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I've tried searching on this but am not finding anything, so here goes

Bryan @ BNR emailed me asking if I'd be interested in using 2nd gen rotors in my rebuild vs 3rd gen because they are heavier and less prone to detonation under high boost (sounds good to me). I've never heard of that before, and I didn't get any replies when I asked about it on here.

Now he has a set of 3rd gen rotors w/3mm seals and he wants to know which route I want to go - 2nd gen or 3mm 3rd gen rotors. And I have no idea.

As I told him, my biggest concern is durability and longevity of the engine (in other words, I don't want to replace it again under 60k miles).

Has anyone done/heard of FC rotors in an FD, and would you go with those over 3mm FD rotors? I've read/learned a lot on here over the years, but I have NEVER seen this particular dilemma before!

Thanks in advance,

skunks

I have read about this, that FC rotors are lighter and other things like that but have have heard of any real testing done on the topic. I'm not sure about less prone to detonation under high boost, if your running lean, your gonna detonate! No doubt about that.

How much is he gonna charge you for the 3mm seals? If its free, I say go for it!

BTW: How much boost are you gonna be running on this engine? If you don't wanna replace the engine under 60k, I'm assuming, your gonna stay at stock boost levels and at stock Hp levels. If you double or triple the boost/power comming out of any engine, its not gonna last.

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I'll be running about stock boost ~10lbs. As far as cost goes, an extra $400 for the 3mm FD rotors.

Thanks for the feedback...anyone else want to join in the fun?

skunks

400 bucks does not really sound that bad considering they will have to mill out the rotors to accept those new seals. I have read some where in which 2mm might possibly be better then 3mm although i have real a lot more which says the other way around. I would get them if i could afford them.

CanadianRex

There is a local guy that always uses fc rotors when putting 3mm seals on an fd. His reason is that it is easier to mill the rotors for the 3mm seals because they are not as hard. I am not aware of any other advantages/disadvantages of doing this, but I know it works. I'm also curious to hear anyone elses thoughts on this as he will be soon using fc rotors in my fd rebuild.

rotorbrain

2mm seals put more pressure on the rotor housing. therefore they seal better. 3mm seals MIGHT give added protection to your motor when pinging.. .but if you detonate they are as worthless as any other seal. the only thing that saves you from detonation is a well checked fuel system and a properly tuned ems.

paul

r0t0r-rooter

https://www.rx7club.com/forum/showth...threadid=118575
and
https://www.rx7club.com/forum/showth...2nd+gen+rotors
.... and about apex seals...
https://www.rx7club.com/forum/search...by=&sortorder=
I hope all that shows. If not, PM me
BTW, to summarize:
1) keep the FD rotors, the gain in torque is usually not worth the extra boost you are allowed (and will need to raise to in order to get the same hp)
2) rotorbrain is right, 3mm seals have the same pressure but are spread out over 2mm. The 2mm ones seal better as a result, but are slightly more resistant to knocking
-jerry

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Dang it, can't ANYthing be at least kind of simple with this car?

Anyone else have an opinion on this? And thanks for the above links and info everyone!

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iTrader: (20)

Well man, Bryan is rebuilding my motor right now as well. I am going with the 3mm sealed TII rotors. They are alot tougher rotors than the 89-newer rotors and will not dent or become damged as easy but you rarely damage a rotor, some have but not often. They offer alott more midrange power but you do lose a some low end torque as well as high end. But you get alot more out of your midrange powerband which you utilize the most of. They are a lower compression rotor at 8.6:1 compression vesus 9:1 on the 3rd gen rotors. So they will accept higher boost applications better. Which is what I am building mine for. I am not going to stay at 10-15psi all the time. I plan on running 15psi with the T78 for daily driving and getting it tuned to accept higher boost runs for the track at around 20psi or more. PM me if you have any more questions. Scott

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Thanks Scott. I'm going with the 3mm FD rotors. I'm not planning on running much above stock boost so high boost tolerance isn't a huge concern for me.

maxpesce

If you are NOT going to be running 20+ psi boost then there is NO reason to run 3mm seals - You WILL get Better POWER and FUEL economy w/ 2mm seals due to their better sealing vs 3mm seals. The ONLY reason to put 3mm seals in for Low-Medium boost applications is to salvage rotors that the apex seal grooves are too worn to accept 2mm seals

jimlab

Yeah, let's start talking about the facts...

