winter39

Just thinking out loud here.
It seems to reason to me that the cranking pressure is different because of the seal width implemented. My view is that the thinner size will have a narrower point contact with the outer housing. This thinner line contact, when cranked slowly (at startup or by hand for a comperession check) will lead to a potentially higer cold cranking pressure. The wider seals (3mm) will have a potential point contact that could occurr with the lenght of the seal (same as the 2mm). This wider area will lead to a lower percentage of point contact along the lenght. This is the reason that the cold cranking pressure is lower. It is interesting to note that all of the 3mm guys who have responded here have "lower compression" using the cranking compression test.
When I think about this simply I could sum it up like this. If we could make an Apex seal as thin as possilbe (like a hair for example) and make the width perfect then it will seal better then a 1" wide block. Especially considering that our outer housings varry along the length. I am not sure if I have explaned it very will but I can picture it.
Why are the used in the race engines primarily? When under load and seals are elastically deforming they can both gerenate the same (or very similar) compression. Under load the seals would almost surely show some kind of bend to them (the portion that is sticking out of the rotor) which tends to make a thinner line contact (like a hair) in either scenario. That being said the thicker seals also allow for more internal force (detenation scenario) before they break.
Anyway, it is an intersting disucssion. Only one way to know for sure in the end and that is with the comparitive dyno test.

Maxthe7man

I am afraid I have to disagree that leakage amount even at high rpm does not effect horsepower, Ive seen the difference on a dyno, and as I posted before it, it was a 100 rwhp, that motor cranked out 6's and made 400 rwhp at 1.2 kg cm3, about 18.5 psi, once it cranked 9s with a new motor it made 500 rwhp, same car, same turbo, with less fuel..Testing compression also shows the seal to rotor relationship as well, if that area is not right, there is reduced gas pressure to seal the apex seal to the housing, a good engine is the sum of parts, and subtractions of all the tolerances internally. I also disagree that 3mm makes a stronger motor, adding 3mm seals, makes a motor chatter earlier, and lower the useable rpm of the engine, as soon as the apex seals start to chatter, you start losing seal, and power, Mazda itself concluded that 3mm seals cause the rotor housing wall to distort under power earlier, and that the greater volume under the seal was also a problem in compression numbers and leakage. In the end adding more weight to the rotor tips, creating more chatter, more leakage, and machining the hardened surface out of the rotor tips, and neccesitating more boost to make the same power does not increase the strength of the motor, and under serious power, I have not found 3mm to withstand any more abuse , I have had stock 2mm suffer more abuse than 3mm seals, even though they survived the detonation, other parts didnt, so goes the domino effect...If the apex seals dont fail, something else will.. Nothing makes a mess of a turbine blade like a 3mm seal...
I couldnt find anyone in Japan using 3mm seals in 86 and up motors, and no one recommended it for reasons of practicality ,and durabilty. There are guys there building 2mm 850 hp drag motors, even the high boost circuit cars all used stock 2 mm seals...3mm seals have become popular for recycling rotors here , probably more from a cost standpoint than really a performance standpoint, I know the process the original grooves are cut under, and it cant be recreated accuratly enough to ensure the same tolerances as a 2 mm seal in a stock good rotor slot, in regards to seal fitment in a running engine, seal slot location, and wear rate..Max

