MicroSquirt.com read only forum (Jan.15,2018)

I think you will find that the firing sequence for a Ducati V-twin is that after the rear cylinder fires the front cylinder fires 270 degrees of crankshaft later and then the rear cylinder fires again another 450 degrees later. I hope this is of some help.

Paul

Paul_H wrote:I think you will find that the firing sequence for a Ducati V-twin is that after the rear cylinder fires the front cylinder fires 270 degrees of crankshaft later and then the rear cylinder fires again another 450 degrees later. I hope this is of some help.

Paul

I think you skipped one firing of the rear, or, at least, this sequence does. Wouldn't it be Fire 1 (270) Fire 2 (90) Fire 1 (270) Fire 2 (90) ...?

The rear cylinder would fire 450 degrees after the front, but that would be the second time, the first time would be 90 degrees after the front, since each cylinder must fire every 360 degrees.

The engine has a 90 degree angle between the cylinders and the conrods share a common crank pin. The engine rotates in a clockwise direction when viewed from the primary drive side of the engine ( some people refer to this as running backwards). When the rear cylinder is at TDC on the compression stroke, the front cylinder is at 90 degrees past TDC on its intake stroke. 270 degrees of crankshaft rotation later the front cylinder is at TDC on compression and the rear cylinder is on its exhaust stroke approaching valve overlap. And so it continues, hence there is a firing event on each cylinder once every 720 degrees of crankshaft rotation.

OK. But isn't this a wasted spark setup? I was under the impression that it was being run w/o a cam sensor.

No, that is just how a four stroke IC engine works. What makes it a bit weird to deal with is the odd firing angle. Whether it is wasted spark or not will depend on how and where you setup and configure your triggers.

I think we're not communicating well here. I am talking, among other things, about how the triggers are set up.

I understand how four stroke engines work. Each cylinder will have a power stroke once every 720 degrees. To fire ignition once every 720 degrees correctly you need to know where the cam is. In this particular setup, I was under the impression that only a crank sensor was being used. If that is in fact the case, each cylinder needs to be fired every 360 degrees, because the ECU will not be able to tell when the cylinder is at the top of compression versus when it is at the top of exhaust. By firing once per rev you'd still be "wasting" every other spark.

Matt,I think you should check your mechanical setup first. Ifyou want your tach input to occur 15 degrees BTDC make sure that this happens on the first tooth after the missing teeth when the rear cylinder is on compression and wire output #1 to the coil for this cylinder. Then set your trigger offset in MT to -345 degrees. Because you are skipping 24 teeth this means that another tach event is happening approximately 360 crankshaft degrees later and this will trigger output #2 which will be wired to the coil for the front cylinder. But because compression on the front cylinder occurs 270 degrees after compression on the rear cylinder, you have already gone 90 degrees past where you need to be. So you need to shift the trigger back by 90 degrees by applying -90 degrees in the advance offset for #2 output. The same initial trigger offset will apply to both cylinders because it is determined by the physical setup. This is only how I think it is designed to work and I hope that it does not serve to confuse the situation further.

Paul,

My mechanical set up is as follows:

Cylinder 1= horizontal cylinder

TDC compression stroke occurs on cylinder one ( the sensor is in the gap) and then 15 crank degrees later the first tooth after the gap is lined up with the sensor. 630 ( 720-90) crank degrees later cylinder two is at tdc compression stroke. There is one cam sensor and no crank sensor.

I guess that it would be easier to switch the wiring for cylinders. My original thought was to use the horizontal cylinder as cylinder one because it lined up with the missing teeth. The new configuration would then look like this.

Vertical cylinder = cylinder 1

delay teeth =36 trigger offset = 15 degrees offset for cylinder 2= -90 degrees

Now TDC CS occurs on cylinder one after 3 teeth + 15 degrees and 90 degrees later cylinder 2 is at TDC CS.

I think that this set up makes much more sense. I will switch the wiring while I am waiting for my new coils to arrive.

Let me know how this sounds.

Matt, when the horizontal (front) cylinder is at TDC compression, the vertical (rear) cylinder is at 90 degrees BTDC on its exhaust stroke. So the vertical cylinder can not possibly be at TDC compression 630 degrees of crank rotation after the horizontal cylinder has been at TDC compression. Anyway, moving on. From what you have said in your previous post, tach1 is setup to occur 15 degrees ATDC of the horizontal cylinder on compression. I think you should try staying with this configuration and changing your trigger offset in MT to -15 degrees and and set the advance offset for #2 output to +90 degrees. Iam on the same learning curve as you so I'd be interested to know if this actually makes an improvement.

Paul,

I am going to have to disagree with you on the cylinder timing. I definitely know that cylinder 2 Vertical is at tdc 90 degrees before cylinder 1. A very easy test shows this. All I had to do was bring the horizontal cylinder to tdc by lining up the mark on the flywheel with the pointer on the stator. It can be confirmed that cylinder 1 is at tdc by sticking a small object like a screw driver in the spark plug hole and physically feeling the piston. Next I rotated the engine clockwise looking at the flywheel cover( which is backwards for this engine) and 90 crank degrees later cylinder 2 is at tdc 9 again this was checked with a screw driver). Since this engine is a 90 degree oddfire the pistons have to be on the same stroke. ( I know that that isn't always true but comp on 1 imead follows comp on 2.)

Paul_H wrote:From what you have said in your previous post, tach1 is setup to occur 15 degrees ATDC of the horizontal cylinder on compression. I think you should try staying with this configuration and changing your trigger offset in MT to -15 degrees and and set the advance offset for #2 output to +90 degrees. Iam on the same learning curve as you so I'd be interested to know if this actually makes an improvement.

I Already have my trigger offset set to -15 degrees and in the mega manual " For dual spark mode we always want a negative trigger offset, so you would use -320° instead of +40°." This makes me think the trigger deff should be negitive.