L-series Fireing Order (why?)

[BRAAP]

No, you are correct. #1 and #5 are 120 degrees apart, #5 to #3 are 120, and #3 to #6 are 120 degrees, which puts #1 and #6 at TDC together.

 

Exactly!

 

These pistons arrive at TDC together in this order;

 

1-6

2-5

3-4

 

Note the stagger of the firing order... Exactly how the engineers intended it.

[BRAAP]

Oh, and keep it civil boys. Many ways to interpret the events taking place, and what dictates or determines what.

 

Ultimately the engineers that design an engine determine the firing order and they have the crankshaft AND camshaft manufactured to give that firing order.

 

 

Which came first, the crank or the cam?

 

:lmao:

Edited January 28, 2010 by BRAAP

[jc052685]

Awwww.......that aint right lol

[thehelix112]

i've heard tell of people doing this with L4 rally engines, so that _both_ pistons at tdc fire at the same time. Supposedly creating more torque, but one would have to assume, doing terrible things to the harmonics? Anyone have any experience/research about this?

 

dave

[kiwi303]

i've heard tell of people doing this with L4 rally engines, so that _both_ pistons at tdc fire at the same time. Supposedly creating more torque, but one would have to assume, doing terrible things to the harmonics? Anyone have any experience/research about this?

 

dave

 

You'd need one heck of a flywheel to even out the pulses, that would be no better than a 2 cyl.

[Flexicoker]

The point is not to have even pulses...

 

http://forums.vwvortex.com/zerothread?cmd=print&id=4191600

[jc052685]

Now this is where I was looking for this thread to go!

[rejracer]

The old timers way to remember firing order:

 

15 - 36 - 24, in other words: Too young, Too old, just Right.

 

Now if we were to regrind the cam we could have the following:

 

12 - 36 - 54 - hrm.. no that ain't doing it for me.

15 - 46 - 23 - Yep there's a possibility there...

12 - 46 - 53 - no good options here either.

 

Have fun arguing your preferences..

[johnc]

A 3 big bang L6.... just need a custom cam, a good ATI balancer, and computer controlled injection and ignition.... Tony!

[MAG58]

i've heard tell of people doing this with L4 rally engines, so that _both_ pistons at tdc fire at the same time. Supposedly creating more torque, but one would have to assume, doing terrible things to the harmonics? Anyone have any experience/research about this?

 

dave

 

IIRC this started in the Moto GP world. Most of those engines run the 'big bag' concept, as putting down two big bangs with more space between them was found to be easier than putting down 4 evenly spaced firings to the rear wheel. This is why yamaha now has the cross plane I4 in their R1. Even though it has uneven exhaust pulses, it puts three of the four cylinders firing very close to one another and then the 4th is offset in the firing order. I think it makes it sound like a 125cc dirtbike though.

[BRAAP]

i've heard tell of people doing this with L4 rally engines' date=' so that _both_ pistons at tdc fire at the same time. Supposedly creating more torque, but one would have to assume, doing terrible things to the harmonics? Anyone have any experience/research about this?

 

dave[/quote']

 

A 3 big bang L6.... just need a custom cam' date=' a good ATI balancer, and computer controlled injection and ignition.... Tony![/quote']

 

This concept ranks right up there with screen doors on a submarine, almost any how!

 

1) The biggest issue is for a 4 cylinder that fires 2 pistons at the same time, much like a similar displacement 2 cylinder! Now whey would you want to add the extra drag/friction of 2 more pistons and its rings, 2 more rod bearings, 2-3 more main bearings, (depending on design), 2 more cylinders worth of valves and springs, cam journals, etc! Not too mention the addiotinal weight and length of having 4 cylinders vs only 2? Firing pulses would be the same!

 

Same can be said for the 6 cylinder? Why not just have a similar displacement 3 cylinder? It would have much smaller packaging and lighter weight, less moving parts and that induced friction, etc.