RX7specialties

I hate to be the one to break the bad news..but 3mm is a choice and a choice of preference when used...NOT for economics(reclaiming rotors). Agreed, there are circumstances which I can attest to first hand as a builder where the customer asks to keep the costs down. We receive rotors every week and use machined rotors at least once or twice a month to help accommodate those who wish to minimize costs. However, the greater majority of those who deliberately machine rotors and purchase 3mm seals are those who KNOW their strength benefits! The references to people in Japan may be more common to 2mm..but...we have world class racers in North America too who use them! Its funny when I mention people like Francesco Ianetti(who is paid by MAZDA to produce a product for them and sold through MAZDA Comp who do not only sell 2mm)Able Ibera, Carlos Gonzalas, Ari Yallon, Ray Lockhead, and the Puerto Ricans...these people go unrecognized and discredited. And the majority of the creditation goes to a select few individuals who have no business or racing involvment in the RX7 world. The racers and myself have direct, hands on, every day experience using BOTH seals in a multitude of applications. The 12a's didn't chatter..they just had an outdated meathod of chroming and rotor hsngs. peeled. Same for thye GSL SE and early 13b's. The mention of perfecting a groove and removing hardness in the slot needs to be magnifyed. The rotor machining can be done just as accurate or more (unless its Hurley who grinds crooked with the corner seals) as cutting to the factory line is the key. As long as you hit that line you can have any tolerance or spec you desire...or tighter and better finish if you use an end mill or EDM. The hardness was only installed on Twin turbo and some Jap S5 stuff (its easy to tell as there are heat spots from the induction hardening at each and opposite end of the slot. None of the early stuff had it which means you should say "you should only use 2mm rotors which were hardened!"...which we know not everybody has and they do just fine with the 2mm rotors they have unhardened. I mention the names of those who are actively building scince they would have long scince determined that if a 3mm "chattered or lost power" and believed that 2mm were just as strong...they'ed build only 2mm! And lets face it...it aint economics to a racers budget! Lack of lubrication and carboned and sticky seals are the #1 contributor to chatter(FACT). I understand it was mentioned in a personal experience the same car was used,same fuel, turbo, etc. But the same engine was not mentioned! I highly doubt that the engine was torn down and rotors cut and tested with 3mm seals...especially scince the claim was made by someone who does not support 3mm seals. The HP losses mentioned were exactly 20%.
400 compared to 500. If this were true, and the beleif that high RPM has no bearing on less loss , this would indicate that Able Ibera's race car turning 1300HP with 3mm's would translate to 1560Hp and no greater chance of breaking.
In the racing world, HP and strength is everything, and if Chatter and HP loss
were noticed...don't you think it would have been realized by now? After all, these individuals are not listening to Mazda and their supposed 3mm theory as the theory cannot be proved in a 11,500RPM 1300 HP application! In most all my experiences and racers experience, 3mm is not about saving money..rather..costs money. It is a prethought, deliberate, calculated form experience...CHOICE!
I've heard the claim of why 3mm aren't stronger because of eledged negative repercussions and downsides...what I still haven't heard is an aknowledgment
that a 3mm seal is PHYSICALLY STRONGER than a 2mm???
Adam Heyman

rx7_turbo2

I'm not going to write some giant post regarding this, just some real quick points. I think there are WAY to many factors involved to say 3mm is stronger based on the increased mass and thickness alone, that's kind of a pointless arguement that's been beaten to death. The difference in metallurgy as a variable alone is enough to stop the arguement cold.

Now as far as cranking compression is concerned. I'm no expert, don't claim to be, but if one motor makes 100psi and another makes 60, shouldnt that tell us all something? One motor is built "tighter" than the other. That's enough for me, I want a tight motor, as far as I'm concerned if it's tight while cranking it's going to be tight while on boost, and I'm getting what I paid for. If you drove your 60psi turbo motor into a Mazda dealer and had them do a compression check on it, they would tell you you need a rebuild and that your motor is worn out. I want a strong motor, 60psi is not a strong motor. Just my opinion.

jreynish

iTrader: (2)

do we want to argue as well that titanium is stronger than steel? no because it is all about the metallurgy and the composition of such metals dictating their resistance to facture or shattering. righ? so lets argue the percent differentce between identical metals of 3mm to 2mm. You being an educated man.. as well as your parents as you have stated before, why don't you do the math and tell me what the difference weould be in Newtons per square meter between the two?
As soon as you answer that question for me I will tend to believe you more. Of course leaving asside the extremely complicated calculations of pressue and all that that max was explaining asside, just strictly speaking of difference perent wise of the seals?
Sincerely,
Jeffrey

