Which plug takes more energy to fire in a boosted engine, the leading or the trailing?

 

Anyone?

 

Using just what I've learned from working in the field, I'd assume there would be more energy *required* to fire the leading. Reason being is because at the 5deg ATDC, there is more compression in the chamber, therefore more resistance to overcome. Sounds retarded, but it's really the truth. Shoot, just by looking at an ignition scope (which shows kilovolts being discharged from a coil) I can tell if an engine has a compression problem because the kv's will be lower on the hurt combustion chamber.

On the other hand, there could be more energy fired through the trailing in order to clean up what the leading did not combust.

I don't believe that the combustion inside the chamber would have time to fill the whole area with pressure by the time it hits 20deg ATDC, thus making a high energy spark necessary.

I suggest looking at the scope pattern on your car if you have access to an ignition scope, or at least try to find someone who can do it for you.

 

the leading, the compressed a/f mix is harder to detonate than raw unburnt fuel after main combustion occurs. Just theory i'm going on here.

 

Thanks for the input guys.

 

Wouldn't there be more pressure in the chamber after the charge was fired. Don't trailing plugs come with less gap?

 

that could be also, but i think because the oxygen would be pretty much gone from the combustion chamber, that it would be burning pretty much just the left unburnt fuel, basically resulting in a very rich condition. The amount of oxy to air would be a lot less, so i think it would be easier to fire on the trailing end.

 

The more I think about it the more I think they are the same, or maybe alittle more for leading because it fires two plugs.

 

The leading requires the biggest *****. Leading has to combust the main majority of the air fuel mixture and makes the majority of the power, its a bigger strain on the ignition. By the time trailing fires its basically burning off the excess that the leading didnt combust.

If you want to get an idea of the strain our plugs and ignition system have, think of a V8 making 800 hp at the crank, each plug is combusting 100hp worth of air and fuel. On a 800hp rotary your leading is making at least 80-100% of the power which is 320-400hp worth of air and fuel per leading plug. Thats equal to the strain of a 2500-3200hp V8 lol. Hell, even if you ran no timing split where all 4 plugs fired together that would still be 2x the strain that a V8 sees on its ignition. Not to mention its actually even more than that because the rotary is typically around 20% less efficient than a good V8 so it takes 20% more fuel for the same power. So a 800hp rotary is combusting the same a/f as a 1000hp v8

Anyway, if you want to make big power and if you want to run some meth (like you were saying you want to do) then you need to have a good ignition setup.

 

This may be getting away from the question at hand. Even though I agree that the leading ignition sytem does nearly all the work and should be where the upgrades go, how about this?

If you had two 40kV coils firing the same type of plugs through the same resistance wires. 1 leading and 1 trailing. Then you indepently gapped the plugs bigger and bigger until they stopped firing. Then you went back to the gap that still could fire. The gaps would show where the biggest ignition demand is. But, wouldn't the energy spent by each be the nearly same?

 

Im not sure I follow you but for the most part being able to jump the gap is more a function of having enough amp. I think if you kept on making the gap larger and larger till the spark wouldnt jump that would tell you more about the strengh of the amp than how well its combusting the mixture. I suppose at some point you run into a situation where the spark gets "blown out" which really just means you didnt have enough amp to jump the gap in the given conditions.

Actually all you have to do if you want to see which conbusts the most mixture is disconnect the trailing and see how the car runs, then disconnect the leading and see how the car runs lol. That will tell you which is doing the majority of the work. When that leading plug fires it will combust a vast majority of the a/f, most people dont fire the trailing till 8-15 degrees later which is really a pretty long time. To me, based on seeing cars on the dyno with the trailing not working then comparing those results to the dyno with leading and trailing working Ive come to the conclusion that leading is doing about 80% of the combustion. Of course, Im sure that changes as the timing split gets less and less and the 2 start to fire closer together.