rotarygod

OK, after someone told me that the Renesis does not fire in wasted spark mode like the previous rotaries after '85, I started to dig a little to verify this. I found some very interesting info on how it does fire and possibly why the Renesis floods easier than previous rotaries as well as explaining idle rpm gas guzzling.

If you go to the online Renesis technical training program that is stickied around here somewhere, there is a PDF file that you can open. In it there is a small tidbit under ingnition that really got my attention. First a little history as to how Mazda has fired their ignition systems on older rotaries. I'll get to the findings after everyone knows how they have worked up to this point.

In the old days (late '60's-early '70's) Mazda used 2 distributors per 2 rotor engine, 1 for each rotor. In the early to mid '70's they progressed to using only a single distributor per 2 rotor engine. The distributor was used through the 1985 model year RX-7. The older distributors (pre-'81) used a points system which we all know is not the most reliable or powerful system on the planet. These old systems would fire the leading plugs independently of each other and then follow them with the trailing plugs. However, depending on rpm or load the trailing plugs may not fire at all! In 1981 they moved away from the points system to an electronic distributor and now the trailing plugs always fired after the leading plugs. In 1986 with the 2nd gen RX-7, Mazda completely did away with a distributor and went full electronic direct fire (no spark gaps other than the plugs) with ecu control. This marked the first year that Mazda used the "wasted spark" firing order. In wasted spark, the leading plugs always fire at the same time as the other one. Only the trailing plugs alternate back and forth. When the leading plug fires everytime, 1 plug is always on the combustion side and the other leading plug is always on the exhaust side. At this point the apex seal is directly between the leading and trailing plugs in that housing which is why you can not fire the trailing plugs at the same time. You would pre-ignite the incoming mixture. This leading plug in the exhaust side fires to clean up any remnants of combustion that didn't originally burn. It did have some neat side effects. Firt of all the exhaust note changed a little. My 1st gen GSL-SE has been converted to wasted spark arrangement and now it sounds like my 2nd gen! Yes they did sound different. The second thing that wasted spark did was to clean up emissions a little. Another side effect was more power. This was due to the fact that there is always (even on the Renesis) a small amount of exhaust gas recirculating back to the intake stroke. A cleaner amount of gas going back leaves a little more room for power building. Gas mileage also went up. This wasted spark arrangement has been used from 1986 up until the end of the 3rd gen RX-7 recently. This takes us to the Renesis engine. I'll just start a new paragraph for it.

The Renesis does some weird stuff. First of all it does not fire in wasted spark mode which is intriguing since emissions and economy are obviously design points of this engine. At idle the engine fires totally different than it does anywhere else. At idle the engine fires in this order; Trailing 1, Leading 1, Trailing 2, Leading 2. WTF??? That makes no sense. Anywhere other than idle and it fires at; Leading 1, Trailing 1, Leading 2, Trailing 2. That is how it should fire. Wasted spark mode would fire like; Both Leading, Trailing 1, Both Leading, Trailing 2. That is the mode which has always made more power. I am going to do some experimentation on my distributor equipped 1st gen to see if I can get the engine to idle like this. Unfortunately I have to undo my wasted spark arrangement. I've got a hunch that the car will be much harder to start and suck down gas like no other. I will in no way try to drive the car though as this will most certainly break seals. I hope I don't break them in the experiment!

Some info that I don't know about the ignition system are the degrees of seperation between when the leading plugs fire vs the trailing plugs. In '84-'85 the difference between the leading and trailing fire points was 15 degrees. For the '86 and later engine it was reduced to 10 degrees split. When I reduced the split on my 1st gen it gained power. The split is most important at lower rpms. At higher rpms a smaller split and possible even no split may make the most power. There is still much debate on this within the RX-7 community but there is definitely power to be had by changing this. I also do not know how long the plugs fire for. Canzoomer had said early on that they do not fire for very long. This also puzzles me. It seems like Mazda took some weird steps on the ignition system of this car. I'm not sure what the results are since we don't have an identical engine with a wasted spark setup. This would be a goal of mine though for a future modification. I am going to shoot Paul Yaw a message about his and see what he thinks. He is running his with a Motec system and I don't know if he has any input on this or not. I suspect he will though. In the meantime, don't try to add aftermarket ignition boxes to the car. They will not work until we get this figured out.