Maxthe7man

The reference to the one motor in that tested in the 6's and the one in the 9's was not about 3mm seals but about cranking compression, the motor in the 6's had excessive wear in the seal slots with 2mm seals, ws rebuilt to 9's with new parts. That was simply to show a comparison that a motor that cranks low, makes less hp, a percentage of leakdown on a seal is not going to disappear with rpm, if its leaks more at cranking, that engine is going to leak down more through the entire rpm band, as the pressure gets higher, so does the leakage.
I will differ that the 12a's and earlier 13b's didnt chatter, I have seen chattering in 12 a motors, and it was testing of the earlier seals and motors that led mazda to use a lighter and lighter seal as time went on to reduce chattering, hence the reason, they have also found ways to get the production apex seal lighter and lighter, and the rpm of the engines has subsequently risen as the apex seal has gotten lighter. They found the answer by drillin passages throug the iron seal to decrease its mass, the more mass they removed, the seal was prone to less chatter, hence in an iron seal the thinner and lighter it was, the less it chatter. The mass has another effect beyond distortion and momentum, the greater a mass the more heat it will retain, testing of seal sizes also shows that 3mm seals retain more heat, making them more prone to heat failure, than 2mm seals, with a 3mm seal, less percantage of the seal body mass is in contact with the rotor itself to give up heat comparitive to a 2mm seal, if my math is right, its a 1/3.. The distortion phenonema of the housings is no different than what happens when people push the bore to far on a recip motor, as the sealing surface deflects the seal is compromised and less power is made, wonder why chrome pealed so readily on the earlier 3 mm motors? Get Chris Ng to show you his front housings, that housing shows all the signs of wall distortion..
I cant argue against that some people do use the 3mm seals in race applications, I could argue though they simply dont have the information availabe to them the Japanese racers do, and when they do blow motors, which they do, that the causes of their failures could be in fact their own attempts to fix them. Making something bigger doesnt make it better, there are dynamics in motors that all are interlinked, adding mass and size to certain parts, is often worse than taking it away, when its a moving part.
All Re amemiyas cars use production 2mm seals, Afrs 850 car uses 2mm seals, all the cars in D1 Grand prix, use 2mm seals, and had time has marched on with the rotary in production applications output has gotten better in both forms of engines , rpm has increased, with thinner and smaller seals, you think mazda is wrong? They have run engines with sensor in the seals themselves, which is alot more insight into a running motor, than anyone on this side of the pond has into the motor.
Alot of the Japanese, also shake their head at what goes on over here, as was said to me by the guy that puts RE's engines together, we need to quit trying to reinvent the wheel here, and just learn how to tune, which is in fact the real secret to keeping a rotary engine together, I know if I posted my motec data sheets from Japan on this forum, it would create a giant shitfest and people would argue with the parameters tooth and nail, which is perhaps why the rotary in Japan doesnt have the same repuation it does here.

The following is directly from a rotary engine history book written in Japanese by Mazda engineers, "seal slot hardening commenced on all engines from 1985.5 onward." except I could type it in Japanese, but nobody else would understand it.

Just about all the facts put forward in the replies so far, run pretty much counter to the books written on the subject.
By the way seal slot hardening process isnt what alot of people think it is, its also a chemical process.
In regards to the cutting, I havent seen a 3mm rotor yet that had all its seal slots in the right place, or were straight, and nobody has the machinery outside of mazda to properly do the seal slots, not only does it reference the slots to a known master rotor, it also references all the slots to the rotor face measurement and the first slot cut to ensure that every face is exactly the same displacment and compression ratio, the machine itself does 3 position checks simultaneouly to cut the seal slots. refercing a line on a rotor, to one line , especialy a worn one to cut a groove is not enough, and far to many machines have to much wobble over an 8 cm cut to provide machining comparable to mazdas, there machine has a couple of tons of mass to it, to eleminate vibration in the cutting process and has enviromental controls on it so that its cuts are repeated perfectly evertime. Luckily the rotary will run with alot of loose tolerances, bad machining doesnt show, unless you have something perfect to reference the results to.
I look at the power and reliability the Japanese guys make with their setups, compare to whats going in the North American scene and its completly opposite, they make more power with stock parts, with smaller turbos and less boost than pretty much everyone here, the difference is in the motors , the tuing and the knowledge base behind it, alot of the guys building the fastest cars in Japan, are guys that worked at Mazda as engine assemblers, or were mechanics for Mazda, just because a select handful of people here do someting doesnt make it right, none of those people here have the testing data that mazda has and its past and present employees that struck out on their own in performance shops in Japan have access to.
Whats going on here with cutting for 3mm seals and new types of seals , materials etc etc, already went on in Japan about 10 years ago, this stuff isnt new to the rotary, its just new to us, and in the end the oem tolerances and parts has been proven to be the better parts. Even the extend length corner peice of the apex seal that has been touted as the saviour of the rotor housing is not a new idea, it was tested by mazda in the mid 1970's, but was deemed as unaccetable design through long term testing. Its all been done before, maybe we should learn from that. Max

couturemarc

Leakdown is a function of time and pressure. As RPM's increase the "time" for leakdown decreses hence reducing the total leakdown.

