Originally Posted by spartantrap (Post 4876893)

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Originally Posted by UnknownJinX (Post 4877883)

Correct me if I am wrong, but looking at the rotary engine's structure, I simply can't see how blow-by can even get in the oil pan. Blow-by gas will simply end up in the adjacent air pockets in the engine itself. It's not like a piston engine where the blow-by will end up in the crankcase.

Originally Posted by Loki (Post 4877857)

You don't want to create vacuum in your crankcase at idle, nor give your engine a huge air reservoir to suck on while you're not at full throttle. Other cars PCV systems have a check valve that prevents this. Mazda chose to solve it by routing to before throttle body. As soon as you're on the throttle, the PCV is doing it's job.

So I'd leave it well enough alone. A healthy RX8s intake is bone dry, so the problem you're trying to to solve is not the problem that needs solving.

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Originally Posted by UnknownJinX (Post 4877883)

Well, PCV takes care of two things that can build up pressure in the oil pan: blow-by and water vapour.

Correct me if I am wrong, but looking at the rotary engine's structure, I simply can't see how blow-by can even get in the oil pan. Blow-by gas will simply end up in the adjacent air pockets in the engine itself. It's not like a piston engine where the blow-by will end up in the crankcase.

As for water, well, it's just water vapour. It's not harmful in a small amount, and shouldn't leave anything behind as it goes through the intake.

Also, from I have looked, this PCV design was already used for 95+ FD RX-7, so there must be a reason they maintained this design.

Originally Posted by Loki (Post 4877905)

Also true, the path isn't as direct as piston engines. The way I reckon, if gases get by a side seal under pressure, they mix into the oil and come out of it once the oil enters the pan and depressurizes. Like a continuous SodaStream, I guess.

Originally Posted by spartantrap (Post 4877925)

I appreciate everyone's contributions. You've given me things to think about.

I don't know why I didn't remember about the PCV valve... Honestly, the lack of a constant vacuum source (if necessary) concerns me. I know Mazda knows rotary engines better than anyone else, but I still have my doubts/concerns about why they set things up the way they do (like why Mazda put the dish on the middle of the rotor... it should've been put on the leading side so the combustion process would help push the rotor around...). Having the PCV hose routed behind the throttle body would seemingly eliminate the oil in the intake tract (from oil fill mishaps or otherwise) and should remove the milkiness on the dipstick tube and oil filler neck. It just kinda seems like a no-brainer if it achieves those goals. :dunno:

Now, since Mazda went to this PCV design in 95, my question is why? Was it because it was cheaper to make because it didn't need a PCV valve or some other reason? I've never heard of the FD having these problems, so something had to have changed from the FD to the FE; so my question is what?

I'm cool with modding mine to see how and if it helps. Especially if I make it easy to put back to stock. When I have the time I'll do it and see what happens; I'll let you guys know when I reroute it and report back how it works after a while :dunce:

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Originally Posted by UnknownJinX (Post 4878256)

Maybe they figured it's just not necessary. As mentioned, I don't see how a healthy rotary would have much blow-by in oil other than the tiny amount of blow-by that may make past the side seals. RX-8 is also naturally aspirated unlike the FD, so less blow-by and pressure in general as well.

Besides, I think the OEM design of putting it on the accordion tube also makes more sense. If you have a small amount of oil sprayed in there, it will just end up in the pits inside the accordion tube and that won't do much long term damage. On the other hand, if you spray it after the TB, it's a lot more work to clean it up, and it has a higher chance of jamming up your SSV, APV and VDI.

So if oil getting puked up from PCV is a problem you have, a catch can will be a short-term solution but you really need to look into what's causing it.

And having the dish closer to the leading side... Wouldn't that decrease the compression ratio? Renesis is the highest compression ratio RE and even then, 10.0 for a NA engine is pretty low by modern standards. Heck, the 2.5T Skyactiv-G actually has a compression ratio of 10.5 and that's a turbocharged engine. NA Skyactiv-G are in the 13~14 range.

Originally Posted by thebubbadog (Post 4878258)

Catch can for sure so you can see that amount of oil that it is puking up. I just bought mine off of ebay for like $30 and zip tied it below the tube that hooks to the to the intake where you put oil in. You car should have crazy blow by, Also make sure you didn't over fill you're oil because it could have went into the intake that way. If you're car has a lot of blow by you may try this to help, https://youtu.be/ETYmhdSd-Sk. I did it to my car and it helped clean it up and I could tell a difference for sure and I only ran a glass jar of water thought each rotor.