I'll post back more as I do some experimentation on my own older rotary. IF I can get it to idle with the plug wires reversed I will post results on idle fuel consumption and how hard it is to start. I must hope I don't kill that little engine in the process. Oh well, I have another one on a stand in storage. I may have left out some info so please by all means chime in about it and let me know what your thoughts are.

MazdaManiac

iTrader: (3)

Yeah, I figured most of this situation out by trial and error with the E-Manage.
I am about to attempt to wire the ignition control harness into the coil setup to see if I can control the spark situation directly.

The thing with a wasted spark on an engine with little or no overlap is the increased pressure on the non-combustion side of the rotor. This would be counter-productive to power, I would think.

rotarygod

I don't think the overlap issue would have anything to do with it. The wasted aprak arrangement still fires the plug before the exhaust port is open.

zoom44

You've got me a little confused there rotarygod. since when does the renesis flood easier than previous rotaries?mine hasnt flooded once and neither has many other people's on this board.(my grammar in that sentence just bugs me,sorry) also one of the things mazda is so proud about with this engine is gas usage at idle. when most people say things like "this car is supposed to be 20% more fuel eficient than previous rx cars" they are paraphrasing mazda marketing comments from the launch and before which claimed 20% better fuel economy at idle than the previous 13b found in the 3rd gen rx-7. so when did our idle economy go south?

MazdaManiac

iTrader: (3)

Because it did, despite anything Mazda claims to the contrary.

Data points for you to ponder:

1) For two days now I have logged plot after plot with my LM-1. The bulk of that time, the motor is idling between runs and programming. During idle, the A/F is between 13:9 and 14:1 which is stoich/rich. At idle, A/F ratios should be in the 16:1 range.

2) I typically get 200 exactly per tank. The distance between 1/2 and 1/4 tank on the gauge is 36 miles (these are observed values). I idled the car for that same gauge span and it was only 40 minutes. You do the math.

Genom

I have noticed that idle on this car SUCKS gas down as much as highway cruising. I would really like to figure a way out to change that.

Stiull learning about all this stuff though and I aint smart enough (yet) to go with something as advanced as your using. But I will get there eventually.

zoom44

nonono. you've got the wrong guy there. i hate doing math. i let wakeech (and buger when he is around) do my figurin' for me :D .

1. fully admit i don't know what are the "correct" a/f is for most engines let alone this one. do you have somespecs from say the JDM spec rx-8's as to their a/f at idle. then we could see if this detuning to preserve the cats is what has thrown the idle a/f on US spec cars out.

2. someone is going to reply to you that saying "200 per tank" is not valid. you may fill it at 200 miles when the light goes on but because of driving conditions you may have only used 12 gallons sometimes and used 13 or 14 other times. i understand what you are saying , im just warning you that someone is going to say it. and that disstance between 1/2 and 1/4 is also suspect without using the same rpm range and gear and road and conditions every time. again i understand what you are saying, but the data you provided is not enough for me.

not argueing here, just trying to understand.

syntrix

Do you have the aux box with the rpm pickup? If you do, ever notice that the rpm line averages well, but it usually produces some jagged results?



I finally got the ecu pinouts, now to trace the rpm output line to get a cleaner signal

MazdaManiac

iTrader: (3)

I don't have the RPM converter. I couldn't justify the $100 for a cable and a current converter.

There are only 4 places to get an RPM signal from on the RX-8 and they are all identical quality signals for each of the 4 coil packs. There is no "tach" signal as the dash is purely digital.
I use the front leading, but they will all produce "jaggies".
I am not using the LM-1 data logging anymore now that I have figured out how to feed the Greddy the lambda signal.
With the E-Manage, I can produce data logs with AFM IN and AFM OUT referenced to TPS, RPM and A/F.

Now I just need to get the newer G-Tech Pro so that I can have accelerometer readings to compare to the engine data.

Mazda Monkey

Wasted spark is not used in order to extend the life of the leading spark plugs. I have heard that the igniter / coil packs will not live long if the system is converted to wasted spark.

rotarygod

My '89 coil packs still work just fine. I also have the coil packs from my old '88 car transplanted to my '84. 15 years is a long time. How much longer do they need to extend them? The factory RX-8 coils are pretty small and get very hot. I see that as an error on Mazda's part. As for spark plug life, they aren't going to last long if people flood them alot either.

zoom44

answers? rotarygod? maniac?

MazdaManiac

iTrader: (3)

What are you looking for?

