waste spark and direct fire explained in rotary applications
Thread Starter
Joined: Oct 2003
Posts: 5,107
Likes: 50
From: Central Florida
waste spark and direct fire explained in rotary applications
since there is lacking information on this subject i figured some people may not understand why the latter models use this system and how it affects the running of the engines.
the FC in fact has 2 different types of ignition control systems, the leading is a wasted spark system which fires both rotors at the same time even though one is exhausting while the other is firing at peak.
why is this important? well, the wasted spark system is simple and only requires a single input from the ECU so less drivers and components making it cheaper yet still effective. wasted spark in rotary applications also gives it one more firing sequence before fully exhausting the combustion to improve upon emissions and mileage further.
the trailing is a direct fire ignition system that only fires each plug at the appropriate timing in the engine and not an additional fire on the exhausting stroke of the engine.
why is this important? pictures.... sorry some of them are hazey my camera seems to be having issues.
here is TDC(top dead center) of the engine for that particular rotor where both plugs will be firing at their appropriate timing.
here is what i call bottom dead center(though many people refer to this in different views, another argument), anyways it is when the 2nd rotor will be firing both leadings(bottom spark plugs).
now look at the plug locations, the top pocket is the intake stroke coming into the engine and the bottom is exhausting the spent exhaust from combustion.
now let's think about why it is important to not have the trailing also in a wasted spark format. see the top chamber full of air and fuel? what would happen if you ignite that trailing plug in that position? yes, a backfire through the intake system and possibly engine damage if severe enough. the leading can fire again cleanly as it is still on the exhaust stroke helping to burn any unburnt fuel from combustion UNLESS timing is severely retarded to the point that it is firing a number of degrees after TDC.
this is why these engine use this format and why the ignition system is split into 2 different configurations. this also makes it difficult when upgrading the ignition system as you need 2 different ignition controllers or capacitive discharge boxes.
many people know the cars have 2 systems but most do not really know why. this thread is to help with that confusion.
the FC in fact has 2 different types of ignition control systems, the leading is a wasted spark system which fires both rotors at the same time even though one is exhausting while the other is firing at peak.
why is this important? well, the wasted spark system is simple and only requires a single input from the ECU so less drivers and components making it cheaper yet still effective. wasted spark in rotary applications also gives it one more firing sequence before fully exhausting the combustion to improve upon emissions and mileage further.
the trailing is a direct fire ignition system that only fires each plug at the appropriate timing in the engine and not an additional fire on the exhausting stroke of the engine.
why is this important? pictures.... sorry some of them are hazey my camera seems to be having issues.
here is TDC(top dead center) of the engine for that particular rotor where both plugs will be firing at their appropriate timing.
here is what i call bottom dead center(though many people refer to this in different views, another argument), anyways it is when the 2nd rotor will be firing both leadings(bottom spark plugs).
now look at the plug locations, the top pocket is the intake stroke coming into the engine and the bottom is exhausting the spent exhaust from combustion.
now let's think about why it is important to not have the trailing also in a wasted spark format. see the top chamber full of air and fuel? what would happen if you ignite that trailing plug in that position? yes, a backfire through the intake system and possibly engine damage if severe enough. the leading can fire again cleanly as it is still on the exhaust stroke helping to burn any unburnt fuel from combustion UNLESS timing is severely retarded to the point that it is firing a number of degrees after TDC.
this is why these engine use this format and why the ignition system is split into 2 different configurations. this also makes it difficult when upgrading the ignition system as you need 2 different ignition controllers or capacitive discharge boxes.
many people know the cars have 2 systems but most do not really know why. this thread is to help with that confusion.
Last edited by RotaryEvolution; Jan 23, 2012 at 02:42 PM.
Thread Starter
Joined: Oct 2003
Posts: 5,107
Likes: 50
From: Central Florida
twin power and stock coils.
the stock coils are actually very well built units and i have personally tested them for extended periods in 500whp builds.
they are also cheap and still easy to find. the twin power will just help to increase the spark output.
with E85 you will just have to play with your spark plug heat range for good results. if you really want/need more than that then the LS2 coils can't be beat for price and output.
for ignition controllers, i wouldn't be the one to ask as i have limited experience with CDI boxes/controllers pointing towards the fact that the FC stock coils can usually be adapted to handle most decent builds. right now i'm working with a Dynatek box that has some of the best output ratings i have seen but you would need 2 if you want to utilize the 2 step launch feature.
the leading plugs are the most important so upgrade that system first and foremost. i have gotten by leaving 9 heat range plugs in trailing position for that same horsepower level spraying methanol/water at 20psi of boost.
