I was walking towards my computer, and a new question popped into my head. When is appropriate to switch to bigger apex seals? How much chamber heat and pressure can the current seals hold before they are compromised? What about the side seals? I don't have CFD or FEM...yet, so I can't do any nerdy analysis. Also, are there better sealing materials for rotary engines, other than rubber, assuming it is rubber? I fear the broken O-ring if and when I crank up the boost.

We'll, upgraded seals are never really required. Detonation breaks apex seals, not chamber pressure. As long as you tune the car right 2mm are fine for all the power you can make. someone calculated once that it would take something like 2500 hp per rotor before the seals were comproimised. 3mm seals on an rx8 would lower the redline to something like 7000 rpm due to seal chatter and seal float because of there increased mass. Some of the top 600-700 HP rx7's use 2mm apex seals. Side seals also never need upgrading. Things that fail due to extreme HP are the rotors, the eshaft and the side plates near the dowl area. No one knows how stong these componets are on the rx8 yet, but i would suspect that the eshaft and housings are stronger the previous cars. the rotors may be weaker due to there thinner lightweight casting, but only time will tell. generally High GP has a tedency to dent rotors, stake e-shafts and the twisting motin between the housings causes dowl pin seat to crack(these things only occurs at ubsurdly high HP's) This is why dowl pinning or tenstion bolt studs are often used on high HP cars. Lastly apex and side seals are not rubber. The only "rubber" seals in the motor are the inner and outer water o-rings (think headgasket) and the o-rings for the oil control rings. These both do not fail unless the car is severly overheated. There are ceramic apex seals avaliable, and ive heard of protoypes from Ianatti, but these are mainly used for racting due to there expence. The benifits of ceramic seals are less engine wear, less friction, Less mass which allows a higher redline ( i think the rx8 seals are allready light enough to spin the mottor much faster thne stock) and the ability to run higher exhaust temps (this only really comes into play on NA race engines where they are leaning them out for every once of power, a turbo cars exhaust temps would be much cooler thne this due to the extra unburnt fuel in the exhaust. They are also more resitant to bening (only helps a car with periphreal exhaust and/or intake as there is no real bending load on the seals in the rx8) and they are a little stronger, but wills till break from detonation.

In short there are no seals immune to detonation. Rx8 seals will take almost anything you can thow at them as long as there is no detonation. There is no need to upgrade, and thicker apex seals would be a redline reducing downgrade. Other parts fail first in ultra high HP operation. Ceramic seals are great, but will not save you from detonation if it occurs( not to mention the 2k a set price tag). If you want the motor to last, tune it right with nice fat AF ratios, down in the 11's.

I had forgotten about the issue of detonation. Sorry I had implied that an apex seal is made of rubber. I was referring to the O-ring seal. So, I suppose the stock seals will suffice for a street/track car? Though the benefits of ceramic apex seals are clear, do they have more of a tendency to wear out? Also, what type of material is a typical apex seal made of? I just wanted to have someone clarify that, since there aren't many threads that discuss the strength of the RENESIS. Thank you for the info 86rx7 :).

Ceramic seals will outlast stock seals due to there hardness and lower coeficient of friction. Carbon apex seals on the other hand, which are only used for racing, non FI rotaries wear out in ~20k miles on the street, however i am not aware of carbons being avaliable for the rx7 (probably never will be because the stock seals are pretty light/ the only advantage of carbons is ther light weight which alows a higher redline) Stock apex seals (i'm 98% sure rx8 seals are manufactured the same way rx7 apexes are ) are bainitic cast iron with an electron beam chill hardend tip.

I had forgotten that ceramic is quite a durable material.

Alright. I found a link with more information (anecdote) about the usefulness of ceramic apex seals.

http://www.selectmaz.com.au/apex_seals.htm

How many pieces (one-piece, two-piece, etc.) make up the RX-8's apex seal? Also, what type of material is the apex seal spring, and what is the spring constant? What is the purpose of the electron beam-chilled tip for the apex seal?

I wonder if 86rx7 has the answer...

2 pieces, a main piece and a corner piece. This is so the seal runs zero end clearence. The springs are some kind of stainless steel I think, there are two of them an inner and an outer. I'm unsure of the spring rate, but in a rotary the seal springs are mainly for starting . Apex corner and side seals work off of gas pressure to press them into there sealing surfaces. the chiill hardend tip is to increase the hardness of the wear surface of the seal for improved life and less friction.

pics

Thank you for the information 86rx7. You are a true beacon of knowledge :).

What are the differences between a one-piece, and other segmented apex seals? What kind of advantages/disadvantages they have over each other?

