines until very recently.
 

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.....but....back on point here... based on what some of you have stated, perhaps the 4/7 firing order/cam swap thing for BBC engines is a fad or a trend, and nothing more. I must admit that I didn't think that I would be drawing that conclusion about this topic since reputatable engine builders like Reher Morrison, and Pat Musi include 4/7 cams with some of their BBC racing engines. For instance, I see that Pat Musi has teamed up with Edelbrock to design and sell a 1200 HP sportsman 632 cid engine, which uses 12 degree heads and a 4/7 cam. But I cannot overlook nor dispute some of the replies which have been made here in this thread by at least some of you guys who are much more knowledgeable than I am in hi-perf engine design.
 

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From what I've gathered over time the swap contributes to improved harmonics. That's all I know about it and have used that firing order for some time now. Haven't done any back to back because it's a pita to change cams in a 66.
 

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When you change the firing order of the cam from the original firing order you swap the tubes for proper exhaust expulsion. That is how we build them on ALL motors with the firing order changed. Look it up.
Huh? That doesn't explain your claim of two cylinders firing at the same time.
 

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When you change the firing order of the cam from the original firing order you swap the tubes for proper exhaust expulsion. That is how we build them on ALL motors with the firing order changed. Look it up.
I'm assuming you mean if you are using tuned header primary lengths? On equal length headers this should make no difference. Though I have a hard time thinking the primary tubing is going to have a significant impact on overall engine performance based off of swapping 2 cylinder's firing order. I would suspect the tuned length is based as much off of individual cylinder combustion as it does on firing order.

Can you explain more on what you are saying? I am either completely confused or I need to learn.
 

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When you change the firing order of the cam from the original firing order you swap the tubes for proper exhaust expulsion. That is how we build them on ALL motors with the firing order changed. Look it up.
I agree. The theory is that if you increase velocity that will cause a depression to the adjacent area. Refresh the Bernoulli effect. Pipes are paired so the velocity created from the exiting exhaust mixture will create a depression on the nearest adjacent pipe and begin the evacuation process. This does several things. First it lowers the pressure in the primary. The primary will evacuate the cylinder due to the differential pressures thus reducing the pumping loss for the engine.This will also begin the flow into the cylinder of the fresh air/fuel mixture. The trick is to get the primary pipes and intake runner lengths correct so all of this works together at the rpm you want the engine to operate. No matter what the length of the intake runner and headers they will be tuned for some rpm, just maybe not the rpm needed. Getting this to all work together is part of the way pro stock engines can achieve 120-130 volumetric efficiency.

Pipes are paired to allow time for all this to happen. In a normal 4 into 1 collector the effect is not as great as a 4-2-1 collector like the Flowmaster and Hookers that were popular in the early 90's. Tri y also respond more than the tradition 4-1 collector. In the late 60's Mickey Thompson built what was called a Super Scavenger header. The trick was to get all the pipes the same length and as straight as possible. The primarys were run into a long collector and none of the primary's ended at the same place in the collector. That was successful according to MT's marketing but soon faded.

In a conventional Chevy firing order pipes 1-5, 3-7 would be paired. On the even bank 8-6, 4-2 would be paired. In a 4-7 swap 1-3, 5-7 would be paired, even bank 8-4, 2-6 would be paired.

This may or may not show additional performance. Same with the 4-7 swap cam. All the changes together might be 10 horsepower, maybe nothing hopefully more. You can run a 4-7 swap cam and your headers will be just fine. You can swap your pipe pairs around and your engine will run fine. However the guys that go faster than the rest spend a lot of money to find very little power. There are no magic headers and there sure is no magic cam. All parts have to work together. Odds are most on this board could swap 10 different but similar cams into their engines and at a dragstrip maybe see a tenth of a second difference at most. Same with headers.
 

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With the original Chevy firing order, 1-8-4-3-6-5-7-2, cylinder 4 fires right after cylinder 8 fired. The exhaust pulse from 8 is still in the exhaust manifold which causes slightly more pressure that cylinder 4 fires into. Also, depending on how long the exhaust valve stays off the seat, some exhaust pressure from cylinder 4 can sneak into cylinder 8

The 4/7 swap, 1-8-7-3-6-5-4-2, simply creates the same situation but now with cylinders 4 and 2.

The LS firing order, 1-8-7-2-6-5-4-3 again creates the same situation but now with cylinders 2 and 6.

So, none of these firing orders should have an “advantage” when it comes to the pressure pulse that’s inside the exhaust manifold.

I think it’s safe to assume the 4/7 firing order and the LS firing order might an advantage in crankshaft harmonics or controlling block hot spots.

The exhaust “problem” disappears when long tube headers are used instead of stock cast iron exhaust manifolds.
 

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With the original Chevy firing order, 1-8-4-3-6-5-7-2, cylinder 4 fires right after cylinder 8 fired. The exhaust pulse from 8 is still in the exhaust manifold which causes slightly more pressure that cylinder 4 fires into. Also, depending on how long the exhaust valve stays off the seat, some exhaust pressure from cylinder 4 can sneak into cylinder 8

The 4/7 swap, 1-8-7-3-6-5-4-2, simply creates the same situation but now with cylinders 4 and 2.

The LS firing order, 1-8-7-2-6-5-4-3 again creates the same situation but now with cylinders 2 and 6.

So, none of these firing orders should have an “advantage” when it comes to the pressure pulse that’s inside the exhaust manifold.

I think it’s safe to assume the 4/7 firing order and the LS firing order might an advantage in crankshaft harmonics or controlling block hot spots.

The exhaust “problem” disappears when long tube headers are used instead of stock cast iron exhaust manifolds.
Paul,

The "LS" firing order actually fires 1&3 consecutively.

1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3, etc.

So all of the firing orders have 2 adjacent cylinders firing in sequence at some point.

The 4/7 and 4/7, 2/3 swaps just move those consecutive cylinders to the front of the engine, which just happens to be closest to the water pump on most V8's we play with.
 
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Thousands of years ago, there was a published interview of various people involved in the LS engineering.

I have been entirely unable to find that article on the internet for ten years or more. I must be using the wrong search terms. (This is NOT the Hib Halverson "The MIllenium Motor" article.)

Anyway, the GM Powertrain "cam guy" said the new firing order was requested by the GM Powertrain "crank guy"; the new firing order supposedly removed load from #4 main bearing (which was "overloaded") and moved that load to #2 main bearing (which was under-loaded.) In short, the new firing order evened-out the bearing loads somehow. This improved the smoothness of the engine as well.

Oldsmobiles have problems blowing the #4 main webbing out of the block. Same firing order as the "traditional" Chevy.
 
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