mikejokich

iTrader: (1)

Good news and a correction. My machine shop guy was able to simply move the original crush washer out of the way and still cut back the collar. This means the original crush washer remains in place. He is finishing tomorrow and said the machining was rather easy to do with his metal lathe. I will post a pic once I get them and ship four plugs to Howard for testing. Fingers crossed.
Mike

GucciBravo

Mike, I'll probably do a run of 20 of these for myself. Try to let us know a price for his services when we get an idea on a quantity/run length.

mikejokich

iTrader: (1)

Here we go. They came out great. There is slight variation in the thickness of the collar between 2.08 and 2.11 mm, which should be negligible, particularly with the crush washers. In the future, he can make a custom holder for his metal lathe to make them all the same and closer to 2 mm on the head. The cost over the typical original plug itself we are trying to figure out to make it viable for mass production, yet not be too expensive. He can machine hundreds of these a week, if needed, and the interest is there to make them available to everyone on an ongoing basis. I will send the first set to Howard ASAP for testing. Let's see how they do and if this makes sense for a viable little business.
Mike

dguy

iTrader: (8)

I'd probably take a few sets for both my street running projects as well as to use on my dynos, if they cut the mustard I'd be happy to start suggesting them to people I build engines for.

cewrx7r1

iTrader: (2)

Just post the cost for the 10s and 11s with shipment. Paypal would be safer.
Will there be a discount if we want them without a washer if we want to use our own copper washers?

1badFB

iTrader: (1)

Looks to be a fairly safe area for modifications and I'm thinking about doing this myself, but has anyone cut a plug further to see what sort of margin we are working with? I'd hate to break one during installation or removal, and don't have any extras to play with at the moment.

I do have 4 of these sitting here and a metal lathe, though.

TeamRX8

iTrader: (2)

what you really need is a sealing gasket with a ground wire connector per this post

https://www.rx7club.com/3rd-generati.../#post12569644

or maybe a properly sized ring terminal connector put on between some of those copper gaskets to eliminate the threaded connection from the process
.

scotty305

iTrader: (2)

The spark is already jumping across an air gap which is thousands of ohms, I would be pleasantly surprised if it helps to bypass the resistance of the aluminum rotor housing. Something like a 16V electrical system or a Kenne Belle voltage booster might help to supply more energy to the primary coil windings, but there are already CDI ignition boxes that have been proven to work for that purpose.

GucciBravo

I'm doing Cylinder Head Temp via K-Type Thermocouples over CANBus, which could easily be retrofitted as an extra grounding strap.

M14 Ring Terminal... Not hard to get ahold of.



Here's the problem with that idea though. The engine should already have it's grounding properly and when spark plug is seated to 18ft-lb, the damn thing is grounded via the entire aluminum housing which should have at least individual 12ga on them to match the electrical load on the housing.

I'm not going to showcase all of mine, but there's a 00ga on my center iron that daisy chains to the alternator body, starter body, chassis, etc. Those are also all direct connection to the relocated battery with zero vehicle resistance.

My CDI is 50A and is grounded accordingly. It's a circuit. Grounding and Power are the same size everywhere, as it's supposed to be.

ptrhahn

iTrader: (9)

Somebody should call NGK and suggest that if they made these in 10/11 at the correct length off the shelf, half the rotary world would buy and use them like candy.

GucciBravo

Y'all are forgetting the Denso S29A... 21.5mm Reach, Same Design, and ALMOST the heat range we want. S31A is Heat Range 10. 0.055" Gap which is known to kernel better with adequate spark energy. These suckers on CDI = Winning Setup.

https://www.densoproducts.com/denso-...29a-spark-plug


This is a $5.99 Plug.

Heat Range 29 = an NGK 9.5.

R_PROWESS

iTrader: (3)

How is it that NGK has the gap listed at .4mm/.016" yet when I measure what I perceive to be the gap with my Mitutoyo calipers, I get this? (see pic.) Is this not how a surface discharge plug gap is measured? I am wondering if Denso s29A's plug gap spec is accurate as in comparing them, I see a large difference in gap ( on official spec sheets) being the outlying difference.