Well, one piece seals need to have there end clearence set. Because of this the will allways leak a little pas the ends of the seal. This doesnt matter to much if your motor is spinning really high rpms all the time like a race motor (hence why carbon apex seals are one piece) Two piece seals effectivly run zero end clearence because the seal spring pushes the corner piece against the side end plate. There is still a small leak because the seals are machined slightly longer then the rotor width so that the seal doesnt leak from the gap where it is divided. The corner piece is actually slid down slightly away from the rotor housing in operation due to this, but this leak is tiny compared to one piece seals. Some aftermarket apex seals for rx7's have larger corner pieces which leak somewhat more, but it is still much much less then one piece seals. Two piece seals work good for low and high rpm. Three piece seals are what was used on previous rx7's after 86(now replaced by 2 piece seals) and are duvided once again lengthwise across the main part of the seal. These seals effectivly run zero groove clearence as well as zero end clearence. The draw backs to the three piece design have been debated for a long time and i havnt seen enough evidence either way to make a conculssion, among the possible drawbacks are a thermal break in the seal which hurts heat transfer and more apex groove wear. Three piece seals seal even better at low rpm the two piece and prefore equally well at high rpm. I have it on fairly good athority that mazda went with 2 piece seals for the rx8 (and replacment seals for the rx7) because threepiece seals extra machining steps nearly doubled the cost per seal, and the slight bump in low rpm compression wasnt worth the extra cost. I believe they are right,.. the difference in performance between two and three piece is fairly small.

Thoose are the 3 major types of apex seals used today. There was atleast one more type at one time, an early three piece seal composed of a main piece and two corner pieces on each side, but this does exactly the same thing as a two piece seal with twice the leakage, so it evolved into the two piece.

Basicallly in terms of starting ease and low rpm sealing three piece are the best, followed very closly by two piece, then one piece. All seals will have similar performance at high rpm (two/three piece seals still slightly outpreform one piece at high rpm) Mazda used two piece ceramics on the 787b, and they saw a ~2% increase in torque starting from low rpm, peaking at a little over 2% at 6k, and falling of to ~0% by 9k over one piece seals.

thats all i can think of right now.. heres the paper i got the r26b #'s from http://www.mymazdarotary.com/mazda_rotary_general/r26b/html/r26b_paper_html.htm

Thank you for the info 86rx7. Are the different types of apex seals more than just speed dependent? Which of the three you mentioned is best suited for forced induction?

It is great to see a post like 86rx7 does as he has correct information, not like a number of the so called rotary experts that post on this site.

I will give you a little more background. 1st is any auto manufacture has a few main issues in developing an engine for the street (pure racing is an exception). 1st is cost of manufacture. Just because it is better it may not be used if the improvement is not worth the cost. 2nd is reliability for the general customer. This is where the engineers are constatly making chages because of warranty and customer issues. 3rd is EPA fuel milage. Commonly automatics can get better EPA restults, like the 8 does, because the engineers can design the shift patteren arround the EPA test.

As for the seals. The carbon seal was eliminated in production because of all three reasons. Cost, reliability, and low speed sealing for the EPA. The two piece was much better for all three. The three piece, like stated by 86rx7, benifit in sealing was probably not worth the cost.

Now for a few technical points. As stated by 86rx7, the springs are just for starting, so only issue is that they keep there springyness when hot. I had a rotary pickup. After a real hard 200 full throttle miles pulling my boat back from Lake Havasu with a strong head wind the engine started to have hard starting. When the rotor first started turning it would spinn freely, so the starter was able to spin it fast enough so centrifical force pushed the apex seals out enough fo the engin to start. Once running I still had good power and normal gas milage, so I drove it for a few months untail I had time to take the engine apart. When I did the only thing I found wrong was flat apex seal springs.

The apex sel width is an interesting issue. This is just like piston ring width on a 2 stroke. A wider seal does have more material to resist wear, but is also heavier. On a pistone engine at high rpm the piston ring is forced up durring the up stroke and reaches a high speed when ~ at mid travel. Then the piston and ring must slow down to a stop by the time the piston is at top dead center. The weight of the ring (& piston) has inertia and will want to lift from the bottom of the ring grove to the top. Well the primary sealing surface of the ring is both the face to the cylinder and the bottom of the ring to the piston. Normally compression and combustion pressure pushes the ring down and holds it on the bottom piston ring grove surface. If the ring lifts from the bottom, as it will do at high rpm, the gasses will excape and you will lose power. This is why racing engines have thin rings - so they have less weight and less inertia and seal at high rpms. A similar problem occurs in the rotary. The rotor never comes to a stop, but the tip with the apex seal does slow down and speed up. So a thinner sae is better at high speed. But a thinner seal is weaker and will wear faster, so may not be the best for the street. Now a ceramic seal is lighter and very strong, but very costly to make, so again not for the street.

Mazda did have an issue with the 74 to 84 generation 3 mm two piece seal that is interesting in this discussion. This may be the reason they tried the additional pieces. When new the apex seal and the rotor housing would, at times, not properly seal. (This is one reason the milage increases with break in.) That would cause some blow by gas that would cause localized heating of the apex seal and it would worp! A slight "U" shape that would not seal and the nww customer would have hard starting and other problems. They preventer this problem with a coating on the seal that would last through the break in period, but the coating cost money. SO the multi piece seal was tried to eliminate the problem at a lower cost.

The inner rubber seal, head gasket, was the main reason for engine failures back in the 1970s to 73 models. During warm up the aluminun will expand different than the steal and the rubber was being burned. The 84 and later seals had a teflon coating to resist the busrning. THen they moved the O ring from the AL housing to the Steel housing and is no longer a problem.

Enough.

Please forgive all the bad typing and spelling. I need to go and no time to fix.

Where does one draw the line on picking the right seal for the right application? I hear the stock seals will fare well against, I guess, at the most, 15 psi of boost. I'm not sure; this is the first time I have ever dealt with a rotary engine.

