Wasted Sparks VS Sequential Spark

[1jzracing]

UPDATE#2

On the weekend my car turned 876RWHP, wasted spark setup on my 2JZGTE, with STANDARD TOYOTA coil packs driven by an Autronic CDI ignition system.

As before, it goes to show how good factory Toyota coil packs are in conjunction with a decent ignition system.

cheers
Jo

thats pretty impressive power!!

what sort of rpm and boost do you have to use?

any chance of a little rundown on your setup? fuel, ecu turbo etc

no secrets just the basics, cheers

oh .. to stay on topic.... it makes no difference,
more a case of what best suits your hardware combonation, cdi will always be better for high boost either way

[stradlater]

Something to consider, I know it's not in many peoples cases, but with LPG, wasted spark is a fair no-no, because of the gas floating around in the non-compression cylinder that gets fired.

Many a bad backfire/frontfire has been caused by thus...

[fixeruperer]

wasted spark is useless sequential spark is always gonna turn up on time and not fuk around, with wasted spark it rather just have a few cones and plod along.

[Billzilla]

COP is good for everything, though wasted spark can sometimes make a little more power on forced induction engines.

[thechuckster]

A sequential setup will have more time for the coil windings to charge and will have more time between ignition fires to cool over a wasted spark setup witch will fire twice in the same cycle and have half the amount of time to cool down.

que?? - modern transformer coils take anywhere from 3-5 milliseconds to charge and no more than 1 millisecond to discharge - any longer and all you do is heat up the coil and loose spark energy as you start to increase the secondary winding resistance (from the heat).

You have an arseload more than 6 milliseconds between each ignition event in a 6cyl and a waste spark pack will not fire the same coil twice in succession anyway so the increased charging time argument is bogus.

Sequential spark makes your engine management more difficult because you have to keep spark control constantly in sync with two sensors (cam & crank) instead of just a crank sensor. One erroneous signal and you have to drop back to waste-spark mode until the ECU re-syncs.

[BlackSupra]

my 7m with factory toyota coils and factory nissan RB26 ignitor, running wasted spark pulled 500rwhp on pump fuel.

Once again, is it perhaps all in the tune?

[cambelt]

And all cop coils are unreliable compared with wasted spark coils that never seem to die, (toyota)
Dave

[GasedT18]

Hi All,

while a lot of your discussion is over my head it was interesting to see the antilag and LPG issues raised. I'm new to all of this so if you could please take this into account.

I'd like, eventually, after I've done my homework and saved $$$$'s, to have a crack at running LPG on the twinspark 3TGTE (got one last week - sitting on a crate). As I understand it the period between sparks is built into the dizzy as offset between rotors. The engineering intention as I understand it is to reduce emissions by more complete combustion of residual fuel. It has however crossed my mind, as Shinybluesteel mentioned, that any additional burning of residual fuel may increase exhaust pressure &/or temperature and may provide more boost. How much I have know idea. As I understand it LPG burns more completely than petrol.

Also where does the 'waste' spark occur in the cycle - does the second spark follow very shortly after the first in the compression/power stroke or somewhere on the exhaust stroke? I haven't pulled my dizzy apart yet.

I have also had concerns in figuring out how to prevent possible frontfire as Stradlater has mentioned. Having a plenum/intercooler blow to bits (even with blow through set-up) has crossed my mind as have various design methods to stop it.

This may have passed me by in the previous discussions, but what ECU/Ignition set-ups might allow variation in the timing between the sparks in the same cylinder, i.e., the electrical equivalent of being able to vary the offset between the two dizzy rotors?

Lastly, I would like the opportunity to run propane from time to time but will be limited to the vagueries of LPG 'blends' most of the time. I may also keep the option open for petrol.

Given all of the above what brand and model ECU would you recommend and what ignition system would you recommend?

I hope I haven't said anything that has got you rolling your eyes or ROTFL

Cheers

David

[6_SPEED]

thats pretty impressive power!!

what sort of rpm and boost do you have to use?

any chance of a little rundown on your setup? fuel, ecu turbo etc

no secrets just the basics, cheers

oh .. to stay on topic.... it makes no difference,
more a case of what best suits your hardware combonation, cdi will always be better for high boost either way

Motor: built 2JZGTE
Rpm: 8500
Fuel: VP C16
Injectors: Bosch 1600cc
Boost: 35psi
Power: 653rwkw - 876rwhp
Turbo: J&J Custom spec
ECU: Autronic SM2 & CDI
Stock Toyota Coil Packs

[stradlater]

Yeah, but there's a small thing of the fuel there mate. Of course c16 is going to be easier on ignition systems, it's more volatile.

