Dual fire sparking.

Any form of normally aspirated power mods.
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Dual fire sparking.

Post by boosted » Tue Dec 05, 2017 12:29 pm

So hypothethical question for the boffins to mull over...
So we know each chamber has 2 coils and 2 sparks..a leading and a trailing and the trailing fires a short while after the leading in order to complete the burn due to the large combustion area..
The coils are fired by there individual trigger from the pcm (ecu)..
So my Q is..on each housing link the leading and trailing triggers....and fire both sparks at same time for each housing...so 4 sparks in all..in 2 seperate goes slightly apart...more boom..more bang more power. Better bhp better mpg. Zoom zoom.
Would this be of benefit? And apart from the obvious killing of standard coils what would be detrimental...
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Last edited by boosted on Tue Dec 05, 2017 12:29 pm, edited 2 times in total.
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Re: Dual fire sparking.

Post by Phil Bate » Tue Dec 05, 2017 12:44 pm

That wouldn’t fit the desired pattern of combustion. The idea is the flame front progresses as the mixture rolls around with the rotor - remember it’s a smooth burn rather than an explosive bang ;)
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Re: Dual fire sparking.

Post by boosted » Tue Dec 05, 2017 12:44 pm

If this is a rotary revolution i claim all rights to idea....if however complete rubbish then i blame my cat, lack of sleep and general stupidness...i suspect the latter...lol

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Re: Dual fire sparking.

Post by boosted » Tue Dec 05, 2017 12:47 pm

Phil Bate wrote:That wouldn’t fit the desired pattern of combustion. The idea is the flame front progresses as the mixture rolls around with the rotor - remember it’s a smooth burn rather than an explosive bang ;)
I was watching 1 of those you tube animations and yes i agree...

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Re: Dual fire sparking.

Post by PeteH » Tue Dec 05, 2017 1:36 pm

Oooops, I've gone off on one again.....

The rotary has one crucial difference to a piston engine (well, it has lots, but for this idea it has one....);

On a piston engine the entire combustion chamber is at a single point in the combustion cycle. So you fire the spark plug at a known time ("x" before TDC).
On a rotary the combustion chamber is at a range of timings all at the same time (if you see what I mean). If you fire the trailing plug too early you apply a load to the rotor that it is not supposed to take, applying loads to the stationary gears that they won't like, and that will not produce efficient torque. You will also produce high combustion pressure in the trailing half of the combustion chamber, which cannot be relieved by the normal expansion cycle. In fact those combusted gasses will actually be forced into a smaller volume because that part of the rotor still has to pass the "neck" of the toroid. My guess is that you will blow the apex seals into the intake chamber.

We want all the combustion to take place on the expansion stroke (0deg to 270deg ATDC), where it can do useful work. The trailing plug just gives a kick to the rear part of the combustion chamber, late in the process, because without it the flame front can't reach the rear of the rotor before the exhaust port starts to open.

So, firing the trailing too early will be inefficient, will probably make the engine knock and vibrate, and will be bad for efficiency. Firing the trailing plug to late (or not at all) will make your exhaust louder, make the emissions terrible, and be bad for efficiency.

People get too hung up on sparks. Sparks are just the tiny bit of energy required to initiate the burn. The engine make its power because of the expansion of burning gasses. Bigger sparks don't make bigger burns, any more than a bigger match will make a bigger bonfire.....

We all know that detonation is bad for rotaries, and early firing of the trailing plug has exactly the same effect. Don't do it folks! [-X
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Re: Dual fire sparking.

Post by boosted » Tue Dec 05, 2017 1:49 pm

Lol just told the cat hes stupid and im off for nap!

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Re: Dual fire sparking.

Post by Vian » Tue Dec 05, 2017 10:54 pm

Why does my brain feel like it's been through a blender every time Pete posts?
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Re: Dual fire sparking.

Post by PeteH » Wed Dec 06, 2017 12:57 am

Brain smoothie. Yummy.

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Re: Dual fire sparking.

Post by geofftl1000r » Wed Dec 06, 2017 6:49 am

My knowledge of rotories just quadrupled 😅
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Re: Dual fire sparking.

Post by Clive » Wed Dec 06, 2017 8:38 am

I thought I would sit back on this one and see what people had to say as many years ago I carried out an on the ground experiment.

20 years ago we all really knew nothing about tuning Rotarys and its one of the reasons I set up Mazdarotaryclub,com which was a deliberate .com to try and attract overseas people with knowledge we at the time did not have!

One of the things that came up was that PAC Performance in Australia had solved its big power detonation issues by not running the trailing plugs.

I already knew that the NSU engine only ran one plug so it seemed feasible to try.

I made up a relay box whereby the trailing plugs could be turned of as soon as a sensor saw boost, which on my engine at the time was just over 3000 RPM.

We tuned the car at Abbey Motorsport in conventional Leading/ Trailing spark plug mode and with its fairly small GT35 turbo produced 380 BHP.

Once fully tuned I connected my relay box and told nobody what was going on and carried out another full power run.