No one knows how stong these componets are on the rx8 yet, but i would suspect that the eshaft and housings are stronger the previous cars.

The e-shaft is stronger than the older ones. Mazda actually published that somewhere. I wish I remembered where. No clue about the housings though.

Don't feel like your're hijacking the thread, Charles :). I started this because maybe someone here can put some serious input about properly sealing the engine, especially if we want to use FI, nitrous, etc.

I think the myth of nitrous and rotary engines is stemmed from using nitrous on 4-ports like the 13BT, and 13B-REW. I suspect bad tuning. Also, I believe Mazda stopped using carbon seals a long time ago.

I want to learn more about rotary engine seals, from the different designs to materials involved. I'm still curious about the spring rate in the apex seals, side seals, etc.

For nitrous, I think the stock seals will do just fine. I wish I had an FEA program to simulate the stress these seals face. If you wanted some extra insurance, not to mention an empty bank account, you could invest in the Ianetti ceramic apex seals. I hear they are the Rolls Royce of apex seals ;).

Mazda did have an issue with the 74 to 84 generation 3 mm two piece seal that is interesting in this discussion. This may be the reason they tried the additional pieces. When new the apex seal and the rotor housing would, at times, not properly seal. (This is one reason the milage increases with break in.) That would cause some blow by gas that would cause localized heating of the apex seal and it would worp! A slight "U" shape that would not seal and the nww customer would have hard starting and other problems. They preventer this problem with a coating on the seal that would last through the break in period, but the coating cost money. SO the multi piece seal was tried to eliminate the problem at a lower cost.

The inner rubber seal, head gasket, was the main reason for engine failures back in the 1970s to 73 models. During warm up the aluminun will expand different than the steal and the rubber was being burned. The 84 and later seals had a teflon coating to resist the busrning. THen they moved the O ring from the AL housing to the Steel housing and is no longer a problem.

Enough.

Mazda still used teflon linners on the inner combustion o-rings after they moved the grooves. Also, for the rx8 they moved the grooves back to the rotor housing for a reason i'm not sure of..(possibly because of the groove wall corroding away when they were in the side plates on very high mileage cars / cars run without antifreeze or another corrosion preventer?)

Also rotor housings were coated with ptfe to prevent seal scoring during initial startup/breakin. this was switched to a graphite coating on the 93+ engines, the rx8 probably uses the same graphite coating.

The Main thing that let mazda switch from carbon seals was the micro porous chrome plating on the housings. When mazda was first working on the design, they were plauged with seal chatter problems making the housings unusable after a few thousand miles. This was solved by using carbon seals which were self lubricating. The first mazda rotary, the cosmo sport used these 6mm carbon seals. The draw back as TRZ750 stated was wear and low rpm sealing (from being one piece). Mazda tried a few things to use steel seals in the rotary, (seals with holes drilled in various places to change the harmonics of the seal etc) But what finally worked was a coating of chrome on the housings that had microscopic holes and grooves in it to retain lubrication. This let mazda use the steel seals we see today. but i digress..

For a street car i'd stick with two piece seals. All the seals preform similarly under boost. It's not horsepower that breaks seals, its detonation. FI it,.. just tune it properly and you'll be ok. I'd contact a tunner atleast for advice on tunning it. I believe the safe zone for previous FI rotaries under high boost conditions were AFR's around 10.5:1...but i'd talk to a few other people and get more opinions before you settle on a target AFR.

the only other problem i can think of is insuficient output from the OMP. Previous FI rotaries had slightly higher output from the OMP then there NA counterparts. You could probably reprogram the rx8 ecu, or trick it somehow to inject more oil, but the simple solution may be to add a little premix to make up for it. This is only really for long term reliability anyway..

What is PTFE, and why did Mazda make the switch to a graphite coating?

Also, what kind of advantages/disadvantages would one see in single spring, or multiple spring designs (apex seals)?

BTW, Rotary Aviation has a good FAQ for their apex seals :).

http://www.rotaryaviation.com/apex_seal_faq.htm

Also, for the rx8 they moved the grooves back to the rotor housing for a reason i'm not sure of..(possibly because of the groove wall corroding away when they were in the side plates on very high mileage cars / cars run without antifreeze or another corrosion preventer?)



It was really a very simple reason why. They wanted the extra casting thickness between the seal grooves and the exhaust ports. If they kept them in the side housings there would have been less material between the water seals and the exhaust sleeves. Since the exhaust is very hot, unlike the intake, they felt that every last little bit of material was needed.

That makes sense Rotarygod, good to know.

