Gekitotsu

I am curious..

I have a.. fairly stock 85 RX7 with the 12A motor.
A buddy and I are fabricating a custom intake, fuel injectors, Megasquirt, etc etc etc.. And the main question I have right now is:
How high can a stock 12A rev without engine damage?
And, say I'm racing, how high will it rev before I have to worry about things ripping themselves apart?

trochoid

iTrader: (6)

Without porting, 7k, with porting up to 8k (street port). Above that you will need supporting internal mods for longevity. You can rev to 8k as it sets, with headers and exhaust, but the power curve really isn't worth it on a stock ported motor and wear increases conciderably.

Gekitotsu

Mmkay

So no use buying that 10,000 rpm guage I've had my eye on.. >:P

Thanks for the info!

trochoid

iTrader: (6)

Sure you can, especially if it is one of those that tattles on max revs. Then you will know how high it reved before you blew it.

Zyrano

trochoid, why does porting make a difference on rpm in regards to engine damage? I'd think they'd be the same...

Alvin

dj55b

iTrader: (2)

the reason that you can rev your engine higher when you do proting is because with the stock ports the engine can only exist the gases up to a certain speed before it starts turning around the hole without having to work extra hard ... thats my understanding of it ... correct me anyone if i'm wrong

a13btrx7@hotmail.com

ill tell u something those rotarys can hekka take punishment ,way more than my mr2 supercharged thats why we had to replace the engine . when i drift w/ my fb i always redline dat **** ,hekka fun .

mwatson184

8400 rpm is when the apex seals start to chatter. There is no point reving that high on the stock ports but you can do it without damage.

-Marques

trochoid

iTrader: (6)

Porting allows the engine to rev higher, because it can breathe better, increasing the power band and moving it up in the rpm range. The porting itself does not increase wear. The use of the higher rpms that the porting allows increases the wear factor, as with any engine.

Revs are revs. Higher revs increase wear, ported or not. Sorry if I was unclear on that.

woodonastick

iTrader: (1)

i let go of throttle when i dont feel anymore pull. thats pass 8k rpms. i have a stock port with header and pre. so far so good.

Zyrano

ok, that makes more sense now, cauz i've had the car between 7-8k when i'm autoxing and i wasn't paying attention to the tach, so i know it goes that far, it's not necessary more power i'm looking for, it's just that it was faster to keep it reved then to shift to third (especially when the corner is right there), glad to know i didn't cause any damage...

trochoid

iTrader: (6)

Before I built the bp, the stock 12a had a mikuni and headers and I would wrap it to 8k. A friend on mine that has a TII couln't believe that I would do that on the 'lowly' 12a. He and I plan to go head to head to see how the bp performs.

With the bp, when broken in, will probably see higher rpms, maybe 8.5k. I didn't do any internal mods, other than the 85 psi oil pressure regulator, other wise I would be looking at a 9 to 9.5k rpm limit.

There are times when racing, that exceeding the point where the hp starts to fall of can be benificial, when the next gear puts you right in the sweet spot. The stop watch or lap times will tell what works best.

FB II

i've taken mine to 8k a couple times in 3rd. was at 16lbs of boost and it was awesome!

Pen_Two

You can rev it as high as you want, but I bet it won't be too pretty after a certain point.

Directfreak

iTrader: (2)

Reving it to 8k or so is fine, as long as you don't "Hold" it there. That's when the chattering can become evident.

I have my Rev Limiter set at 9000, but my shift lite at 8200 -
with a mild street port.

LongDuck

You guys are helping him to feel confident in blowing his engine.

With a stock port 12a - you will not generate power above about 6500rpm. Therefore, there is no reason to rev any higher than that because you are already beyond the torque peak and your next shift will place you right where you want to be.

If you want that 10k rpm tach - go and get it, but realize that if you make this a 'challenge' to see how high you can rev that stock engine, it will be popped like popcorn very quickly. Apparently you don't realize that 6500rpm is high revving for any stock piston engine - and it will be nowhere near as smooth as a rotary.

Have at it and let us know where and when it blows,

Siraniko

iTrader: (13)

thats what I call BS. Bury the tach but only for a few seconds then shift. As long as you have the right timing & fuel, you should do fine.

hammmy

Why? Max HP on a stock 12A is like Duck said, between 6500 and 7000 RPM, hence the redline. Unless you're in 3rd on a drag strip, why bother passing that? And if you're still stock, why are you on a drag strip?

-dave

FB II

yea if you are just that... STOCK. with a nice opened exhaust, and all the following mods... you are still making power up there. when i dyno'd my old n/a setup i was still climbing at 7600rpms. i shut it down because i was scared but the dyno guys were like "wtf are you doing, it's still going!" so yes, even on stock ports there is power to be made up there ,and it helps because it throws you in a a sweet spot for the next gear.

but true, if the car is bone stock and you have nothing done to it, then shift at 7,000 so you can still get in the next gear at a decent spot.

Kentetsu

Yeah, my car has the RB exhaust and improved ignition, so it rips all the way to 8 grand and feels like it could keep going. That's with stock fuel delivery (except for mech secondaries). I don't take it that high though, because by that time I've got enough torque in the next gear up that I might as well shift anyway. But in an autoX, hell yeah, if that corner is coming up anyway I'd keep it in 2nd gear a few more seconds and not worry about it.

