Spark plug issues

[NoDOHC]

My camera is on the blink, so I can't get any pictures, but I have been experiencing a lot of spark plug issues since I upgraded my ignition. The most recent problem is erosion of the electrode. The engine didn't start as well as I was used to after a hard drive down some curvy roads. I pulled my spark plugs and found that the electrode has retracted way back into the plug. These plugs have about 200 miles on them. The trailing plugs were fine, the leading plugs were not.

I have also been experiencing pre-ignition at very low advance numbers (32-34 degrees) this only occurs after prolonged hard acceleration up a steep hill. I am running 9.2:1 polished S4 NA Rotors. I ran 38 degrees just fine with non-polished 9.4:1 S4 NA rotors with the stock ignition system.

Add to this the failure seen on the dyno (corners of two apex seals broke exactly as Barry Bordes illustrated in This Thread (http://www.rotarycarclub.com/rotary_forum/showthread.php?t=9290)), obvious failure point right after leading spark plug hole, black residue on both sides of highly polished leading plug hole. The same housing also had a crack going out from the trailing plug hole. I will get some pictures when I get a different camera.

This behavior is all very indicative of excessive spark plug temperature.

Questions for the community:

How many of you have tried the really cold NGK plugs (BR10EIX, R6725-105, R6725-115)?

Has any one tried running a BRK9EQ from the trailing position in the leading position for a high-powered NA application?

I have no trouble with fouled plugs, so I am not worried about using slightly colder plugs, I will try the colder plug even without feedback, but I will appreciate feedback on non-stock plugs.

Thanks!

[RETed]

I have also been experiencing pre-ignition at very low advance numbers (32-34 degrees) this only occurs after prolonged hard acceleration up a steep hill. I am running 9.2:1 polished S4 NA Rotors. I ran 38 degrees just fine with non-polished 9.4:1 S4 NA rotors with the stock ignition system.

Is there a typo in there somewhere?
I assume TOTAL advance under WOT = "0" vacuum?
If so, 30+ degrees if advance is a LOT of ignition advance.
Are you running some kinda exotic fuel?
The engine doesn't typically make that much more power with that kinda ignition advance, but it does make the EGT hot!

Speaking of which...

Do you know EGT's?


Has any one tried running a BRK9EQ from the trailing position in the leading position for a high-powered NA application?
I assume this is a typo - BUR9EQ?
I don't see why you can't try it...
As of this point, this is your cheapest option versus 10.5, 11, 13 heat range plugs...


-Ted

[NoDOHC]

I do not have means to monitor EGT at WOT. The headers were white hot on the dyno with the old ignition, but only over 6500 rpm, below that they were normal looking grey.

Why does advancing the timing increase the EGT? My experience would indicate that EGT goes down with advanced timing. Coolant temp and oil temp go up, but EGT goes down. (This is piston engine experience again...)

I made peak power at 38 degrees total advance last time on the dyno. There was about 4% improvement between 30 degrees and 38 degrees. This was with no hint of pre-ignition, 43 degrees lost power but did not cause any pre-ignition. I was running 8.2:1 polished rotors at that time.

I never heard any pre-ignition on the dyno with 9.4:1 non-polished rotors before the seals failed in the front rotor either (although the AFR was so rich that I really shouldn't have worried about it anyway).

I tried running a higher octane fuel (89) and have not experienced any pre-ignition since. It might just have been that batch of fuel.

[RETed]

I do not have means to monitor EGT at WOT. The headers were white hot on the dyno with the old ignition, but only over 6500 rpm, below that they were normal looking grey.
That sounds really too hot.
Is this a daily driver or a dedicated race car?


Why does advancing the timing increase the EGT? My experience would indicate that EGT goes down with advanced timing. Coolant temp and oil temp go up, but EGT goes down. (This is piston engine experience again...)
In my experience, EGT's will start to climb when you start to edge into early preignition.
Once you overly advance the ignition timing, then you start to get serious preignition which misfires and drops power drastically.


I made peak power at 38 degrees total advance last time on the dyno. There was about 4% improvement between 30 degrees and 38 degrees. This was with no hint of pre-ignition, 43 degrees lost power but did not cause any pre-ignition. I was running 8.2:1 polished rotors at that time.
My only recent experience with non-turbo application was a 20B in an FC.
I settled in at 30-degrees total advance.
I tried to edge the total advance to 35-degrees, but EGT's started to climb - sorry, I forgot the actual EGT #'s.
The set-up eventually settled at 232hp at the wheels on a DynoJet.
It did pick up about 5hp at 35-degrees, but EGT's were just too hot for my liking - this was a dual purpose track / daily driver, so reliability was a concern.
Stock 20B, no turbos, stock 20B intake, engine was never opened up - stock 9.0:1 rotors, restrictive cone filter, FC chassis, custom tube header into a 3" exhaust, Haltech E6K, no split on trailings, BUR9EQ's in all 6 positions


I never heard any pre-ignition on the dyno with 9.4:1 non-polished rotors before the seals failed in the front rotor either (although the AFR was so rich that I really shouldn't have worried about it anyway).

