Cranks

[Fingers]

I've been bothered by an earlier post about the resonate frequency of the crank. Roughly saying that the frequency was proportional to I/L. Well, that's not correct.

The frequency of a torsion spring (which the crank is more or less):

Note that the more inertia the crank has, the lower the frequency. However, it is not a linear relationship.

Now the inertia calc is non-trivial for the crank because of the varying mass distribution along it's length. I suspect the torque constant (springiness of the crank) is also non-trivial. But it follows that the mass of the harmonic balancer is critical to the base frequency for the crank system.

 

[Mike L.]

You keep dodging what your firing order is.

I can give you those numbers.

 

[PACougar]

How many firing orders could even be possible in a Duramax?

 

[JoshH]

How many firing orders could even be possible in a Duramax?

Unless I'm thinking about it wrong, there are 8 possible without changing the crank. Here's something I put together a few days ago The first set of linear numbers are the firing order in cylinder number. The two 4 number rows below the firing order are a visual representation of where each cylinder would fire if you are looking down on top of the motor in numerical sequence (the front of the motor would be to the left).

12784563 (stock)

1863
2574

15784263

1823
6574

12684573

1867
2534

12734568

1463
2578

15684273

1827
6534

15734268

1423
6578

12634578

1467
2538

15634278

1427
6538

 

[PACougar]

Unless I'm thinking about it wrong, there are 8 possible without changing the crank. Here's something I put together a few days ago The first set of linear numbers are the firing order in cylinder number. The two 4 number rows below the firing order are a visual representation of where each cylinder would fire if you are looking down on top of the motor in numerical sequence (the front of the motor would be to the left).

12784563 (stock)

1863
2574

15784263

1823
6574

12684573

1867
2534

12734568

1463
2578

15684273

1827
6534

15734268

1423
6578

12634578

1467
2538

15634278

1427
6538

Nice work Josh, I guess we have a 12.5 percent chance of guessing EPD's order Finger's what happens if you model other firing orders?

 

[JoshH]

Nice work Josh, I guess we have a 12.5 percent chance of guessing EPD's order Finger's what happens if you model other firing orders?

Slightly better than that because we know he isn't using the stock one

 

[PACougar]

Slightly better than that because we know he isn't using the stock one

Duh, now I feel like an idiot.

 

[Fingers]

Permutations

Not rocket science here, but let me spell out the possible permutations for the Dmax firing order.

First are your piston pairs. These are the pistons that are at TDC at the same time. Then you have the following piston pair which is the next pair that will come to TDC. You end up with the following pair order.

(1,4) - (2,5) - (6,7) - (3,8)

Which gives you the following 8 permutations: (Dmax in Blue)

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

The ones marked in red are not desirable because they have more than two cylinders in a row firing on a given side of the engine.

This leaves the following 4: (Dmax in Blue)
1 1 1 1
2 2 2 5
6 7 7 6
3 3 8 3
4 4 4 4
5 5 5 2
7 6 6 7
8 8 3 8
1 1 1 1

Now, what follows here is a rough evaluation of the magnitude of the twisting of the crank based on the distance from the flywheel. This averages the twist over three piston firings and has been normalized to show just the variation is twisting force.

3.67 3.00 3.00 1.67
3.00 2.33 0.67 1.00
2.33 1.67 0.00 1.33
2.67 2.33 0.67 2.67
1.33 1.33 1.33 1.33
0.00 0.00 1.67 0.00
1.33 1.33 3.00 0.33
3.00 2.67 4.33 1.00
3.67 3.00 3.00 1.67
3.00 2.33 0.67 1.00
2.33 1.67 0.00 1.33
2.67 2.33 0.67 2.67
1.33 1.33 1.33 1.33
0.00 0.00 1.67 0.00
1.33 1.33 3.00 0.33
3.00 2.67 4.33 1.00
3.67 3.00 3.00 1.67

The max values for each:

3.67 3.00 4.33 2.67

Which would indicate that

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

would put the least twist variation on the crank. Note that the Dmax order puts the Maximum twist variation on the crank.

 

[PACougar]

Not rocket science here, but let me spell out the possible permutations for the Dmax firing order.

First are your piston pairs. These are the pistons that are at TDC at the same time. Then you have the following piston pair which is the next pair that will come to TDC. You end up with the following pair order.

(1,4) - (2,5) - (6,7) - (3,8)

Which gives you the following 8 permutations: (Dmax in Blue)

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

The ones marked in red are not desirable because they have more than two cylinders in a row firing on a given side of the engine.