the stock coils are actually very well built units and i have personally tested them for extended periods in 500whp builds.
they are also cheap and still easy to find. the twin power will just help to increase the spark output.
with E85 you will just have to play with your spark plug heat range for good results. if you really want/need more than that then the LS2 coils can't be beat for price and output.
for ignition controllers, i wouldn't be the one to ask as i have limited experience with CDI boxes/controllers pointing towards the fact that the FC stock coils can usually be adapted to handle most decent builds. right now i'm working with a Dynatek box that has some of the best output ratings i have seen but you would need 2 if you want to utilize the 2 step launch feature.
the leading plugs are the most important so upgrade that system first and foremost. i have gotten by leaving 9 heat range plugs in trailing position for that same horsepower level spraying methanol/water at 20psi of boost.
Last edited by RotaryEvolution; Jan 23, 2012 at 03:01 PM.
Trending Topics
Hopefully this simple post will help some newer people understand another facet of the Mazda rotary engine. Mazda did a lot of unique things to increase power, reliability, etc on their engines. The auxiliary ports and the S5 VDI were among some of my favorites.
Thread Starter
Joined: Oct 2003
Posts: 5,107
Likes: 50
From: Central Florida
yep, in all honesty i completely ignored the fact that you in reality actually get 3 sparks per firing sequence of each rotor. understanding how things work helps us all move forward.
Last edited by RotaryEvolution; Jan 23, 2012 at 03:58 PM.
Joined: May 2006
Posts: 3,881
Likes: 3
From: Jacksonville, Tampa & Tallahassee
Excellent info (voted).
In your experience at what whp level would you reccomend the addition of a twin power? (assuming no AI as that obviously taxes the ignition system). Also, do you have whp figures for ditching the 7 range plugs and running all 9's ?
In your experience at what whp level would you reccomend the addition of a twin power? (assuming no AI as that obviously taxes the ignition system). Also, do you have whp figures for ditching the 7 range plugs and running all 9's ?
Thread Starter
Joined: Oct 2003
Posts: 5,107
Likes: 50
From: Central Florida
i would say about 300whp for 9's all around, 350whp for either twin power or 10.5 leadings and 400+ for both twin power and at least upping leadings heat range. preferrably install a CDI before upping the heat range.
in my 350whp FC i have 100% stock coils, no CDI and 9's in all 4 locations WITH straight water injection and have no issues, but that is pushing it and it also has the benefit of lower compression being a series 4. i can only barely feel the ignition break up sometimes, usually in colder weather when the boost is creeping up to about 16psi.
that is just my opinion and not fact though, there are few hard known facts in tuning these engines still.
in my 350whp FC i have 100% stock coils, no CDI and 9's in all 4 locations WITH straight water injection and have no issues, but that is pushing it and it also has the benefit of lower compression being a series 4. i can only barely feel the ignition break up sometimes, usually in colder weather when the boost is creeping up to about 16psi.
that is just my opinion and not fact though, there are few hard known facts in tuning these engines still.
Last edited by RotaryEvolution; Jan 23, 2012 at 04:31 PM.
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 15
From: Perth, WA, OZ
http://www.ausrotary.com/viewtopic.php?f=16&t=96724
in pictures,,, lifted from the aussie DLIDFIS thread
in pictures,,, lifted from the aussie DLIDFIS thread
Originally Posted by pattmckay
OK this thread has gone down the (wasted spark) Leading Direct Fire route while I wasn't looking. :oops:
The diagrams are large so you can download print out and they won't look ****.
I am just a bit upset jobro has f*%ked his engine sounds like a shielding problem
with signal wires for remote igniters though. This system is not for use on your trailing ignition.
I didn't use this system until much research via the
internet, books and the sage Mr Potts. Kevin used this system
on his drag car until ecu's became cheap enough.
------------------------------------------------------------------------
Do not use non ECU Direct Fire on your trailing
-----------------------------------------------------------------------
In answer to a PM see bellow the system used on my car, I use
a Ser 4-5 leading coil so I only need two igniters. Any dual outlet
coil will do. Comodore V6 coils for example.
As you can see the two leading plugs fire at the same time.
Thus (wasted spark) this helps the fuel air mix to fully combust reducing
emissions, as the rotor not at TDC is into its power stroke.
Because you have a direct link from coil to plug there is a cleanner
more powerful spark, thus more power.
You can now also use the
leading contacts in the dizzy cap for your trailing circut. This means
only one air gap for the spark to jump before getting to the plug because the input contact uses the springloaded carbon button.
Which means a better spark for the trailling. So its a win win.