We overlayed the previous run with the run with the trailing being turned off and staggeringly the car produced exactly the same power and not only that the power and torque curves were 100% identical !

As recently as last year, I found that one of the trailing plugs had stopped working on the race car and I hadn't noticed.

Make of this what you will but the above is fact rather than hypothetical and because of this I have always wondered why Mazda use this ignition set-up due to what I found.

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Re: Dual fire sparking.

Post by warpc0il » Wed Dec 06, 2017 9:38 am

Clive wrote:I thought I would sit back on this one and see what people had to say as many years ago I carried out an on the ground experiment.

20 years ago we all really knew nothing about tuning Rotarys and its one of the reasons I set up Mazdarotaryclub,com which was a deliberate .com to try and attract overseas people with knowledge we at the time did not have!

One of the things that came up was that PAC Performance in Australia had solved its big power detonation issues by not running the trailing plugs.

I already knew that the NSU engine only ran one plug so it seemed feasible to try.

I made up a relay box whereby the trailing plugs could be turned of as soon as a sensor saw boost, which on my engine at the time was just over 3000 RPM.

We tuned the car at Abbey Motorsport in conventional Leading/ Trailing spark plug mode and with its fairly small GT35 turbo produced 380 BHP.

Once fully tuned I connected my relay box and told nobody what was going on and carried out another full power run.

We overlayed the previous run with the run with the trailing being turned off and staggeringly the car produced exactly the same power and not only that the power and torque curves were 100% identical !

As recently as last year, I found that one of the trailing plugs had stopped working on the race car and I hadn't noticed.

Make of this what you will but the above is fact rather than hypothetical and because of this I have always wondered why Mazda use this ignition set-up due to what I found.
Our NSU Ro80 was originally had a 2 plug engine but when the rotor seals blew we tracked down another engine, this being one that had been built for the the factory rally team. The NSU rally team had been disbanded when the company was bought by Audi.

Anyway, this rally-spec engine was 4 plug and it took a while to find a matching distributor. Once fitted we found the new engine ran really strong and was quite a lot louder than the original, which we assumed was down to the extra plugs.

Having done more investigation since I'm now convinced that the rally engine had been ported. The extra plugs may have been associated with the revised port timing.

Mazda chose to use 4 plugs for a few reasons:
- the engine starts on just the one plug per rotor to reduce kick back
- the firing order of the plugs changes between idle and acceleration to provide a smooth transition.
- the trailing plug significantly reduces unburnt hydrocarbons in the exhaust.



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Re: Dual fire sparking.

Post by PeteH » Wed Dec 06, 2017 10:10 am

That makes sense Clive, and I've also read that in the US the drag racers often run without trailing plugs. In a race engine the emissions and noise don't matter. I think the efficiency loss is small at higher revs, and the protection from detonation seems important in very highly tuned engines.

We should also remember that Mazda used three plugs per chamber on the 26B. I think they did this to reduce fuel consumption. So a perfectly optimized multi-plug setup should (in theory) be slightly more efficient, if you have the time and facilities to set up all the timings perfectly so you don't risk det.
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Re: Dual fire sparking.

Post by warpc0il » Wed Dec 06, 2017 11:31 am

Some (slightly) related history that people might find interesting...

A few racing (piston) engines ran twin plugs per head and these were even used by Kawasaki in some of their performance bikes.

The theory is around flame-front management and getting as much of the mixture to burn in the shortest possible time.

I'd had long and detailed discussions on this with the engine development engineers at both Ford and Yamaha and they agreed that the benefits were barely detectable, compared with a good head design with a single central plug. This was the conclusion from testing with research and pre-production engines. There was a measurable difference with a twin-plug head with only one plug firing but this was down to the firing plug being offset.

They also did experiments to determine if the orientation of the earth electrode of the spark plug made any difference, as there was a lot of talk at the time about "flame-shading" and people were marking the outside of their plugs and tightening until the gap was facing the right way. I even remember seeing one guy in Halfolds opening all the boxes to find a plug that had the earth electrode in just the right place, in relation to the thread. Turns out that this was bollox and even in the most sensitive research engine they couldn't detect any difference in power; though over or under-tightened plugs could cause engine damage.

If the valve layout doesn't allow for a centralised plug then a twin-plug arrangement avoids having a pressure wave across the crown of the piston, which can make the piston rock and increase skirt wear and drag. Racing engines often run short-skirt pistons and shorter skirts are required with over-square bore/stroke engines.

The Yamaha guys were adamant that the Kawasaki production bike engines got no engineering gain from their twin-plugs and that it was more to do with customer perception and marketing. Eventually Kawasaki dropped the twin-plug layout because of servicing costs (8x spark plugs).

Some production bike use a "spare-spark" system where the single plug per cylinder is fired on both the ignition and exhaust strokes. People believed that this was to extract more power or clean-up emissions, though the true reason is much simpler. A 4-cylinder engine either needed a single coil and distributor, or four individual coils. Motorcycle engines rev too high for a single coil to fully charge between firing and the packaging and reliability of an exposed distributor is a problem, so bikes had one coil per cylinder. Some bright spark came up with the idea of a double secondary coil, so a single coil pack could fire two plugs at the same time - on the ignition cycle of one and the exhaust of another, then vise-versa. The dual-coil packs were cheaper than two single coil packs and fitted into a smaller space, so it really was just economics.

