FB + AWDDSM

For the first time ever today, we drove the FB on the Highway. It was nice, but it got me thinking when trying to get up to speed...


What happens when a car without valves are over-revved? There can't be valve float or the pistons smacking valves...

Thanks

Acuspeed

From what I've read/heard/seen, our 12A's should be safe up to 8,000 rpm. At 8,500 rpm, the apex seals start to "chatter" and skip off the rotor housing. Of course, if the engine has a lot of miles or hasn't been well maintained in the past, you probably would want to go with a more conservative redline...also, without some exhaust mods, and likely intake mods too (such as carb), it probably doesn't do much good to go all the way up to 8K as your power band would trail off well below this.

genrex

Others can answer this question better than I can, but a few months back someone asked the same question, and the answers had to do with the balance of the center shaft... kinda like pistons being a gram or so out of balance, at higher rpm's the slight out-of-balance causes the shaft to rotate slightly out-of-true.
It was mentioned that this happens above redline. If this is true, then if you take it to redline basically all the time, then engine wear will be high, and the engine won't last as long as it would if you take it to redline less frequently.

Pele

iTrader: (28)

Another thing that can happen is bending of the eccentric (crank) shaft.

The eccentric shaft is supported by bearings only at the ends. The engine is balanced by positioning the rotors 180 degrees out of synch. At high speeds, the centrifugal force of the rotors twists the shaft. If this happens too severely, you tear up the stationary gears, the rotors can hit the rotor housings and.. well damn... you're screwed. Time for a rebuild with new rotors, housings, and an eccentric shaft... Basically a new enigne.

Hardened stationary gears can help with this and I believe bring your redline up to close to 10,000 RPM. One rotary tuning group, I believe Racing Beat, was working on putting a third bearing in the center housing to add support and bring the redline up higher. Anyone know if they were successful, and if so, where to get the modified center housing and eccentric shaft with the bearing?

riffraff

the risk of cracking the stationary gears is the one that i am fimiliar with too. and generally that will lead to needing to replace your motor..

pele: where can you get hardened stationary gears? also, how could you get a large enough power band so that you would even want to take it up to 10k.

bylinepjw

I can tell you only this: I was autocrossing my first 7 in about 1988 and missed a 1-2 shift. I buried the tach at probably 10-11,000 RPM. I drove it home and it never missed a beat.
Reciprocating parts or not, with RPMs comes friction; with friction, heat and with heat, seizure.

peejay

Apex seal chatter begins at about 6000-6500, and gets potentially fatal at 8500, with stock iron seals. Carbon-aluminum seals don't have this problem, and I get conflicting reports on the 3-piece seals used in '86-up engines.

If you go over 8500 you'll want hardened stationary gears, ALTHOUGH I've heard some scuttlebutt that the OPPOSITE is better, which makes sense - soft things don't crack like hard things do. I dunno, for the time being I'd go with the status quo.

You also have to deal with the rotor gear walking out. This can be nasty, the best thing is to have them held in place with clips, because pins hold them TOO rigidly. I've also been told that it's "not necessary" to retain the rotor gear. Hmm.

You will also need more rotor-to-side housing clearance and a lightened rotating assembly. There are just the two bearings on the E-shaft and it can flex, which will allow the rotor tips to hit the side housings - instant cruncymunchscreechkaboom. Lighter, more balanced assemblies help with this.

I'm told the most you can expect to get out of an engine with all the mods short of a 3-bearing conversion is 10,500rpm, and then you're limited pretty much by the rotor tips problem and OILING. I've heard of one person whose PP briefly saw 16,000 when the throttle stuck open, and then the bearings siezed from poor lubrication. Rotaries have HUGE bearings, and the bigger the bearing, the more oil pressure you need, and the higher you wind it, the more you need, so you end up with absurd amounts of oil pressure (250psi?!?!?) just to keep the engine alive at high RPM.