Flamage fans may be a bit disapointed though as the more complete
combustion means less afterburn. Well I guess you can't have you cake
and eat it to. How sad. :cry:
I have also done a diagram to demonstrate what wasted spark is all
about. This also graphically shows why not to use this system for trailing.
You can imagine what would happen to that apex seal and jobro has first hand experience of it.
Unfortunatlly it took for that kind of post for me to do this.
-----------------------------------------------------------------------------
Don't rush into anything boys and girls.
-----------------------------------------------------------------------------
The diagrams are large so you can download print out and they won't look ****.
I am just a bit upset jobro has f*%ked his engine sounds like a shielding problem
with signal wires for remote igniters though. This system is not for use on your trailing ignition.
I didn't use this system until much research via the
internet, books and the sage Mr Potts. Kevin used this system
on his drag car until ecu's became cheap enough.
------------------------------------------------------------------------
Do not use non ECU Direct Fire on your trailing
-----------------------------------------------------------------------
In answer to a PM see bellow the system used on my car, I use
a Ser 4-5 leading coil so I only need two igniters. Any dual outlet
coil will do. Comodore V6 coils for example.
As you can see the two leading plugs fire at the same time.
Thus (wasted spark) this helps the fuel air mix to fully combust reducing
emissions, as the rotor not at TDC is into its power stroke.
Because you have a direct link from coil to plug there is a cleanner
more powerful spark, thus more power.
You can now also use theleading contacts in the dizzy cap for your trailing circut. This means
only one air gap for the spark to jump before getting to the plug because the input contact uses the springloaded carbon button.
Which means a better spark for the trailling. So its a win win.
Flamage fans may be a bit disapointed though as the more complete
combustion means less afterburn. Well I guess you can't have you cake
and eat it to. How sad. :cry:
I have also done a diagram to demonstrate what wasted spark is all
about. This also graphically shows why not to use this system for trailing.
You can imagine what would happen to that apex seal and jobro has first hand experience of it.
Unfortunatlly it took for that kind of post for me to do this.
-----------------------------------------------------------------------------
Don't rush into anything boys and girls.
-----------------------------------------------------------------------------
can someone explain this to me:
my old setup (the way I bought the car when I was super-ignorant) had 3 MSD boxes on the ignition, and the haltech was set to "direct fire". The tune was ****, and I wanted to try and fix some things. My idle ratios were horrible. Mid to high 10's! The car was tuned this way! I read about advanding timing, tightening split, et cetera. The split was set to 15 all across. I tried lowering it a few degrees at a time and nothing would happen. Eventually it wound up with a split of 0 degrees and the idle ratio was the same. In fact, nothing seemed to change. Does direct fire utilize split? The only way I could alter my AFRs was to drastically change the fuel levels, but the idle became very unstable. Ultimately I got rid of everything and went back to stock ignition. It was overkill for my car to begin with.
my old setup (the way I bought the car when I was super-ignorant) had 3 MSD boxes on the ignition, and the haltech was set to "direct fire". The tune was ****, and I wanted to try and fix some things. My idle ratios were horrible. Mid to high 10's! The car was tuned this way! I read about advanding timing, tightening split, et cetera. The split was set to 15 all across. I tried lowering it a few degrees at a time and nothing would happen. Eventually it wound up with a split of 0 degrees and the idle ratio was the same. In fact, nothing seemed to change. Does direct fire utilize split? The only way I could alter my AFRs was to drastically change the fuel levels, but the idle became very unstable. Ultimately I got rid of everything and went back to stock ignition. It was overkill for my car to begin with.
Thanks for taking time to explain some of this weird rotary ignition stuff, Karack. 
Now the question is what about for really high HP applications where you want more time to charge the leading coil(s)? In those situations, a single leading spark per rotor face allows more time to charge the coil than a dual leading spark/wasted spark/DLIDFIS setup, which have to fire twice as often.
But for 99% of every other setup, wasted spark is best.
Now the question is what about for really high HP applications where you want more time to charge the leading coil(s)? In those situations, a single leading spark per rotor face allows more time to charge the coil than a dual leading spark/wasted spark/DLIDFIS setup, which have to fire twice as often.
But for 99% of every other setup, wasted spark is best.
