I've been hearing people say that N/A 13Bs can be made to spin in excess of 10,000 rpm so that they can make more power without using turbos.

what does it take to get a motor to spin this fast and what holds a stock motor back (if anything) from doing this effectively?

just curious, any thoughts are welcome.

 

ummm 10,000 on a stock motor is just not possible. Not to mention how inefficient the stock engine would be at that rpm. These engines do have redlines and fuel cuts. While they do like higher rpm's that redline is there for a reason, and you aren't going to make much power after it. It takes quite a bit of modification to get an engine tio wind that high up, still be making power, and still be safe.

 

Yeah stock ports don't flow enough to have the engine operate at that RPM, plus the stock internals just wouldn't take it.

 

The problems that I keep hearing, when it comes to reving much beyond 8500 are four fold.

1) e-shaft flex can cause the rotors to contact the housings. I'm unsure exactly the conditions that cause this, but have heard this kicks in aroun 10000.
2) stationary gear deformation. This is the major reason that S5 13B's had a higher redline than S4, they hardened these. I know that at high rpms, the harmonics are what destroy these.
3)Apex seal float/chatter. This was one of the biggest issues mazda faced when bringing the rotary to life. Luckily they found a way to both decrease the amount of float and increase the rpm that this kicks in. This starts to become bad around 8.5k-9k.
4)Port and IM design are such that it doesn't really provide very much power past redline. Porting your motor can substantially push this 'falling off' much higher in the rpm, if its your hearts desire to rev high.

 

thanks i was just wondering but that was realy helpful guys

 

Andrew : Read the thread titled : "what is needed for 13k rpm" or something like that.

I`am sure your questions will be answered there!
Karis

 

I dissagree. I was talking to a mechanic who builds muscle cars and Can Am cars. He told me back in 80's he was given funds to research rotary engines. He went on to tell me that they could easily rev the mazda rotories up to 14k rpm all day. Ironically enough , it wasnt the apex seals that went, it was the ecentric shafts- theyt would snap. BTW, the shop is called Galant Racing, in Oakland/ Montclair, CA.

 

the important thing is there's no point - even with a stupendously large bridgeport, the power stops at ~11k.

 

$150 Fc : That is highly debateable.I have seen and heard a 12A that revs to 13K+.
It makes power untill 13000 and it lasts as well,a whole season of every 2 week racing,without being opened up!

 

No one has said anything about the water pump cavitation. Racing Beat says, the stock main pulley and water pump pulley can only run tp 6300 rpm, then cavitation starts and doesnt allow the water to circulate properly.Which doesnt matter as long as you dont hold it for extended periods of time. To fix the problem, just need to get a $50 smaller main pulley and you can hit 10,000 all day, unless you are talking about a 13b, then you would need racing apex seals which wont chatter like the heaving metal ones.

 

I think a lot of it depends on the motor. I know there have been people who have revved stock 12a's up to 10k by adding fuel and tuning them out a little more. My conclusion on this has always been that rotaries don't really have a 'redline', but more like a boom point. Redline has always been used with piston motors to designate the limit of the valvetrain and other internals.

On a rotary, as long as you have proper fuel you can rev them much more. When they rev out higher on the stock fuel they are spining higher RPMs, thus drawing in more air with the same amount of fuel. This leans them out. When you have added fuel there they are capable of spining higher, but to a point of course.

As everyone else mentioned, yes, there are limits to the stock internals, but they can be revved more as long as the proper fuel modifications are made, but as someone else pointed out, your powerband will fall off after 11k anyway.

 

I have personally seen stock 13b 4-ports revving up to 10k at the track and pulling high 13's or very low 14's.

 

so what sort of fuel modifications have to be made? is it just a matter of running higher octain fuel or physically feeding it more fuel? or NOS for the financially stable.
DAVE

 

You have to give it more fuel, pump, injectors, higher octane doesn't have much use in NA 7's.

 

one point that no-one has so far mentioned is this:

as great as it may be to be able to 10k+ rpm on your stock engine, they are NOT designed for this and it's not becuse they can't it's becuse everything else in your stock car can't.

Have you considered what your gearbox is going to do at 12,000 rpm it's not going to last very long at all.

i also question if your synchros will even let you shift your gears at that rpm.

and then you have your clutch your drive train and all the other stuff.

So even if you can get your stock 13b to be able to rev upto and beyond 10krpm i'd expect everything else is going to break before your engine goes pop.

 

I had an 84 GSL-SE and from 185,000 miles to 207,000 miles I spun it to 8k every day. 8500 fairly often and to 10k a couple times during tuning. With the Racing Beat Dellorto intake, exhaut and other items it ran a 14.38@93mph. It seemed to make power to around 8300rpm, which is where I shifted.

I acquired an S4 6pt and transferred all the RB parts over to it. Along with a bit of weight reduction and shifting it at 8500rpm, I ran a 13.96@97mph.

I am now running a street port 13B, all very old and used parts. 84 heavy rotating assembly and very old seals. I've tried to keep it to 9500 at a max (with the help of a rev limiter). Nothing special was done to the engine(just ported). I shift (and speedshift) at 9100-9300rpms and ran a 13.53@102 on street tires.

