I was thinking about this the other day, if they made n/a four rotar with 700 hp, how come they can't make a 350 hp two rotor???

I know it doesn't quite work like that, and that race applications are different than street applicatoins, not to mention pricing, bu that was 15 years ago, and I would think there would be even greater potential due to increase in technology.

So what would it take to make a 350 hp two rotar. Obviously we all now the answer is not the Renesis, although a great engine.
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the FC rx7 in N/A form made 146 hp. With a turbo it made 189. The FD rx7 made 276hp with the help of turbos.

the rx8 makes somewhere between 220 and 240 N/A.

that's quiet a bit of improvement. not to mention the improved fuel economy.

 

I"m kinda basing this off what they did with the 787b. Why can't do something similiar for production?
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The 787B's engine was optimized to run well in the upper rev range, not for street usage.

Why is the Renesis not the answer? The engine has so far proven to be very stout. If you want a streetable 350hp 2 rotor, look no further than a forced induction Renesis. And the beefier torque/horsepower curve will be much better than any NA option.

 

A couple of reasons might be economic feasibility, reliability, safety, emissions requirement, and no doubt some I haven't mentioned. A production car has to be reasonably reliable, safe. It must meet emissions standards in the country of sale and it must be priced so as to make it a profitable undertaking for the manufacturer. If production costs dictate a selling price of say $80-100K for example, there are other, possibly more desirable choices already on the market. Not rotary-engined, of course, but some pretty great machines nonetheless.

 

Well, think of having that much power na and then the potential you would have if you went FI later. I'm just wondering why technology hasn't made it easier to achieve a more potent engine, because I do understand the many hurdles to overcome in designing an engine like this to be streetable and reasonably safe; however, I was wondering why 15 years of R & D hasn't led us to this yet?
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I bet if our engines ran to 15-18,000 rpms it'd make 350hp...at least. (That's 475 in MAZDA HP numbers )

 

To get a 350 hp 2 rotor takes absolutely no regard for emissions, gas mileage, or overall street drivability. It's just not going to happen. The most powerful naturally aspirated rotaries out there use either big bridge or peripheral ports. You aren't getting around all of the above listed with these setups. The 787B used a variable length intake manifold that wouldn't even fit within the space of the RX-8 engine bay. They didn't rev that engine up any higher than the Rensis does in the RX-8 and they shifted it at 9000 rpm. There have been some others to get over 350 hp up at higher rpms but you run into more issues depending on how you did it. You are basically asking for well over 2 hp per cu. in. of displacement to get 350 hp. Technology can really only take you so far. The last decade has been an enormous leap in naturally aspirated rotary power. Not sure why you think technology hasn't given us a more potent engine? They went from 160 hp to nearly 238 hp and they are getting cleaner emissions on top of that. A 48% leap in power is pretty impressive for 1 generation difference in engine and the single biggest power increase from generation to generation since the invention of the rotary. Not good enough? They've found ways to make more power on the street engines when compared to the older street engines but in regards to making more overall max power when you place all the cards on the table, they've pretty much maxed that out. There's not really anything else to do other than revving it up even higher and then trying to hold it all together. The street engines will never have the breathing ability of these no holds barred race engines and will never make their power levels without forced induction. 15 more years of R&D can't accomplish the impossible. Once you get to the top, it's really hard to try to go any higher. It's just going to take a much bigger engine to hit that power level and still be streetable. I'm not expecting anyone to make my little Civic engine do 350 hp and still be nice on emissions, mileage, and drivability. That wouldn't be a reasonable request. Technology would have to have one seriously impressive breakthrough somewhere on the order of perpetual motion to make that a reality. Either that or our atmosphere will have to get much more dense.

 

I was waiting for you RotaryGod! I guess that sounds pretty reasonable. Thanks for the details. I'm not saying the renesis is no good, but rather I was just curious as to what limitatins there were in designing an engine like that. I know emissions, and gas consumption will suffer, that's just a given. I was just wondering if it was possible.
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I belive it would be possible, actually maybe not that hard, with the increse of displacemnt in a 2 rotor - 15b?

 

So you think a 15% increase in displacement will get us a 47% increase in power?

 

Im not sayin that 15% would yeild 350hp, just gave an example since there was thread on here with wider rotors, however maybe a 30% increase would do it. I havent had any experience with rotory engines so I have no idea what effects or consequence would a displacemnet increase bring, nor did I do any research. Im sure one would be worse gas mileage, but not neccesarily worse emissions. Maybe you, rotarygod, can elaborate on this a bit.

 

So, I’ve heard that the above helps the rotary make more power compared to our "side port". Wait…I’m not done, keep reading…

Since the Renesis does not have “peripheral ports” what exactly did Mazda change to gain another 78 HP? I understand the new design helped fuel economy and emissions but how did they find 78HP without the use of “peripheral ports”?

