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I’ll raise the Rotor 2 correlation again. Because some past info I received from a longtime notable race engine builder for not-to-exceed EGT values always stated Rotor 2 EGT as 50° - 75°F lower than Rotor 1. Not equal as some might suppose.
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FWIW, my RXParts seals warped super evenly across both rotors judging by the compression numbers, and the motor never saw anything hotter than 10 plugs.
for track/heavy extended throttle use -11 or -11.5 is the recommended range.
I used to argue against it due to a lack of understanding that Howard is stating, not any more.
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I fouled my first set of 11.5s after many years of use during the initial start up of a new setup. I think it all depends on your tune
They must have been on the car since 2015 or so
Might be worth trying a 10/11 combo to see how it lasts I guess. I'm trying to avoid swapping plugs for track days though. I find it an oddly tedious process, probably on account of my crappy mechanics abilities.
high energy IGN-1A coils help a lot, not just for boost conditions
I’ve always had concerns about the nickel electrode on the 6601 wearing quickly with high energy coils, but for $15 each from Motorsports it’s worth trying a pair of Ts.
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Stupid question for someone who's been in rotarys for so long, but I've run the same heat range plugs for so long I can't recall.
Are you saying run the colder plug in the leading (lower) position, or the trailing (upper), and have I got those correct? I thought the stock config was to put the hotter plug in the leading (lower).
You can also laugh at me, but in my mind the "leading" plug would be the first one rotor encounters in rotation (top). The should have just said upper/lower.
as you may recall Mazda uses the colder plug in the trail/top/upper.
Mazda found the TTU position needed to be shielded or the center of the apex seal would be damaged... the tiny hole size is a compromise... too small no ignition effect, too large apex seal damage. this placed the working/hot end of the plug in a chamber which called for a colder plug that would transfer heat away better.
i am currently breaking in my new motor and am running NGK R7756 (11) in the L position and NGK R6601- 4017 (10) in the TTU position. i have the R6601-4586 (11) and will probably swap them in the top after break in. i have a few hundred miles on the motor and have been up to 13 psi at modest throttle and rpms.
i do feel it is a plus to run as cold a plug as works w your system. IGN-1A coils, Magnecor wires, 4.5 mS dwell in boost.
i share your feelings re timing nomenclature... the plug that is first exposed to the new rotor face is the top plug, so it might be considered "lead." of course "lead" refers to the timing. generally in the piston world more "lead" refers to more advanced timing before TDC. if you add "lead" you are increasing the amount of degrees before TDC.
Stupid question for someone who's been in rotarys for so long, but I've run the same heat range plugs for so long I can't recall.
Are you saying run the colder plug in the leading (lower) position, or the trailing (upper), and have I got those correct? I thought the stock config was to put the hotter plug in the leading (lower).
You can also laugh at me, but in my mind the "leading" plug would be the first one rotor encounters in rotation (top). The should have just said upper/lower.
^I was wondering the same thing - Mazda does specify the hotter plug in the leading position. But, and I could be completely wrong on this, I believe Mazda specified a hotter leading plug because they were engineering for a stock, unmolested spec engine that needs to have a reasonably long spark plug life and must also meet warranty requirements. In that type of scenario, and with the stock ignition system, a hotter leading plug simply lasts longer before fouling becomes an issue.
Now if you add more boost and modify the ignition system, all of that goes out the window.
imo spark plugs are a little tough because the plug you (or Daryl Drummond) would pick to run at Daytona is different from the one i need to go 2.5 miles to get coffee in the morning.
at Daytona its full throttle for a day, you need a cold plug, they ran 13's.
my coffee run, is barely enough to even get the car up to temp, let alone full throttle.
most of you guys are somewhere in the middle.
