Wasted spark ignitions

[Parksy]

Hi all

I was planning on running a wasted spark system on my v4, but I may have issues with this. The plan was to run a dual output coil on each bank with 2 sensors on a wheel located on each camshaft. So both spark plugs running off the one coil on each bank.
But I've realised that there is a possibility of while one cylinder is firing, the wasted spark on the other cylinder will be while it has completed the downward intake stroke and will have a chamber full of air and fuel. The intake valve will also still be open slightly. Is this a bad thing?

Andrew

 

[kadora]

Parksy
vasted spark ignition fires during compression stroke before TDC
and during exhaust stroke before TDC.
"spark while it has completed the downward intake stroke " is bad thing
you can damage con rod or crank + fire will escape throug carburaror.

 

[Charles Lamont]

Hi all

I was planning on running a wasted spark system on my v4
[ ]
But I've realised that there is a possibility of while one cylinder is firing, the wasted spark on the other cylinder will be while it has completed the downward intake stroke and will have a chamber full of air and fuel. The intake valve will also still be open slightly. Is this a bad thing?

Andrew

Probably. A wasted spark system is mostly for 360° twins.

 

[kuhncw]

Parksy,

I built a Bob Shores Silver Bullet and modified the crankshaft so that one piston is at TDC when the other is at BDC. The original design had both pistons at TDC at the same time. I have two magnets on a disc driven by the cam. The magnets are 90 degrees apart and trigger a Hall sensor. Cylinder #2 fires 180 crank degrees after #1 fires. I'm waste firing the engine and always firing into the intake stroke on one of the cylinders. The engine runs well and I've had no problem with this setup.

Chuck

 

[makila]

Parksy,

Wasted spark arrangements were common in many 4 cylinder motor cycles during the 70s-90s and probably still use this method. My motorcycle had 2 coils supplying the HT for 4 plugs where the wasted spark occurred at 360 crankshaft degrees with no issues at all. The arrangement was for nos 1 and 4 cylinders to spark as a pair, and nos 2 and 3 cylinders to spark as a pair, as long as the wasted spark occurs at about TDC - but not at 90 - 180 degrees of crankshaft rotation or something as you might have issues.

Therefore you will have no issues as the wasted spark should occur at the non firing cylinder at 360 degrees from the firing one. It was good for my bike running up to a 10,000 RPM red-line!
So no reason why it should not work as you suggested using 2 coils for 4 cylinders.

Steve

 

[Parksy]

Thanks all for your responses, I appreciate it a lot.

Chuck, it's very interesting that your setup works that way. I may have to run it that way, or spend more money and have four individual sensors, or make a distributor.

Steve, unfortunately due to the v bank angle and the crankshaft setup, I'll never be able to have the wasted spark firing 360 degrees on the non firing cylinder. The banks are 180 degrees apart, or if I choose to spark on opposite sides of the v it's 270 degrees or 90 degrees apart.

If anyone has any good fool proof methods, I'd appreciate it.

 

[gbritnell]

Parksy,
Here's a video link to my 90 degree V-twin with a wasted spark ignition. I use one magnet and two window openings in my timing disc. Normally the wasted spark hits on the exhaust cycle but it can't on a V type engine so it sparks partly on the intake stroke but being as there is no compression the mixture won't ignite. It was used on V type motorcycle engines for years.
gbritnell
https://youtu.be/FTtyO_voUU0

 

[Parksy]

Thank you Gbritnell

Are you able to provide further details on your V-twin? When you say you run one magnet with two window openings, does this mean you have two sensors?

I'm fairly confident I have this sorted now. Instead of treating each bank as a seperate engine, I'll have two sparks firing on opposite corners, this way they are 270 degrees apart, not 180(longer dwell also if I ever run into that issue). I believe the wasted spark on the non firing cylinder will only just be starting it's intake stroke.

 

[Hopper]

Sounds like you are on the right track.
Harley engines (45 degree V twin) still use a wasted spark ignition as standard. At idle, full ignition retard, when the front cylinder fires at (nominal) TDC on compression stroke, the rear cylinder is 45BTDC on the exhaust stroke. But when the rear cylinder fires at (nominal) TDC, the front cylinder is also sparked at 45 degrees after TDC on the intake stroke. It has worked for well over 100 years so far.

 

[Parksy]

Sounds like you are on the right track.
Harley engines (45 degree V twin) still use a wasted spark ignition as standard. At idle, full ignition retard, when the front cylinder fires at (nominal) TDC on compression stroke, the rear cylinder is 45BTDC on the exhaust stroke. But when the rear cylinder fires at (nominal) TDC, the front cylinder is also sparked at 45 degrees after TDC on the intake stroke. It has worked for well over 100 years so far.

Perfect! Thanks for sharing this.

I did a lot of googling and all the articles I found regarding wasted spark ignitions only spoke of 360 degree systems and nothing else.

Cheers

 

[gbritnell]

Parksy,
Attached are several pictures of my V-twin ignition setup. The only thing that's different is the timing disc is made from steel instead of brass. Brass won't work.
gbritnell

 

[Parksy]

Now that makes sense. Thanks Gbritnell.

I was going to ask if the second cylinder fires 270 degrees from the first cylinder? So your gap is 135 degrees?

 

[Hopper]

Oops, just realized I got my after and before TDC erse about in previous Harley post. Of course, when the rear piston is at TDC, the front pistion is still 45 degrees BTDC and so forth. Makes no difference to the viability of wasted spark though.