 

Again, makes about as much sense as a screen door on a submarine...

 

Ignoring the that, lets continue.

2) There is no "free" extra torque to be had by having paired cylinders sharing firing pulses. After all the events have taken place, the sum of the torque produced should still be the same. More pulses in that complete cycle means a smoother "delivery" of the torque to the wheels.

 

3) Where the real issue starts. (You have to stop and really think about his in terms of degrees of crankshaft rotation, keeping in mind that 720 degrees of crankshaft rotation is required for a complete cycle to take place, i..e 2 crank revolutions, i.e. 4 stroke engine).

Because the crankshaft rotates 2 revolution s for complete event, an inline 4 cylinder with a 4 cylinder with combined cylinder firing, withe standard crank design would have a firing pules, then either either 180 degrees or 540 degrees the other would fire, firing pulses are can NOT be evenly spread. With the traditional up-down-down-up configuration 4 cylinder crank, the firing pulses would be;

bang-bang-pause-pause-bang-bang-pause-pause-bang-bang-pause-pause.... and so forth.

 

To get evenly spread firing pulses in an inline four cylinder that has 2 cylinders sharing fire pulses, ALL 4 crank throws would have to be inline with each other, up-up-up-up configuration, i.e. all pistons would arrive at TDC at the same time. Then you could have cylinders 1 & 4 fire, then 360 degrees, cylinder 2 & 3, then 360 degrees 1 & 4, and so forth;

bang-pause-bang-pause-bang-pause-bang-pause-bang-pause.. and so forth.

 

That would make for a VERY harsh, buzzy engine with all 4 pistons arriving at TDC at the same time, (think of how buzzy your one cylinder Briggs and Stratton lawn mower is! Now multiply that by 4 because it is now 4 cylinders and add for the longer stroke and larger heavier pistons!) This sharing of firing pulses for a 4 cylinder might work for a flat/opposed 4 cylinder, but not an effective design for an inline four cylinder, too many issues arise from such a design.

 

For an inline 6 cylinder, forget it! bang-bang-bang-pause-pause-pause-bang-bang-bang-pause-pause-pause-bang-bang-bang-pause-pause-pause...

Or;

bang-pause-bang-bang-pause-pause-bang-pause-bang-bang-pause-pause-bang-pause-bang-bang-pause-pause....

 

 

Summation;

For the inline 4 cylinder, with the conventional up-down-down-up crank, it is a lose, lose scenario. With an up-up-up-up configuration, the rocking couple induced by firing pulses would be eliminated, but to a MUCH larger degree, harshness and buzziness would be gained. Inline 6 cylinder?... that is a submarines screen door!

[MAG58]

Yamaha did this for a big bang solution... And yeah, it sounds terrible imo.

[BRAAP]

Yamaha did this for a big bang solution... And yeah, it sounds terrible imo.

 

Ahhh, a Dual plane crank for a inline 4 cylinder, using the same pin config as the domestic, Japanese, German production V-8's. First and last crank throws are 180 degree out from each other, middle two are 180 degrees out from each other but 90 degrees out from the first and last, i.e. dual/cross plane design.

 

 

Firing pulses are not evenly spaced, but none are shared at the same time. Firing pulses are spaced/sequenced just like either bank of a V-8 and the dual plane design rids the engine of the 2nd order harmonic inherent in a typical single plane crankshaft, which is why it is so common in V-8s, especially in larger displacements. Smoother running, less vibes.

In my DIY crankshaft thread has quite a bit of discussion regarding the second order harmonic and the influences that exaggerate it, that are inherent with single plane crankshafts used in inline and V-8 applications vs dual plane, post #75 & #80 cover it pretty well.

Edited January 28, 2010 by BRAAP

[MAG58]

Actually, the cross plane idea in motorbikes has little to do at all with harmonics (the cranks only have a 56mm stroke as it stands)... All to do with power delivery

 

Will "Big Bang" Engines Come To The Street?