This leaves the following 4: (Dmax in Blue)
1 1 1 1
2 2 2 5
6 7 7 6
3 3 8 3
4 4 4 4
5 5 5 2
7 6 6 7
8 8 3 8
1 1 1 1

Now, what follows here is a rough evaluation of the magnitude of the twisting of the crank based on the distance from the flywheel. This averages the twist over three piston firings and has been normalized to show just the variation is twisting force.

3.67 3.00 3.00 1.67
3.00 2.33 0.67 1.00
2.33 1.67 0.00 1.33
2.67 2.33 0.67 2.67
1.33 1.33 1.33 1.33
0.00 0.00 1.67 0.00
1.33 1.33 3.00 0.33
3.00 2.67 4.33 1.00
3.67 3.00 3.00 1.67
3.00 2.33 0.67 1.00
2.33 1.67 0.00 1.33
2.67 2.33 0.67 2.67
1.33 1.33 1.33 1.33
0.00 0.00 1.67 0.00
1.33 1.33 3.00 0.33
3.00 2.67 4.33 1.00
3.67 3.00 3.00 1.67

The max values for each:

3.67 3.00 4.33 2.67

Which would indicate that

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

would put the least twist variation on the crank. Note that the Dmax order puts the Maximum twist variation on the crank.

Now that's some interesting info!

 

[Fingers]

It is interesting to note that a NASCAR style flat ground crank would have a twist variation of only 1.00 when using a firing order of 1-8-3-4-7-2-5-6 and be lighter and internally balanced. Shame they generate second order vibrations that most people would find offensive. Much like a 4 cylinder engine does.

 

[Balindir]

Awesome thread going on right here! :thumb:

 

[S Phinney]

Now what do we have to do to change to your calculated order Jon?

Sent from my DROID RAZR using Tapatalk 2

 

[MAXX IT OUT]

Now what do we have to do to change to your calculated order Jon?

Sent from my DROID RAZR using Tapatalk 2

A Cam and tuning would be my guess, when will the Fingers Cam be available....

 

[x MadMAX DIESEL]

If its that far off just thinking here you would need a different crank. Otherwise wouldn't it be to far off to that there wouldn't be equal throws before certain cylinders are at tdc??

 

[Fingers]

All 8 of the possible orders would require a cam change and swapping some of the injector wires. The 1-5-6-3-4-2-7-8 order would require a retimed cam and swapping the wires between the 5 and 2 injectors and the 1 and 4 injectors. (or the 6,7 and 3,8 injectors, your pick)

Reordering the firing sequence is only one aspect of the forces on the crank. The only way the twist values I pointed out should be an issue, is if there is a harmonic at play.

 

[EDP]

I respect people like Fingers that actually do research and leg work the correct way rather then jumping on the tail of others.

Jon I have another run of blanks with your findings (Ding Ding 1,5,6,3,4,2,7,8) coming out in the next couple weeks. Any grind you want to put on them can be done.

Problem is to keep the cost down on these things We have to buy 10 blanks at a crack and all the others we have used in the past ended VERY VERY bad.

Like Fingers stated its not the most ideal final stress number but its the best scenario we have to work with.

Really installing this application is a lot simpler then many think. Nothing needs to be changed in the tuning for that the tune does not care or know what cylinder is firing at each particular time all it needs to know is #1 then it sends out the signal to start the fire pattern. So simply moving your injector wires harness to the appropriate location is all that needs to be done.

Now that the cat is out of the bag for those that are looking to make the swap will notice on initial start up the smoother idle and all around different tone of the motor along with the ability to be able to relate to others using the cam with out asking. Its a whole different animal as far as sound goes. Also things you will notice is the ability to spool larger chargers at a faster rate for the sled pull and drag race guys.

Awesome work Fingers!!! :thumb:

 

[smarquis]

OK, EDP, don't keep us hangin, how much for a cam with a stock grind?

 

[duratothemax]

very cool thread, excellent work Jon! I really enjoyed reading this.

I wonder why GM/Isuzu chose the firing order they did??

 

[SSchmi5519]

very cool thread, excellent work Jon! I really enjoyed reading this.

I wonder why GM/Isuzu chose the firing order they did??

The same reason they chose the timing table they did. Crack cocaine. :spit:

 

[gmac32]

Good Job Jon. My personal opinion is that harmonics could play a role but what about all the breakage behind 1&2 rod journal. To me, that seems more vertical flex than torsional flex. Not at all discounting your findings, but looking at how small #1 main bearing and all the added leverage from the crank snout with the heavy balancer and tension from the belt is what (in my opinion) is the reason it is breaking behind 1&2. The is the area with the least amount of material, hence the weak spot. I have no concrete evidence and I have no idea how it could ever be proven.