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 15
From: Perth, WA, OZ
26b 3 plug system gave them an economy edge , a very far ( distance ) trailing event , -something about that in the various released papers
wastespark is a late, 2nd leading event and it cleans the emissions but importantly reduces the end gas components to inerts in the recycled internal EGR
the idle note change at otherwise identical timing when you install DLIDFIS to the earlier cars is an obvious clue to a more stable combustion in the subsequent stroke
when comparing the wastespark leading to the sequential fire 4 coil ignition
then the 2 firing events has the disadvantage of halving the available dwell periods for the L coil to recharge
the practical limits for mild boost will come over 8500 rpm,, when most mild engines are already past peak port anyway
the full ignition cycle period for the wastespark engine is 3.33 ms at 9000 rpm
,, and obviously below the peak dwell required for optimum performance for most HEI coils
by nature of the flip/flop / single igniter on the trailing coil pair,, the same dwell restrictions are happening to the trailing coils
these periods are SAME as what is demanded from the 2 coil dizzy setups
the sequential 4 coil setup has twice this dwell window,, and at 9000 rpm, there is ample dwell and discharge and rest periods even for ls2 coils
when dwell time becomes critical on HEI systems,, the trick is to run higher system voltage,, having drastic effect on the time to rise to decent amps
as such ignition boosters have their place,, given short usage ( drags ) they can give large boosts to the ignition performance
( at risk to failing the coil or driver/ igniter at longer periods )
or -
can be used on the street or race car for longer periods , given attention on tunable ecus to adjust the dwell period down accordingly,, in view that the 8500 rpm limit is lifted
wastespark is a late, 2nd leading event and it cleans the emissions but importantly reduces the end gas components to inerts in the recycled internal EGR
the idle note change at otherwise identical timing when you install DLIDFIS to the earlier cars is an obvious clue to a more stable combustion in the subsequent stroke
when comparing the wastespark leading to the sequential fire 4 coil ignition
then the 2 firing events has the disadvantage of halving the available dwell periods for the L coil to recharge
the practical limits for mild boost will come over 8500 rpm,, when most mild engines are already past peak port anyway
the full ignition cycle period for the wastespark engine is 3.33 ms at 9000 rpm
,, and obviously below the peak dwell required for optimum performance for most HEI coils
by nature of the flip/flop / single igniter on the trailing coil pair,, the same dwell restrictions are happening to the trailing coils
these periods are SAME as what is demanded from the 2 coil dizzy setups
the sequential 4 coil setup has twice this dwell window,, and at 9000 rpm, there is ample dwell and discharge and rest periods even for ls2 coils
when dwell time becomes critical on HEI systems,, the trick is to run higher system voltage,, having drastic effect on the time to rise to decent amps
as such ignition boosters have their place,, given short usage ( drags ) they can give large boosts to the ignition performance
( at risk to failing the coil or driver/ igniter at longer periods )
or -
can be used on the street or race car for longer periods , given attention on tunable ecus to adjust the dwell period down accordingly,, in view that the 8500 rpm limit is lifted
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 15
From: Perth, WA, OZ
can someone explain this to me:
my old setup (the way I bought the car when I was super-ignorant) had 3 MSD boxes on the ignition, and the haltech was set to "direct fire". The tune was ****, and I wanted to try and fix some things. My idle ratios were horrible. Mid to high 10's! The car was tuned this way! I read about advanding timing, tightening split, et cetera. The split was set to 15 all across. I tried lowering it a few degrees at a time and nothing would happen. Eventually it wound up with a split of 0 degrees and the idle ratio was the same. In fact, nothing seemed to change. Does direct fire utilize split? The only way I could alter my AFRs was to drastically change the fuel levels, but the idle became very unstable. Ultimately I got rid of everything and went back to stock ignition. It was overkill for my car to begin with.
my old setup (the way I bought the car when I was super-ignorant) had 3 MSD boxes on the ignition, and the haltech was set to "direct fire". The tune was ****, and I wanted to try and fix some things. My idle ratios were horrible. Mid to high 10's! The car was tuned this way! I read about advanding timing, tightening split, et cetera. The split was set to 15 all across. I tried lowering it a few degrees at a time and nothing would happen. Eventually it wound up with a split of 0 degrees and the idle ratio was the same. In fact, nothing seemed to change. Does direct fire utilize split? The only way I could alter my AFRs was to drastically change the fuel levels, but the idle became very unstable. Ultimately I got rid of everything and went back to stock ignition. It was overkill for my car to begin with.
"direct fire"
"3 MSD boxes"
direct fire on haltech = 4 coil seqential ,, of which 3 coils has no place
3 msd boxes on 3 stock FC coils = you require the "toggle" flip flop command and this mode is called "distributer mode" on a haltech configured to a 13b FC
when you selct the various modes, the ecu will reconfigure / re-assign the ignition and aux out wiring colour sequences
by effect turning off the t2 spark,, all while wastesparking t1
also, some MSD requires the ignition trigger output to be inverted and will cause all sorts of phantom trigger events
Last edited by bumpstart; Jan 24, 2012 at 10:13 PM.