See I’m curious about the crazy people who run close to 10 thousand rpm on their rotaries. What’s allowing them to be able to do that?

I recall the e-shaft begins to flex and wobble even in a short and stubby 2-rotor until the rotor faces kiss the housings being a cause for engine failure. If so, would investing in one of the those X40/X50 e-shafts with the centre bearing or bearing support be able to allow me to ride happier at higher revs? And would hardened stationary gears help me provide the centripetal force keeping my lovely rotor faces away from the housings? Thank you so much

 

Depends on what you are starting with for an engine.

If you have 2mm apex seals and 12-pin rotor gears, all you really need is a little more oil pressure, and lead-in/lead-out grooves in the eccentric shaft. I would use the smallest oil pump that fits your setup, large pumps are good for feeding turbo engines at low RPM but they don't flow as well at high RPM.

Mind you, engine life drops logarthmically with increased RPM, and the transmissions don't shift worth a damn over 7000-8000 or so.

 

Oil pressure, e-shaft flex (by virtue of a center bearing or balancing), clearancing to combat said flex, proper oil pressures, and last but not least - the ability to actually breathe properly up there. I'd also modify the front iron to accept the FD pump (or realistically just run an FD front iron with peripheral ports) to achieve the best of both worlds with regards to efficiency of pressure down low and flow up high with its 'relief stage'.

 

The pre '99 highpower" spec engines need the flanks of the rotors shaved down a tad as the e-shaft flex tilts the rotors and they rub the side housings smearing the side seal grooves shut.

My rpm experience was only 9,000rpm. 1993 spec engine didnt last long. 1999 highpower spec had no issues.

 

Of the little research that I have done on the issue, blowing apart a clutch disc would be my #1 fear. You could do damage to your car, yourself and bystanders without a shroud of some sort. Find out what people are using and prepare accordingly.

 

I have found that a large streetport not only makes power up there, but it ONLY makes power up there.

That's why i went back to bridge... it makes the same power but at lower RPM and a much broader powerband,

On my EFI setup, the large street and the bridge had almost exactly the same fueling 7k and up but the street port needed a LOT of fuel taken away below that.

 

Let’s say I did clearance the side of the rotors, and moved to a better oil pump with an external feed, as well as those deep-grooved ‘race bearings’ on Mazdatrix. The ‘limiting factor’ per se would become the transmission and the porting at 10K yes?

 

Well, what are you trying to do?

Just want 10,000rpm without any performance goals?

Porting isnt any limit on rpm if you dont care what power it makes.

Transmission. Again, what are you trying to do? Transmission isnt a limit if you dont care how slow it shifts at 10,000rpm.

Ive done 2nd gear 8,000rpm to 1st gear 14,000rpm shift and wait till ot came down to bumping the 8,000rpm revlimiter before realizing what was going on and the engine was fine.

This was on 3mm apex seal, heavy 8.5:1 CR rotor engine.

But its abouth how reliably and how often you can do it.

 

You don't really NEED the loop line.

You don't super really NEED the race bearings.

I like the lead-in lead-out grooves because they are cheap and simple, like me. Lynn Hanover did testing where he put an oil pressure sender in the eccentric shaft to see what the oil pressure in there was, At some RPM (8000?) with 100psi from the pump, there was only 7psi in the eccentric shaft. That's because of the centrifugal force in the passage from the mains to the shaft fighting the oil pressure.

Mazda's method to handle this was a dry sump oil pump to ensure there was no aeration in the oil, and a large well of oil for the oil holes in the shaft to access.
Pete's method is lead-in grooves in the main journals to scoop the oil in to the shaft, and lead-out grooves to pull the oil out of the shaft into the rotor bearings.
My bearings always look great. I also run 80psi oil pressure with a 12A oil pump and don't see any pressure dropoff at high RPM, because the smaller pumps don't cavitate as much at high RPM.

Also bear in mind, what do you want to do with the engine? If it's circuit racing, even with all of the best parts, you're looking at about 6 hours of high RPM use between rebuilds. This is enough for a season of racing.

Yes yes 787B 24 hours yada yada... also note that they had an 8000rpm limit during the race.

You WILL also need underdrive pullies because the water pump basically stops working over 6000-7000rpm, you WILL need to make sure your apex and corner and side seal clearances are as tight in the slots as possible to prevent seal flutter. Oddly enough when you get to stratospheric RPM excess end clearance on the seals isn't as critical, though. That mainly affects low end operation.
Rotor housing life will enjoy as much oil as you can stand in the fuel. With Atkins seals I run 50:1, and would run more but the exhaust starts to get visible any more oil than that.

 

If I’m being 100% honest, its kinda a longer story. See I usually spend my time making ‘ideal’ builds of what I’d do to cars if I could afford to do so. That kinda extended to video games too over the years, and I’m working on an ideal NFS Heat atm, kinda what I’d do to the game if I were EA. What that involves is a more in-depth upgrade system, especially for rotaries (since I can’t get enough of them). What I wanted info for was because I’m writing the descriptions for the e-shaft related upgrades. Embarrassing-ish motive but it’s the truth. Besides, you guys have really helped me out so thank you!

 

On a side note probably more closely linked to the forum, how much power do N/A 13B’s build if they can rev to the moon? I’ve seen 300 to 350 hp from the crazy time attack guys before. I would assume those guys have the works, PP/full bridge port, lightened and clearanced rotors, all the required modifications to the oil pumps and galleries, and all of the other supporting mods

 

300+ is doable with a street port. It won't be as tractable.

350+ is doable with bridge ports. You don't need to rev to 10K to make this power.

The highest I've heard for a 2 rotor was 450hp and there were some surprising things about it.