This is all info I've gleaned from asking the same question over and over in various forums, newsgroups, and mailing lists. Every time I ask i get different answers... Basically I keep it under 8500, which most everyone agrees is the max safe RPM for an internally stock engine. "I left it in 3rd and wound it out to 12000 or so on my street ported stock 13B..."

Pele

iTrader: (28)

You get em at rotary performance shops that rebuild engines.

rx7gslse

quick interjection of stupid question.. Is 8500 a similiar number on the 13b, or is it less because of the larger rotors and related, larger rotating mass?

Just curious...

SilverRocket

I thought I'd share a stupid thing I did a certain time... I was taking a girl for a ride in the seven when I was 17, and of course had to impress so I was pushing the hell out of her (the car, not the girl...). As I wound out the top of third gear I shifted to fourth... only I shifted into second instead.

This brought forth bar none the highest pitched engine note I have ever heard from a street engine. The tach was just bouncing off the top.... I have no idea exactly what revs I was at, but holy hell it was a lot.

This was 4 years ago and my engine still runs flawlessly and makes great power. I'm sure sustained operation at that kind of engine speed is an altogether different story though...

rx7passion

for a short period of time i dont think its going to do alot too your motor aka a missed shift. i read somewhere about a college class that took a 12a and wound it out to something obserd like 28k and kept it there it went for like 5min before it melted down.

its the same on a 13b, rx7gslse 8500 is the celing for stock motors.

i dont really belive that at all sorry but lots of tuners and engine builders recommend stock seals in ported motors and high reving ones you just need big hefty springs like dual fd apex springs would take care of chatter.

Felix Wankel

Bridgeport.

madaz07

i now a guy who takes his 12a pp to 11.000rpm

von

So with a bridge port will I be able to spin to 10k safely without chatter using 13b stock 3piece sealz and turbo oil pump ?

Pele

iTrader: (28)

Since you have it apart for the rebuild, it is reccomended that you get the hardened stationary gears, 3 window bearings, and better apex springs.

Porting will not stop chatter. Unless it's the M@d JDM p0rT y0. (In refperence to your spelling of the word "seals" as "sealz".)

Just a few days ago, not paying attention to what the hell I was doing, and more on the idiot I was trying to pass, I downshifted from 4th to 3rd at like 60 or 70 MPH... The guy accelerated as to not let me pass. In a fit of road rage, I temporarily thought I was in 5th and downshifted to 4th, which was really 2nd... And pegged my tach... In the Honda... Freaked me out... I'm used to hearing rotaries sound high pitched. Not boingers...

Now it feels low on power, even for a Honda... More like a moped or something... And I know I screwed up an engine mount; I can hear it.

Felix Wankel

Better yank the head and see how many valves you bent

thorin

is apex seal "chatter" something you can hear? because i can hear a wierd chattering noise once i hit about 6000. I have well used motor.

Terrh

iTrader: (7)

bah.. hondas can take it

A similar thing happened to me in my '84 prelude (200,000mi, 1.8l 12valveSOHC)... going about 80KPH (50mph). Downshifted from 5th into 3rd.. but really, it was first. Oops. WACK goes the engine.. first gear at that speed has got to be 11-12krpm. Hit the clutch, engine revved down to idle. and idled. Phew, I thought. Put it in 5th and it ran fine. No valves bent, no chunked rings, no pistons in the head. no timing belts thrown. Nothing. I liked hondas after that event

HadaGSL-SE

iTrader: (6)

I was attempting to downshift from 4th to 3rd but really put it into first. I dont know what the revs went to but the clutch certainly went to hell, a brandnew centerforce stage 2 shattered to pieces.
Oh this was a stock gsl-se besides the clutch.

Pele

iTrader: (28)

Meh. It'll be allright... The H on the hood means it's slow, but it'll run forever.

I have a feeling that the distributor cap is full of oil again... (Honda wants $114 for the distributor housing, without the sensors, ignitor, and coil in it... They won't sell me the seal for it... )

The lack of power actually happened a little after the downshift incident, I think...

coldy13

I hope that's not what that noise is, because mine does that too.