 

By Alex Edge

 

If you've been following technical developements in MotoGP for a while, you've certainly heard about the "big bang" engines. The "big bang" concept - which is basically a change in the firing interval of the cylinders - was originally developed back in the days of 500cc two-stroke GP bikes, and has recently been applied by both Yamaha and Kawasaki on their inline-four MotoGP engines.

A standard inline-four fires its cylinders at regular intervals - one cylinder every 180 degrees of crank rotation. This creates a constant delivery of power to the rear wheel, which can make it difficult to maintain rear-tire traction, or to regain said traction once it has been lost via wheelspin. Since this effect becomes more pronounced as power output increases, it is especially noticeable in current Superbikes (many putting out 200+ horsepower) and MotoGP bikes (220-250 horsepower).

Years ago, Superbike racers discovered that it was easier to modulate the power to prevent wheelspin on the Ducati V-twins than it was to do the same on the Japanese inline-fours. This is because there is a longer interval (in terms of both time and crankshaft rotation) between cylinders firing, which gives the rear tire a "break" - time to recover traction and match its speed to that of the motorcycle.

The "big bang" engine attempts to transfer this characteristic to the inline-four by changing the firing intervals of the cylinders. By firing two cylinders close together, followed by a long break, then the other two cylinders in close succession, then another long break before the cycle begins, a "big bang" motor gives the tire some recovery time. This gives enormous benefits to rideability and tire wear.

The disadvantage is that these uneven firing intervals throw off the balance of the motor, creating excess vibration that can be damaging to the bike and annoying to the rider. The life span of the motor's internal components is also affected, since there are now effectively two large power pulses per power cycle instead of four smaller ones. To get an idea of how this will affect the durability of the motor, just walk over to the nearest glass window and knock on it lightly four times. Now knock on it twice as hard, two times. See what I mean?

These negative affects can be counteracted, however. Stronger internals will resist the bigger power pulses, and a balance shaft can dampen the excessive vibrations - although balance shafts create parasitic losses that sap horsepower.

Recently we have seen reports that Virgin Yamaha is using a "big bang" firing order on its Yamaha R1 race bikes in the British Superbike Championship. This is the first we've heard of the "big bang" in a road-based bike, rather than the pure racing prototypes of MotoGP. Hearing about the Virgin R1, we started to wonder if the "big bang" design will ever make it into a production inline-four streetbike.

As the power output of modern 1000cc sportbikes climbs to ever more ridiculous heights, rideability will start to become the deciding factor for many potential buyers (hopefully it already is!). If a production inline-four 1000cc from one of the Japanese "big four" were to be redesigned to utilize the "big bang" firing order, it could dominate the category by allowing more of its excessive power to be safely used on the streets.

Our bet on which manufacturer will be first to debut a "big bang" streetbike lies with Yamaha. They have a tradition of thinking outside the box (a 400cc four-stroke motocross bike!), and they have already been using the "big bang" design since last season in MotoGP. Seeing a private race team like Virgin Yamaha using it in an R1 might be just the inspiration Yamaha's engineers need!

 

 

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[BRAAP]

Currently, I do not subscribe to the theory of fewer yet harder pulses being easier on the tire, as it is currently described/proposed. Logic says it should be harsher and more aggressive, not as easy to manage.

I'm not saying what is being claimed by these bike magazines, etc are false, but I am a bit skeptical of how they are interpreting the results and what they are attributing those results of improvement to, i.e. smoother application of power, less tire wear etc.

 

Momentum and stored energy from flywheel effect of a heavier crankshaft could be playing a major part in this as could other design changes that affect "how" the power is being produced and those affects could very well be responsible for the smoother power deliver, and somehow the magazine writers could be incorrectly linking those benefits to the revised firing pulses?!?! (HotRod magazines have misinterpreted and spread many a engine-building myth since those magazines became available, as such I am bit gun shy of such claims that don't seem add up 100%).

