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Yours is more bowed. I was right at the point where the car was having hot start issues and warm compression was about ~70-75psi, evenly across all faces ~1300 miles or so. It still made 310hp on the dyno like this. As soon as you got above 2000rpm it drove ok.
So here's the front rotor housing. This time the front rotor was the one giving me more trouble.
Assassin's Creed, anyone?
Carbon trail plus chatter marks. Why? All is fine until the seal crosses the factory exhaust port.
The top and bottom of the housing look just fine. No real chatter marks or carbon deposits. Only a little extra wear on the sides from the ends of the apex seals.
Here's where my concerns were: the casting around the plugs suck. Look at that tiny hole above the leading plug. It's the same with the other rotor housing. I'm going to clean that up and hopefully get things cooling off better.
why? if you put the apex seals in the oven do they bend?
That's a good question. I think if you put them in a kiln they might warp because of the asymmetrical design. At first I thought they were seeing too much heat in the engine. But looking at the evidence of "spark plug mountain" and steady EGTs I think SPM is poking into them while they're hot.
I sure hope I'm not detonating. My tune is about as safe as I could get it for being done on the street. I can't explain the carbon deposits behind the side seals though. How do you get blowby through them? Maybe it's a byproduct of running with crappy compression?
put the apex seal on a "spark plug mountain" and put them in the oven at broil and see if they bend
I'm not sure what you're getting at. I surmise the only conclusion I'll be able to draw from that is how hard my girlfriend can hit me when she finds out I put car parts in the oven.
I'm about to order a pair of S4 TII rotors. I don't want to mess around with this high compression madness anymore. Each iteration of experimentation is costly and causes me to miss events.
I'm also ordering a new water pump, apex seals, and 6601-11 plugs. I figure with the lower compression rotors I might not be forced to run colder plugs all the time. On race days I'll swap the 9s out for the 11s. I suppose I can start out running the 11s full time and see if they foul with the way I drive. Then do the switcharoo only if needed.
I only bring it up because high coolant temps/high temps around the spark plugs lead to a similar wear pattern, although it's usually reversed - shiny near the plug and dark around on the sides. And the way the wear pattern looks "even" elsewhere makes me think your rotor housings may be inverse barrel shaped.
Using my ultra-precise digital caliper from Harbor Freight, the front housing is nearly completely parallel with no more than 0.02mm variance. The rear housing had some variance of about 0.05mm, but still within spec from what I understand.
Yeah, this has me scratching my head.
Update on the new parts: the rotors and water pump are backordered on Mazda Motorsports. Much to my bank account's--and girlfriend's--relief, I'm going to put the rotors off for now. *Sigh*
Blue TII - Hey, they're only $14.99 from Mazda Motorsports! It seems as though they don't have anything warmer than an 11 plug. I do drive my car around town a fair bit, so I'll see about getting a warmer version elsewhere. I like the idea of not having to worry about a grounding strap. I keep reading good things about the R7420, but I think those have grounding straps. And they're much more expensive. And they require thin-walled sockets.
R6725/R7420 do not need a thin socket, pretty much every single rotary powered drag car runs this type of plugs, +1000 rwhp on these cars, spark plugs is not an issue on their setup.
why do the seals bend? what would cause the seal to bend? if you just heat it up does it bend or stay straight?
There are so many unknown variables here. What is the annealing temperature of the seal? How much is the spark plug boss getting raised? Am I experiencing preignition? The most I can do is tackle each individual potential problem the best way I can think of until the seals stop bending.
I have ordered RA Super Seals. RA described them as having an 80% higher annealment point than the classic seals. I'm of course taking this with a grain of salt. It's worth a shot though.
I intend on opening the cooling passages around the spark plugs. I've decided not to cut ridges into them but instead focus on flow over turbulence.
The cooler plugs should help reduce any preignition I might be getting.
I'm considering getting an updated/larger AI nozzle.
I just don't have the resources to properly use the scientific method. I would love to know exactly what causes seals to warp. Is it temperature? Pressure? Spark plug mountain? A combination of these? The most I can do is throw multiple "solutions" at it until I've reached my goal of a reliable 400whp car. I was going to put reliable in quotes, but that doesn't seem too farfetched.
What I see is under max load and especially with detonation you get the spark plug "mountain" in the rotor housing from thermal expansion.
The "mountain" wears the one side of stock hardened 2mm or 3mm apex seals or wears and bends soft seals on the side where it is way leaned over running across that spark plug area.
Once the rotor housings cool a bit the "mountain" goes down and you are left with a gap between apex seal and rotor housing from the worn apex seal that leaves the carbon tracking on the rotor housing when the seal is at that extreme lean angle passing over the plugs.
Here is detonation wear/damage on stock 3mm seal. In my experience stock 3mm are strong enough side housing irons crack before the seals break- no need for the 3mm aftermarket seals that really trashed my rotor housings.
Update! I cleared the coolant passages and measured and assembled the engine. I got the engine back in last weekend and almost immediately started driving like normal. The bearings aren't new, so why not? So I got into my testing.
I pulled a couple degrees of timing from the boost columns and tried it out up to 11psi. I began losing some compression, from 15 InHg to upper 13s, even using the 11 heat range plugs. I pulled even more timing, probably two more degrees all around. Even though EGTs rose slightly, I stopped losing compression. I'll post some comparisons between my ignition timing maps later. Picture Arghx's 9.4:1 timing map for Rtek but a couple degrees lower. I'm feeling pretty good about it.
