derSchwamm

iTrader: (1)

I went autocrossing in my SE this weekend and found myself wanting to stay in first gear for certain stretches of the track while revving up to the redline. i didn't always have enough time to shift to second so I stayed in first and let the buzzer go off for a few seconds before braking and turning.

I was not watching the tach but I am sure I went over the 7k redline at least a few times, maybe even over 8k. I've heard there's no rev limiter in these cars, so am I doing damage to my engine if I let the RPMs go for a few seconds? Will the car stop the engine from revving into dangerous territory or do I need to ease up when I first hear the buzzer?

I'm trying to avoid damaging my engine and I want to be sure I know what the limit is. Thanks

Qingdao

iTrader: (3)

As long as the bearings have oil it'll be fine... but that's as long as the bearings have oil.

I used to run around at high rpms because I was under the belief that "there is no rev limit", but I soon learned that bearings can and will spin.

However, I'm sure you aren't doing 70mph in second just dragging it out for no reason like a jerk. LOL

peejay

Never exceed 8000rpm. The engine will FOD much past that. Have never had a bearing issue, but iron 3mm apex seals hate RPM.

That said, out of a sampling of two Series 3 tachs, both read high. The one in my '84 is about 5% high and the one in my '85 was 10% high. So, I would say, unless you have an accurate tach in the car, you have no idea how fast the engine is going anyway.

There are two interesting/funny things about them, too. I say "about" because the inaccuracy isn't a straight percentage, there's an offset too. And over 9000rpm actual, the stock tach stops sitting on its peg and starts bouncing around wildly

t_g_farrell

iTrader: (1)

From dyno runs I can tell you there is no power on a stock 12A over 7200 rpm. I'm betting thats pretty
much true for 13Bs as well.Exceeding that can be done for small intervals to allow for up shifting or as
you have done to avoid a shift in certain situations.

For example when I'm running some twisties in the mountains I'm usually in 2nd gear most of the time
at about 6000 rpm. I only shift up or down as needed and sometimes hit 7K in the process. Like Peejay
says, just keep it below 8000 rpm, damage happens much faster up there because of oil starvation and
other nasties.

peejay

I found that the best shift point for a stock 12A is 7700 rpm. This with a proper fuel system and a header and an un-f'ed-with carburetor.

I also found that exceeding 8500rpm for any length of time would result in an apex seal breaking the next time 6200rpm is attained. 8500 is the absolute limit for 3mm iron seals, and 6200 is when they start to bounce. It's like the five point palm exploding heart technique of rotaries.

Install carbon seals, and the next failure point is the stationary gears and rotor gears. With the 9-pin rotor gear arrangement, gear loading shoots extremely high at about 9000rpm. This can be dealt with by installing hardened stationary gears and circlipping the rotor gears to keep them from walking out. The real fix is 12-pin rotor gears like every 2mm seal rotor had. The extra shock damping of the three additional roll pins keeps the gear loading from going so high.

I've been using >9000rpm with stock 2mm seal/12-pin rotors, unmodified GSL-SE stationary gears, stock bearings, and a 12A oil pump since 2012, haven't had any bearing related issues yet.


SO, keep it under 8000.

j9fd3s

iTrader: (3)

on an engine with new rotors/housings/seals, i think 8500 is absolute limit for a 3mm seal engine, but with a used engine with old seals, and V'd rotors, i wouldn't spin it much past 7000-7200.

the 2mm seal engines can go to 9k with junkyard parts and still be fine, the extra roll pins, and smaller seals really really help. wear goes up, obviously, but they won't catastrophically fail like the 3mm seal engines do

Qingdao

iTrader: (3)

Ah... that's the difference. I only have experienced 2mm apex seal engines.


I didn't think about apex seal chatter though. I can see that as being a big thing especially with larger seals.

hcaulfield57

iTrader: (1)

Interesting about tachometer inaccuracies. I've never hit the rev-limit buzzer in my car (83' GS), although I have no idea whether it's working or perhaps was removed by a previous owner. I have come close to 8,000 RPM a few times (by accident in 1st gear), but I don't make a habit of it. I rarely shift before 5,000 though. While I understand the context, it's funny to say that 3mm rotaries hate RPM, I guess they give you a false sense of security by their smoothness.

KYPREO

depends which 12A.

When i dynoed my internally stock series 3 12A almost 15 years ago it made peak power at 7800rpm. Mods were exhaust, lightened flywheel, thermo fans and ewp (deleted mechanical pump). Carb was stock unmodified. It went harder up high once i modded the carb.

this was the later style 12A with the tallport primaries.

they rev plenty hard.

13Bs not so much i agree. I used almost exactly the same setup on a s5 turbo block (but with long primaries to the diff) and peak power was the same as my old 12A but at only 7000rpm.

80's old school

iTrader: (7)

When I autocrossed years ago with a 12a I regularly took it to 8000 RPM. Yes you lose power up there, but you lose time if you shift.

I found out I needed to wring out 2nd gear a lot of times. Shifting to third would have been futile because I would need to immediately shift back to 2nd.

To help with oil issues, I ran a baffle sandwiched between the engine and the oil pan and always premixed 2 oz per gallon of gas.

LongDuck

Just to be very clear on this; THERE IS NO REV LIMITER on our cars. The ignition system is so simple that it will let you peg the throttle until the engine spins a bearing from over-speed or explodes, as there's no electro-mechanical system to cut fuel or ignition in the event of high engine RPM.

For anybody new searching and reading this, it behooves us to be clear in mentioning that. The only thing keeping your engine from grenading from excessive RPM is your brain and your right foot!

If you went with an aftermarket ignition module, you could probably work that out, but in the meantime - listen to your tachometer 'buzzer' and trust that Mazda saw fit to install a buzzer for a very good reason, i.e., to keep the uninitiated from ruining their engine.

peejay

Don't install a rev limiter, either. That will kill an engine quickly if you hit it under heavy load.

I deliberately tuned my car to have a "soft" limiter in that it starts pouring fuel in so the engine loses a ton of power at the high end, and then there's an actual fuel cut at 10,5 to catch things if I zing the engine on a mis-shift. The engine won't rev that high under load unless I'm holding it there for long enough that I really should know better.

swbtm

iTrader: (2)

Correct me if I'm wrong here... I think the 79-81 tachometers had the rev buzzer, the 82/83 did not for some reason and I think they went back to it with the 84/85's. My 83 has never had the buzzer and I've been a few full second counts (one one thousand, two one thousand) past pinning the tach for my old 12a in first WOT then absolutely crunching the second gear synchro/gear since it had no chance of catching up to that speed. In only learned later how lucky I was that the centerforce clutch and flywheel (much more of a concern with the lightweight steel flywheels) didn't explode and cut my legs off since I didn't have a ballistic blanket installed.

peejay

All tachs have the buzzer that comes on at 6200-6500 or so. They don't always WORK but Mazda put them in all RX-7s.

t_g_farrell

iTrader: (1)

80 SAs did not have a buzzer. I know because when I swapped in a 79 speedo when mine broke, the
buzzer wasn't there. The pcb had the traces but no buzzer installed.

I wanted to fix the buzzer so I could be like the cool kids but none was there

peejay

My '80 definitely had a buzzer. And it was definitely an '80 cluster, green gauges with an 85mph speedometer.

Oddly enough, electronics fail sometimes I bet most Series 3s have inoperative low-fuel lights, too.