Dual plane cranks by design have MORE mass in the counterweights vs a single plane design due to balancing requirements, i.e. have more polar moment vs a comparable stroke length single plane crank, like a heavier flywheel. Note the massive counterweight cheeks on that dual plane Yamaha crank. That extra flywheel affect alone would help reduce tire wear and ease of power application as it absorbs the firing pulse energy to release it smoother, much like a heavier flywheel does in our cars.

 

The best analogy I can come up with is hitting a nail into a board. Not a very good analogy, its all I got off the top of my head.

Liken the traction available from a tire on the road to that of the friction of the nail going into the wood. As the nail is driven deeper, it is "losing" its traction each time, like a tire looses its traction.

 

Granted, this dual plane Yamaha crank is not firing 2 cylinders at the same time, they are still spread apart, just bunching the pairs closer toegether, bang-bang-pause-pause-bang-bang-pause-pause... so technically my analogy is not a direct carry over, but based on my interpretation of how and why the benefits are being proposed, this analogy mostly fits their description.

 

Using a hammer hitting with the same velocity every strike, (same energy being input into the nail) hit it twice simulating two power pulses at a level that just breaks traction and the nail drives slightly deeper with each hit.

 

Now with the nail at the same depth as before, hit it only once but with twice the forced simulating two power pulses delivered at the same time, it will drive the nail deeper than the two smaller blows did, i.e. traction loss was more severe. Again, this analogy is not exactly as the Yamaha dual plane crank delivers it power, but it does follow the "reasoning" as used in the claims being touted by many bike magazines currently.

 

 

 

I do want to make it clear that I am not saying they are wrong and that I am right, but until I see more substantial logical supportive evidence showing how and why, I am skeptical of the claimed reasoning behind how those improvements are being had.

Edited January 28, 2010 by BRAAP
Clarifications.

[ktm]

Bike engines spin at much higher rpms than a typical v8 or L6. It may work in a high rpm application. The high Tom's will help to smooth out the delivery would it not?

[hunterzed]

Ducati have changed their engine from a screamer configuration to the 'BIG BANG' setup that everyone is talking about. It has to do with the balance of the bike in relation to getting the power to the ground when leaning over in the turns. As you can probably guess there is a very fine balancing act for motorbikes between when and how the power is delivered compared to the lean angle of the bike. If you can get the power down smoothly then you can start to power the bike up earlier when exiting corners. Ducati are going back to the double pulse configuration which is like having 2 V-twins bolted togeter with 2 cylinders firing at the same time as each other but I don't know about the spacing between firing of opposing pairs. There are benefits for something that is as light as a motorbike where just pushing your leg out to the side changes the roll center. However they are not doing this to gain more torque or power. They are only doing this to change the way the power is delivered and as Paul has said there are no tangible benefits to doing this in a vehicle as heavy as a car where the engine alone is nearly as heavy as a complete motorbike. Just my 2 cents.

[Tony D]

In a ZCar.com moment, I will add "no man, that's wasted-spark you're talking about!"

[Flexicoker]

ya, the giving the tire time to 'recover' argument is ridiculous.

 

To paraphrase the article I posted before... you've got a signal, which is the power generated by combustion, and the noise, which is inertia torque. At high RPMs inertial loads dominate, and this creates alot of 'noise' in the torque seen by the tire. So 2 big bangs, or 4 smaller bangs should have the same average power output, so the signal is staying roughly the same. The inertia torque (noise) however, is significantly reduced. Note that inertia torque is different than vibrations that may occur in the engine, and apparently the big bang motors have more vibration than the screamers. Also, with larger peak torque pulses, the internal engine components will also have to be stronger. So its a not win-win scenario, just a better compromise in some cases.

[johnc]

Regardless of the "theory" behind the success of the odd fire race bike engines, you can't argue with the lap time improvements.