I was mistaken on the date of the change to graphite, it appears that it toke place in 1984. This document goes into why more in depth.

http://www.thecarricos.com/ACRE/Documents/Recent-tech84-1-6.pdf

>As far as rpm lomits I can say I have had my RX-8 to 11.5k rpm and it still runs great.

is there an easy way to defeat the rev limiter (which i think is set to 9.5K)? does the motor make power over 10K? and i would rev the heck out of my 1984 rx7 (way past the 8K limit of the tach) during racing and never blew the water pump (which is what i thought was the limit).

if accessory explosion limits the rx8 in revs, can we make more power with underdrives and a raised rev limiter?

thanks,

james

> It is said there is no substitute for displacement

no, there is, its called revs :) and this is where the rotary excels. i am pretty sure the renesis will be limited on a street car by the accessories, so a brief blip wont hurt anything. hold it there for long and the water pump will explode or cavitate (and rotaries dont like to overheat at 11K). electric water pump? maybe we have one now, i dont even know!

ok, i understand the 11.5K now. S2000s are pretty easy to blow up with missed downshift to 2nd instead of 4th. since on the freeway you need to downshift at least to 4th to get in the powerband, it is even easier to accidently hit 2nd in the rx8. done it myself :P.

if the intake and exhaust and computer can handle it, raising the rev limiter 1K should be a nice improvement in peak power, if not driveability.

james

i wonder if that's a clearance issue, with the S2000's...??

anyways, awesome thread. thanks 86rx7 and TRZ750, i always enjoy learning new tidbits.

as for the A/F ratio, for the RX-7 guys they're always all about screwing the tuning and just going uberrich (substituting more boost and waymore fuel for better tuning) to get good power on a turbo, they seriously won't even entertain the idea of running at 12:1.
if your setup is efficient enough you won't have to worry about the classic 10:1 (i guess 'cause it's a round number) the FD guys run at 20psi on 91 octane.

raising the rev limit on the engine, in stock form, won't really gain you much power (you can see torque starting to take a nose dive at about 8500) 'cause the ports are inadequately sized to flow at that rate, not to mention the resonances in the SDAIS system are all for lower rpm points. supposing you could retune your hardware AND software, without changing internal components yes i do believe you could make plenty of extra power from this motor with more rpm.

i think the S2000's are easy to blow up on downshift because the piston speeds at redline are already almost the same as an F1 engine. i dont think there is much leeway for a boinger (reciprocating) design.

my memory thinks the 6 port 13B in 1984-85 had 3mm apex seals. the other years in general had 2mm (at the rx7's). i am no expert, but i did own and race an 84 gsl-se.

great thread, thanks guys!

james

i think the S2000's are easy to blow up on downshift because the piston speeds at redline are already almost the same as an F1 engine. i dont think there is much leeway for a boinger (reciprocating) design.

my memory thinks the 6 port 13B in 1984-85 had 3mm apex seals. the other years in general had 2mm (at the rx7's). i am no expert, but i did own and race an 84 gsl-se.

great thread, thanks guys!

james

F1 cars can rev up to 18000 rpm and sometimes higher. I don't think the S2000 has piston speeds near that high.

All rotaries before 1986 had 3mm apex seals. 1986 and on use 2mm. In the early rotaries of the late '60's and early 70's there were 6mm carbon seals.

Road & Track Road Test Annual 2001
“No question, Honda has bragging rights, having produced the first 2.0-liter production-car capable of 9000 RPM-and producing an astonishing 120 bhp/liter in the process, with piston speeds that exceed those in Formula 1 racing.”


thats what i remember from when the car came out. the F1 motors are 18K rpm, but the stroke is very short in comparison to the S2000 so the maximum piston speed can be compareable.

i would imagine the speed of the apex seal on the casing could be even higher.

james

As others have sai,S2000 piston speeds exceede thoose in F1 cars. The B18C has piston speeds in the range of F1 engines http://dwolsten.tripod.com/articles/sep93a.html. formula one motors are EXTREMLY short stroke ~5 CM (http://www.f1mech.co.uk/engines.htm)

Previous rotaries max rpm were defined by the point where the weight of the rotors and counter weights starts to flex the e-shaft into an S shape, when this gets bad enough you get shaft to bearing contact and spin a bearing. this is why racing engines use tapered e-shafts and bearings with larger clearnences (often screw locked). After that point is passed the rotors can contact the rotor housings/ side housings from the shaft flex. This is why proper race clearencing is preformed. Also the spring pins holding in the rotor gear can fatigue if held at high rpm and let the rotor gear walk a tad and jam the rotor, which is why gears are often snap ringed in (ive heard of the snap rings fatiguing at over 10k and shattering however) these things generally started to happen somewhere north of 8500-9000 rpm in the previous 13b's.

Now,.. the rx8 has lighter rotors, a stronger eshaft, and probably a refined rotor gear . I'd guess that mazda also worked on some of the cleaences for the rx8 also. But what rpm does that get us? We wont know until someone starts porting/racing the 8 and blows one up from being over reved.

One interesting product that helped reduce e-shaft flex in the RX7's was guru's two piece e-shaft. The shaft alows for a center bearing that GREATLY reduced shaft flex.Ive heard of as high as 14k rpm for short bursts with the guru shaft.


If yoiu want to kill two birds with one stone, porting the renesis with something like a bridge port would alow the ports to flow more AND move the S-dias rpm higher (more port duration requires longer runners for the same rpm, even with DEI like the renesis uses)

One interesting product that helped reduce e-shaft flex in the RX7's was guru's two piece e-shaft. The shaft alows for a center bearing that GREATLY reduced shaft flex.Ive heard of as high as 14k rpm for short bursts with the guru shaft.

let's get some pictures of this awesomeness, it appears they use the same coupling approach as Mazda does with their 2 and 3 peice e-shafts.

http://www.rotorsportsracing.com/images/guru/Complete_eccentric_kit_8_1.jpg
http://www.rotorsportsracing.com/images/guru/Assembled_eccentric_shaft_1_1.jpg

this little beauty will set you back a mere $2500 Aus... pocket change.

porting the renesis with something like a bridge port would alow the ports to flow more AND move the S-dias rpm higher (more port duration requires longer runners for the same rpm, even with DEI like the renesis uses)

that'd be a problem with the bridge port, but a full blown p-port on the intake side may be workable for the extreme side of semi-streetable (probably not even close to emissions legal) performance.