I'm not saying that this is the best way to go or that it will last forever, but in 20 years I have yet to hurt a stock engine while keeping it under 10k. If you want more power, there is always a tradeoff.

 

Some of you keep mentioning adding more fuel. Thats not what makes power in these engines. You have to have sufficient quantity of air.

The question is at what point does the rotor start traveling to fast to allow the port to stay open long enough to get the required quantity of fuel/air mixture in the engine and still make more power than the previous rpm segment? Now I don't know if this is a concern with our rotary engines but it could be. I imagine it will take someone capable of caluclating the amount of intake charge the time the port is open at a certain rpm to figure it out. Many variables involved but would be interesting to know. Anyone want to try?

 

Why would you want to spin the engine up THAT HIGH... I thought the purpose of making more power was to accelerate a car? And that rotational inertia goes up with the square of RPM? So all that mass attached to the engine (say 50-70lb of steel) takes twice as much energy to accelerate at 11000rpm as it does at 7800... now how much energy does it take to accelerate just the engine at that RPM level, figuring also that you need a higher RPM/second acceleration rate to make the same vehicle acceleration rate... at some point you will be losing net acceleration even though the HP number is physically higher.

You shouldn't be asking "How can I make it rev higher?"... the better question is "How can I make more power in my existing powerband" and "How can I make my car accelerate more quickly"....


- Pete (Three words: Proper peripheral port)

 

it doesnt matter how much power is being made at the rotor face or how much of that is being wasted. all that matters is that the net HP on the e-shaft keeps going up.

altough you make a good point about incresed force needed to spin an engine at high RPM you neglected that an engine can often be under static or near static load. in other words the rotational acceleartion will be very near zero. this is why a car with a lightend flywheel will feel practicaly zero difference at highway speeds, because the engine is undergoing very little roatational acceleration. once an object is spinning, whether that be at 750 or 12000 rpm no more force is eedet to maintain that rpm save countering friction which is largely independent of mass.

however, in a drag racing situation the engine is rapidly accelarting rotationaly so it is even more important for a high output/rpm N/A to have a lightned and balanced rotating assembly while it is not so important for a lower rpm turbo motor that achives the same net hp.

regardless, the weight of the parts will have no effect on a brake dyno which measures static load. the power will always be there and always have a chance to get to the wheels. the only question is how much of the engines power are you going to use to rapidly accelerate it along with the car. this is more a factor of gearing than the redline itself........

 

Sure. When you're running a steady speed, such as crusing down the highway at 25hp output. Or if you're pulling a trailer up a steep grade... but I don't think that is what we're concerned with. Likewise top speed running.... top speed isn't *racing* IMO, it's just sitting there like a lump with the throttle bolted to the floor.

When you're going down the dragstrip, you're concerned with acceleration.

When you're coming out of a corner on a road course, or the autox, you're concerned with acceleration.

 

firsl t, i want to shoot down all negative thoughts of high rpm engines... Formula engines spin like crazy... in excess of 17,000 rpm.
ok, i have given a lot of thought to creating a high rpm rotary, and I am more ambitious than andrew... i want a 20,000 RPM motor. Heres the parts list.

electric water pump
dry sump oil system-- high volume
extermal oil pump-- high volume
2 mfr oil coolers
big *** radiator
2 alternators(alternator rpms cut in half)
2~4lb rotors
one ****** HUGE pp rotor housings
there that takes care of the engine

now for the drive line... we need to reduce the flywheel rmps a bit... so lets put a gear reduction before the flywheel, aft of the engine... say 2:1.. there the drivetrain is safe from excessive rpms, but now the transmission gearing is all off... so lets put in some custom gearing with dog teeth that can handle, oh... say 1000hp. oh yeah you might want to put a bigger rear end.

i figure with all of that, the speed each gear nets is ~85mph,

1st 85
2nd 170
3rd (maxspeed-170)/3 + 170
4th ((maxspeed-170)/3*2)+170
5th maxspeed

there it is kids...

 

Yeah, there's only a few problems with that. Keeping the eccentric shaft together at those RPMs, keeping the apex seals from chattering and grinding the housing away, where exactly to get rotors that are half as light as the ones Mazda came up with for their racing programs, keeping the stationary gears from deforming... and a big one, having enough port. You can't make a peripheral port big enough to flow enough air for 20k RPM. I sincerely doubt there's any combination of porting you can do to a 13B that will manage that. Oh, and gear reducing the flywheel... uh, why exactly? With a custom transmission it seems redundant. Finally, I have to wonder where exactly you came up with the speeds for the transmission... kind of... optimistic.

Oh, and holy thread resurrection, batman!

 

Have fun when your clutch flies apart and takes your legs off.

 

id have to say that is one of the bigger peices of talking out of one's *** ive seen in a while. dude it just isnt gona happen.

 

When you are talking formula engine, I assume you man formula 1 right? A formula 1 engine car can't really be compared to any other cars out there. Definatly not rotaries. Formula one uses very short stroke PISTON engines to get those revs, and even then the engines only last 1 race, sometimes not even that much.

I really want you to share the awsome **** you using, I don't think I ahve been f-ed up that much in my life dude.

And for all of you that want to find out about high reving engines, talk to the guys on Aus Rotary about some of those IPRA bridge engines, I think one guy is revving his engine up to 12,000RPM.