[Norbie]

Nope. Higher octane = less volatile, which is the reason it's less prone to detonation.

[stradlater]

yes, but it's easier for the spark plug to ignite. Agreed on the octane thing though, my mistake.

[thechuckster]

Also where does the 'waste' spark occur in the cycle - does the second spark follow very shortly after the first in the compression/power stroke or somewhere on the exhaust stroke? I haven't pulled my dizzy apart yet.

two cyls fire at the same time

the pistons for each pair of cylinders firing will be at the same position in the bore but their cam phasing will be 180 degrees apart. In terms of combustion cycle rotation, they will be 360 degrees apart (because a 4-stroke combustion cycle is two revolutions of the crankshaft).

one will be full of air+fuel ready to spark at anywhere from 40 to 10 degrees BTDC, the other will be near the end of the exhaust stroke where burnt gasses are being pushed out of the zorst valve.

The ready-to-fire cylinder easily sparks and the burnt-gasses cylinder has a high resistance across the spark gap so it only gets a weak spark.

Personally, i cant see how this setup (waste-spark) would destroy an LPG intake manifold as the weak-spark cylinder is only open to the zorst. If anything, you'll either spin up the turbo or damage it if you have an explosive combustion event with the zorst valve open.

[YelloRolla]

As I understand it the period between sparks is built into the dizzy as offset between rotors. The engineering intention as I understand it is to reduce emissions by more complete combustion of residual fuel. It has however crossed my mind, as Shinybluesteel mentioned, that any additional burning of residual fuel may increase exhaust pressure &/or temperature and may provide more boost. How much I have know idea. As I understand it LPG burns more completely than petrol.

There is no period between sparks, they fire at exactly the same time - I have personally tested this with a timing light. The reason for 2 spark plugs is more complete combustion - more likely due to the combustion space not being very efficient (so add twice the spark energy).

Also where does the 'waste' spark occur in the cycle - does the second spark follow very shortly after the first in the compression/power stroke or somewhere on the exhaust stroke? I haven't pulled my dizzy apart yet.

The wasted spark usually occurs at approx TDC at the end of the exhaust stroke ie # 4 wasted spark on your 3TGTE (if you were to run a wasted spark set up) would occur at the same time as # 1 firing spark.

I have also had concerns in figuring out how to prevent possible frontfire as Stradlater has mentioned. Having a plenum/intercooler blow to bits (even with blow through set-up) has crossed my mind as have various design methods to stop it.

Use EFI - there will be no fuel in the plenum and the should NEVER be ANY FUEL in the intercooler. A pop off valve or burst plate will stop things blowing up should you go the blow through method.

I hope I haven't said anything that has got you rolling your eyes or ROTFL

Cheers

David

well not too much.

Now for an on topic reply - I use 3.5ms dwell time. The coils might stay cooler if they are not being used in a wasted spark system, but the amount of heat generated by "on time" is most likely insignificant when compared to engine bay heat and coils sitting on the cylinder head.

I also think that it has been well demonstrated by 6SPEED and Blacksupra that wasted spark set ups are able to supply spark energy to make lots of power.

The benefits for and against must then come back to intended purpose.

[30psi 4agte]

que?? - modern transformer coils take anywhere from 3-5 milliseconds to charge and no more than 1 millisecond to discharge - any longer and all you do is heat up the coil and loose spark energy as you start to increase the secondary winding resistance (from the heat).

You have an arseload more than 6 milliseconds between each ignition event in a 6cyl and a waste spark pack will not fire the same coil twice in succession anyway so the increased charging time argument is bogus.
the ECU re-syncs.

I think you are taking me out of context here.I didnt mean that you can run more charge time ( dwell )for the but meant the time between being charged and dissapated is greater.

correct me if im wrong but a coil will fire once on the ignition stroke on cyl 1and at the same time on exhaust stroke on cyl 4
It will then fire on the ignition stroke of cyl 4 and at the same time the exhaust stroke of cyl 1
This all happens in 1 complete cycle of the combustion engine. (suck squeeze bang blow)

So the coil will fire twice per combustion cycle ????? It may not be in succession but it is twice the amount of time a sequential setup. Hence less work load for the coils.