I didn't think about stroke when it comes to piston speed. That would make the difference.

A PP would be nice but would require at least a custom cast lower intake manifold, which may be avaliable for the rx8, as they are avaliable for the 3rd gen rx7 from scoot(and another company in australia too i believe)

I was saying the bridge would help the s-dias by extending its effectivness further into the upper rpms. a bridge that opens 100 degrees before TDC would increase the intake duration by ~22%. If you figure the ratio between the intake length required and port timming is 1:1 (it's probably not, someone help me out here?) that would move peak power somewhere close to 10k. seing as how the current rev limiter is at 9500, I dont think a 10,500 rpm redline would kill her. Could be wrong though as this is uncharted territory.


I swear im gonna save up and buy one of thoose shafts one day.....

A PP would be nice but would require at least a custom cast lower intake manifold, which may be avaliable for the rx8, as they are avaliable for the 3rd gen rx7 from scoot(and another company in australia too i believe)

who needs a cast one?? fab up a tubular one, no biggie right?? ;)

i have no idea about the resonant tuning stuff, i know only a little outside what rotarygod preaches, so... i'm not the guy to answer that. makes sense, though, that a longer wave with a different pulse intensity may have a lower resonance, right?

i owned a small company that designed and sold a product that allowed tuning of the resonant intake system on a different mazda (piston) engine, specifically for modified engines. it is reasonably straight forward as long as you stick to the stock configuration. when just the EFI intake was changed, we obtained a 12% increase in peak torque by changing the tuning of the resonant intake with our product over the stock ECU settings.

james

The longer the port timing, the longer the manifold runners need to be to maintain the same acoustic resonance. Most people that run longer timing generally want higher rpm power though so they usually do the opposite.

By the way, the apex seal springs are vital for more than starting. This is why cars equipped with Iannetti apex seals produce 5 to 10 more hp than stock. They are typically run with much more spring pressure, because they can. Sealing efficiently in the upper range is critical to power production; centrifugal will not do it alone.
Ceramic seals are going to be a renesis owners best friend. There, I've made my prediction.
I thought quite carefully about a screen name and am very proud of affiliation to a product of such high quality. Simply put, they are to rotary sealing what the HANS device is to racing safety; revolutionary and top notch in quality.

They are typically run with much more spring pressure, because they can. Sealing efficiently in the upper range is critical to power production; centrifugal will not do it alone.

but gas pressure does all the sealing while the motor is running anyways...??

I'm a little confused on this as well, the books and such ive seen on the seals says they work off of gas pressure, however mazda does use duel speings, and usually you use two differnt springs in things like this so that they have differnt harmonics then each other and still work where a single spring would hit harmonics and not doe its job. So that implies that the springs are used at high rpm, which is contrary to everything ive read. Anyone know for certain? Maybe the springs amainly help out on the non combustion side of things?

no that's completely impossible. how is a seal suppost to stop anything with a crush pressure of next to nothing?? the gas pressure is what does the sealing, and the springs locate the seal in the groove. for one peice seals, there's only one spring, and the double spring system is for the two peice seal, and i can't see how the spring contributes anything to sealing beyond locating it in the groove while the seal is going through its vertical travel during its trip around the rotor housing and while starting the engine.

The springs still exert outward force against the seals even at high rpms.

:rolleyes:

But i think that outward pressure is next to nothing compared to the gas pressure pushing them out...

Wakeech, what you said makes sense, they only need the duel spring because of the corner piece, i dont know why i didnt think of that. The world feels right to me again.

True, but wouldn't a carbon apex seal have a much shorter life than a cast iron seal?

By the way, the apex seal springs are vital for more than starting. This is why cars equipped with Iannetti apex seals produce 5 to 10 more hp than stock. They are typically run with much more spring pressure, because they can. Sealing efficiently in the upper range is critical to power production; centrifugal will not do it alone.
Ceramic seals are going to be a renesis owners best friend. There, I've made my prediction.
I thought quite carefully about a screen name and am very proud of affiliation to a product of such high quality. Simply put, they are to rotary sealing what the HANS device is to racing safety; revolutionary and top notch in quality.

I don't understand how a ceramic apex seal can free up 5 to 10 hp. Also, where on the rpm band do you experience this power gain? My guess is the weight of the ceramic seal versus the cast iron may free up some power, but 5 to 10? I'm skeptical about that. Besides, aren't ceramic seals very expensive?