If you are getting constant leakdown at all RPM's then i would suspect that there are other problems.

The "time" factor is exactly why proper compression reading are done at a specific RPM, lower RPM will result in lower reading and vise versa for higher rpm.

rx7_turbo2

Precisely

And as mentioned metallurgy is just one variable. There are plenty of other variables as well. Chris Ng mentioned the difference he saw when Adam demonstrated the seals. That's enough testimony for me to believe the composition of the metal in these non-Mazda seals is totally different than that of stock. With the money behind stock Mazda seals compared to all these new non-Mazda seals (2mm or 3mm) it's enough of a reason to stick with the stock seals. And I just havent seen much benefit of 3mm seals. I've seen more motors go with 3mm seals than I have 2mm.

Maxthe7man

Yeah so what, I already posted that earlier, except
If a motor is not sealing, rpm will minimize the time, but it wont heal the motor, if motor 1 makes a 100 psi at 250 rpm, it will have less leakdown underpower than motor b that makes 60 psi at 250 rpm and at any rpm. being that the source of leakage is a fixed amount, the percentage gas loss between the 2 motors will be the same regardless of rpm.. So while its ok to say a sick motor will make pressure if you turn it faster and make power, it still holds less than a motor that makes 100 psi at 250 psi, in fact 40% less if we say that 100 psi is a perfect motor, and that will hold true regardless of rpm..
But there was a claim made that the 3mm seals will seal at higher rpm, and that , that leak down was acceptable for added toughness to the motor and will go away with rpm.. The problem with that as Graham points out if you had a stock 3mm motor say gsl-se, and roll into any dealer with a 60 psi 3mm stock motor, they would tell you your motor is shot.

So whats the difference between the compression testing of a stock 3mm motor and a 2 mm motor modified to 3mm... Why would factory built 3mm motors test higher, and have a 80 psi minimum, spec if 60 psi is all supposedly a 3mm seal can hold at 250 rpm..The seal slot machining and housing condition is the culprit I would have to say.. max

winter39

Max,
This is not meant as a jab just a question. With all this info you have why did you ever put 3mm seals in your engine?
I am going to rebuild my engine this Winter if all goes well. When I was initially planning this I was really contemplating 3mm seals. When I considered how to propperly machine the slot it scared me off of this thought. When I do a rebuild it will be 2mm seals and it will be stock (I have +200K on a TII engine so why would i mess with that now).

jreynish

iTrader: (2)

I am pretty sure that is the motor he bought the car with, it had 3mm's in it when he bought it.

Max, I know heat has a HUGE part to play in all of this, but would have any insight from your trip as to compression loss or leakage due to heat?

Schnide

As I said earlier the I'm sure the Mazda engineers know a bit more about the rotary then some guy in a garage with a wrench.

Its very unlikely that you will out engineer Mazda on the rotary without a hideous amount of luck, talent, experience, education and of course money. period.

didn't mean to rant sorry.

rx7_turbo2

No rant That's one of my arguements. Mazda did at one point use 3mm seals, now since then a TON of money has been spent on R&D for the motor, look at the money spent on the Renesis, and Mazda has chosen to stay with 2mm. That speaks major volumes in my opinion.

Max's 3mm motor came in the car he bought. One of the seals promptly folded over on the dyno under perfect air fuel ratio's, and relatively low boost. It was a dud motor from the begining, it fit into the super low cranking comp that we've been discussing (despite it's low kms) Nobody shed a tear when it went.

