rotarygod

Just thought you guys might find this interesting. I spoke to Paul at Mazmart about the Renesis for a bit and discussed some things that I'd like to see done with the engine. Rick Engman has been playing with a couple of Renesis engines lately and has stumbled across some interesting info about the motor. I'm sure when Paul sees this he'll elaborate further.

Rick has an apparent issue with the design of the cutoff seal in the Renesis. First off he has found alot of carbon inside the Renesis as compared to the older rotaries which isn't anything new. As many here have assumed for a while, he thinks the excessive side seal clearance is to help aid with the removal of carbon from the side seal area. The interesting thing though is what he thinks of that cutoff seal. It is designed with basically the same flat profile as the oil control rings. Rick has found that this design can actually let some of the carbon that gets scraped off go under and past the cutof seal. He has even found carbon that went past the oil control rings. His initial discovery of this was when he removed a Renesis oil pan and found carbon buildup in the bottom of the pan! This alone should emphasize the importance of regular oil AND filter changes. It's unlikely your oil will have broken down. Change it to get all the crap out of it.

From what I got out of Paul, there is no way around the carbon issue as long as the engine is running as rich as it is with Mazda's tuning. One way to really get rid of this carbon issue is to run 2 stroke oil premixed in the gas. This assumes of course that you are no longer using the factory oil metering system. I propose that we modify a stock oil metering pump to accept oil from an outside reservoir rather than from the engine. I actually performed this mod on my RX-7 and use an external oil metering tank with 2 stroke. Obviously most don't want to do this but it's the best idea I can think of.

The real question that I have is that if carbon can be cut down heavily in the engine, would it be possible to successfully use a tighter side seal clearance in the engine to reduce leakage and gain power? It would make sense but only time and experimentation will tell.

Another issue that has surfaced is with the Formula Mazda Renesis engines. Those guys run leaner mixtures than the RX-8 does and they hold their engines at higher rpms most of the time which is harder on the engine. Some of them have reported that the apex seals can slightly bow or warp at real lean mixtures at steady high rpms which leads to detonation. This too is troubling. There are a few people that have run Ianetti ceramic apex seals in the motors and haven't had this issue which is nice. At $1600 for 6 apex seals there'd better be no issues! I don't really see this as an issue on a street engine though so don't lose any sleep over it.

The corner seals appear to be a source of wear in the Renesis as well where it wasn't much of an issue in the past. Dave Lemon at Mazdatrix has reported that using Renesis rotors and corner seals in an older 13B engine will cause the corner seals to absolutely chew up the 13B side housings. I told Paul about this and he is going to look into the coating differences between the Renesis housings and the 13B's. This info was news to him. My idea was to use 13B apex seals and corner seals and have the Renesis rotors milled out to accept them. This would create a new issue though as the larger 13B seals can chatter and skip at higher rpm's as compared to the Renesis apex seals. This is why Mazda made them smaller. The corner seals wouldn't be as harsh on the housings and the seals could be stronger if 2 piece seals were used but seal chatter isn't good either. This leaves Ianetti ceramic 13B seals which again are very expensive.

Paul and Rick are still looking into the different issues so that Mazmart will be able to offer a better than stock rebuild one day that addresses many issues. Hopefully Paul can come in here and potentially correct an errors I may have made but that's what I've gotten out of the conversation with him. They took apart the engine I was going to buy from them! Damn it!

Just thought everyone would find some of this interesting. I'm not sure how or if any of it is a longterm issue for street use so don't worry about it to much but at least people can be aware of it and know that there are those out there working to solve any potential problems with this engine.

Keith

interesting tidbits. keep us informed of more details.

alcimedes

Excellent information, thanks for the post.

crimson-rain

Carbon build up? Can the Renesis do that "steam cleaning" trick that people used to use on the 7s? You know, where they purposely ingest water into the engine. Don't know much about the technique but have heard of it.

Also, I thought Renesis apex seals where bigger and stronger than the 13B?