MarkJ knows of what he speaks; staying in contact with the housing is what it's about. Even if you could achieve as much horsepower with steel (which you can't) the losses would only be a matter of time. Combustion pressure, temperature and insufficient support will cause sagging.
Another advantage with ceramics is lack of apex groove wear( Rotor).
In the long run they're worth the money, heck I think they're worth it in the short run too.
To answer the question of where the increase exists, it is; as expressed by MarkJ, when they would begin to float or lose contact with the housing. This will not happen with the proper spring pressure. Problem is you cannot run that kind of pressure with steel seals. This sealing improvement has another advantage: it helps prevent detonation by preventing hot ignited gases from migrating into the upcoming one that would be undergoing compression. This means that ceramic equipped motors can run leaner mixtures and more ignition timing safely whilst not even requiring as much oil metering.
Too good to be true? That's why they aren't cheap. They've been the seal of choice since about 1991. They are what were used in the Le Mans winner except that today's version are much better.

Right,.. To quote Kenichi Yamamoto's book "Rotary Engine"

These are from the section on apex seals:
"The pressing force applied to the seal must depend on the gas pressure, except when starting. Therefore the clearences in seal groove, which are shown in Fig. 4. 10 as (delta)G (delta)W and (delta)C, which form the gas passage to the seal grooves, should be determined carefully. Furthermore, the clearences should be tested out to determine the optimum setting by experimenting with an actual engine." (page 59)

Further down the page he describes conditions in which the gas pressure doesn't raise fast enough and can result in partial noin sealing, in describing solutions to combat this he adds

" To prevent this, a cavity on the side of the apex seal (see Fig. 4. 14) is helpful. This cavity provides a passage for burned gas to reach the bottom of the seal to maintain the sealing effect, even when the top of the seal is pushed to one side by the frictonal force at the top or by sudden increase of pressure." (page 59)

In describing apex, side(both "line" type seals) and corner seals(cylindrical type seals) general working princibles earlier in the chapter he writes:

"Each of these seal types is pushed two ways by gas pressure, first to one side of the groove, and then onto the sliding surface. The former is referred to as the "Secondary sealing surface" and the latter, the "Primary sealing surface". The basic requirement of a gas seal is to maintain sealing effect on these two surfaces."(page 53)

Further: "As was explained in the previous chapter, which deals with the basic principles, the pressure for pushing the gas seal, while the engine is in operation, is obtained from the gas pressure and the pressure drifference between two adjoining working chambers. Therefore, the spring installed beneth each seal piece serves primarily to provide the necessary push on the seal at the time of engine start. therefore the initial spring load can be made light." (53)

There are also various graphs charts and equations used to figure out how fast this gas pressure will rise and exert force on the apex seal, the intertial force on the apex seal, force applied to apex seal by gas pressure ETC... infact there is more technical stuff on apex seals using gas pressure to seal than i feel like digging through right now..

And of course if you dont believe Mr. Yamamoto there is no help for you........

Thank you for the info guys :). It's been a while since I've written on this thread (other than those recent posts).

MarkJ, once again you hit the nail on the head. Myself and a friend of mine are trying to figure out who you are and whether he (or we) know you. Do you by chance live in SC? If you prefer to pm it would be appreciated. I may be able to help regarding some seals etc. Thanks for your tremendous input.

The book does go into iron seals and i dont really believe that ceramic seals work off a completly differnt principle then all previous seals. Springs= starting, Gas pressure= sealing If youve ever felt the spring pressure actually on an spex seal you would know this, its very low. you can easily pus the seals into there groove with your pinky finger, no way it would seal the engine very well against blowby.

This gas pressure sealing thing effectively ended in 1973.

uhhh.... you're telling me that steelies and ceramic seals have spring pressures in the thousands of lbs/sq.in. ??

side seals and corner seals still use gas sealing, not to mention piston rings.

With that said, does anyone know what the spring constant(s) are the for RENESIS' apex seals? My guess is a spring spec'd around at least 1 ksi is over-engineered. ;)

Why would I want a rotary engine with no springs?!

Apex seal springs are not only effective at startup and low rpm's. They are very effective everywhere. Inertia from the engines rotation assists the seals in sealing at higher rpms but they are not the only thing responsible for it. You always have spring tension against the seals. There is never a time you don't. If people think that the seals themselves are only held against the housings at high rpm's by inertia then I'll throw this little tidbit in. The springs have mass too and are being forced against the seals. This is in addition to their normal tension against the seals.

Sorry shellys man, that was directed to wakeech, who seems to think that springs dont do anything. You are correct in your statement about springs being vital to performance.
Inertia is also responsible for the heavy seal lifting off the housing at high rotor speeds. that is why ceramics and carbons survive high rpm, and cast irons do not.
You guys have got me thinking.....
The forces on the seal at the sealing contact surfaces will be
1 - Inertia, a radial force which is a function of the housing profile. It will force the seal outwards where the housing profile is concave and inwards where the profile is convex.
2 - Drag, a tangential force at the housing/seal contact and a radial force at the rotor/seal contact.
3 - Pressure Forces, radial and tangential forces due to chamber differential pressures which vary widely during the cycle.
4 - Spring force, essential constant radial force (ignoring housing profile error, temperature effects, and spring aging).
At any point during the cycle the actual sealing forces will be the sum of the instantaineous values of all of these.
If you want a uniform, predictable housing seal force then less inertia and stronger spring force seems an obvious way to go. The lighter, stiffer ceramic material will have much higher resonant frequencies for the same size & shape
of seal.
That said, do the deficiencies of the iron seals relative to ceramic have any impact on someone like me driving the stock motor on the street at no more than beep speed? :confused:

I give, you can drag a thirsty horse to water, but you should'nt have to sit on his head to make him drink. If you dont believe, try assembling an engine with no springs, put it
on the dyno and let me know what you find.

don't take it the wrong way MarkJ, it's not like i think you're completely mistaken, i just find it really really hard to believe.