Schnide

its good to see that there are others who realize that Mazda has poured tonnes of money and time into developing and improving the rotary and produced a Le mans winning car so they don't only focus on production car performance levels.

well I'm still curious why people use and suggest use of 3mm seals, has there even been strictly documented tests that prove they offer any advantage at all over the standard 2mm rather than just disadvantages?

couturemarc

I wasn't arguing for or against, just saying that a "perfect" motor that makes say 120psi compression (or whatever you like) @ say 800 RPM will make less compression at 250 RPM, this is fact.

I've read a lot of post on the internet in general refering to "compression values" and passing judgement on engine quality based on these values but the RPM at which these different values are being read is not always mentioned. In my opinion a compression reading in "psi" WITHOUT an associated RPM value means nothing at all.

I could hook a gauge up to my motor and say it has 10 psi and still have an excellent motor but this means nothing unless i specify that it has 10 psi @ 30 RPM (and even then you can't get an accurate reading at that low RPM).

Im not for or against this thread, just seems like the basis for a lot discussion is based on incomplete data. If it is commonly understood amongst all the people who post compression values that they must be taken at the same RPM value if compared to others at face value and that is what everyone IS doing then that is great and I am out to lunch and saying all this for nothing.

Chris Ng

You make a point.. compression values will change depending on the rpm that the motor is spun at.... however, it has also been mentioned several times in this thread that the mazda specified values are at 250rpm.. I think it's safe to assume that most people are testing their motors by simply allowing their starters to spin the motor... I also think it's safe to assume that given a fresh battery, good connections, and a good starter, you are not going to see the motor doing 400 or even 500 rpm during initial crank.... unless of course.. perhaps if it had really really low compression ... given all of this, I think it's safe to assume that most of the compression numbers you are seeeing are in fact within an rpm range that is close enough to assume accuracy between readings...

I'm not entirely sure how this topic ended up becoming a debate over 2mm - 3mm seals.. the debate has been played out over and over on this and other forums...
so perhaps the question at hand was not obvious enough....so I'll try and restate it again...

A stock Mazda motor shows compression numbers of 100+ psi when tested at 250rpm... this signifies a healthy motor...
Engine rebuilders have been able to build motors that put out from 90-100 psi compression numbers at 250rpm... they state these motors are healthy..
a stock GSL-Se motor with 3mm seals shows compression numbers of 100+ psi when new
Engine rebuilders have been able to build 3mm motors that put out 90-100psi at 250 rpm...

one particular engine rebuilder has been claiming that cranking compression numbers do not matter when it comes to rebuilds.. and especially not when it comes to builds using 3mm seals...
compression numbers from all the motors tested put together by this builder has shown numbers of 60-80psi...
If this builder claims the lower compression numbers are due to the 3mm seals not sealing as well as 2mm seals at low rpm, then how come the gsl-se 3mm motors can show high cranking compression numbers?? (as a note, the seals used in the low compression number motors were gsl-se seals as well)
Let's take this one step further.. If the newly rebuilt motor was in fact put together correctly, using new apex seals, side seals, etc... what else could contribute to low compression numbers? The only thing I can think of is using out of spec or damaged rotor housings, side plates, or rotors...
so let's take this another step.. assuming that the low compression in this motor was not due to the seals, but due to the use of out of spec, damaged components, is it not safe to assume that ability for this motor to compress the intake charge at ANY given rpm.. be it 250 or 8000rpm, will be compromised??

arguing that cranking compression numbers don't matter is a crock of poop.. and in my opinion is just one way to justify the fact that motors built by the builder are substandard... I have no doubt in my mind that is it entirely possible for this builder to put together a motor that shows 90-100psi cranking compression.. and that is with the use of 3mm seals and used housings... however, in order to achieve this, the ability to offer lower cost rebuilds would suffer, since the out of spec parts can no longer be used...
mind you, earlier in the thread, it was also stated by a builder that they are putting together a motor utilizing brand new rotor housings etc... and if the motor only showed 60psi cranking compression, who cares?? ...

rx7_turbo2

Chris is right on the ball. It's been said a few times but all sorts of smoke screens have been thrown up to keep us off topic.