I tried running a higher octane fuel (89) and have not experienced any pre-ignition since. It might just have been that batch of fuel.
"Hear" preignition?
Not the real early preignition events...
On a dyno, you'll see it on the graph.

Side story...
I just got done tuning a customer's car a few weeks ago.
FC, built 13BT, 60-1 but O-trim turbine, HKS turbo exhaust manifold, 3" exhaust, eBay FMIC, Haltech E8, Walbro, 720 primary / 1600 secondary, BUR9EQ all 4 positions, Mallory Hy-Fire VIa on leadings
Wastegate was a Tial 44mm (I think) with a supposedly 10psi spring.
The car eventually put down 267 at the wheels on a Dynapack dyno.
Dynapack also indicated 11.5psi of boost, so it was slightly higher than the 10psi spring rate.
Anyways, I was trying to lean the fuel down more when it started to misfire.
We eventually figured out that the customer still had some old fuel left over in the tank...87 octane.
DOH.
We pulled the plugs, and the plugs still looked slightly rich for that boost level.
I knew I could still get some low-end power, but it just did not like it when I kept trimming the fuel maps down.
We came to the conclusion that it was just misfiring due to the low octane fuel it was trying to burn and trying to lean it too much.
The set-up put down almost a ruler flat torque line from around 3,800 RPM all the way to the 7k RPM redline - that surprised me because the O-trim is typically too small for a 13B.
I'm sure we'll start to see the power choke as we crank the boost up, but for now the owner is really happy for the results.
12psi of boost at around an estimate 300bhp at the flywheel is not bad for 87 octane pump gas...


-Ted

[project86]

My only recent experience with non-turbo application was a 20B in an FC.
I settled in at 30-degrees total advance.
I tried to edge the total advance to 35-degrees, but EGT's started to climb - sorry, I forgot the actual EGT #'s.
The set-up eventually settled at 232hp at the wheels on a DynoJet.
It did pick up about 5hp at 35-degrees, but EGT's were just too hot for my liking - this was a dual purpose track / daily driver, so reliability was a concern.
Stock 20B, no turbos, stock 20B intake, engine was never opened up - stock 9.0:1 rotors, restrictive cone filter, FC chassis, custom tube header into a 3" exhaust, Haltech E6K, no split on trailings, BUR9EQ's in all 6 positions

-Ted

Im just gonna take this and try to learn a little here.. dont mean to take away from the actual problem solving.

That sounds like pretty good number on an internally stock NA 20B. What are the reasons for advancing the timing in general? Also.. .cant running too rich lead to pre ignition just like running too lean?

[RETed]

That sounds like pretty good number on an internally stock NA 20B. What are the reasons for advancing the timing in general? Also.. .cant running too rich lead to pre ignition just like running too lean?

Yeah, another 20B with stock twin turbos managed to put down 8hp more than our 232 #.

From my experience...

In a very simplified procedure for tuning, you want to advance the ignition timing for any "cell" in your ignition map right before it start to hit preignition.
This will give you best power.

Yes, overly rich conditions can cause "afterburn" out the exhaust.
Due to this afterburn, it can cause a lot of bad harmonics, which tends to hammer bearings and seals.
I've personally seen engines let go due to too much fuel (burning out the exhaust).


-Ted

[j9fd3s]

Yeah, another 20B with stock twin turbos managed to put down 8hp more than our 232 #.

-Ted

that was my friends truck! he bought a cosmo front clip GOT RID OF THE ERROR CODES, and then swapped it into a b2600. it was totally stock except it had a 3" exhaust (so stock unopened engine, ecu, turbos, running sequentially, etc etc).

it dynoed 247rwhp... it did make more torque than Ted's NA, but still....

it was AWESOME in the truck too, its the BEST sleeper i've ever been in. when the second turbo came on in the lower 3 gears the right rear tire would just go up in smoke....

mike

[j9fd3s]

I made peak power at 38 degrees total advance last time on the dyno. There was about 4% improvement between 30 degrees and 38 degrees. This was with no hint of pre-ignition, 43 degrees lost power but did not cause any pre-ignition. I was running 8.2:1 polished rotors at that time.

I never heard any pre-ignition on the dyno with 9.4:1 non-polished rotors before the seals failed in the front rotor either (although the AFR was so rich that I really shouldn't have worried about it anyway).