Aircraft engines commonly have twin-spark heads but this is about reliability rather than performance. There are usually two totally separate ignition systems, each firing one plug per head, to reduce single-points-of-failure.

I've been flying an aircraft when the MAG warning light came on to indicate that one of the magnetos had gone off-line and we were only firing on one plug per head. There was no decrease in power but a noticeable increase in buttock tension. Thankfully it was a deHavilland Dove and we also had two engines (4 magnetos).

Back to the RX8, I once "cured" a hot starting issue on a members car by swapping around the coil packs on the bracket. It was unclear if the dud coils were previously on the same rotor or both leading or both trailing, just that taking them off to check underneath and then replacing in a different order "cured" the problem - at least as a get-you-home fix. The more permanent fix was replacing the whole set with good used ones from someone upgrading on a Rotary Revs Group Buy.
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Re: Dual fire sparking.

Post by 350matt » Wed Dec 06, 2017 11:34 am

I'd say the rexi 2nd plug is mainly there to clean up the burn and improve emissions more than anything, what may be worth trying is multiple spark events though

so keep the initial spark timings the same so as not to induce det or upset the cycle but has 3 or 4 sparks on each plug after the initial event

MSD used to sell a multi-spark unit but I've never seen much advantage to them on a conventional engine but maybe on a rotary?

at work we're also using a multiple spark plug system on a conventional engine ( its a big bore) as its very helpful in cleaning up emissions but it does actually cost power on full load

also Mazda published that they are considering 'plasma' ignition on the RX9 engine ( if it ever happens)
now I'd hope that this is either the new very high energy systems that federal mogul have been developing or the turbulent jet injection system that F1 is using

http://www.federalmogul.com/en-US/OE/Ma ... ductId=224

http://www.mahle-powertrain.com/en/expe ... -ignition/


and on that note this system looks credible but no rotary test that I could see

http://www.ionfireignition.com/

however I suspect the amount of EMF it puts out may switch everything else off (including pacemakers)

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Re: Dual fire sparking.

Post by warpc0il » Wed Dec 06, 2017 11:42 am

350matt wrote:
Wed Dec 06, 2017 11:34 am
we're also using a multiple spark plug system on a conventional engine ( its a big bore) as its very helpful in cleaning up emissions but it does actually cost power on full load
The Yamaha guys noted a similar thing on their research engine. Multiple plugs create multiple flame fronts and they then produce less overall power than a single flame front - something to do with the interference between the pressure waves.
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Re: Dual fire sparking.

Post by boosted » Wed Dec 06, 2017 7:35 pm

My mother in laws 1.4 honda 2005 has 8 spark plugs i thought they were taking the p at the motorfactors.

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Re: Dual fire sparking.

Post by ChrisHolmes » Thu Dec 07, 2017 2:10 pm

I thought the same when Kathys 05 1.4 Jazz was serviced, still cheaper than 4 plugs for an RX-8!
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Re: Dual fire sparking.

Post by V8 Power » Thu Dec 07, 2017 6:49 pm

Some of the older Mercedes V8 engines have twin plugs. Imagine that having to replace 16 of the buggers!
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Re: Dual fire sparking.

Post by Azimuth » Fri Dec 08, 2017 8:10 am

350matt wrote:
Wed Dec 06, 2017 11:34 am
MSD used to sell a multi-spark unit but I've never seen much advantage to them on a conventional engine but maybe on a rotary?
Carl Ryan sells them. I'm getting a set sent over from the US to try on my 8.

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Re: Dual fire sparking.

Post by 350matt » Fri Dec 08, 2017 9:49 pm

V8 Power wrote:
Thu Dec 07, 2017 6:49 pm
Some of the older Mercedes V8 engines have twin plugs. Imagine that having to replace 16 of the buggers!
the V12 we're working on has 3 per cylinder.....

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Re: Dual fire sparking.

Post by 350matt » Fri Dec 08, 2017 9:49 pm

Azimuth wrote:
Fri Dec 08, 2017 8:10 am
350matt wrote:
Wed Dec 06, 2017 11:34 am
MSD used to sell a multi-spark unit but I've never seen much advantage to them on a conventional engine but maybe on a rotary?
Carl Ryan sells them. I'm getting a set sent over from the US to try on my 8.
does Carl have any evidence of the benefits?

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Re: Dual fire sparking.

Post by Azimuth » Sat Dec 09, 2017 1:27 pm

350matt wrote:
Fri Dec 08, 2017 9:49 pm
does Carl have any evidence of the benefits?
You would have to ask him. I understand he runs them himself.

I figure that it's an LS2 coil but a well known manufacturer, so should be at least as good as a d585 upgrade. The idle multi spark thing is a complete unknown to me but I don't see it could do any harm.

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