Sorry if dumb questions, but this is my first rotary.

rotarygod

I should quantify that the carbon buildup assessment came from a low power 4 port engine from an auto that they took apart. We know these have more carbon buildup.

rotarygod

The stock 13B seals were 3 piece. The Renesis is a 2 piece. As a whole the Renesis seals are smaller/ However if you compare a Renesis apex seal to any one part of the 3 piece 13B seals, they are larger. Mazda also made these seals stronger. When I wasy I'd like to see a 13B seal, I'd like to use a 2 piece seal as opposed to a 3 piece which is stronger.

crimson-rain

Is the reason for multi-pieced seals is to compensate for warping due to heat? And with those ceramic seals, are they multi-pieced also ($1600!!!!!!!!!!! - can I get a dang!!!!)?

newcastle

iTrader: (3)

Thanks for the information. I'm glad I change my oil every 3K miles instaed of the 7,500 thats called out for in our manual.

rotarygod

Mazda has gone back and forth over the years between 2 and 3 piece seals. The upgraded seals they sell for the 13B are 2 piece. The ceramic seals are 2 piece.

ZoomZoomH

iTrader: (1)

think 'italian tuning' will help with reducing carbon buildup?? lol

Nemesis8

iTrader: (3)

Nice post, and your right about Paul, Rick, and the Dr. We need to freeze those guys for future research

Was there talk about the Formula Mazda Renesis engines going to the 4-port? I thought I heard that somewhere...

Jedi54

iTrader: (7)

hmmm, very interesting info.

Note to self: Change oil every 3,000 miles from now on.

Mazmart

iTrader: (12)

I like a 2500 mile interval myself (For all my cars) and am currently running semi synth
5W30 in my 8. I'm using Yamalube Racing (Synthetic) pre-mix also as a supplement to the metering system.
My dream list right now for a perfect normally aspirated Renesis is as follows:
Ceramic apex seals (Iannetti of course)
Ceramic corner seals (Don't currently exist but would also preferably come from the Doctor)
And an even more durable catalytic converter so that we can run 'better' air fuel ratios.
There are other things I'd like to see if money was no object. I've always liked the separate oil metering tank concept. Hopefully Mazda can pull that one off themselves someday. The engine oil level shouldn't have to be checked with the frequency that is currently recommended. The ceramic apex seals could allow stable compression indefintely (No heat related sag).
The future is exciting to a dreamer like me.
By the way RG has quoted me with fair accuracy.
Paul.

Nemesis8

iTrader: (3)

And to further elaborate on this setup, and dash mounted oil level gauge for the separate tank.

rxeightr

Thanks RG & Paul for sharing the 'real' facts.

It leads me to ask (2) questions:
1) How will forced induction play into your findings?
2) What were you planning on doing with the RENESIS motor Mr. God ?

T-von

You guys not running and engine flush before your oil changes? I've been doing this on my Fd every 3k (which has over 100k on the original engine) with great results. My oil changes are nice an clean.

With the Renesis creating lower combustion compression than the older 13b's (because of larger side seals clearance), I really don't see the oil really being the main culprit to excessive carbon build-up. Sure it's working it's way under the oil seals and back into the oil pan and being circulated back into the oil system, but weak combustion of the rich A/F mixture will also create a ton of carbon build-up more so than the oil being injected by the OMP. The injected oil mainly creates a protective film on the rotor housing and is designed to drip and not squirt oil into the chamber. I feel even if the tune is more lean you are still going to have carbon build-up problems since there is so much side seal clearance therefore weakening the combustion event and burning less fuel. This is where all your carbon is coming from and why the Renesis is so prone to flooding.

The reason I can say this is because recently I rebuilt my 91 NA Vert engine. Due to a failed experiment, all my side seal to corner seal clearances was way out of spec. I could only get no more than 60psi compression after the run in. When I broke the engine back down again, there was already carbon build-up on the rotor faces and apex seals after only 30 min of operation. Keep in mind I had 2 cycle premix in the tank and the OMP had new lines and no oil was fully flowing through them at the time.

In my experience, the type of fuel you use will make the "BIGGEST" difference in the carbon deposits. I use to use the cheap stuff and would get black smoke out of my tail pipe after heavy acceleration. I've since switched over to Texaco w/Techron and noticed a "HUGE" improvement. Now when I got WOT, I get a grayish smoke out the tail end and it's nearly clear. Also keep in mind that a my stock Fd also runs a super rich 10:0 A/F ratio under boost and probably has less internal carbon build-up with over 100k original miles than you guys with these new engines. Bottom line use better fuel guys it really makes a difference.

rkostolni

I am also very interested in what the experts would change in the Renesis for FI applications. Would lower compression rotors be worthwhile if they were ever made available?