I tried running a higher octane fuel (89) and have not experienced any pre-ignition since. It might just have been that batch of fuel.

i'm not used to low compression NA, we usually try to run the 9.7 rotors. the last one we did, was IT spec, so its stock 6 port engine, with stock S4 intakes, and custom exhaust.

anyways, that one made peak power with like 26BTDC L, and it dropped on either side of that. this is at an AFR of about 13 too. i can see running more timing with lower compression, but 38 just seems like too much?

we've also learned since, that you won't hear preignition. since the rx7, we've been endurance racing a honda, and stock those run like 12.2AFR, and you pick up power leaning it out. so we leaned it out to 13.2ish. then we advanced the timing 5 degrees, and it didn't pick up any power, but warren just left it.

and that motor died from preignition, the head, block and pistons look like someone took a punch to it and just had fun.

when we put the new motor in, we dynoed the stock map vs the +5 ignition map, and the stock map made more power.....

octane; if you're making a lot of power, you might actually need a little more octane. the competition prep book from 79 is the newest ive seen, and its a 12A PP with a carb, and they want you running 90 octane (doesn't say RON or MON or R/M2) and the cold spark plugs @the 260hp level

[NoDOHC]

For future reference, this is my daily driver. I do want reliability. I ran 13,000 miles with very advanced timing and had no problems with it, so I thought that I had a reliable tune.

Anyway, so what I am taking from this is that If I hear something that sounds like metal hitting metal, it is severe detonation and that the pre-ignition is inaudible. That would explain some of the symptoms that I saw on my spark plugs.

Based on Ted's advice, I retarded the WOT timing to 28 BTDC at 3,000 RPM and tapering down to 15 BTDC at 750 RPM and found that the engine felt more responsive. I drove it 800 miles only stopping for gas and the plugs looked as good as new at the end of this.

I also noticed that the engine is much smoother at low speeds (below 3,000 RPM).

My previous WOT ignition curve was completely flat to 1500 rpm (34 degrees BTDC) and tapering to 25 BTDC at 750 RPM.

I am thinking that my original theory was incorrect and that the spark plug erosion that I observed during hard driving was due to pre-ignition, not incorrect plug heat range. The worst detonation that I felt was about 2,700 RPM before (the 90% VE breakover point). This may have also been a contributing factor in the engine failure on the dyno.

Thanks for the advice Ted! I think this information is very good for posterity.


"Hear" preignition?
Not the real early preignition events...
On a dyno, you'll see it on the graph.


Please expound on what you see on the graph that indicates preignition...
I will see if I can scan the graph of my 5,400 RPM blowup in and see if you can identify the event.


In my experience, EGT's will start to climb when you start to edge into early preignition.
Once you overly advance the ignition timing, then you start to get serious preignition which misfires and drops power drastically.


Ok, so that explains the drop in power when going to 43 degrees.
What I hear you saying is that the 8.2:1 engine really made 210 WHp at 33 degrees BTDC ignition timing, the extra 6 WHp that I picked up going to 38 degrees was due to early pre-ignition.

I had EGT ports installed on my Defined Autoworks headers, so I will get EGT numbers when I run with those headers on the dyno (probably at least a month out).

[j9fd3s]

For future reference, this is my daily driver. I do want reliability. I ran 13,000 miles with very advanced timing and had no problems with it, so I thought that I had a reliable tune.

.

it depends on the drive cycle, with our race car, for 3 years, our drive cycle was WOT for 25hours at a time! which is almost the opposite of the drag racers, their season is less than 15minutes of run time. the honda guys expect to rebuild the engine at least once in that 15 minute season too.

so there is a HUGE difference between an engine with a 25 hour design vs one with a 7 minute lifespan. if the engine runs in like 7, i minute increments, they can run cardboard apex seals...

a street car yet again is different, as it needs to do stop and go and things, and the WOT cycles are short, at least here in CA.

i've been looking at the timing curves of various engines mazda has built over the years and i must say its surprising. the 85 and earlier timing curves are all in the FSM's, so i was interested to see what timing they ran in like a non emissions engine.

the answer? its like 15 degrees@wot. the later 70's engines with reactors run about 20, the catalyst engines run more like 27... i suspect the non reactor/non cat engine still runs 15 degrees because of emissions still, but more isn't always better, as you just found out.

the FSM's are all at www.foxed.ca the REALLY weird ones is the late 70's rx4/cosmo, its runs a normal mechanical advance, so there is a 15 degree timing split, and L&T advance together, but it ONLY has a vacuum advance on the trailing. so the vacuum advance ONLY changes the timing split.

the other weird one is the 74? rx3, its got a timing retard box, so whenever this box is on, leading timing is retarded 20 degrees. it MUST be to get the reactor warmed up fast, but when this is on, the trailing fired before the leading....

anyways, start small, and work your way up...

[RETed]

Please expound on what you see on the graph that indicates preignition...

There's multiple stages of preignition...