Originally Posted by UnknownJinX (Post 4878266)

Skyactiv wasn't a thing back then. I know my 08 Accord V6 had a compression ratio is 10.5:1. So maybe not that low, but imagine having it lower by moving the dish towards the leading side.

Originally Posted by spartantrap (Post 4878328)

I understand why you think the OEM design of putting the PCV on the accordion tube makes sense. I'm not discrediting that or saying it is an improper way of doing it. I'm just raising the question of why not manage the system like a piston engine? If blow-by is getting into the accordion tube, it will get into the intake manifold by default, so periodic cleaning is just one of those things :dunno:

When I have time, I'll figure out how to post pictures here so I can show you guys what my catch can looks like after 3-4 months of quite regular use; just to make sure I'm not seeing anything out of the ordinary (not looking for a how-to to be written up, I'll look it up later)

As long as the volume of the dish stays the same; no, it shouldn't decrease compression. It would just aid in the process of spinning the rotor and make more power in the process

After months of use, it has VERY little in the catch can. I'm talking so little there isn't even a puddle, just tiny dropplets

That might be worth looking into. After I do a couple of maintenance items

I see what you're saying about the compression ratio lowering, but it wouldn't take much to get the compression ratio back: just lower the volume of the dish :dunno:

Originally Posted by spartantrap (Post 4877876)

Originally Posted by spartantrap (Post 4878328)

After months of use, it has VERY little in the catch can. I'm talking so little there isn't even a puddle, just tiny dropplets

That might be worth looking into. After I do a couple of maintenance items

Originally Posted by UnknownJinX (Post 4878392)

Probably because there is no point to a PCV system like a piston-engined car? Again, the amount of blow-by in the crankcase is probably small enough to not warrant a system like that, especially on a naturally aspirated engine.

And now that I think of it, the dish position wouldn't really decrease the compression, so you are right. I had a brain fart. I suspect it has to do with more complete burn with the dish towards the middle, but I am no expert. Might also have to do with rotor balancing.

Originally Posted by Loki (Post 4878415)

Well not really though. If the dish were at the front, the dish would be passing the spark plugs before top dead center, and at top dead center you would be igniting the rear of the combustion chamber, which will just get quenched by the mass of metal and rich mixture at the trailing end of the chamber. And if you tuned to correct mixture at the rear of the chamber, you'd be HIGHLY susceptible to knock, because everything forward of that would be lean. Take a look on youtube of videos of transparent model rotaries running, there is no confusion about which way the engine should rotate. [edit] actually, consider where the primary spark plug is. It's in the forward part of the dish at TDC, and that's where the initial impulse comes from, so it's not super necessary to offset the dish. The second spark plug fires with different timing and is there to prolong the burn for efficiency.

It sounds like there's an assumption that a (healthy) rotary produces the same amount of blow-by gas as a piston engines, and has the same ventilation requirements. But as pointed out above, the path for that to happen is much less direct and requires compromised seals (so a non-healthy engine, probably not what they designed for). The gas that gets past the side seals is far more likely to get picked up by the adjacent face through its side seal as it undergoes the intake stroke, than to be pushed into the oil. You need the volume of blowby gas to be substantial and create pressures that force gas into the oil. That's, in my opinion, why oil in the intake is such a common early indicator of losing compression: the ventilation system is not designed to accommodate a failing engine which produces more blowby.

Originally Posted by spartantrap (Post 4878503)

There is a point to having a piston-like PCV, and its ramification are what I've been after this whole time... If we had a piston-like PCV, fundamentally we shouldn't have issues like this:

https://www.rx8club.com/rx-8-discuss...-111760/page2/

Because said piston-like PCV would draw the moisture out of the system much more effectively. Then we wouldn't have needed the TSB, and then the subsequently redacted TSB, to change the system to prevent oil getting into the accordion tube or having the condensated oil dipstick issue. The condensation problem was my only thing I was trying to solve, especially since it appears that my FE1 didn't have the TSB performed on it.