I’m guessing that the drawback of “peripheral ports” is the reduction in fuel economy and worse emissions. Am I right?

So…how did Mazda pull out another 78HP?

Also, other than the Cosmo 3-rotor why has Mazda been reluctant to try a 3-rotor since it's obvious they don't really prefer FI in their rotary engine. (for the street at least)

Like I said in the other thread, I'd take a smaller sized 3-rotor (which might negate any possible fuel economy hit) to avoid the whole FI thing.

 

I would assume the greater hp on the renesis came from better parts manufacturing. I think I remember reading how the rotors are machined now was not even possible 10/15 years ago. and that the slight new designs are what give it power. Plus it rev's higher than any other na rotary before.

It would be nice to see them develop a more powerful na rotary even if it was more expensive. (not that I could afford any more expensive car) Bu t it would be cool to see ont he street.
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Other thing too that no one has mentioned is limited capital investment. Mazda is small, and probably expends very limited resources into the rotary. It's only in one car, this isn't like Nissan's VQ architecture where they find a way to fit it into everything. There is no place to spread the R&D costs of the rotary, but yet we get the RX-8 for a reasonable price. If Mazda had more resources and there was more public acceptance of the rotary, it probably would be more powerful than it is now because Mazda Engineering would have had more justification to the Financial arm of the company. As RG says above, Mazda's made a huge step forward with the Renesis. But they haven't hit the wall, in my opinion anyway, there is no finite limit to be reached technologically. All it takes is research and a bit of imagination. I'm by no means close to being an engineer, so I'll just sit back and hope someone out there is smart enough in this arena to stumble across the next big step.

 

The Renesis has 2 very important changes that make it more powerful than the 13B. The first is larger intake ports and a slightly higher redline. However if we compare a dyno chart of a 13B to a Renesis we see that the Renesis is way ahead of the 13B everywhere including the low end. This alone wasn't accomplished by larger intake ports. There was something else happening. It is with the side exhaust ports! Port size and flow is one thing but another very important aspect is with port timing. The peripheral exhaust ports quite simply have too much timing. They are open too long. The side exhaust ports have more exhaust port area but may flow less total air than the peripheral port exhaust. The important aspect of them though is with their port timing. The side exhaust ports apparently still flow enough air to make the power it does so airflow definitely wasn't the biggest issue.

As with everything there is an exception to all of this and when it comes to a full race engine, it's all about flow and scavenging. You can get away with more timing in a race engine. In each setup it's all about the total package and what combinations work best. On the street it is all side ports. On the race track it is all peripheral ports.

Although not containing a rotary, check out desktop dyno. You can simulate many different engines and play with cam timing and the effects on the powerband. Look at one run on a fairly normal setup and then change only one thing. Change the exhaust cam so that the exhaust is open for about 50% longer. Power goes down noticably! How can this be? There's more potential flow from it since it is open longer. It's all about the timing.

 

Fred,
You failed to mention the increased compression. Our local professor says the intake seems to be a vast improvement in design for flow also. There's a lot going on there.
350 has been achieved but just as you pointed out, it wasn't by a renesis although they are still quite impressive.
Paul.

 

The intake manifold is definitely far and away better than anything Mazda has used on a rotary before. The increase in compression is small but there are also other drawbacks. The people that have tried the RX-8 rotors in 13B's have actually gotten more power out of the slightly lower compression RX-7 rotors! The seal tolerances were better.

 

I agree on the peripheral port issue for road use it has nice power but not driveable like the renesis.They made good progress on the renesis.I just think there isn't going to be big changes in future as now it will go slower in development or power out of the development.(excluding the addition of turbos)some more power can come from a bit of porting,exhaust and mapping but then the enviromental spec also falls.To keep enviromental specs they cant go to peripheral port, the only thing that can happen is add another renesis rotor.i think much easier and cheaper,3 rotor renesis.
I did think of something else, If they can use the idea of the variable length intake on 787b,that did work well. and try to make a variable inlet exhaust timing like on the vtec and the variable inlet and timing control.maybe differant on a rotary as there are no valves but as technology goes......who knows, maybe they alter the side plates to accomodate a sliding or "size changing" port.can be complicated !?
Lets see

 

I agree with that. I think the next big rotary leap in technology is going to be in making the engine's powerband stronger overall with even more variable timing ability. This would probably help mileage out a bit too. In the immediate future we'll porbably see direct injection put into production. With added timing benefits and better mileage numbers, it would make it possible for them to make a larger more powerful engine in the future with the mileage of the current engine. I just don't see too much more peak power coming out of the current size.