Fact: 3mm seals are a waste of time and money. They won't last any longer under detonation than a 2mm seal, and they actually seal worse and cause accelerated wear. If 2mm seals are good enough for Abel Ibarra, they're good enough for you.

2mm seals can handle boost up to 45 psi with adequate fuel, so there's no reason you can't make power with 2mm seals. If you damage a rotor's apex seal channel(s) and it is salvageable, then you might consider having it machined for 3mm seals, but there's no justification for using them otherwise.

Fact: '87-'88 FC turbo rotors are heavier than FD rotors (10.04 lbs. vs. 9.54 lbs.), and the reason shops (like Hayes Rotary) want to use them instead of FD rotors is because they're a lot cheaper and readily available, so they can keep a surplus of pre-machined rotors in stock instead of sending out your FD rotors to be machined. They can also have them machined in bulk, so they save even more money.

Unfortunately for Hayes, 3mm Ianetti ceramic apex seals don't just "drop in", and require custom fitting. One engine they built using the "drop in" method cracked two seals within 500 miles because the tolerances weren't correct. Luckily, we found out about my engine (same seals, same hack assembly job) before any damage was caused, and Hayes was forced to remedy all the short cuts they'd taken in building me a big pile of crap, but that's another story...

Ianetti ceramic apex seals, by the way, will only take a few more pings than a stock seal before breaking, and I know someone who had several sets broken while a well-known (and respected) tuner was tuning his car with a new Motec engine management system (not to be confused with the new TFATF Motec exhaust...). It turned out they had a bad engine harness from Motec, but he said that the seals still only held up to 3 or 4 pings and that was it. They're a huge waste of money, in my opinion, and I'm sorry I let myself be talked into buying a set.

Fact: The reason the FC turbo rotors are more resistant to detonation is because they're also lower compression than FD rotors (8.5:1 vs. 9.0:1). Therefore you may be buying yourself some small margin of error, but you'll have to run more boost to make the same power. Worth it? No, not really. Not to mention that you're slowing your engine down and putting more strain on the eccentric shaft because they're heavier.

My advice? If you have an FD, stick with FD engine parts. If you're having an engine built, stick with 2mm seals and spend the extra money on fuel/engine management. The only way you're really going to have an engine last appreciably longer is by ensuring that it has enough fuel under all conditions (coupled with adequate cooling) to avoid detonation.

Felix Wankel

Wouldn't you have to have the Series 4 counterweights in order to use the TII rotors?

jimlab

Hayes was/is substituting FC eccentric shafts also, as far as I know.

They completely pocketed my ~6,000 mile 13B-REW and not one single part from my orginal engine was used in the engine they built for me... as I found out later. I got a whopping $250 core credit for it. Great. I could have sold just the one good rotor for that.

Felix Wankel

That's pretty shitty.

Seems like it would have a vibration with the stock FD flywheel.

I suppose if you're sinking that much money into an engine, a little more for a light flywheel and the FC counterweight is chump change.

rx713bt

iTrader: (4)

That's lame. So Kenny Bernstien's top fuel dragster's engine parts is good for my daily driver? How many miles before Abel take apart his engine and rebuild it? I really don't think 3mm are a waste of $$. Yes, they don't seal as good and cause more wear. But they do handle more detonation.

It all comes down to tuning. With a daily driver there are too many variables. Gas octane from various pumps, temperature etc. If your running high HP on a street car
go with 3mm esp if you don't have a good standalone with the proper tuning equiptment/knowledge.

I agree with everything else Jim has said. I have a set of broken 2mm ceramic seals. Those can break just as easy. Stick with lighter and higher compression FD rotors. Use 2mm if you don't have many mods. Go with 3mm if you aren't too good at tuning or have all the neccessary tuning equiptment or are running at the ragged edge. Good luck!

-Jeff

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iTrader: (20)

I have heard to many storied about a mistuned car that blew the motor with 2mm seals. Not saying that it won't happen with 3mm seals but maybe, just maybe, that second or two longer that the 3mm held together could have saved your engine. Also the heavier TII rotors will create more midrange horsepower while sacraficing torque which should help your traction issues because horsepower wins races and torque seems to smoke tires more. So I should not have as big a problem hooking up in 2nd and 3rd gear with the less torque and more midrange horsepower. For my purposes, drag racing and street racing, the midrange is where it is all won and lost. That is why I went the way I did.