Howard Coleman

iTrader: (6)

i received the the MikeModded plugs a few days ago. here's comparison showing the additional reach. i don't think it is at all speculative that they are a significant uptick by virtue of their reach. closer to the explosive mix is always better.

i am delighted that Mike was able to source a high quality shop to do the machine work while retaining the crush washer.

my experience with running them without the washer led me to conclude a washer/seal is needed. a thinner copper washer would be a very slight advantage reach-wise but a disadvantage in that it would have a larger I D to clear the threads. the crush washer has a smaller I D and will not clear the threads. further, the I D will tighten as it crushes. sign me up for the NGK crush washer.

as to the $5.99 plugs... even if you are running close to OE power output you need to run cold(er) plugs... 10 minimum. based on my experience of taking 160+ BREWs apart, i predict there will be a growing realization that many of our internal problems such as worn (probably not warped) apex seals come from rotor housing surface distentions from hot plugs.

hot plugs create SPM/Spark Plug Mountain..

last Friday i took a motor apart that had two cracks on each of the housings at the lower plug bosses. the motor came from a lowish mile 1995. the cracks had traveled all the way to the plug threads. both rotor housings were only .0005(!) from parallel so it wasn't a coolant issue. .

the customer is now having to replace two rotor housings. colder plugs probably would have saved around $1700 and perhaps the whole rebuild.

i am just finishing some maintenance on my front swaybar, am waiting for an adapter for my new steering wheel and am mounting my rear diffuser. it will be a few days before i am out and about with the MM plugs.

REnaissance_Sle7in

iTrader: (8)

They weren't forgotten (they were brought up briefly a few times earlier in the thread), they were more glossed over.....and I can't really see why we haven't discussed them a bit more. I'm really not as knowledgeable on this stuff as the rest of you guys, but the S31As seem to tick all the boxes: Surface gap - check, Resistor - check, Heat Range - check (for those of us needing to be in the 10 range anyway), Reach - check.

Is there something I'm missing as to why we are going to such lengths as to machine out the 6601s when the S31As are available and relatively cheep? @GucciBravo you say the S31As work well with CDI, how about with IGN-1As? Is there an 11 heat range in this plug? I can't seem to find one on the website. I'd imagine that it should be coded as S34A, but even a google search does not pull anything up for that.

Not trying to come off as combative, I'm genuinely trying to learn.

tqm397

iTrader: (2)

They have a bigger gap than the 6601s and the electrode is made of nickel, which I think are the reasons why they were glossed over.

I'm running all 7 and 9 NGKs in my engine right now, but I'm planning on switching over to the S31a in the trailing position pretty soon.

GucciBravo

Nothing on the market checks all the boxes like this.

The difference of 10 to 11 or 11.5 heat range is minimal. You can use a cylinder head combustion area pipet and measure the 7420-10 and 7420-11 just like I did to see just how minimal it is. The difference is negligible. Going from a 7 to 9 though is huge, and 9 to 10 is pretty large as well. Everything past 10 is basically the same air gap around the electrode.

So I just bought my 16x S31As for $100 shipped and taxed.

They won't foul. They won't cause issues with stress fracture as per Howard's point of the thread. They have a 5k Ohm Resistor, and they don't break the bank.

Just remember that these are NOT tuning plugs and you'll need a ground strap to identify what the engine is truly after. These are post-tuning plugs. After setting up an engine initially for lower boost applications and cleanup, I'll have my clients send me pictures of their plugs so I can see what else is on the table.

From there we trim up that given boost target lambda and change ignition curves to optimize the plug. Once the plugs read how I like, we swap in a fresh set of race plugs and add power until we can't or get close to a known (from me) breaking point.

Lifespan of these vs. an NGK R7420-11 should be less due to Nickle vs. Iridium, but at 1/7th the price, I really don't give a ****. I like the idea of full depth and no ground strap.

​​​​

Howard Coleman

iTrader: (6)

i do agree that the Denso S31A looks like a good plug for those where a 10 heat range is the fit. given the 21.5 mm reach it is a better choice than the 6601.

i disagree w the comment that there is little diff between a 10 and 11 heat range 6601. i have run both and there is a clearly observable difference as to how they run. further, many NGK R7420 10 heat range show a fully annealed ground strap indicating they were running too hot whereas 11s typically show the strap is 50% annealed which is indicative of a happy plug heatwise.


whatever the difference is quantitatively i want the colder plug as i have looked at too many damaged rotor housings and center worn apex seals.. there is a positive financial calculation relating to parking your original ignition setup and adding four IGN-1A coils and Magnecor wires so you can, easily, run 11s...versus causing unnecessary wear on your housings & apex seals and losing compression.

GucciBravo

When you CC the spark plug like I had said, here are the results.