It's real simple for me. If I pay my hard earned money for a rebuild, and after break in it can barely make 60-80psi(3mm or 2mm who cares) I'm super pissed off. Sure it may run, sure it may make Ok power, but that's not what I paid for. I want a TIGHT well built motor, that has maximum horsepower potential. As far as I'm concerned a 60psi motor is a slush puddle, Mazda would tell you the same I suspect. Believe what you want to believe people, but try not to be swayed by fancy words, long paragraphs that don't end, and words like "FACT" in brackets, just cause the author of a post adds the word "FACT" after their statements doesnt mean it's Gospel, in fact it just makes me do more research, I suggest everyone do the same. And I contend that if the author is bold enough to add such a word to there comments that after the addition of that word there had better be a link to some serious imperical data to back up such a bold claim.

jreynish

iTrader: (2)

^^^ AMEN!!!
I believe what I can justify in my mind. I choose to simply find out the facts, and formulate my own hypotheseis, this in fact would then be collaborated by asking specific questions, and having a civil discussion. I suggest to everyone to do as rx7 turbo2 has stated to search and find out for yourself... don't just believe because someone calls themselves an;
1) Expert
2) Specialist
3) Awsome guy
4) Know it all
5) God
This topic based on 2mm vs 3mm will go on for years to come... because there are some who believe and some who do not.. it will always be this way.
as for the sub topic whether cranking 250 +/- RPM compression matters... I believe that answer to be YES it matters.

offrotor2

this is silly... every fricken' time... the same 3 or so people jump all over a guy (a particular engine builder).(do some searches, you can see these same 3 people are all from the same location as the Builder in question......) anyhow, Rx7_Turb2 said it best do your Research.. you will see, every time this stupid debate comes up, you 3 are right there... feed'n it.. why? Oh maybe you have a lil animosity toward this individual, maybe....not maybe.... you do! you all do... not because you had bad motors... (motors blow from tuning and miss handling of all the variables......) other wise motors would'nt make it all the way to Oh, lets say Winnipeg..... and then some.. Guys give it up... open a shop and build your built proof motors.. you ALL seem to have the talk, but DONT walk the walk...? Lets see it... max?

offrotor2

Max... sorry, I should'nt pull you in like that... My apologies... Stick to Board moderation and not building rotary engines... you know as well as I do, the rotary aint as good as the ol' 360...

Maxthe7man

I have no idea what you are on about really besides sidetracking the topic....
I am gonna move this thread, since this stuff always seem to break down into personal stuff and being about me , its about apex seals, not me, clear?..Max

offrotor2

tough get going.. going get tough... end it, move it, allways the way it goes anyhow..


Readers take note...

rx7_turbo2

Whatever offrotor. Deal with it huh! Same 3 people? You bet it's the same 3 people. Who else would it be? We have large post counts so we are active on the forum, plus who else locally is building their own motors, and taking apart numerous Adam motors? Makes sense to me that we should be vocal. Once again if you don't like it, and you want to keep throwing up the smoke screen to keep people off the real topic here, I think most intelligent people will see right through it.

I think maybe I'll start a couple polls in various forums, lets see what the consenses is shall we? Lets get a real good idea on the topic at hand. I think the poll question will be "A new turbo motor with 5000-10000kms has 60-80psi cranking compression is it" A)A strong well built tight motor or B)A poorly built weak motor. I'll post up the links so we can see what the results are.

rx7_turbo2

Ok

I'll post the poll in more forums when I get the chance.

http://www.teamfc3s.org/forum/showth...threadid=41764
https://www.rx7club.com/forum/showth...84#post4317484

offrotor2

Its allways about a 'smoke screen' with you...? there's no smoke screen. I was'nt straying from the topic... At the beginning, all i said was the faster you turn your motor over, the higher the PSI will be... This has be said twice now... Your poll is a useless poll... its like asking weather or not peanut butter sandwich is better with fresh bread, or is it better with moldy bread.....?? no brainer there... You have basically set up a lop-sided poll... For a motor that apperently makes 60 psi (agin at what rpm?) And how would 'black93rx7' know this? He doesnt even know how to check his compression.. anyhow... Have your silly little fun with you silly little poll.. After all you have a reputation to uphold.

I cant seem to see my keyboard anymore... for all the smoke......