Firing Order (Engine Builder Tech)

PHARTMAN...NO there is no advantage in firing order, only C.I. and race parts...POP.

 

Holeshot, seems like there are a couple builders who would disagree with you, but I don't have the technical know-how here to take one side or the other. And I have no dog in the fight.

My original question was, "Does firing order matter?" and you say "No, hell no!!" and I certainly respect that. But there seem to be quite a few others who say firing order is something that might be altered for a little performance gain. An area of exploration, if you will. A little here and a little there.

You are correct that all things being equal, nothing beats cubic inches and performance parts. But I'm getting at something a little more subtle.

See above, for example, the Flathead reference to changing the firing order AND the headers to pick up horsepower. Not a lot, but enough to make the change interesting. So evidently, there is something to be exploited. We're talking marginal differences, but a couple horsepower on a competition motor MIGHT be significant.

For the average rodder, nope, probably not. That is what I am picking up here.

Again, I dunno. But if you have a valid point, I'm all eyes and ears and want to learn from the masters. Please speak up, sir.

 

We've been through this before, but I'll try again! The Ford 302, and the 302 H.O. have different firing orders. The 302 H.O. has the same firing order as the 351, so the same cams can be used in either engine, without changing firing order. If you use the 302 H.O. or the 351 cam in the standard 302, then the firing order must be changed to the 351 firing order. If you use the STANDARD 302 cam in either the 302 H.O. or the 351 then the firing order must be changed to the standard 302 firing order.

 

With all that said,don"t wonder anymore,why theres a smallblock chevy in that ford!

 

Hot Rod did an article on the 4/7 swap. Wish I could find the article in the rag. this looks very much like the same article though.

http://hotrod.automotive.com/23368/113-0701-lunati-cams/index.html

 

Thats what Carrol Shelby did......................

 

Once you have a V8 with a 90 degree crank, you will have pairs of cylinders that CAN be fired. You ask if it matters from there. Well, I have never set foot in an engineering room, but I'd imagine that harmonics and fuel/air flow would be the next things that would be considered. All of these engines were sold to the public, so you want to keep them smooth, and intake manifolds have to work well and be cheap to make.

 

Draw a representive engine 0000
0000

Number the cylinders as they are on your engine then using your firing order draw a line from the firsr cylinder firing to the second. Now draw a line from the 3rd cylinder firing to the fourth cylinder firirng. Now do the same for the 5th and sixth and then the Seventh and eight.
Study the lines and imagine you are a crankshaft . Do you want to be hit twice on the same throw from opposite sides? Not really if it is avoidable. Spreading the wack around evenly from front to back and from one throw to the other gives the engine reliabilty. (Remember the V8 has two rods on each journal , one from each bank of the engine.)If you study this and think about it it will become clear on some of the whys and werefors. It isnt the whole story but it is a good start. I hope this helps you in your quest for understanding why.
Don
I cant get the four 0s to stay under the others after I send but I hope you get the idea.

 

Dolmetsch, you are a master of the language. That is precisely the mental image that we have been grasping for here. You and RodStRace have come to the rescue, I do believe. Thanks.

 

Actually both the SBC and Flathead Ford Firing orders have 3 rod journal pairs firing across from each other. IE the flathead fire 1-5 on the first lobe then 4-8 which are on the same lobe as well as 3-7 pair later in the order. SBC fires 4-3 then 6-5 pairs on the same lobes, then at the end of the order it fires 2-1.

The difference between them is that the FHF order puts 2 of the 3 pairs on the outside cylinders whereas the Chevy puts 2 of them in the middle.

The interesting thing about this observation is that if "double" firing on the rod journal was an issue, it could be that with only 3 main bearings on the FHF the harmonics of the double firing was pushed mostly to the 2 outside bearings instead of on center bearing.

Again just a guess

 

That Hot Rod article is interesting. They basically say that the 4-7 swap sometimes does nothing, sometimes makes more power, sometimes looses power.