We do know that preignition = "uncontrolled combustion due to uncontrolled ignition events", right?
There's an old racer adage about "lean is mean" - you can lean it to the point that it'll produce power, but...
At this point, BMEP starts to spike - this is why the power starts to gain a little.
This is a pretty ragged and very narrow range though.
The dyno might or might not show this, depending on the dyno (and dyno set-up) - it could manifest itself with a more "ragged" looking graph.
(Be careful about blaming preignition on your ragged dyno graph - there's a LOT of other factors that can do the same thing, for example: insufficient spark due to bad plugs, wires, coils, under voltage, bad ground, etc. or bad fuel delivery due to fluctuations in fuel rail pressure, dirty fuel injectors, bad ground, dying fuel pump, dirty fuel filter(s), fuel temp too hot, etc.)
EGT's will start to spike also, but only experienced tuners will know that it's too hot.
You will almost never hear this with the human ear.

Keep pushing it past this point, and power will start to fall off on the dyno.
This due to the uncontrolled combustion - the engine is fighting itself to harmoniously push the crank (well, in our case, it's the eccentric shaft) in the right direction to put the power (technically, torque) down to the wheels.
EGT's will significantly increase at this point.
You may or may not hear this.

Keep pushing it even further...
You'll start to induce ignition misfire cause either, 1) mixture is too lean to ignite properly, or 2) ignition timing is too advanced and way outside the power producing range.
EGT's at this point will drop due to the fact that it's a misfire - you're not getting proper ignition and combustion, i.e. BMEP plummets.
Obviously, something it very wrong at this point, cause the engine just does not sound good at all.
Depending on the dyno model, you can get all kinds of weird lines.
My recent experience with Dynapack shows spikes - I'll try and grab some pics, as we're going to retune a customer car next Sunday.

Side note...
As dangerous preignition and detonation are (to the rotary engine), the absolute more critical point in the graph is at PEAK TORQUE.
When you make your runs on the dyno, keep an eye out on when torque peaks at what RPM range - you will see a general idea of the torque graph / peak over multiple runs.
Peak torque = peak BMEP, and having the engine detonate at this point is almost instant engine failure.
Keep this in mind when adjusting your maps in those ranges.


-Ted

[RETed]

it dynoed 247rwhp... it did make more torque than Ted's NA, but still....

Oops, sorry about that...make it ~15hp.
My aging brain is failing me again. :P


-Ted

[j9fd3s]

Oops, sorry about that...make it ~15hp.
My aging brain is failing me again. :P


-Ted

hmm, maybe im wrong then, i wanna say it was like 8hp... either way it was a surprisingly small number!

-Mike

[scotty305]

...
Anyway, so what I am taking from this is that If I hear something that sounds like metal hitting metal, it is severe detonation and that the pre-ignition is inaudible. That would explain some of the symptoms that I saw on my spark plugs.

Based on Ted's advice, I retarded the WOT timing to 28 BTDC at 3,000 RPM and tapering down to 15 BTDC at 750 RPM and found that the engine felt more responsive. I drove it 800 miles only stopping for gas and the plugs looked as good as new at the end of this.
...
I am thinking that my original theory was incorrect and that the spark plug erosion that I observed during hard driving was due to pre-ignition, not incorrect plug heat range.
...


I'd be very interested to see photos of the eroded spark plugs, if you've still got them.

[NoDOHC]

I intend to post photos when I get my camera working again. I have the plugs on the bench in the garage so that I can take pictures when the time comes.

[NoDOHC]

I'd be very interested to see photos of the eroded spark plugs, if you've still got them.


I got my camera working again!

The one on the left is the leading (which was much worse)

I apologize for the pictures, my camera wasn't that good when it was new.

If you look carefully you can see that the tip of the center electrode is about 3 mm retracted from outer electrodes. On new plugs it is almost flush.
http://i594.photobucket.com/albums/tt25/NoDOHC/P1010582.jpg
http://i594.photobucket.com/albums/tt25/NoDOHC/P1010583.jpg

[Barry Bordes]

NoDOHC, does your camera have a flower symbol which designates the macro setting.
Select the flower and refocus that picture of the plugs.
Thanks,
Barry

[NoDOHC]

I need a new camera, that was macro mode.

I tried very hard to get the focus right, but I think that the lens has lost some mobility over the years and sand-infiltration events.

Hopefully you can see ok in those pictures, I can take some from further away too.

[scotty305]

Yes those aren't the best photos... my work had a camera that would never focus well when too close, and the display was not a high enough resolution to show that you had just taken a blurry shot. You could sometimes get a decent image by using very high resolution and taking the shot from further away. Taking photos in an area that got lots of natural light helped too, but stay away from direct sunlight or fluorescent lights.

It got to be such a pain that we brought our own personal cameras in when we knew we would need to take photos, and eventually the company picked up a decent camera for about $50-100.