RustyRotary

iTrader: (2)

As previously stated, on a technical course the extra revs are VERY helpful.

Sometimes when you are approaching a corner and are at the shift point you have to decide whether to shift up to the next gear or to just keep going into the redline. It's tough, because shifting to the gear would take longer than the time you're even going to spend in that gear before you brake. There's nothing you can do but keep going past the redline until you enter the corner. Just because the power drops there doesn't mean you would get a better lap time by shifting up.

Siraniko

iTrader: (13)

You will get "owned" if you do what he said. I never paid atttention to tach. I go by feel. I shift when it stops pulling. Besides, revving the motor hard once a day is good for the motor

Boswoj

Always lots of people around to encourage you to blow up a motor.

Listen - stock 12a's make their max hp somewhere in the 6500 - 7000 range. If they made more HP in a safe fashion BEYOND that, the factory redline would have been set higher. Contrary to popular belief, most auto makers don't set things like redlines, capacities, and service intervals just to **** people off and cheat them out of "extra" performance. They set them to give a good balance between performance and longevity. Want to work your motor harder? Expect a shorter "duty cycle". If you have to have more performance, expect shorter life. Think about the way that rotary motors are assembled. They are a stack of structural elements tied together by bolts that go all the way through the assembly. Increased revs cause stresses that will eventually lead to "distortion" of the stack which can cause small misalignments of the structural components. Add the large amount of thermal stress present in a rotary and this can contribute to a number of things that can destroy your motor. A small bind can shear the teeth off of the stock stationary gears which is instant death. The eccentric shaft is a reasonably short and stiff piece, but any torque provided via "motor flex" can eat bearings, compromise side seals, and cause high speed spinning parts like rotors to "walk" even making contact with the cast irons - again - instant death. Ported rotaries make their power higher in the rev band because of port timing and overlap - so solutions have been developed to handle that. Carbon or ceramic apex seals, hardened stationary gears, high volume and pressure oil mods, lightened and balanced assemblies, and bearing modifications can be made to raise the safe operating rpm of your motor. The question remains though: even if you had built these things in properly (and let me tell you from experience, it ain't cheap!) why would you rev beyond where your power is? If your car was built to safely rev to 12,000 but it made half as much power there as it does at 7,000 would you let people talk you into doing it? Now throw in the fact that if you rev to even 9000 on a regular basis with a stock motor it will probably last less than a month does it sound even less appealing? I know it's hard to believe, but Mazda actually has engineers put some thought into this stuff. There is even an outside chance that they know more about it than some of the forum hacks who can't even operate the shift key, much less earn an engineering degree. Advice is only as good as the person giving it, so go find someone that has experience building and racing rotaries who has an opinion that you can trust.

Oh - and to kill just ONE more engineering "old wives tale", it isn't any less damaging to "bury the tach" for just a second or two. Accelerating and decelerating the eccentric shaft actually exaggerates torsional deformation, and it gets worse the quicker you do it. It would theoretically be less stressful for a rotating assembly to be held at a steady high rpm than for it to be accelerated and decelerated to that rpm quickly. Keep in mind, this is just the informed opinion of someone who can actually back it up with an education in engineering.

Siraniko

iTrader: (13)

if your concern is blowing the motor, then you shouldnt race it at all. IF you cant bite a bullet, dont do it. Just an opinion from someone who can back it up with experience in "bury the tach" for many years, and who have mastered common sense.

Boswoj

Depends on what kind of racing we are talking about. If it is drag racing, then operating the car within it's stated limits doesn't relly have to be much more stressful than driving it on the street. Wackyracer stated: "if your concern is blowing the motor, then you shouldnt race it at all". Well - I guess if you are going to make up rules, then why not go all the way to "if your concern is blowing the motor, then you shouldnt START it at all". Shifts can just as easily be missed on the street as on the strip - and the typical car gets shifted a few thousand times on the street for every time that it happens on the strip, if that EVER happens. I don't drag race, I roadrace in sanctioned events at several West Coast tracks. Just because I race, it doesn't mean that I don't care if I blow up motors! The opposite is true! My motors cost more than street motors to build because I know they will have to survive the rigors of redline on every shift, and I need as much RELIABLE horsepower as possible to be competitive. Your argument just doesn't hold water, regardless of road OR racing use. Blowing up motors just because of ignorance, or indifference is a luxury that most of us cannot afford.

Finally, your "opinion" as someone with experience in "bury the tach" "for many years" proves that there is nothing "common" about "common sense", as it appears to be pretty scarce in your particular case. Could it be that you are just annoyed that your "opinion" isn't being accepted as gospel even though you have no real facts to back it up? There isn't a reputable professional rotary engine builder of either street or racing motors that would back you up. ALL of them have serious and intelligent discussions with their customers about the parameters that their engines are built to operate within to maximize their performance and longevity or they don't keep their customers for long. Everyone has a responsibility to evaluate the advice that they recieve and decide what is useful, and what is crap. Why anyone would take technical advice from someone who loves seeing his words in print enough to make over 3000 posts, yet not learn to capitalize or punctuate is beyond me. Just to be safe, perhaps you should keep your bad advice for yourself, and blow up as many of your own engines as you feel comfortable paying for - just don't encourage others to do the same. They might not get the enjoyment out of it that you do.