I think a more meaningful test would be if they built engines with the following firing orders and tested them all:
1-8-4-3-6-5-7-2
1-8-4-2-6-5-7-3
1-8-7-3-6-5-4-2
1-8-7-2-6-5-4-3
1-5-7-3-6-8-4-2
1-5-4-2-6-8-7-3
1-5-7-2-6-8-4-3
1-5-4-3-6-8-7-2

I think they would find that the firing order could be optimized for a particular engine. But somehow I think that confirmation bias on the 4-7 swap will continue to prevail, leading most to believe that it is the thing to do.

 

"Not really if it is avoidable."

Sombody did not read this part of my answer. Maybe i should have said "in as much as it is possible. "
If you started at the front and kept firing al the way back front to back by the time you get to the rear there would be a tendancy of the Crank to twist or wind up. it would probably break eventually. By spreading it around you reduce this tendancy as much as possible. However within the V8 there are inescapable limits of design so some compromise it required . Still it is far better than doing nothing. A real good book to read if engine design interests you is Design and Tuning of Competition Engines by PH Smith. Not a lot of pictures but no BS
Don
Fires front to back. / then across I . then accross the other way I and then back to front \. for 18436572 however it is better to write it 1843 and then directly underneath write 6572. That gives a better idea in you mind what is where.
Draw the picture . See the even distribution.

 

V8 firing pulses jump all over to reduce strain on the crank and bearings. Sooooo, why are V6's immune from this? They fire 123456 or 165432! Seems like a recipe for twist to me!

 

Draw the pic. beats 1000 words.
Even for a V6. Draw the picture.
BTWYou can argue about this till the cows come home but in most engines there is an established pattern.
90 degree block V6s are not the best to study since they are an exercise in stupidity brought on by the desire to use one gang boring machine for several engines(V8s and V6s) . By fudging the crank throws and fooling around they got them to work but really anyone with a engineering degree involved in such a ridiculous project should hang their head in shame. The first ones in the Buicks actualy had a V8 distributor cap with two holes not serviced. Then they got more creative and began staggering the crank throws so all were not quite right but no one would notice. Easy now! I did not say all V6s I said 90 degree V6s.
Don

 

OK, so give the limitations of a 90 degree crank, we're captive in firing order to cylinder pairing in order to spread around the load. Some racecars have used 180 degree cranks with no counterweights. Is there any other alternative to the way cylinders are paired??? I'm trying to think what it would be, but it's late and I've had a glass or three of wine and can't do much more figuring tonight....Go back to a straight 8 design maybe?

 

I said 90 degree V6 not 90 degrees in general.
. A v 6 should be 120 degrees (720/6)
a V8 90 degrees (720/8)
A V10 72 degrees (720/10)
A V12 60 degrees (720/12)
Where does the 720 degrees come from? A "4 cycle engine" (suck squeeze bang and blow) must make two complete revolutions (720 degrees)to fire all its cylinders. (no matter how many it has. )
In a 90 degree V6 there is a coruption becaue to fire evenly spaced the engine should fire every 120 degrees. Since the block has a 90 degree angle that is impossible. At first Buick just dropped of two cylinders and left everything else the same. if you are not sure what i am sayng is true then order in a dist cap of an early 70s buick V6 and you will see the two blanked out towers in what otherwise looks like v8 cap. (Why Buick did this is another story and too big for right here but it involved Rover and the sale by GM of the 215V8 rights)
As time progressed the companies making 90 degree V6 began offsetting the journals on the crank (by about 12 degrees each way I think if my old memory serves me) to get the piston to arrive at tdc in a little better time and to smooth out the engine to an even spacing between cylinder firings. It worked not bad too but a proper 120 degree block would have been much better. Some companies did make a proper V6. not all are 90 degree fudgings. However in a V8 a 90 degree V8 is a very good design. Probably one of the best ever.
Don

 

Phartman, last night I was doing some thinking and wondered how you did your remapping of the Ford firing order -- I hate having THOSE dreams. Try remapping Ford's numbers again to match the Chevy order. This time pay attention to what squirrel said above. Ford started #1 cyl on the pass side and Chev started #1 on the drivers side. There is an important reason why you need to make that distinction. Both the Chev and the Ford crank turn clockwise in rotation from the front. That means that on the first crank throw there is 90 deg separation rotating from Chev #2 to #1, so to compare the firing order better you should map Ford Flathead #5 cyl to Chev #1. If you remap this way instead of 1357 on the pass side see what the Ford maps out to be.