;) and of course we both know that the springs are entirely necessary when there is no gas pressure to speak of (like, when you start the engine).

Sorry shellys man, that was directed to wakeech, who seems to think that springs dont do anything. You are correct in your statement about springs being vital to performance.
Inertia is also responsible for the heavy seal lifting off the housing at high rotor speeds. that is why ceramics and carbons survive high rpm, and cast irons do not.

It's all good MarkJ. :)

The nice thing about ceramic seals is that they are essentially self lubricating. Don't get this confused with not needing oil injection. What I mean is that they are slippery compared to ordinary seals. They have a lower coefficient of friction. This is one reason why they make more power. Their light weight actually lets them use less spring pressure and this too contributes to less wear.

MakJ has obviously built and dynoed more than a few stock and race engines, those who haven't please stop arguing.

I got a little confused over the spring tension comment so I just went and did a little digging to make sure which it was. This is a quoted passage from Scuderiaciriani.com about the benefits of ceramic apex seals.


"The advantages in any engine are that the ceramic material used has a lower coeficient of friction than the more conventional ductille iron seals, and the material is a lot harder. The lower friction, means less wear to the surrounding parts (apex seal grooves, rotor housings, and side housings), and less wear to the seals due to both the lower friction, and harder material. The wear characteristics have been described to me as negligable, but initially enough for them to break in correctly.

Other advantages, are that the ceramic material has less physical mass, so requires less spring pressure to keep them in contact with the rotor housing surface at a given rpm, plus due to the lower coeficient of friction you can use more spring pressure without causing an appreciable increase in wear. Either one of the above means the engine can run at higher rpms without the seal floating, which can cause hot exhaust gasses to travel back into the intake cycle of the other rotor chamber and cause pre-detonation which is one of the major concerns in any non diesel engine.

Stock apex seals can overheat, and warp which is not a concern with the ceramic seals. The ceramic seals although not indestructable, can take a lot more detonation than stock seals. They can also stand up to a lot more boost/power output.

Now for why people stray away from them: ceramic 2 piece 2mm or 3mm seal set costs $1770, plus in the case of the 3mm seals you have to buy double the number of apex seal springs. You could go for the single piece 2mm or 3mm seals for $1200, but will have less compression under 4000 rpm over the 2 piece seals.

After getting past the 'you don't want those!...why not?...because they cost a lot'....banter, I have heard from several rebuild places, and Franchesco Ianetti himself that when it is time to rebuild the engine, you can re-use the ceramic seals over and over again (the gift that keeps on giving?)."


At least I know I was right as far as spring pressure and lower friction coefficient. I haven't been the one arguing with MarkJ about anything else but this part I am absolutely sure of. I'm just glad I could confirm it elsewhere.

Just how much is the apex seal friction reduced with ceramic vs. stock seals?

All other considerations aside, the reduced friction, times the rotor "radius" times the number fo seals engaged at any given time (it would seem that spring compression of two seals should reduce regardless of seal material at the instant of a "flat" on a rotor being at its closest point to the long face of the housing) would equate to a direct increase in torque at the crank, even if all other considerations of the seals are assumed to be constant.

If the interface friction is a small force (or if the actual difference from stock to ceramic is small), then this could mean a relatively small gain due to this effect, but if the change in force is significant.....

still, i'd be curious to see spring pressure numbers, and compare them to theoretical gas pressure numbers. i'm still quite sure that we'll see that during operation gas pressure contributes the vast majority of the sealing pressure.

none, and how many times do i have to reiterate that springs alone ain't going to do it?? like i said before, it's not like i think you're being dumb, but i'm not convinced.

lets go absolutely nuts and say that it's 80lbs/mm compression. it's 160mm^2 surface area (80mm length, 2mm width), and is under 5 mm of compression when at TDC right at the point of a combustion event.

80 * 5 / 160 = 2.5 lbs/mm^2 * 625mm^2/si = 1562.5 psi crush pressure

now i dunno about you, but even with that level of outrageous spring pressure, it won't get the job done when it needs to stop five times that much.

Isn't the combustion pressure mostly coming at the seal from the side?

Spring pressure in a rigid seal would act perpendicular to the housing wall, from the look of it, so there probably isn't going to be a 1:1 corelation in terms of blow-by at TDC, and the relationship between the two would appear to get more comlez as the chamber moves around and the angle of the seal to the housing wall (as well as the spring compression distance) changes.

In terms of seal geometry, doesn't using contained pressure to help close a seal generally require a softer, "wiper blade" type of seal?

Then again, I might be way off base, since I'm pretty much a newbie when it comes to the nuts and bolts of these kinds of engines....

