wakeech

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.

Ophitoxaemia

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

rotarygod

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.

Ophitoxaemia

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

86rx7

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)

wakeech

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.




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

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.

rotarygod

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

86rx7

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.....

wakeech

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?

Ophitoxaemia

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

rotarygod

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.

CERAMICSEAL

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.

wakeech

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

86rx7

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?

wakeech

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.

rotarygod

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

wakeech

86rx7

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

86rx7

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.

shelleys_man_06

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

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?

CERAMICSEAL

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.

86rx7

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........

shelleys_man_06

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

CERAMICSEAL

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.

86rx7

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.