 

MNFalcon, sorry, I'm being thick headed this morning. I'm coming up with the same answers. What am I missing??? Pls help me out here???

How about this: the Ford and Chevy aren't the same firing order but rather "mirror images" of each other. Am I close to the right answer???

 

Print this out, mark it up and look at how firing orders really walk around the crankshaft.
http://www.bangshift.com/assets/images/news/2009/Sep/13-19/msd%20firing%20orders.png

More info
http://craig.backfire.ca/pages/autos/v8-engines

 

What a great phrase, "Walk around the crankshaft."

Terrific chart. Thanks for posting. It really shows the various ideas designers have had to balance horsepower vs. reliability.

 

This is true but I would like to say that it is the Chevy that is now the same as the Y-Block with the 4/7 swap, not the other way round, the scrub guys finnaly figured that the Ys guys had it right.

 

OK, FHF firing order is 1,5,4,8,6,3,7,2 and number 1 is front passenger side. Now actually map the Ford cylinders to the Chevy cylinders. Since Chev has #2 front passenger side, Ford #1 is actually Chevy #2, Ford #5 is actually Chevy #1, Ford #4 is Chevy #8, Ford #8 is Chevy #7, Ford #6 is Chevy #3, Ford #3 is Chevy #6, Ford #7 is Chevy #5, Ford #2 is Chevy #4.

So when mapped to Chevy cylinders the FHF firing order becomes:
2,1,8,7,3,6,5,4 or start the order on the mapped Chev #1 and you get:
1,8,7,3,6,5,4,2

So when you actually map Ford's firing order to Chevy cylinders, not renamed Ford cylinders, you get the SBC with the 4/7 swap. Does this make sense?

 

could the sound be because the two cylinders on each side share an exhaust port

 

MNFalcon, got it. Thank you. Very interesting.

Bert, you are suggesting that we hear the offsetting or paired firings in different ways according to the order and, hence, it follows different engines would naturally have unique sound characteristics? Along with the way the ports are structured?

 

Hey, RodStRace, I found two glaring errors in the MSD chart.
1. Y Block Ford engines have the distributor at the flywheel end - NOT the front!
2. Much bigger error: Buick 401 and 425 nailhead engines also have the distributor at the flywheel end plus the cylinder numerical identification is BACKWARD! They have the firing order correctly stated, but Buick Division of GM decided to number their V8s differently from the other GM Divisions. NOTICE: 1357 on the passenger side and 2468 on the drivers side. (check service manuals from that era to verify). What MSD has diagramed on that chart, the engine would not run. Period.

In my 45 years as a journeyman mechanic and teacher of this trade, I have discovered several discrepancies in textbooks, service manuals and even exam question wording. Be very carefull with the information you see for the first time. Cross reference it with other sources, and if there is a discrepancy, a red flag should be raised so that the truth can be accurately determined through further investigation.

Don't get me wrong, I am pleased with my MSD-6 in my early Olds powered roadster which has the 1-8-7-3-6-5-4-2 firing order established by GM in 1949.

Adding to Dolmetsch's comments, the GMC truck V-6 is a 60* cylinder bank design with the 120* crankpin separation angle. The 2.8L Mustang II engine is of the same design. Everything I've read on the subject indicates that the V-6 is among the most difficult engine to balance, to get to run smoothly, vibration free. Surprisingly the in-line six is among the easiest (engineering wise) to balance.

 

von Dyck, sorry there is bad info there. I did a search and found that page. Looked like it had quite a few different firing orders all in one place, and that's as far as I went before posting.
As a technical editor, I am very aware of the issues in "reference material". Heck, I have made some! I do wonder though if some places induce errors to 'mark' their work. I know some map makers do.