ignition mapping-dizzy vs wasted spark
Discussion
hi folks.i wonder if you could help a numpty on a steep learning curve make a decision.ive modified my griff 500 and im going to fit an aftermarket ecu(omex probably)so that both the fuel and ignition can be mapped.ive pretty much decided to stay with banked injection,but cant forsee how far ill go with the ignition.in order to choose my ecu i need to decide weather ill want to go further than mapping through the dizzy,ie wasted spark,or even coil per plug(almost certainly not the latter).assuming you use a crankwheel sensor for the dizzy based system input,then what are the main advantages of wasted spark over the dizzy.is it just a quicker reaction to timing change,or is there more?im also a little concerned by some of the things ive heard about wasted spark causing combustion whan its not required,or is this more to do with forced induction set-ups?someone please educate me!cheers,mike v.
I'm interested to hear what the experts have to say on this one. One difference is that the multi coil system gives you more 'dwell' at the top end which could enable a stronger spark. Another is that wasted spark gives you a wasted spark (duh) at the end of the exhaust stroke, which in some situations may occur while the inlet valve is open. Inlet manifold full of warmed compressed (for a forced induction setup) air/fuel mixture plus spark may not be such a good idea?
I used to run a dizzy based map system then moved to a wasted spark , 4 coils set-up on my V8. Gave a big improvment in the amount of mid- range / part throttle torque as I could run the amount of spark advance required not the maximum dictated by the ' window' in the dizzy ( aboout 32°). Also you get a fatter spark and more accurate timing so you can run closer to the limit with encountering detonation.
So in summary: more power, better fuel consumption, better control and better starting
other than that not worth it
Matt
So in summary: more power, better fuel consumption, better control and better starting
other than that not worth it
Matt
Running a dizzy is not wasted spark. It simply means using a single coil firing to operate all 8 cylinders, one at a time, via the distributor.
If you are using the ecu to control ignition, there will be no timing scatter. The dizzy no longer has control over the timing. It simply distributes the spark to the relevant cylinder.
Usually you would weld up the advance mech inside and ensure the rotor arm points in the correct place, for firing each cylinder..
Using anything more than 1 coil, and less than 8 coils would be a wasted spark system.
Example, 4 double ended coils, that fire pairs together. You would have to fire a spark on a cylinder that wasnt on a firing stroke, in order to also fire a spark on a cylinder that was on firing stroke.
Not all multicoil systems are better. There is such a wide variety of high power coils etc for single coil/dizzy applications, that power/performance isnt an issue. And unless you actually need more ignition power, its almost a waste of money to change.
Perhaps in a 8000rpm+, multi coils do take over with obvious advantages.
Using sme wasted spark coil packs, can make ign lead routing tricky, depending on what pairs fire together.
Using 8 coils can make this neater.
Using the dizzy can either be messy, or neat.
On an RV8 with 4 double ended coils, you would fire these cylinders together wasted spark
1+6
8+5
4+7
3+2
Im not sure about the Omex, but my DTA P8Pro can fire up to 8 individual coils.
I paired them in a wasted/twin spark setup, for an 8 coil system although they fire in pairs. I had to do this, as I did not use a cam sensor, so the ecu has no recognition for No1 TDC.
So although Im using 8 outputs, they may as well be 4/wasted.
I used a 36-1 crank trigger only, group fire.
If you are using the ecu to control ignition, there will be no timing scatter. The dizzy no longer has control over the timing. It simply distributes the spark to the relevant cylinder.
Usually you would weld up the advance mech inside and ensure the rotor arm points in the correct place, for firing each cylinder..
Using anything more than 1 coil, and less than 8 coils would be a wasted spark system.
Example, 4 double ended coils, that fire pairs together. You would have to fire a spark on a cylinder that wasnt on a firing stroke, in order to also fire a spark on a cylinder that was on firing stroke.
Not all multicoil systems are better. There is such a wide variety of high power coils etc for single coil/dizzy applications, that power/performance isnt an issue. And unless you actually need more ignition power, its almost a waste of money to change.
Perhaps in a 8000rpm+, multi coils do take over with obvious advantages.
Using sme wasted spark coil packs, can make ign lead routing tricky, depending on what pairs fire together.
Using 8 coils can make this neater.
Using the dizzy can either be messy, or neat.
On an RV8 with 4 double ended coils, you would fire these cylinders together wasted spark
1+6
8+5
4+7
3+2
Im not sure about the Omex, but my DTA P8Pro can fire up to 8 individual coils.
I paired them in a wasted/twin spark setup, for an 8 coil system although they fire in pairs. I had to do this, as I did not use a cam sensor, so the ecu has no recognition for No1 TDC.
So although Im using 8 outputs, they may as well be 4/wasted.
I used a 36-1 crank trigger only, group fire.
GreenV8S said:
Another is that wasted spark gives you a wasted spark (duh) at the end of the exhaust stroke, which in some situations may occur while the inlet valve is open. Inlet manifold full of warmed compressed (for a forced induction setup) air/fuel mixture plus spark may not be such a good idea?
I too would like to know about this. Ignition timing is more retarded on boosted engines. But on a boosted engine should the valve opening events be shorter (and possibly later) than an nat-asp cam, and therefore ignition be much less likely to occur?
Seight... I adapted one of DTA's triggers to fit the front pulley, and made a bracket for the crank sensor.
As for the idea that a spark/ignition may occur when the inlet valve is open.
I think it would be under very very extreme circumstances such a thing might happen. Given virtually every modern turbocharged car runs wasted spark ( in fact virtually every modern car )
It would need a very wild camshaft and odd ign timing settings.
Given that blown engines dont need wild cams, and work better with milder cams, the inlet/ignition issue isnt something anyone should worry about.
>> Edited by stevieturbo on Friday 1st April 18:21
As for the idea that a spark/ignition may occur when the inlet valve is open.
I think it would be under very very extreme circumstances such a thing might happen. Given virtually every modern turbocharged car runs wasted spark ( in fact virtually every modern car )
It would need a very wild camshaft and odd ign timing settings.
Given that blown engines dont need wild cams, and work better with milder cams, the inlet/ignition issue isnt something anyone should worry about.
>> Edited by stevieturbo on Friday 1st April 18:21
Just had a nosey at the Emerald site... While it does relate mostly to 4cyl systems, it does give clear diagrams and write up about various control systems.
www.emeraldm3d.com/ems.htm
www.emeraldm3d.com/ems.htm
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