Realistically, rotaries hit an internal airflow wall where it takes more power to squeeze the airflow past the pinch in the combustion chamber than can be gained from higher RPM. That's why you generally don't see rotaries making peak power higher than 8000-9000 or so.

 

Also, as a former sim racing dork, I get where you're coming from I modded the escort in Rally Trophy to have a R26B engine and what amused me was that the sound mechanic realistically faded from the idle engine sound to the acceleration engine sound with throttle, not RPM, with no effort on my part.

Not that RT was a sim in the modern sense but it was very, very moddable!

Realistically the eccentric shaft is one of the few things that can be left alone. But as a game mechanic, one might go for things like requiring flywheel/clutch and cooling system upgrades to unlock higher RPM and various porting, intake, and exhaust upgrades to unlock more power.

I've been thinking of getting into BeamNG next year if I ever get around to building a new rig. I havent been into it for almost 20 years, these new hydraulic pedals and direct-drive wheels look really tempting.

 

450 hp from an N/A 13B! That’s some turbo levels of power right there, damn.

On your mention of the internal airflow wall around 8-9K rpm, my mind was taken back to these few pages in Kenichi Yamamoto’s Rotary Engine 1971:


Mention of the K value as R/e here + affect of K on general engine characteristics apparently

The affect of K on theoretical compression ratio

Affect of K on port area for a given opening/closing times

I wonder if varying the value of K (albeit by genuinely building an engine from scratch!) would vary when the engine meets that airflow wall. Maybe its a smaller value of K you want or a bigger one! I’m not smart enough at the moment to know. From just guesses, would the higher compression ratio of K=10 engines (assuming the maximum possible despite the 25:1 being ) need more energy to compress the air? I wonder what the actual reason for that airflow wall is. Plus, I still have no clue what leaning angle is since the explanation isn’t at all intuitive to me…


To address your other reply, BeamNG absolutely blows my mind! I mean, apparently it simulates any and every component in your suspension and frame. With the automation mod you can also just go ham and make your own cars entirely, although watching Filman86’s videos leaves me feeling that all Automation-born cars are super jiggly and unstable upon braking and acceleration, which makes them super twitchy. I think the prices of the good direct drive wheels and hydraulic pedals have begun to come down (not sure about this though), so best of luck with that!

 

The 440-500hp naturally aspirated 13Bs run on nitromethane fuel, so the air (O2) is in the fuel. More fuel= more power, so low compression= more fuel capacity available before dynamic hydrolock happens.

A restrictive port like a streetport has to rev higher than a peripheral port to attain the same VE since the restriction of the port saps the inertia of the intake charge which would be compressing the intake charge over the volume of the displacement (over 100% VE) plus the streetport has more port face area so for a volume of air colum the port pressure is lower making compression stroke reversion easier.

This is why Dave Lemon (Mazdatrix) had a hard time getting his 4 ported 6 port NA to peak torque UNDER 10,000rpm which he held as the max reliable rpm for E- production rules (only balancing of stock rotating assembly allowed- no clearancing nor lightening).

Conversely, even the HUGE keyhole peripheral ports only used for qualifying peak torque 7-9,000rpm range.

 

I’m not quite sure I understand this paragraph, so you’re saying the streetport’s restrictions basically cause a loss of intake air velocity? I would’ve thought with Bernoulli’s Principle that smaller restriction -> more velocity. If you’re talking air volume, I get that. The idea about lower air pressures due to the larger port area creating more of an opportunity for the rotor to push air back into the intake is also interesting, does that happen with peripheral ports as well?

 

What happens to fluid pressure after the restriction of the venturi?

Why do post carbeurator intake manifolds ice over yet post fuel injector manifolds do not ice over?

Is the intake and compression chamber volume after the intake port restriction?

Is there a balance between velocity and restriction in fluid nozzle pressure dynamics and would a restriction that also lowers velocity (a 90 degree bend) ever be a benifit to post nozzle chamber filling?

This fact also affects peripheral ports.
The huge keyhole qualifying spec peripheral ports require more rpm to achieve peak torque and have lower torque at lower rpms compared to "as cast" MFR peripheral intake ports.

 

Street ports don't make as much midrange torque because they don't have very much overlap period. Having a lot of overlap hurts drivability when at part throttle, but at full throttle, the longer-opening port window (and reduced shrouding of the inlet flow) makes for lots of power without having to close late.

Basically, when the port CLOSES defines where in the RPM range the peak power will be, but when it OPENS defines how wide the powerband can be. Which is why 6 port engines suck, they close way too late to make useful power anywhere.

This of course is pretty simplistic as there are a whole lot of other factors like port velocity, blowdown efficiency, and on and on.

That's how you can have two street ports with the same opening and closing times but one makes 170hp and one makes 300hp.

 

its a side thing, but ive been wondering if its some combination of port velocity being wonky and or it just doesn't flow well.
if you just look at port area it should do better than it does.

i mean i guess you could just run an Rx8 motor if you wanted 6 ports.

 

I'd be curious what my weird 6 port experiment engine ( https://www.rx7club.com/naturally-as...erent-1130673/ ) would do with a S4 ping-pong manifold. I know a bridge port T2 engine really liked it vs a T2 intake.

That engine with the Holley manifold didn't have a discernable torque peak, it just kept pulling harder and harder the higher you revved it. It had a lot of airflow but the late closing hurt chamber filling at speeds lower than what it took to make the port move air. This sucks for an engine you have to drive because your shift points should bracket peak power. Anyway with the gearing options available to me I'm usually exiting corners at 4500ish so a strong midrange is much more important than a theoretical peak power number

 

Go smaller and you can get up to 17,000rpm