I don't know what I will do about the coil packs. They are expensive.
At some point, I'll probably replace them with an Electromotive coil pack rail once I figure out the impedences, dwell and duration.

As far as why Mazda went to individual firing, I still maintain that it is a combination of all of the above mentioned reasons - coil longevity (lower load/heat), less need for "after burning", lower secondary combustion temps and pressure.
I think the coils are run particularly hard to begin with - lots of duration and current. I don't think they could survive if they were fired twice as many times.
There is a reverse firing order at idle and only idle.
I'll need to sit down with a rotary model on paper to really noodle that through.

rotarygod

Like I said the factory RX-8 coils are weak and suck. I'd rather transplant some older ones or the Electromotive ones that Maniac mentions. Canzoomer has already burned out a factory set by changing the duration. My 1st and 2nd gen RX-7s both use 2nd gen coil packs. I also have an MSD 6A running through them for added juice. Add to this the fact that the coils now fire for a total of 20 degrees of eccentric shaft reveolution and they work much harder than stock. They also fire in wasted spark. These are the original coils and I have had the MSD on one of them for about 5 years now with no issues what so ever. When I converted my 1st gen to wasted spark direct fire, it became easier to start too. I just don't believe that Mazda would change the firing order to extend the life of coil packs because they used cheap new ones. This makes no sense. That is still alot of research time to determine a new firing order for something so small. It must be something else although that would be something the finance department at Ford err.. Mazda would come up with. More importantly I believe this to be the source of easier flooding as compared to the older cars.

There is no way that you wouldn't want to do a wasted spark system. Combustion chamber temps are still on par with those of the older engines. There is no less pressure or temperature here in the Renesis vs the 13B. In fact, due to a higher compression ratio thermal energy is probably greater. The exhaust gasses would be slightly cooler though do to the way the exhaust ports are designed. I'll have to get into that at another time. Every engine will also still have some unburned gasses get past the combustion phase. The difference between the Renesis and the older engines is which gasses will make it around again into the intake cycle to get reburned. The advantage is cleaner emissions and a slight gain in power in wasted spark mode. In both the Renesis and the older engines, the exhaust port is not yet open when the plug fires in the exhaust chamber. The gasses here and the conditions between each engine are identical at this point. Even Mazda race cars have used wasted spark and they don't even worry about emissions. I maintain that wasted spark will make the most power, ease of startup, and have lower emissions. If the factory coils can't handle that then I hope they can handle a trash bag because that is where they should be.

MazdaManiac

iTrader: (3)

I think it is time I hit the books.
I just don't know enough about this to offer any more constructive insight.

rotarygod

You and me both! I am very interested in what you find with the e-manage software.

I found some old info from Paul Yaw that I printed up. This is no longer on his website. The RX-8 is a direct fire system so it does apply to this car. It appears that you may be rith on target about why the smaller coils are there. Oh well. No one's perfect.

"These direct fire systems are very good, but still leave room for improvement. The biggest problem is that the bean counters at Mazda, and all other manufacturers have more to do with the finished product than the engineers do..." "These distributorless systems are known as inductive discharge ignition. Inductive discharge ignitions suffer from poor spark at high rpm, and this is aggravated by the wasted spark arrangement on the leading ignition which fires twice per revolution."

Sounds like a good explanation as to why wasted spark isn't there. The Renesis has a higher redline than previous engines. He goes on...

"Without going into alot of detail, the simplest explanation is that the coils do not have enough time to build a strong magnetic field at high rpm, and so the spark continues to weaken as the engine speed increases. The bean counters don't give a ****, because this system works great at low speeds and gives good gas mileage and driveability. this is the number one priority, even in a sports car."

Now we need to find a way to either use better coils or make the spark more intense. Paul goes on again about an MSD which isn't known to work on the Renesis at this time. His writing is still very relevant though.

"Luckily this is easy to fix. Buy an MSD." "The MSD is a capacitive discharge system which does not lose spark intensity at high rpm. Capacitive discharge systems deliver a very strong , but short duration spark. To overcome this, the MSD delivers multiple sparks over twenty degrees of eccentric shaft duration. This ammounts to as many as six sparks at idle, and as little as two at high rpm, but no matter how many times it fires, each spark always lasts for a full twenty degrees. this is the best of both worlds, a high intensity, long duration spark. Just about every racecar on the planet has one and you should too." "I have installed many MSD's and the results were always more power, better drivability, and better gas mileage."