0.226 grams for the 7
0.197 grams for the 9
0.93 grams for the 10
0.76 grams for the 11

I'm not sure how else you can define plugs in the real world, or if your one dataset of plug reading is as accurate as you think it is.

Mind you, I'm doing 6-8 cars a week and have a much broader testing range than most. So I'll focus on factual measurements, not a singular test datapoint.

​​​​

Howard Coleman

iTrader: (6)

very nice work.

it certainly shows, as you posted earlier, there is a big diff between the 10 and hotter plugs. while not in the same ballpark, i consider the 18% difference between the 10 and 11 meaningful. given the rotary combustion chamber pressure and heat at 400 on up i will take the additional margin. this is a decision for each of us to make. you are really right moving clients to colder plugs. as our OE turbosystems age into oblivion and more switch to singles it is very important for everyone to switch to colder plugs.

GucciBravo

While I can disagree with you here, I'd like to bring up another subject for discussion for pouring heat into the plug region.

CDI has been the solution for decades to break through the richest combustion events and ignite things in a precise manner with a very short, high energy burst (0.2ms average spark duration). I would propose that the long duration ignition coils like the IGN1A (3.2ms average spark duration) would actually be dumping more heat into the spark plug than people wish to admit, which is why I've said earlier that I have CHT K-Type Probes on mine to test this theory.

We're talking about pulling heat out of the system, so the idea of a long duration spark event seems like the opposite that we want. The other inherent flaw of this is that ignition timing will be less precise with a weaker spark energy spread across a longer duration. Think about, and visualize the amount of rotor degrees that pass in a period of 3ms at 9000 RPM. It's quite a bit, enough in which to overlap into the next combustion event if not kept track of. Now, while modern ECUs will start to reduce this duration (without reporting back a real world figure to reference), we have no way of having this exact information without scoping it externally. It leaves a very large margin for error and a misunderstanding of the spark event operation.

This is why I've always stated, IGN1A is good up to 8500 RPM or 25psi, whichever comes first. Once we start pushing these engines beyond 300whp/rotor, there are better options for consistency and reliability. Having your ignition event happen within a VERY short period of time (0.2ms average spark duration) makes honing in on actual MBT for an ignition curve to be far more fruitful.

Remove Heat from the system by using a stronger, more focused spark energy instead of focusing on a 0.17 gram volume difference in spark plug heat ranges.

scotty305

iTrader: (2)

I might be thinking of this the wrong way, but it seems like a colder spark plug would transfer more heat into the rotor housing. I agree the tip of the plug should run cooler, but can someone help explain how that might affect the thermal expansion of the rotor housing near the spark plug opening?

Also, this thread from Barry Bordes seems relevant, I forget if I've linked it here before.
https://www.rx7club.com/3rd-generati...em-fix-989811/


GucciBravo, I've run ECUs and ignition coils and spark plugs on desktop test benches in the past, using simulated crank inputs to trick the ECU into triggering the coils. You're absolutely correct that the spark plugs get warm. I suspect it should be possible to measure the difference between CDI and IGN1A without even running an engine.

GucciBravo

Yeah, I truly believe a CDI will have less excess heat dumped into an engine than a long duration spark event. It gets the job done by igniting everything, then shuts off, not continually pouring energy into a weak spark event until something lights randomly over a long period of time. Once the kernel is lit, it goes. It doesn't need some crazy long duration to burn cleaner.

TeamRX8

iTrader: (2)

I occasionally find R7420-10.5 or colder for $20 each, but currently $31 on rockauto

still not entirely convinced on these ideas, but watching …

however, I know several of the most professional builders here in the USA will always swear to run 11 or 11.5 for extended wot; road racing and such.

hard to sway me from their 40+ years of hardcore pro race engine experience, but obviously drag, street, autox etc. need their own consideration.
.

Howard Coleman

iTrader: (6)

i happened to have a lengthy and very pleasant conversation w Dr Iannetti today. Capacitive Discharge Ignition had been rolling around in my head and i asked for his view. i had run CDI for a few years before switching in 2013 to inductive... IGN-1A. while Dr I is conversant w piston engines as well as many other engineering pursuits, NASA comes to mind, his specialty is the rotary engine. being a 2 cycle motor in that there is no cooling TDC like a 4 cycle, heat is the challenge. and heat is the primary consideration in this thread.

one of the unusual aspects of our motors is the combustion chamber. in a world where OE piston motor's combustion chambers are modeled on supercomputers so as to get optimum burn our chamber is crude. it is long... (needs 2 sparkplugs) and it is... moving!