The main reason for moving the dish to the leading edge is in this video:

https://www.youtube.com/watch?v=pCteBhr4dGY

Look at how the rotor only fires in the proper direction because of him pull-starting it. That is the main reason for moving the dish to the leading edge, to have a proper rotation bias innate to how the rotor fires. How many early RX8 starters fail? Even the TSB starters aren't as good as the FE2 starters (hence why I put a 14 tooth in my FE1). How many times does the starter go in reverse because of the way the air fuel mixture fires? The two reasons why the engine stays running is because of its own inertia and the timing of the spark plugs... Moving the dish solves that whole issue



The videos I'm posting in this comment are ones I've already seen before you said to go to youtube. I'm just posting them for reference material so you guys can see where I'm coming from.

It wouldn't take much offset to accomplish sending the rotor around much more efficiently; hypothetically, you could probably dump the trailing spark plug and be fine, as long as you changed the dish's location to accommodate the proper rotation of the rotor. And yes, there's no confusion to us as to how the rotor should be spinning under its own power; but, just watch the video where the guy is pull-starting it and you can see that if it wasn't for him *forcing* the rotor around the *proper way*, the rotary might even start running in reverse....

Here's a video that has a very small snippet about the offset dish; I wish I could find the first video I found about it... but it got taken down... :icon_no2:

https://www.youtube.com/watch?v=m3pCLjHZmhM

Your last paragraph made a very simple concept seem like a revelation to me :lol2: For some reason it never occurred to me that the combustion chamber and the oil cavities are sealed from each other that well, so thank you for making that simple concept get understood in my brain; but that's not why I want to have a different PCV system. Getting the condensation out the oil is my only concern, especially when I don't have too long of a commute to work, and the oil is barely warmed up by the time I get there. My work is about twelve to 15 miles away, and I can barely run her hard enough to get the oil looking like oil if I push her *very* hard and go to extracurricular speeds :wink2: Just trying to think outside the box to help myself so I don't hurt the car with not really being able to drive her the way she needs. Yes, I drive her hard whenever I can; but that's not as often as I like

Thanks for the discussion, I always appreciate discussions like these :)

Originally Posted by UnknownJinX (Post 4878506)

I personally never had any moisture in my oil and I can do some short trips in the winter. I don't know if S1 is significantly different in that area.

And since I am not an expert, I broke out a book(well, the PDF version of it, anyway) written by Kenichi Yamamoto, who was the lead of RE department and later president of Mazda. There was a study on the effect from the location of the recess/dish. Having the dish closer to the leading side apparently emits more HC. And just to think the 8 already has as much trouble as it does with emissions...

https://cimg0.ibsrv.net/gimg/www.rx8...5a73a2da38.png

Lastly, the second video also mentioned having slits for spark plug holes... I am sure Mazda would do that if laser/microwave ignition is commercially feasible. With convetional spark plugs, Mazda's current design is probably as good as it gets, aside from shoving in another spark plug in each rotor like the 787B. His concern is already addressed with the smaller trailing plug hole - it's smaller to reduce the amount of leakage from one chamber to another.

Originally Posted by Loki (Post 4878508)

The dipstick thing is a bit of a red herring. There was a lot of discussion about it, that netted out to: you get condensation there because the dipstick is sticking out in the wind and is cold compared to the rest of the engine, making it a great place for vapours to condense out, and it never gets ventilated, so the goo accumulates there. If you perform a used oil analysis while having a foamy disptick, the moisture content actually in the oil won't be that significant (assuming no other issues). It looks terrible, but isn't really an indicator of anything.

Regarding the offset dish... the video you're showing isn't that representative, because it has a single spark plug centered in the housing. Our leading spark plug, which does most of the work, is at the top of the chamber at TDC, so it's effectively accomplishing what you're looking for. The impulse is imparted in the forward direction. Offsetting the dish makes absolutely no sense if you think about where the dish would be at TDC. The spark plug slit also makes no sense because that's a fantastic way to leak compression from one chamber to the next. I guess it could be harnessed for good EGR or something like but like, it's not that simple.

Ernie Brink (the guy in that video) talks a good game, but over on RX7 club his ideas were shot to pieces, because they don't actually work and/or are not viable to produce. The slit thing? Excellent for creating hot points and detonating the engine.