Sounds good to me. Now if we can figure out how to do it! He does address the issue of wasted spark elsewhere.

"This is referred to as a "wasted spark" system because each rotor receives an additional spark during the exhaust phase. On a rotary, this extra spark is actually beneficial because it fires at the trialing end of the chamber which is where most of the unburned fuel is concentrated. Igniting this fuel will not make more power, but it will clean up emissions slightly"

Apparently you may be right about Mazda just plain being cheap. They can get away with smaller, cheaper coils by not using direct fire. They don't take as long to build up a charge and don't get used as hard. Power isn't affected by wasted spark just emissions. Since the Renesis already meets emissions standards then cheap will probably take the priority over going even cleaner on emissions.

I still can't figure out why the firing order is the way it is at idle though and I still think this may be a big issue with a greater ease of flooding. Good call on the lack of direct fire in the RX-8 though! Damn, now I've been wrong twice in my life!

Mazda Monkey

I still can't figure out why the firing order is the way it is at idle though and I still think this may be a big issue with a greater ease of flooding. Good call on the lack of direct fire in the RX-8 though! Damn, now I've been wrong twice in my life! [/B][/QUOTE]

The reason it floods easier is the same reason it runs cleaner. The side exhaust ports are retarded in order to gain more power due to a longer expansion period. Also, un-burnt HCs gather at the trailing portion of the rotor chamber. As the rotor has totally covered the exhaust ports, the unburnt HCs are trapped & carry over to the intake cycle for combustion. The problem of flooding compounds itself because most of the unburnt fuel is carried over to the intake cycle if the engine does not start. Peri-port engines were not as sensitive because the rotor could easily "sweep" the fuel into the exhaust stream, not so good for emissions though.

rotarygod

Um yeah, I know how the Renesis is different and why the exhaust ports don't help the situation any. The fact that the trailing plugs fire first at idle and startup may have a very big role in it though. If you look at the size of the hole that the plugs fire through into the combustion chamber, the trailing plug is much more shrouded. The hole is tiny and the plug is set back in there farther. The hole has to be smaller so that gasses from combustion don't leak back through the hole around the apex seal and back into the following chamber. With the plug shrouded though it is more prone to fouling. When you unshroud a spark you get more power and more complete combustion. This is true with any type of plug in any engine. With such a shrouded plug why would Mazda try to ignite a mixture with it first? The trailing plug is supposed to be just that, trailing. My question is why does Mazda fire the trailing plugs before the leading plugs at idle? This is what I want to know. I already wrote an entire article about why the Renesis floods easier by design now I am moving on to ignition logic or lack thereof. This may play a bigger role in easier flooding than the side exhaust ports do. I am almost certain that it does.

neit_jnf

I'm no expert but maybe the reverse firing was designed with leaner mixtures in mind and the US rich maps is what makes the car more prone to flooding and an idle gas guzzler?

downshift

This brings up an interesting idea. So far, it seems like the people who had flooded their engines are in the US. I wonder how many of the Japanese owners on this board have flooded their engines. Maybe a poll is in order...

MazdaManiac

iTrader: (3)

Well, I've played around with the E-Manage and it doesn't look like it has a switch setting that will allow for direct control of all four coils (unless I converted to wasted spark which will quickly burn out the leading coils). I haven't scoped it in one of the 4-coil 4 cylinder formats, but I doubt the firing order could line up correctly once I dialed in some advance. I'm not certain of that, however.

So the question is - what would be the effects of leaving the trailing plug timing where it is and advancing the leading plugs only?

I realize that I'd be effectively moving the separation between the leading and trailing firing times upwards of 7° (they are 15° apart stock).
However, isn't the trailing plug pretty much there to clean up the left-overs? I'd think you would want that plug to fire as late as you can without running completely into the exhaust cycle.

rotarygod

15 degree split? Interesting. My 1st gen had a 15 degree split but I changed it to 10 degrees and got more power. The 2nd and 3rd gen RX-7's as well as the Cosmo's both 13B and 20B had a 10 degree split. Mazda is really starting to make me wonder what in the hell they are thinking.

CypherNinja

Smaller split = more power and stress

Wider split = better emissions

MazdaManiac

iTrader: (3)

Yes, but I'm talking about advanceing the leading plug for power, which will widen the split.
Will the additional seperation negate the power gains?

CypherNinja

....maybe.

Would depend on a lot. Guess theres only one way to find out.:D