However, I still managed to hurt the engine. The engine doesn't sound/feel like it's firing fully on all rotor faces. Remember the warped side seals? I think the excess heat from the "aggressive" timing dealt another hit to them. Vacuum is now around 14-14.3 InHg, which is okay considering the apex seals have barely bedded into the housings. I'll do a compression test shortly to make certain. Hot starts are just fine. Front rotor EGTs at idle are much lower than the rear, about 100F despite the fuel compensation I have going to the rear at idle. I am no longer adjusting fuel to the rear rotor in boost.
In any case, I am prepared to tear the engine down one last time if it doesn't eventually run smoother. I'll give it some time and probably a dyno session to make sure the tune is solid before rebuilding. I would hate to do the rebuild, hit the dyno, then hurt the engine again 😬
I digress... My point here is that apparently this is what happens when I use EGT to determine "proper" ignition timing. I'm sure clearing out the coolant jackets near the plugs was a good idea, and cooler plugs are good, but I'm now convinced the real issue was my own idiotic doing by not dyno tuning and giving the EGTs too much attention over common sense. Is my crank pulley marked accurately? Maybe not. I don't think I have anything S5 in my garage, but who knows?
oh for sure if you have the engine apart verify the timing marks. it sort of matters, as you notice the engine kind of wants what it wants.
i'm a little out of my depth to say this, but EGT is more like a limit, than tuning to a specific number. i've been told that once the engine is happy it should stay around 920-950c, but ymmv
I just don't have the resources to properly use the scientific method.
so true. however for this one, i was thinking measure a seal, put it in the oven at ~450f for a while and see if it bends. if yes, well there we are. if no, then grab some pliers (or something) and see if you can bend it.
i'd do it, but my car needs paint, and control arm bushings, and a radiator fan, and shifter bushings, and an alignment, and then i can test the IC pressure drop, and exhaust backpressure, and then change the turbo to a T04.....
EGTs are low to mid 1600s F (875-900°C) at WOT and all seems well. I guess I was just afraid if I saw anything above 1600 my apex seals would die again. Is this trauma? 😆
I'll stick some seals in the oven and see what happens. I don't think anything under 500°F will do much to them though. I was thinking more along the lines of 1000°F+ to get some good warpage out of them. But that's what we're gonna find out eventually. I might have to use a torch and heat them as evenly as possible and use a remote thermometer to gauge them. That interjects some variability into the experiment though. If I had a kiln I'd get much more consistent results. But even then that only tells us at what temperature they bend sitting alone on a grate. Since they're tucked inside and making constant contact with the rotors, which are themselves cooled internally, the seals are shielded from much of the combustion heat. So many variables we can't accurately measure!
I have a lot going on as well... I'm getting a new driveshaft made from an RX-8 shaft I have lying around. The joints are much more robust. They look like TII U-joints. Control arm bushings are going to get replaced here too. They're sitting there waiting to go on. Then the car needs to get corner weighted. Then obviously there's the dyno tuning... It's already a busy summer!
Last edited by Hayamate; 06-15-21 at 01:34 PM.
Reason: Grammar, y0
As far as the timing marks go, I may be able to find a way to print out a degree wheel...? Or maybe I can get creative with a protractor. I don't know how accurate I can get with it is what I'm saying. It definitely wouldn't hurt to do a quick and dirty verification though.
I dynoed the car yesterday on a Dynojet. She made 396whp and ~295lb/ft at 16psi. I can't remember the exact torque number, but it's just under 300. The torque curve peaks around 5000 and stays crazy flat up to redline.
So, a couple things I learned...
1) My timing was only a degree or two too advanced. Not a big deal, I just pulled some timing until I lost 10hp across the board, so I added a little back.
2) Something is crazy here because I'm at 1° BTDC at 16psi. The pulley has to be way off or something. I recon I should be at 11° or so at that boost level. I recently double-checked my timing and made sure there is no wavering in the timing when I rev the engine.
As before, a couple hard pulls here and there don't seem to affect the engine negatively. However, after back-to-back high boost pulls I lost compression again. And then some lower boost pulls brought some back. I was running the Mazdaspeed 6601-11 plugs. I thought I saw low 1700° EGTs at full boost, but honestly I was paying closer attention to the boost and AFR numbers. And I can't remember offhand how to reset the peak EGT on the little units LOL
I'm going to increase the amount of water/meth and see if that helps. If that fails I will be ordering 8.5:1 rotors and putting her back on the dyno.
I'm a little disappointed that the issue persists, but at the same time I was able to make a ton of power and drive home. In my book that's a small win.
Last edited by Hayamate; 07-06-21 at 02:37 PM.
Reason: Added spark plug part number
That would be okay in the long run. However, I'm in a troubleshooting phase, and I'm certain that I would have blown OEM apex seals with the timing I was using a while back. I'd rather drive home with reduced compression.
Quick little update: immediately after my dyno session I ordered a new methanol injection nozzle that is twice the size as my original. I moved to a DO10 nozzle, which is 970ml/min. I haven't had an issue since. I'm running 15-16psi daily and it's taking it in stride.
06-02-21, 06:31 AM