obviously its also true that 7/9 plugs were used up to 280hp in the late FD's, but everything over that got colder plugs, so
its really a 3 axis graph; power, % of time at wot vs spark plug heat range
One thing to remember is when taking plug readings after a run to the coffee shop vs a pass at the drag strip if very different. It’s easily to misinterpret a plug on a predominant street car because of light load and extended idle times. One the tricks I use to use when I was racing boats back in the 90s, adopted from the older generation of guys, was to make a run down the back stretch and when entering the pit area pull the kill switch gliding to a stop. This gave us a very accurate idea of what was going on. I sorta adopted this method on the rotary as well. After a real long pull ( on the street ), when it was safe to do so I would pull over and read the plugs. Kind of annoying with it hot, but it was tolerable. I do run negative split in the vac areas and can tell you they read very differently with normal use ( idle/light load/ cruise ) vs at the end of a long pull. With a Dyno or road racing where are you see sustained full throttle it makes it much easier. I run 4 ~ r7420-10s. My leading is starting to burn most of the strap now I’ve advanced the timing and will probably head to 10.5 or 11s in the coming spring. When I read the plugs after a week of gym runs the trailing plugs are actually the ones burning cleaner and hotter than the leading. I believe this is due to the negative split in the light load and crushing areas of my map. Reading plugs and understanding is a invaluable piece of information.
i do feel it is a plus to run as cold a plug as works w your system. IGN-1A coils, Magnecor wires, 4.5 mS dwell in boost.
This is a bit off-topic, and although I completely agree with Howard on running the coldest plugs that work for your system & application/use case, I'd like to point out a few caveats regarding setting dwell times with the IGN-1A coils. Below are a few excerpts from the IGN-1A spec sheet, and application notes regarding dwell. Key take away points from the specs is regardless of what dwell you set, for continuous duty operation, you need to set the dwell such that the coils don't exceed a 40% duty cycle (on/off time). What that means in practice is that if your running at high RPMs for sustained periods of time, you may have to reduce your dwell time in the higher RPM regions. Probably best to illustrate this with some simple math:
At 8000 RPMs, assuming IGN-1A's are set to run in direct fire/COP mode, the cycle time for each firing event is 8000RPMs/60sec = 133.3 firing events per second, so firing cycle time = 1/133.3 = 7.5mS
Per the spec sheet, the Arc Duration = 2.9mS, (same as spark duration) so at 8000RPMs, with its corresponding 7.5ms firing cycle time, 7.5mS - 2.9mS arc duration leaves you with a theoretical maximum of 4.6mS that you can set for dwell (i.e., "on time", or time to charge the coil before it fires). But if we use a 4.5mS dwell @ 8000RPMs, you can see that we're going to exceed the 40% continuous duty cycle limit:
4.5mS(on time)/7.5mS(cycle time) = 60% duty cycle. Which might not be an issue if you only stay at those RPMs for a few seconds at a time, but for a track car, you'll probably want to reduce the dwell settings for that range of high RPMs down to about 3.0 mS to stay at 40% DC or below (3mS/7.5mS = 40% DC). Fortunately most aftermarket ECUs allow you to set dwell based on a 3D table, dwell time vs. RPM & Voltage, so you can run shorter dwells at high RPM/higher voltage regions and longer dwells at low voltage/RPMs. So dwell can be optimized to fire up easier on a cold morning, and keep the coils happy at sustained high RPMs, or when your alternator fails in the voltage too high mode.
Last edited by Pete_89T2; 01-22-23 at 09:31 PM.
Reason: fix typos
I was thinking we had a discussion with Lance Nist and that proved to a lower number than was actually sustainable; a larger value could be used? I may be mistaken though and will have to go back and see if I can find it.
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What seals are you running in your rew swapped rx-8 ?