air fuel mix is also quite sketchy. the burn efficiency sort of sucks. Dr I suggested that the longer (10X) burntime of inductive versus CDI could be of special help to the rotary. if the rotary had a combustion chamber similar to modern motors i probably would be on the CDI train.

i ran two Jacobs FC3000 CDI boxes for about 4 years. i was curious as to what's out there in the 21st century so i checked two of the top shelf CDI offerings.. M&W (Australian) $1000, and FuelTech $1800. i like to read the manuals and since this thread centers on sparkplugs i found some interesting comments:

M&W
"SPARK PLUGS Non resistor spark plugs will greatly enhance ignition performance however some installations will require the use of resistor spark plugs for correct ECU operation. When using resistor spark plugs it is imperative to check internal resistance as part of regular maintenance! Open circuit or high resistance may cause damage to spark plug wires, ignition coils and CDI. Fixed gap surface discharge and semi surface discharge spark plugs are only suitable for naturally aspirated applications. Keep spark plug gap <= 0.025” (0.6mm) for boosted motors to prevent coil and CDI damage!"

FuelTech
"5.9 Spark plugs Using non-resistive spark plugs greatly increases spark energy with capacitive ignitions, however not all installations will function properly depending on the level of interference generated. In these cases using resistive spark plugs is mandatory. Keep the spark plugs clean and free of oil or grease to prevent electrical insulation problems. Spark plugs that do not allow GAP adjustment or surface discharge are designed for use only in naturally aspirated engines. For turbocharged engines keep the spark plug GAP always less than 0.02 in. WARNING Faults in the ignition system due to excessive GAP damage the coils and also FTSPARK. When the energy released by the ignition cannot find a path to be dissipated, it returns to the coil or to the output of the FTSPARK output."

translating these two similar comments:

non-resistor plugs will "greatly increase spark energy" the corollary being a resistor plug will greatly decrease spark energy. most of us will find that our ECUs will shut down (mine does at 5800) when using a non resistor plug.

excessive gap, or a spark plug wire becoming loose, or a wire becoming loose or... anything that interrupts the spark from finding ground sounds expensive.

i am going to stick w my surface gap plugs and my IGN-1A coils. i like the concept of a longer spark duration given the below par non linear combustion chamber atmosphere. i also run my coils at 16 V in boost w my Kenne Bell Boost A Spark.

GucciBravo

Good perspective, but I do believe these companies are writing this for liability reasons, and not particularly for necessities or performance figures.

• Even the most basic 115mJ CDI setup has run Rotary engines around the world at over 350whp/Rotor, igniting extremely rich (10 AFR) mixtures without a fault, and ALLOWING the engines to rev higher since spark energy doesn't fall away so quickly like the IGN1A.
• I have personally seen reliable 400-450whp/Rotor setups at 230mJ and above, and boxes are rated for 11k+ RPM.
• IGN1A Systems normally fall to pieces by 300whp/Rotor and do not like to ignite richer than 10.4 AFR.
• IGN1A Systems are imprecise on spark timing events; similar to how a Semi-Peripheral Port is a large, untimed air channel vs. a tightly timed and precise bridgeport
• No matter how you cut it, there's not enough total period cycle time allowing sub-80% duty cycle dwell when a long duration coil is run.
• CDI is a precise spark event and will fault a tuner who is running abnormal ignition mapping that doesn't suit the engine.
• Resistor Spark Plugs cut down EMI so heavily; it's a must for a low-noise situation. If you have 250, 400, 750, etc mJ of Spark Energy over a 0.2ms event, of course it'll fall down when RESISTANCE is added. That goes for ANY ignition system.
• CDI Systems should always have shielded wires to not allow signal jumping.
• Fueltech CDI has CANBus Communication and Diagnostics that can be brought to ECU/PMU/Dummy Light for upkeep/maintenance to know if a coil is unhappy
• The only reason why we make SMALLER spark plug gaps is when there is insufficient spark energy available.
• LARGER Spark Plug Gaps allow the opportunity for a more homogenized air and fuel mixture to be ignited
• LARGER Spark Plug Gaps make more power, have longer lasting ceramic, run cooler, and are less likely to foul

Here's an LS Coil and IGN1A Coil Dwell Table that I've made and remade a few times over:






Pete's post about properly grounding IGN1A Coils can be found here: Proper Grounding IGN1A Post by Pete Morel