...when did i say they did?? i said or rather asked if, from post one, that springs do not do most of the sealing, and gas pressure does.

gas pressure is theoretically equal everywhere in the volume. yes, it does change, being at its maximum sometime very soon after the event of combustion near TDC on its way to BDC (how close varying upon rpm, i suppose), which is where you need the most sealing. the apex seal groove allows the high pressure gas to push the seal up, out, and into the rotor housing (in the same way gasses press the side seals, corner seals, or piston rings out against the block) creating a crush pressure equal to the pressure in the chamber, allowing for theoretically no leakage.

high spring pressures contribute a little force to this, sure, but their importance is in locating the seal in the groove when there is no gas pressure to crush them into the rotor housing, and to make sure that they stay up against the rotor housing on the way back out of the groove (where chatter occurs). low seal mass and high spring rates would create the best sealing for any application, allowing for the best sealing possible... i don't know why you're talking about this "no spring" and "soft spring" stuff...

:rolleyes:

ya, i have.

you know as well as i do that the seal needs to be located vertically and longitudinally in the groove, 'cause they're two peice, as without the spring any seal would lose contact with the chamber wall and cease to function.

This is kinda dumb to argue about still, its been printed how the gas seals in a rotary work. they are not going to change the entire operating principle of the seals. they work on gas pressure and allways have. spring pressure is mainly for starting the car as has been stated numerous times. there is no way in hell spring pressure alone would seal the chamber, especially when you accout for the fact that the springs are at there LEAST compressed state during the peak of combustion pressure, thus they are at there minimum spring pressure at maximum chamber pressure doesnt sound to effective to me. Ceramic seals are great but you guys are buying into venders marketing BS. I'm not denying that the springs are stiffer, as ive never been in the same room with ceramics. But i have bulilt a motor and the spring tension isnt very great at all, especially at TDC.

I still dont understand why you guys think that the entire operating principle of the rotaries gas seals has changed for ceramics,.. thats just asinine. Especially when your proposeing a new working principle with no documentation what so ever based on a few ounces of spring pressure... Post something documented and you might have more of an argument, opinions dont really work for me.

Be very careful if all or the majority of your experience in a given field comes from things you read; especially on the internet. If you aren't SURE about something, please don't act like an authority on it. It's okay to speculate and to ask questions but it would be prudent not to go to far beyond that if you don't have hands on experience.
I think I'm going to start a thread on rotary engine experience: How many have you built, how many have you tuned, how many have you run on the dyno, how many races or championships have you won, how many types have you worked on ( 10A through R26b and renesis), have your engines ever run at LeMans with Mazdaspeed as your main sponsor?
Now that may sound silly, and although my personal experience is decent, I have the privilege of sucking information from someone who has covered everything mentioned above many times over. I've seen Japanese engineers from Mazda reverence him even admitting that he knew more than them in some regards. He has met Mr. Yamamoto and is reponsible for a lot of the design and specification on the best of the ceramic seals available.I asked him his opinion on gas pressure keeping the seals in contact with the housings and he smiled as he replied that it may to some extent but spring pressure was the key factor since 1974 when the materials changed.
For those who still don't believe this because they haven't read it in a book consider that Mazda has not printed anywhere as yet (To the best of my knowledge) that the side seal clearances on the renesis have totally changed. When I first had a discussion about this on this forum people said we were full of it because they hadn't seen from their typical sources.
I've probably accomplished nothing here today but I pray that some may pause and consider a different approach, if not to life, at least to posting on this forum.

Hello there,

We have had a lot of R&D and testing with highly modified renesis rotors, we have developed 2 piece 3 mm twin spring ceramic seals for the rx8 rotors or you can use 1 piece 3mm carbons, the reason we have gone to a 3mm and not a 2mm is because we still use the old style apex seals meaning they a deeper and require a deeper apex seal groove, we have tryed to extend the original 2mm groove of the rx8 rotor but after 6 new rotors in the bin we decided to cut a whole new 3mm groove to solve the problem, and that problem is we cannot match the original 2mm groove to the deeper 2mm cut we are making. And if you are every planning to run rx8 rotor with a conventional large bridge port you will soon find out that the original 4mm deep rx8 seals will fall down the bridge as they begin to sweep the bridge as they are normally held up by the corner seal and lower part of a 8mm deep earier seal..

We have also been working along side our seal maker to come up with a 3mm apex seal that has a 2mm tip which like the prevous poster has mentioned has a better sweeping surface and less seal chatter.. and the ceramic seals do offer better torque at lower revs and also better surface contact at higher revs

Thanks

Thanks Charles,

With our sales at work, 70 % of Internet sales are over seas and about 20% of our phones sale are two. We deal a lot with overseas in the last two weeks we have done 2 motors in Perto Rico. We are know for our Rare parts and Engineering and especially our Race Cars, and soon our Drag Cars(sorry guys Iam advertising myself here just establishing who and what we do) So we can help anyone over seas even more so with success of our rx8 motor conversation, into older motors and other.

Thanks,

Another important thing to mention and this from experience, On people who have dynoed there car even with exhaust mods, where has the peak power been, even more so the peak torque in relation to the HP, Lets guess 9000 rpm, well unless you really needed to why would you rev it another 2000 rpm beyond that, your not running short manifolds or exhaust systems that are really setup for that setup, tell me where does the torque start to fall off, Iam interested because with using rx8 rotors and gear in older motors we have seen peak power at about 9600 rpm in race trim, including quad throttle body setups and twin exhaust systems all the way pass the diff and very expensive cold air intakes giving a 5 kpa positive at 200ks per hour.. Tell me if we are onto something compared with other motors as we deal with rx8 motors not cars...

Thanks