I do agree that 2mm seals are better but I am trying to play it as safe as possible just in case I ping one too many times. Scott

jimlab

I don't think anyone would argue that 20+ psi of boost on top of a rotary engine is conducive to longevity. Any time you double (or triple) the output of an engine, you're compromising its life expectancy in the extreme.

The point I was making, and which you apparently missed, is that 2mm seals are more than able to handle the highest boost levels that most people would conceivably run in their street cars.

You're entitled to your opinion, of course, but just exactly how do you know that they handle more detonation? What constitutes handling more detonation? One more ping? Two?

An engine is just as blown whether or not it had 3mm seals, and they are absolutely NOT detonation-proof.

Which is exactly what I just said in my post above.

Spend money on engine management and fuel system upgrades to make sure that the engine gets appropriate fuel for the power levels you plan to make. Not on unnecessary 3mm apex seals.

jimlab

And you'd put band-aids on bullet wounds, huh?

I doubt most people recognize detonation or can react to it quickly enough to it to save a rotary engine. The arguable advantage that a 3mm seal might give you is offset by the fact that if the conditions are right, you'll blow a 3mm seal just as quickly as you will a 2mm seal, and in the end, you'll have wasted more money than you would have if you'd stuck with factory 2mm seals. Especially if you pull your engine apart and find out that your 3mm seals wore the hell out of your rotor housings because of inadequate lubrication...

Sorry, but that's not true. Heavier (or lighter) rotors will not make more or less horsepower or torque. Rotors with lower compression will usually make less horsepower than a higher compression rotor at the same boost level, but weight has nothing at all to do with it.

Power production is solely a function of how much air and fuel you can burn, which isn't affected by component weight.

I would have addressed that concern by tuning conservatively...

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iTrader: (20)

I understand what you are saying about the apex seals. But what if putting that band-aid on may have slowed the bleeding down just enough to save your life. You never know.

I guess I have heard contrary ideas about the heavier rotors. I am going by what I heard from my engine builder, wether it is right or wrong. I have to trust him or why else would my motor be there? Everything you say may be true but I am still learning how to tune my car and would hate to have something go wrong that was so minute that a 3mm seal may have saved it.

Scott

RonKMiller

Milling a rotor to accept a 3mm seal is damn near impossible. It requires a true artist to do it correctly.

If it isn't perfect - kaboom!

Then there's the lubrication issue....

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Okay, now I'm freaking out! Thanks for the continued feedback, even if it just made me that much more uncertain of my decision. Too late now, the engine should be done as I type this - with FD rotors and 3mm seals.

Wish me luck...now I'm going to be REALLY paranoid once I get the car running again! (and yes, it will be tuned).

Time to go lay awake all night worrying and wondering....

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iTrader: (20)

Nah, it will be fine. No need to worry. That won't help anything. Did you remove your engine yourself? How many little pieces did you break. My old brittle vacumn lines broke all sorts of **** without any pressure at all. I am going single so I hope alot of the **** I broke won't be needed again. I am just wondering to see if I rushed mine too much or if that kind of **** breaks all the time anyways.

Who is going to tune your car when you get it back? What are you mods? I really need to find someone around here that knows the PFC a bit to at least get me by until I take it out to see Badog and Jason for a proper tuning session on the Dyno.

Where is Ballwin? Neat STL or KC? Scott

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I started to, but work and time got in the way (not to mention the 100 degree three week heat wave in July!) so I had it towed to Altered Autosports in Fenton. Ian - the owner - has worked on FDs for years and "seems" to really know his ****...but I'm still nervous as hell! I think he'll do a great job and hopefully we'll have someone in St. Louis again that we can trust to work on our cars (which answers your question of where Ballwin is). Ian will also be doing the tuning.

But yes, the lines were extremely brittle. I'm going non-seq and all silicon so a lot of the lines will be eliminated and they should hold up better.

My mods are listed in my signature - it's the list of what I'll have whenever I get it back...hopefully sometime in the next 20 years!

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Random thought...GOD DAMN I'm looking at my avatar and I can't believe how much I miss my car!!!! Everytime I go to the shop I sit in it for about five minutes just to try and remember what it was like...sigh. I CAN'T WAIT!!!!!!

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