T-von

With higher compression, it's all about the timing. There is a guy over at the Rx7 club forum by the name Crispeed, that is a tuning specialist when it comes to tuning high compression rotarys. His 13bs are making 500+ rwhp. Just find a capable tuner and you will be fine.

expo1

With the amount of oil left in the coolers and lines it would take more than one flush to get ALL the oil out. I am not even sure it can be flushed without disconnecting the oil coolers.

T-von

Well when I started doing the flush, I did it once a week for 4 total times over a month. I just used cheap oil and filter during all the flushing. Cost me $10.00 every time I did it. The reason I did it so much was because of the recommendation of another forum member. He told me if my engine had never been flushed, I would need to do it this way to really clean it out. That's what I did. Now I only do it every 2k because of my engine mileage. I also don't worry about the remaining flush inside the system and working it's way through my OMP lines. The flush is designed to break down carbon so it also helps some when it's injected into the combustion chamber.

yiksing

So does running the engine hard in high rpm helps get rid of the carbon buildup? Thanks for sharing RG

brillo

I’m impressed thus far that this post hasn’t freaked everyone out that their engine is going to hand grenade at 50K. It seems that when some one discovers something that was an engineering compromise about our engines, everyone wigs out.

It looks like we now know why the clearances on the seals seemed looser for no apparent reason. It was a compromise to account for the potential for carbon buildup.

Just so that its said, there is no issue with these findings and the life of your engine under street use. In fact, a little hard driving as we all know if actually better for our engines. Wanna prevent carbon buildup? Use a good quality low ash oil (or good synthetic such as Royal Purple or Redline) and rev the engine.

I don’t think this affects boosted Renesis engines at all under 10psi or so. Under 10psi, you can easily make safe changes to the timing to compensate for the high stock compression. Above 10psi, I’m not sure, but if you can’t get the car moving with 10psi to your liking you have other issues as well.

Pololo_RX8

Well look who is replying! This type of discussions and knowledge is what I was missing here! (coming from the Miata.net forum)

Just rev up your engine to redline at least once a day when you drive it, use good gas (I always use 76), change oil every 3K miles but I am sure you all know that already.

Excellent discussion!

Carlos

T-von

No that's not it. The side seal to corner seal clearance was increased because of the extra heat the side seals get with the side exhaust. The side seals expand more because of the heat and need the extra clearance to keep them from breaking the corner seals. This expansion is also why you never clearance the side seals to 0 clearance with the corner seals. Some people incorrectly do this on the older rotarys and wonder why they are blowing the corner seals. The side effect of this extra clearance is the carbon that works it's way past the larger seal gaps weakening the combustion compression and the more potential for flooding.

RichardK

My car is going to remain stock, is a lo-power, and is leased so goes back before the warranty runs out. However, my take on it is this:

Wankel engines are still a very new technology. Whilst the Otto-cycle 4 stroke engine has been around for nearly twice as long, many of the engineering challenges it presented had been tackled in the preceding 150 years of steam technology.

And, 50 years ago - when the conventional engine was a similar age to the Wankel - people thought nothing of having to rebuild their engines every 40K or so. A decoke was nothing to be frightened of on a cooking car, and performance cars - well, when people push the technology you get cars like Ferraris which seemingly need insane attention (I don't get this myself - if Audi can make a 400bhp V8 which has regular service intervals, why is a Ferrari such a big deal to look after?).

Rotary is still young. It's still inefficient and isn't wholly suited to all applications. The improvements in tech have been startling and by my reckoning a major improvement in power or longevity occurs every decade or so, albeit with some of the ancilliary functions being due to developments with regular engines.

With this in mind, I like new stuff. I like odd stuff. If my rotary blows up at 30K and I still have the car, it'll suck, but I accept this as part of being a pioneer.

Are RX8 owners still pioneers? Sure. I think the RX8 is the first truly successful rotary engined a car, a car with mass appeal, with modern tech all around, with appeal to people beyond the usual car geeks and petrolheads, and with the reliability and usability to compete fairly against conventionally engineered cars.

The next 50 years are going to be very interesting indeed for the rotary, I think.