~ GW
odd, thought I had replied last night.
they’re what the previous owner installed when he built the engine a few years before my purchase. Originally he used the Atkin’s seals, but cracked one. I believe it presently has RA Super seals. Cranking compression isn’t great. Which isn’t so unexpected since it is a full BP configuration. A true junk yard dog engine slapped together from many used parts. Though it really is more like a cat on it’s 7th or 8th life. Unlike the stories here, it just won’t die no matter how he and I both tried. Which for my ownership included 3 coolant dumps due to hose failures along with correcting a few things like intake coupler hoses coming off under boost, incorrectly wired MAP sensor, general overheating/fan controls, etc. followed by 16 dyno runs in a 90 minute period at 30 psi boost.
Update. Pulled apart the motor with some interesting findings. To start, my CAS wheel is bent. How and when did this happen? No idea. How much influence this would have on my warping apex seals?
The housings looked excellent. Well lubricated, no signs of wear. No catches with my nail. They are essentially brand new.
Rotors, no dents or bends along the slots. Apex seals. Significant warpage front rotor, less warpage rear. No twisting defect. I can feel an edge or sharp lip on the surface side. There is notable heat discoloration on the front apex seals, not the rear.
Irons. My welded coolant passage held up however interestingly my coolant seals were completely smashed/crushed and bulged over. No cracks. Seems like Chip over-lapped my irons? But the groove was within spec according to my shop which is a headscratcher. I should have been leaking coolant into my combustion chamber based on the pictures. Temps were fine.
I am still curious if my CAS is the culprit. I do not believe this is due to the metallurgy of my apex seal at this point. How can things get so hot without showing on afr/egt? If it is timing related why does it feel fine driving around town and spirited?
There's no evidence of the trigger wheel tooth hitting anything, like OMP lines?
The iron faces don't look great to me. As in, the surface themselves and the wear marks on them-- esp the front iron. Can you post pics of them cleaned up? Never been a fan of lapped irons, I don't care who does them.
If memory serves, the depth of the coolant seal groove on a brand new OEM iron is 1.60mm...... Edit, dug up the pic:
With the motor out, its hard to confirm but I do not remember hearing or seeing anything touching the CAS. I will be very mindful this time around. The only thing that could be touching is the OMP lines I believe.
I will post pics of the irons once everything is cleaned up as well as re-checking the depth. Only reason I went with re-nitriding and lapping was because of unavailable irons from mazda. Nevertheless, a mistake.
Rich, what is your humble take on all this? I understand its guesswork however your opinion still holds value.
One detonation event with OEM seals, and you're out a rotor and rotor housing combo (maybe two) and an EFR turbo. Not worth the risk for anything over low to mid 300s at the wheel in my opinion.
OEM 3mm too?? Them r some tough cookies but nice on the housings!
If you've got a shaved/sharpened edge on the apex seal, that's wear (which would cause localized heat). Gotta be wearing on something. Does this give credence to the "spark plug mountain" idea?
This thread has been very educational!
Can anyone tell me where I can find information on rebuilding engines for single turbos?
I'm sure I'll have to do a rebuild at some point, and I would like to learn how the current standard practices for race engines differ from what's in the Mazda FSM.
My friend has done three or four rebuilds in the last 10 years at a cost of something like $8,000+ each, and I'd like to avoid that...
2) Did you purchase inner coolant seals from Atkins?
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To me, it looks like you had an air pocket trapped at the coolant passage on the Leading plugs.
This is the hottest area of the rotor housing and exceeds the boiling point of coolant/water mix. Boiling occurs and without the AST (air separator tank) constantly bleeding the cooling system the vapor from the localized boiling event becomes trapped and increases to an air pocket.
Air does not conduct heat well so the issue is exacerbated. The Leading spark plug hump distortion becomes greater and excessively wears the apex seals (as you can see).
The Leading spark plug boss has the carbon shadow from the blow by when cold/normal operating temps and the apex seal has the wear spot in the middle.
01-20-23, 05:52 PM
Which for my ownership included 3 coolant dumps due to hose failures along with correcting a few things like intake coupler hoses coming off under boost, incorrectly wired MAP sensor, general overheating/fan controls, etc. followed by 16 dyno runs in a 90 minute period at 30 psi boost.
